Ignore:
Timestamp:
08/05/14 14:08:15 (6 years ago)
Author:
julian.reschke@…
Message:

add keywords (#553)

Location:
draft-ietf-httpbis/latest
Files:
12 edited

Legend:

Unmodified
Added
Removed
  • draft-ietf-httpbis/latest/p1-messaging.html

    r2661 r2662  
    500500      <link href="p2-semantics.html" rel="next">
    501501      <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.629, 2014/04/17 09:22:01, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">
     502      <meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP message format">
    502503      <link rel="schema.dct" href="http://purl.org/dc/terms/">
    503504      <meta name="dct.creator" content="Fielding, R.">
  • draft-ietf-httpbis/latest/p1-messaging.xml

    r2661 r2662  
    120120  <area>Applications</area>
    121121  <workgroup>HTTPbis</workgroup>
    122 
     122 
     123  <keyword>Hypertext Transfer Protocol</keyword>
     124  <keyword>HTTP</keyword>
     125  <keyword>HTTP message format</keyword>
     126 
    123127<abstract>
    124128<t>
  • draft-ietf-httpbis/latest/p2-semantics.html

    r2660 r2662  
    1 <!DOCTYPE html
    2   PUBLIC "-//W3C//DTD HTML 4.01//EN">
    3 <html lang="en">
    4    <head profile="http://dublincore.org/documents/2008/08/04/dc-html/">
    5       <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    6       <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title><script>
    7 var buttonsAdded = false;
    8 
    9 function initFeedback() {
    10   var fb = document.createElement("div");
    11   fb.className = "feedback noprint";
    12   fb.setAttribute("onclick", "feedback();");
    13   fb.appendChild(document.createTextNode("feedback"));
    14 
    15   var bodyl = document.getElementsByTagName("body");
    16   bodyl.item(0).appendChild(fb);
    17 }
    18 
    19 function feedback() {
    20   toggleButtonsToElementsByName("h1");
    21   toggleButtonsToElementsByName("h2");
    22   toggleButtonsToElementsByName("h3");
    23   toggleButtonsToElementsByName("h4");
    24 
    25   buttonsAdded = !buttonsAdded;
    26 }
    27 
    28 function toggleButtonsToElementsByName(name) {
    29   var list = document.getElementsByTagName(name);
    30   for (var i = 0; i < list.length; i++) {
    31     toggleButton(list.item(i));
    32   }
    33 }
    34 
    35 function toggleButton(node) {
    36   if (! buttonsAdded) {
    37 
    38     // docname
    39     var template = "mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&body=<{ref}>:";
    40 
    41     var id = node.getAttribute("id");
    42     // better id available?
    43     var titlelinks = node.getElementsByTagName("a");
    44     for (var i = 0; i < titlelinks.length; i++) {
    45       var tl = titlelinks.item(i);
    46       if (tl.getAttribute("id")) {
    47         id = tl.getAttribute("id");
    48       }
    49     }
    50 
    51     // ref
    52     var ref = window.location.toString();
    53     var hash = ref.indexOf("#");
    54     if (hash != -1) {
    55       ref = ref.substring(0, hash);
    56     }
    57     if (id != "") {
    58       ref += "#" + id;
    59     }
    60 
    61     // docname
    62     var docname = "draft-ietf-httpbis-p2-semantics-latest";
    63 
    64     // section
    65     var section = node.textContent;
    66     section = section.replace("\u00a0", " ");
    67 
    68     // build URI from template
    69     var uri = template.replace("{docname}", encodeURIComponent(docname));
    70     uri = uri.replace("{section}", encodeURIComponent(section));
    71     uri = uri.replace("{ref}", encodeURIComponent(ref));
    72 
    73     var button = document.createElement("a");
    74     button.className = "fbbutton noprint";
    75     button.setAttribute("href", uri);
    76     button.appendChild(document.createTextNode("send feedback"));
    77     node.appendChild(button);
    78   }
    79   else {
    80     var buttons = node.getElementsByTagName("a");
    81     for (var i = 0; i < buttons.length; i++) {
    82       var b = buttons.item(i);
    83       if (b.className == "fbbutton noprint") {
    84         node.removeChild(b);
    85       }
    86     }
    87   }
    88 }</script><style type="text/css" title="Xml2Rfc (sans serif)">
    89 a {
    90   text-decoration: none;
    91 }
    92 a.smpl {
    93   color: black;
    94 }
    95 a:hover {
    96   text-decoration: underline;
    97 }
    98 a:active {
    99   text-decoration: underline;
    100 }
    101 address {
    102   margin-top: 1em;
    103   margin-left: 2em;
    104   font-style: normal;
    105 }
    106 body {
    107   color: black;
    108   font-family: cambria, helvetica, arial, sans-serif;
    109   font-size: 11pt;
    110   margin-right: 2em;
    111 }
    112 cite {
    113   font-style: normal;
    114 }
    115 div.note {
    116   margin-left: 2em;
    117 }
    118 dl {
    119   margin-left: 2em;
    120 }
    121 ul.empty {
    122   list-style-type: none;
    123 }
    124 ul.empty li {
    125   margin-top: .5em;
    126 }
    127 dl p {
    128   margin-left: 0em;
    129 }
    130 dt {
    131   margin-top: .5em;
    132 }
    133 h1 {
    134   font-size: 130%;
    135   line-height: 21pt;
    136   page-break-after: avoid;
    137 }
    138 h1.np {
    139   page-break-before: always;
    140 }
    141 h2 {
    142   font-size: 120%;
    143   line-height: 15pt;
    144   page-break-after: avoid;
    145 }
    146 h3 {
    147   font-size: 110%;
    148   page-break-after: avoid;
    149 }
    150 h4, h5, h6 {
    151   page-break-after: avoid;
    152 }
    153 h1 a, h2 a, h3 a, h4 a, h5 a, h6 a {
    154   color: black;
    155 }
    156 img {
    157   margin-left: 3em;
    158 }
    159 li {
    160   margin-left: 2em;
    161 }
    162 ol {
    163   margin-left: 2em;
    164 }
    165 ol.la {
    166   list-style-type: lower-alpha;
    167 }
    168 ol.ua {
    169   list-style-type: upper-alpha;
    170 }
    171 ol p {
    172   margin-left: 0em;
    173 }
    174 p {
    175   margin-left: 2em;
    176 }
    177 pre {
    178   margin-left: 3em;
    179   background-color: lightyellow;
    180   padding: .25em;
    181   page-break-inside: avoid;
    182 }
    183 pre.text2 {
    184   border-style: dotted;
    185   border-width: 1px;
    186   background-color: #f0f0f0;
    187   width: 69em;
    188 }
    189 pre.inline {
    190   background-color: white;
    191   padding: 0em;
    192 }
    193 pre.text {
    194   border-style: dotted;
    195   border-width: 1px;
    196   background-color: #f8f8f8;
    197   width: 69em;
    198 }
    199 pre.drawing {
    200   border-style: solid;
    201   border-width: 1px;
    202   background-color: #f8f8f8;
    203   padding: 2em;
    204 }
    205 table {
    206   margin-left: 2em;
    207 }
    208 table.tt {
    209   vertical-align: top;
    210   border-color: gray;
    211 }
    212 table.tt th {
    213   border-color: gray;
    214 }
    215 table.tt td {
    216   border-color: gray;
    217 }
    218 table.all {
    219   border-style: solid;
    220   border-width: 2px;
    221 }
    222 table.full {
    223   border-style: solid;
    224   border-width: 2px;
    225 }
    226 table.tt td {
    227   vertical-align: top;
    228 }
    229 table.all td {
    230   border-style: solid;
    231   border-width: 1px;
    232 }
    233 table.full td {
    234   border-style: none solid;
    235   border-width: 1px;
    236 }
    237 table.tt th {
    238   vertical-align: top;
    239 }
    240 table.all th {
    241   border-style: solid;
    242   border-width: 1px;
    243 }
    244 table.full th {
    245   border-style: solid;
    246   border-width: 1px 1px 2px 1px;
    247 }
    248 table.headers th {
    249   border-style: none none solid none;
    250   border-width: 2px;
    251 }
    252 table.left {
    253   margin-right: auto;
    254 }
    255 table.right {
    256   margin-left: auto;
    257 }
    258 table.center {
    259   margin-left: auto;
    260   margin-right: auto;
    261 }
    262 caption {
    263   caption-side: bottom;
    264   font-weight: bold;
    265   font-size: 10pt;
    266   margin-top: .5em;
    267 }
    268 
    269 table.header {
    270   border-spacing: 1px;
    271   width: 95%;
    272   font-size: 11pt;
    273   color: white;
    274 }
    275 td.top {
    276   vertical-align: top;
    277 }
    278 td.topnowrap {
    279   vertical-align: top;
    280   white-space: nowrap;
    281 }
    282 table.header td {
    283   background-color: gray;
    284   width: 50%;
    285 }
    286 table.header a {
    287   color: white;
    288 }
    289 td.reference {
    290   vertical-align: top;
    291   white-space: nowrap;
    292   padding-right: 1em;
    293 }
    294 thead {
    295   display:table-header-group;
    296 }
    297 ul.toc, ul.toc ul {
    298   list-style: none;
    299   margin-left: 1.5em;
    300   padding-left: 0em;
    301 }
    302 ul.toc li {
    303   line-height: 150%;
    304   font-weight: bold;
    305   margin-left: 0em;
    306 }
    307 ul.toc li li {
    308   line-height: normal;
    309   font-weight: normal;
    310   font-size: 10pt;
    311   margin-left: 0em;
    312 }
    313 li.excluded {
    314   font-size: 0pt;
    315 }
    316 ul p {
    317   margin-left: 0em;
    318 }
    319 .title, .filename, h1, h2, h3, h4 {
    320   font-family: candara, helvetica, arial, sans-serif;
    321 }
    322 samp, tt, code, pre {
    323   font: consolas, monospace;
    324 }
    325 ul.ind, ul.ind ul {
    326   list-style: none;
    327   margin-left: 1.5em;
    328   padding-left: 0em;
    329   page-break-before: avoid;
    330 }
    331 ul.ind li {
    332   font-weight: bold;
    333   line-height: 200%;
    334   margin-left: 0em;
    335 }
    336 ul.ind li li {
    337   font-weight: normal;
    338   line-height: 150%;
    339   margin-left: 0em;
    340 }
    341 .avoidbreak {
    342   page-break-inside: avoid;
    343 }
    344 .bcp14 {
    345   font-style: normal;
    346   text-transform: lowercase;
    347   font-variant: small-caps;
    348 }
    349 .comment {
    350   background-color: yellow;
    351 }
    352 .center {
    353   text-align: center;
    354 }
    355 .error {
    356   color: red;
    357   font-style: italic;
    358   font-weight: bold;
    359 }
    360 .figure {
    361   font-weight: bold;
    362   text-align: center;
    363   font-size: 10pt;
    364 }
    365 .filename {
    366   color: #333333;
    367   font-size: 75%;
    368   font-weight: bold;
    369   line-height: 21pt;
    370   text-align: center;
    371 }
    372 .fn {
    373   font-weight: bold;
    374 }
    375 .left {
    376   text-align: left;
    377 }
    378 .right {
    379   text-align: right;
    380 }
    381 .title {
    382   color: green;
    383   font-size: 150%;
    384   line-height: 18pt;
    385   font-weight: bold;
    386   text-align: center;
    387   margin-top: 36pt;
    388 }
    389 .warning {
    390   font-size: 130%;
    391   background-color: yellow;
    392 }
    393 .feedback {
    394   position: fixed;
    395   bottom: 1%;
    396   right: 1%;
    397   padding: 3px 5px;
    398   color: white;
    399   border-radius: 5px;
    400   background: #a00000;
    401   border: 1px solid silver;
    402 }
    403 .fbbutton {
    404   margin-left: 1em;
    405   color: #303030;
    406   font-size: small;
    407   font-weight: normal;
    408   background: #d0d000;
    409   padding: 1px 4px;
    410   border: 1px solid silver;
    411   border-radius: 5px;
    412 }
    413 
    414 @media print {
    415   .noprint {
    416     display: none;
    417   }
    418 
    419   a {
    420     color: black;
    421     text-decoration: none;
    422   }
    423 
    424   table.header {
    425     width: 90%;
    426   }
    427 
    428   td.header {
    429     width: 50%;
    430     color: black;
    431     background-color: white;
    432     vertical-align: top;
    433     font-size: 110%;
    434   }
    435 
    436   ul.toc a:nth-child(2)::after {
    437     content: leader('.') target-counter(attr(href), page);
    438   }
    439 
    440   ul.ind li li a {
    441     content: target-counter(attr(href), page);
    442   }
    443 
    444   .print2col {
    445     column-count: 2;
    446     -moz-column-count: 2;
    447     column-fill: auto;
    448   }
    449 }
    450 
    451 @page {
    452   @top-left {
    453        content: "Internet-Draft";
    454   }
    455   @top-right {
    456        content: "May 2014";
    457   }
    458   @top-center {
    459        content: "HTTP/1.1 Semantics and Content";
    460   }
    461   @bottom-left {
    462        content: "Fielding & Reschke";
    463   }
    464   @bottom-center {
    465        content: "Expires November 9, 2014";
    466   }
    467   @bottom-right {
    468        content: "[Page " counter(page) "]";
    469   }
    470 }
    471 
    472 @page:first {
    473     @top-left {
    474       content: normal;
    475     }
    476     @top-right {
    477       content: normal;
    478     }
    479     @top-center {
    480       content: normal;
    481     }
    482 }
    483 </style><link rel="Contents" href="#rfc.toc">
    484       <link rel="Author" href="#rfc.authors">
    485       <link rel="Copyright" href="#rfc.copyrightnotice">
    486       <link rel="Index" href="#rfc.index">
    487       <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
    488       <link rel="Chapter" title="2 Resources" href="#rfc.section.2">
    489       <link rel="Chapter" title="3 Representations" href="#rfc.section.3">
    490       <link rel="Chapter" title="4 Request Methods" href="#rfc.section.4">
    491       <link rel="Chapter" title="5 Request Header Fields" href="#rfc.section.5">
    492       <link rel="Chapter" title="6 Response Status Codes" href="#rfc.section.6">
    493       <link rel="Chapter" title="7 Response Header Fields" href="#rfc.section.7">
    494       <link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8">
    495       <link rel="Chapter" title="9 Security Considerations" href="#rfc.section.9">
    496       <link rel="Chapter" title="10 Acknowledgments" href="#rfc.section.10">
    497       <link rel="Chapter" href="#rfc.section.11" title="11 References">
    498       <link rel="Appendix" title="A Differences between HTTP and MIME" href="#rfc.section.A">
    499       <link rel="Appendix" title="B Changes from RFC 2616" href="#rfc.section.B">
    500       <link rel="Appendix" title="C Imported ABNF" href="#rfc.section.C">
    501       <link rel="Appendix" title="D Collected ABNF" href="#rfc.section.D">
    502       <link href="p1-messaging.html" rel="prev">
    503       <link href="p4-conditional.html" rel="next">
    504       <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.629, 2014/04/17 09:22:01, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">
    505       <link rel="schema.dct" href="http://purl.org/dc/terms/">
    506       <meta name="dct.creator" content="Fielding, R.">
    507       <meta name="dct.creator" content="Reschke, J. F.">
    508       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p2-semantics-latest">
    509       <meta name="dct.issued" scheme="ISO8601" content="2014-05-08">
    510       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
    511       <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.">
    512       <meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.">
    513    </head>
    514    <body onload="initFeedback();">
    515       <table class="header">
    516          <tbody>
    517             <tr>
    518                <td class="left">HTTPbis Working Group</td>
    519                <td class="right">R. Fielding, Editor</td>
    520             </tr>
    521             <tr>
    522                <td class="left">Internet-Draft</td>
    523                <td class="right">Adobe</td>
    524             </tr>
    525             <tr>
    526                <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
    527                </td>
    528                <td class="right">J. Reschke, Editor</td>
    529             </tr>
    530             <tr>
    531                <td class="left">Updates: <a href="http://tools.ietf.org/html/rfc2817">2817</a> (if approved)
    532                </td>
    533                <td class="right">greenbytes</td>
    534             </tr>
    535             <tr>
    536                <td class="left">Intended status: Standards Track</td>
    537                <td class="right">May 8, 2014</td>
    538             </tr>
    539             <tr>
    540                <td class="left">Expires: November 9, 2014</td>
    541                <td class="right"></td>
    542             </tr>
    543          </tbody>
    544       </table>
    545       <p class="title">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content<br><span class="filename">draft-ietf-httpbis-p2-semantics-latest</span></p>
    546       <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
    547       <p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext
    548          information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header
    549          fields, response status codes, and response header fields, along with the payload of messages (metadata and body content)
    550          and mechanisms for content negotiation.
    551       </p>
    552       <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1>
    553       <p>Discussion of this draft takes place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived at &lt;<a href="http://lists.w3.org/Archives/Public/ietf-http-wg/">http://lists.w3.org/Archives/Public/ietf-http-wg/</a>&gt;.
    554       </p>
    555       <p>The current issues list is at &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/report/3">http://tools.ietf.org/wg/httpbis/trac/report/3</a>&gt; and related documents (including fancy diffs) can be found at &lt;<a href="http://tools.ietf.org/wg/httpbis/">http://tools.ietf.org/wg/httpbis/</a>&gt;.
    556       </p>
    557       <p><em>This is a temporary document for the purpose of tracking the editorial changes made during the AUTH48 (RFC publication) phase.</em>
    558       </p>
    559       <div id="rfc.status">
    560          <h1><a href="#rfc.status">Status of This Memo</a></h1>
    561          <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p>
    562          <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute
    563             working documents as Internet-Drafts. The list of current Internet-Drafts is at <a href="http://datatracker.ietf.org/drafts/current/">http://datatracker.ietf.org/drafts/current/</a>.
    564          </p>
    565          <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
    566             documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
    567             in progress”.
    568          </p>
    569          <p>This Internet-Draft will expire on November 9, 2014.</p>
    570       </div>
    571       <div id="rfc.copyrightnotice">
    572          <h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    573          <p>Copyright © 2014 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
    574          <p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights
    575             and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License
    576             text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified
    577             BSD License.
    578          </p>
    579          <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November
    580             10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to
    581             allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s)
    582             controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative
    583             works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate
    584             it into languages other than English.
    585          </p>
    586       </div>
    587       <hr class="noprint">
    588       <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
    589       <ul class="toc">
    590          <li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
    591                <li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li>
    592                <li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li>
    593             </ul>
    594          </li>
    595          <li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#resources">Resources</a></li>
    596          <li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#representations">Representations</a><ul>
    597                <li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#representation.metadata">Representation Metadata</a><ul>
    598                      <li><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#data.type">Processing Representation Data</a></li>
    599                      <li><a href="#rfc.section.3.1.2">3.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#data.encoding">Encoding for Compression or Integrity</a></li>
    600                      <li><a href="#rfc.section.3.1.3">3.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#audience.language">Audience Language</a></li>
    601                      <li><a href="#rfc.section.3.1.4">3.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#identification">Identification</a></li>
    602                   </ul>
    603                </li>
    604                <li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#representation.data">Representation Data</a></li>
    605                <li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#payload">Payload Semantics</a></li>
    606                <li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul>
    607                      <li><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#proactive.negotiation">Proactive Negotiation</a></li>
    608                      <li><a href="#rfc.section.3.4.2">3.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#reactive.negotiation">Reactive Negotiation</a></li>
    609                   </ul>
    610                </li>
    611             </ul>
    612          </li>
    613          <li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#methods">Request Methods</a><ul>
    614                <li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.overview">Overview</a></li>
    615                <li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#method.properties">Common Method Properties</a><ul>
    616                      <li><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li>
    617                      <li><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li>
    618                      <li><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#cacheable.methods">Cacheable Methods</a></li>
    619                   </ul>
    620                </li>
    621                <li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul>
    622                      <li><a href="#rfc.section.4.3.1">4.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li>
    623                      <li><a href="#rfc.section.4.3.2">4.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li>
    624                      <li><a href="#rfc.section.4.3.3">4.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li>
    625                      <li><a href="#rfc.section.4.3.4">4.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li>
    626                      <li><a href="#rfc.section.4.3.5">4.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li>
    627                      <li><a href="#rfc.section.4.3.6">4.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li>
    628                      <li><a href="#rfc.section.4.3.7">4.3.7</a>&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li>
    629                      <li><a href="#rfc.section.4.3.8">4.3.8</a>&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li>
    630                   </ul>
    631                </li>
    632             </ul>
    633          </li>
    634          <li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a><ul>
    635                <li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#request.controls">Controls</a><ul>
    636                      <li><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li>
    637                      <li><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li>
    638                   </ul>
    639                </li>
    640                <li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#request.conditionals">Conditionals</a></li>
    641                <li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#request.conneg">Content Negotiation</a><ul>
    642                      <li><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li>
    643                      <li><a href="#rfc.section.5.3.2">5.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li>
    644                      <li><a href="#rfc.section.5.3.3">5.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li>
    645                      <li><a href="#rfc.section.5.3.4">5.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li>
    646                      <li><a href="#rfc.section.5.3.5">5.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li>
    647                   </ul>
    648                </li>
    649                <li><a href="#rfc.section.5.4">5.4</a>&nbsp;&nbsp;&nbsp;<a href="#request.auth">Authentication Credentials</a></li>
    650                <li><a href="#rfc.section.5.5">5.5</a>&nbsp;&nbsp;&nbsp;<a href="#request.context">Request Context</a><ul>
    651                      <li><a href="#rfc.section.5.5.1">5.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li>
    652                      <li><a href="#rfc.section.5.5.2">5.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li>
    653                      <li><a href="#rfc.section.5.5.3">5.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li>
    654                   </ul>
    655                </li>
    656             </ul>
    657          </li>
    658          <li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#status.codes">Response Status Codes</a><ul>
    659                <li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#overview.of.status.codes">Overview of Status Codes</a></li>
    660                <li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul>
    661                      <li><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li>
    662                      <li><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li>
    663                   </ul>
    664                </li>
    665                <li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul>
    666                      <li><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li>
    667                      <li><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li>
    668                      <li><a href="#rfc.section.6.3.3">6.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li>
    669                      <li><a href="#rfc.section.6.3.4">6.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li>
    670                      <li><a href="#rfc.section.6.3.5">6.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li>
    671                      <li><a href="#rfc.section.6.3.6">6.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li>
    672                   </ul>
    673                </li>
    674                <li><a href="#rfc.section.6.4">6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul>
    675                      <li><a href="#rfc.section.6.4.1">6.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li>
    676                      <li><a href="#rfc.section.6.4.2">6.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li>
    677                      <li><a href="#rfc.section.6.4.3">6.4.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li>
    678                      <li><a href="#rfc.section.6.4.4">6.4.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li>
    679                      <li><a href="#rfc.section.6.4.5">6.4.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li>
    680                      <li><a href="#rfc.section.6.4.6">6.4.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li>
    681                      <li><a href="#rfc.section.6.4.7">6.4.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li>
    682                   </ul>
    683                </li>
    684                <li><a href="#rfc.section.6.5">6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul>
    685                      <li><a href="#rfc.section.6.5.1">6.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li>
    686                      <li><a href="#rfc.section.6.5.2">6.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li>
    687                      <li><a href="#rfc.section.6.5.3">6.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li>
    688                      <li><a href="#rfc.section.6.5.4">6.5.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li>
    689                      <li><a href="#rfc.section.6.5.5">6.5.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li>
    690                      <li><a href="#rfc.section.6.5.6">6.5.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li>
    691                      <li><a href="#rfc.section.6.5.7">6.5.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li>
    692                      <li><a href="#rfc.section.6.5.8">6.5.8</a>&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li>
    693                      <li><a href="#rfc.section.6.5.9">6.5.9</a>&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li>
    694                      <li><a href="#rfc.section.6.5.10">6.5.10</a>&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li>
    695                      <li><a href="#rfc.section.6.5.11">6.5.11</a>&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Payload Too Large</a></li>
    696                      <li><a href="#rfc.section.6.5.12">6.5.12</a>&nbsp;&nbsp;&nbsp;<a href="#status.414">414 URI Too Long</a></li>
    697                      <li><a href="#rfc.section.6.5.13">6.5.13</a>&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li>
    698                      <li><a href="#rfc.section.6.5.14">6.5.14</a>&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li>
    699                      <li><a href="#rfc.section.6.5.15">6.5.15</a>&nbsp;&nbsp;&nbsp;<a href="#status.426">426 Upgrade Required</a></li>
    700                   </ul>
    701                </li>
    702                <li><a href="#rfc.section.6.6">6.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul>
    703                      <li><a href="#rfc.section.6.6.1">6.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li>
    704                      <li><a href="#rfc.section.6.6.2">6.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li>
    705                      <li><a href="#rfc.section.6.6.3">6.6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li>
    706                      <li><a href="#rfc.section.6.6.4">6.6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li>
    707                      <li><a href="#rfc.section.6.6.5">6.6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li>
    708                      <li><a href="#rfc.section.6.6.6">6.6.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li>
    709                   </ul>
    710                </li>
    711             </ul>
    712          </li>
    713          <li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a><ul>
    714                <li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#response.control.data">Control Data</a><ul>
    715                      <li><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#origination.date">Origination Date</a></li>
    716                      <li><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li>
    717                      <li><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li>
    718                      <li><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
    719                   </ul>
    720                </li>
    721                <li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#response.validator">Validator Header Fields</a></li>
    722                <li><a href="#rfc.section.7.3">7.3</a>&nbsp;&nbsp;&nbsp;<a href="#response.auth">Authentication Challenges</a></li>
    723                <li><a href="#rfc.section.7.4">7.4</a>&nbsp;&nbsp;&nbsp;<a href="#response.context">Response Context</a><ul>
    724                      <li><a href="#rfc.section.7.4.1">7.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li>
    725                      <li><a href="#rfc.section.7.4.2">7.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li>
    726                   </ul>
    727                </li>
    728             </ul>
    729          </li>
    730          <li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
    731                <li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry">Method Registry</a><ul>
    732                      <li><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry.procedure">Procedure</a></li>
    733                      <li><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.methods">Considerations for New Methods</a></li>
    734                      <li><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.registration">Registrations</a></li>
    735                   </ul>
    736                </li>
    737                <li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry">Status Code Registry</a><ul>
    738                      <li><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry.procedure">Procedure</a></li>
    739                      <li><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></li>
    740                      <li><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registration">Registrations</a></li>
    741                   </ul>
    742                </li>
    743                <li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registry">Header Field Registry</a><ul>
    744                      <li><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></li>
    745                      <li><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Registrations</a></li>
    746                   </ul>
    747                </li>
    748                <li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registry">Content Coding Registry</a><ul>
    749                      <li><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.procedure">Procedure</a></li>
    750                      <li><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registration">Registrations</a></li>
    751                   </ul>
    752                </li>
    753             </ul>
    754          </li>
    755          <li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
    756                <li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based on File and Path Names</a></li>
    757                <li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#attack.injection">Attacks Based on Command, Code, or Query Injection</a></li>
    758                <li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#personal.information">Disclosure of Personal Information</a></li>
    759                <li><a href="#rfc.section.9.4">9.4</a>&nbsp;&nbsp;&nbsp;<a href="#sensitive.information.in.uris">Disclosure of Sensitive Information in URIs</a></li>
    760                <li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#fragment.disclosure">Disclosure of Fragment after Redirects</a></li>
    761                <li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#disclosure.product.information">Disclosure of Product Information</a></li>
    762                <li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#fingerprinting">Browser Fingerprinting</a></li>
    763             </ul>
    764          </li>
    765          <li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li>
    766          <li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
    767                <li><a href="#rfc.section.11.1">11.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
    768                <li><a href="#rfc.section.11.2">11.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
    769             </ul>
    770          </li>
    771          <li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#differences.between.http.and.mime">Differences between HTTP and MIME</a><ul>
    772                <li><a href="#rfc.section.A.1">A.1</a>&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li>
    773                <li><a href="#rfc.section.A.2">A.2</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li>
    774                <li><a href="#rfc.section.A.3">A.3</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
    775                <li><a href="#rfc.section.A.4">A.4</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.content-encoding">Conversion of Content-Encoding</a></li>
    776                <li><a href="#rfc.section.A.5">A.5</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.content-transfer-encoding">Conversion of Content-Transfer-Encoding</a></li>
    777                <li><a href="#rfc.section.A.6">A.6</a>&nbsp;&nbsp;&nbsp;<a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li>
    778             </ul>
    779          </li>
    780          <li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
    781          <li><a href="#rfc.section.C">C.</a>&nbsp;&nbsp;&nbsp;<a href="#imported.abnf">Imported ABNF</a></li>
    782          <li><a href="#rfc.section.D">D.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li>
    783          <li><a href="#rfc.index">Index</a></li>
    784          <li><a href="#rfc.authors">Authors' Addresses</a></li>
    785       </ul>
    786       <div id="introduction">
    787          <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1>
    788          <p id="rfc.section.1.p.1">Each Hypertext Transfer Protocol (HTTP) message is either a request or a response. A server listens on a connection for a
    789             request, parses each message received, interprets the message semantics in relation to the identified request target, and
    790             responds to that request with one or more response messages. A client constructs request messages to communicate specific
    791             intentions, examines received responses to see if the intentions were carried out, and determines how to interpret the results.
    792             This document defines HTTP/1.1 request and response semantics in terms of the architecture defined in <a href="#RFC7230" id="rfc.xref.RFC7230.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.
    793          </p>
    794          <p id="rfc.section.1.p.2">HTTP provides a uniform interface for interacting with a resource (<a href="#resources" title="Resources">Section&nbsp;2</a>), regardless of its type, nature, or implementation, via the manipulation and transfer of representations (<a href="#representations" title="Representations">Section&nbsp;3</a>).
    795          </p>
    796          <p id="rfc.section.1.p.3">HTTP semantics include the intentions defined by each request method (<a href="#methods" title="Request Methods">Section&nbsp;4</a>), extensions to those semantics that might be described in request header fields (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5</a>), the meaning of status codes to indicate a machine-readable response (<a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>), and the meaning of other control data and resource metadata that might be given in response header fields (<a href="#response.header.fields" title="Response Header Fields">Section&nbsp;7</a>).
    797          </p>
    798          <p id="rfc.section.1.p.4"><span id="rfc.iref.c.1"></span> This document also defines representation metadata that describe how a payload is intended to be interpreted by a recipient,
    799             the request header fields that might influence content selection, and the various selection algorithms that are collectively
    800             referred to as "<dfn>content negotiation</dfn>" (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;3.4</a>).
    801          </p>
    802          <div id="conformance">
    803             <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#conformance">Conformance and Error Handling</a></h2>
    804             <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
    805                in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
    806             </p>
    807             <p id="rfc.section.1.1.p.2">Conformance criteria and considerations regarding error handling are defined in <a href="p1-messaging.html#conformance" title="Conformance and Error Handling">Section 2.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.
    808             </p>
    809          </div>
    810          <div id="notation">
    811             <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2>
    812             <p id="rfc.section.1.2.p.1">This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list extension, defined in <a href="p1-messaging.html#abnf.extension" title="ABNF List Extension: #rule">Section 7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>, that allows for compact definition of comma-separated lists using a '#' operator (similar to how the '*' operator indicates
    813                repetition). <a href="#imported.abnf" title="Imported ABNF">Appendix&nbsp;C</a> describes rules imported from other documents. <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;D</a> shows the collected grammar with all list operators expanded to standard ABNF notation.
    814             </p>
    815             <p id="rfc.section.1.2.p.2">This specification uses the terms "character", "character encoding scheme", "charset", and "protocol element" as they are
    816                defined in <a href="#RFC6365" id="rfc.xref.RFC6365.1"><cite title="Terminology Used in Internationalization in the IETF">[RFC6365]</cite></a>.
    817             </p>
    818          </div>
    819       </div>
    820       <div id="resources">
    821          <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#resources">Resources</a></h1>
    822          <p id="rfc.section.2.p.1">The target of an HTTP request is called a resource. HTTP does not limit the nature of a resource; it merely defines an interface
    823             that might be used to interact with resources. Each resource is identified by a Uniform Resource Identifier (URI), as described
    824             in <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.
    825          </p>
    826          <p id="rfc.section.2.p.2">When a client constructs an HTTP/1.1 request message, it sends the <a href="p1-messaging.html#target-resource" class="smpl">target URI</a> in one of various forms, as defined in (<a href="p1-messaging.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). When a request is received, the server reconstructs an <a href="p1-messaging.html#effective.request.uri" class="smpl">effective request URI</a> for the target resource (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    827          </p>
    828          <p id="rfc.section.2.p.3">One design goal of HTTP is to separate resource identification from request semantics, which is made possible by vesting the
    829             request semantics in the request method (<a href="#methods" title="Request Methods">Section&nbsp;4</a>) and a few request-modifying header fields (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5</a>). If there is a conflict between the method semantics and any semantic implied by the URI itself, as described in <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>, the method semantics take precedence.
    830          </p>
    831       </div>
    832       <div id="representations">
    833          <div id="rfc.iref.r.1"></div>
    834          <div id="rfc.iref.s.1"></div>
    835          <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a href="#representations">Representations</a></h1>
    836          <p id="rfc.section.3.p.1">Considering that a resource could be anything, and that the uniform interface provided by HTTP is similar to a window through
    837             which one can observe and act upon such a thing only through the communication of messages to some independent actor on the
    838             other side, an abstraction is needed to represent ("take the place of") the current or desired state of that thing in our
    839             communications. That abstraction is called a representation <a href="#REST" id="rfc.xref.REST.1"><cite title="Architectural Styles and the Design of Network-based Software Architectures">[REST]</cite></a>.
    840          </p>
    841          <p id="rfc.section.3.p.2">For the purposes of HTTP, a "<dfn>representation</dfn>" is information that is intended to reflect a past, current, or desired state of a given resource, in a format that can be
    842             readily communicated via the protocol, and that consists of a set of representation metadata and a potentially unbounded stream
    843             of representation data.
    844          </p>
    845          <p id="rfc.section.3.p.3">An origin server might be provided with, or be capable of generating, multiple representations that are each intended to reflect
    846             the current state of a <a href="#resources" class="smpl">target resource</a>. In such cases, some algorithm is used by the origin server to select one of those representations as most applicable to
    847             a given request, usually based on <a href="#content.negotiation" class="smpl">content negotiation</a>. This "<dfn>selected representation</dfn>" is used to provide the data and metadata for evaluating conditional requests <a href="#RFC7232" id="rfc.xref.RFC7232.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a> and constructing the payload for <a href="#status.200" class="smpl">200 (OK)</a> and <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> responses to GET (<a href="#GET" id="rfc.xref.GET.1" title="GET">Section&nbsp;4.3.1</a>).
    848          </p>
    849          <div id="representation.metadata">
    850             <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a href="#representation.metadata">Representation Metadata</a></h2>
    851             <p id="rfc.section.3.1.p.1">Representation header fields provide metadata about the representation. When a message includes a payload body, the representation
    852                header fields describe how to interpret the representation data enclosed in the payload body. In a response to a HEAD request,
    853                the representation header fields describe the representation data that would have been enclosed in the payload body if the
    854                same request had been a GET.
    855             </p>
    856             <p id="rfc.section.3.1.p.2">The following header fields convey representation metadata:</p>
    857             <div id="rfc.table.u.1">
    858                <table class="tt full left" cellpadding="3" cellspacing="0">
    859                   <thead>
    860                      <tr>
    861                         <th>Header Field Name</th>
    862                         <th>Defined in...</th>
    863                      </tr>
    864                   </thead>
    865                   <tbody>
    866                      <tr>
    867                         <td class="left">Content-Type</td>
    868                         <td class="left"><a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section&nbsp;3.1.1.5</a></td>
    869                      </tr>
    870                      <tr>
    871                         <td class="left">Content-Encoding</td>
    872                         <td class="left"><a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section&nbsp;3.1.2.2</a></td>
    873                      </tr>
    874                      <tr>
    875                         <td class="left">Content-Language</td>
    876                         <td class="left"><a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section&nbsp;3.1.3.2</a></td>
    877                      </tr>
    878                      <tr>
    879                         <td class="left">Content-Location</td>
    880                         <td class="left"><a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section&nbsp;3.1.4.2</a></td>
    881                      </tr>
    882                   </tbody>
    883                </table>
    884             </div>
    885             <div id="data.type">
    886                <h3 id="rfc.section.3.1.1"><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;<a href="#data.type">Processing Representation Data</a></h3>
    887                <div id="media.type">
    888                   <h4 id="rfc.section.3.1.1.1"><a href="#rfc.section.3.1.1.1">3.1.1.1</a>&nbsp;<a href="#media.type">Media Type</a></h4>
    889                   <p id="rfc.section.3.1.1.1.p.1">HTTP uses Internet Media Types <a href="#RFC2046" id="rfc.xref.RFC2046.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> in the <a href="#header.content-type" class="smpl">Content-Type</a> (<a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section&nbsp;3.1.1.5</a>) and <a href="#header.accept" class="smpl">Accept</a> (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section&nbsp;5.3.2</a>) header fields in order to provide open and extensible data typing and type negotiation. Media types define both a data format
    890                      and various processing models: how to process that data in accordance with each context in which it is received.
    891                   </p>
    892                   <div id="rfc.figure.u.1"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  <a href="#media.type" class="smpl">media-type</a> = <a href="#media.type" class="smpl">type</a> "/" <a href="#media.type" class="smpl">subtype</a> *( <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
    893   <a href="#media.type" class="smpl">type</a>       = <a href="#imported.abnf" class="smpl">token</a>
    894   <a href="#media.type" class="smpl">subtype</a>    = <a href="#imported.abnf" class="smpl">token</a>
    895 </pre><div id="rule.parameter">
    896                      <p id="rfc.section.3.1.1.1.p.3"> The type/subtype <em class="bcp14">MAY</em> be followed by parameters in the form of name=value pairs.
    897                      </p>
    898                   </div>
    899                   <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.4"></span>  <a href="#rule.parameter" class="smpl">parameter</a>      = <a href="#imported.abnf" class="smpl">token</a> "=" ( <a href="#imported.abnf" class="smpl">token</a> / <a href="#imported.abnf" class="smpl">quoted-string</a> )
    900 </pre><p id="rfc.section.3.1.1.1.p.5">The type, subtype, and parameter name tokens are case-insensitive. Parameter values might or might not be case-sensitive,
    901                      depending on the semantics of the parameter name. The presence or absence of a parameter might be significant to the processing
    902                      of a media-type, depending on its definition within the media type registry.
    903                   </p>
    904                   <p id="rfc.section.3.1.1.1.p.6">A parameter value that matches the <a href="#imported.abnf" class="smpl">token</a> production can be transmitted either as a token or within a quoted-string. The quoted and unquoted values are equivalent.
    905                      For example, the following examples are all equivalent, but the first is preferred for consistency:
    906                   </p>
    907                   <div id="rfc.figure.u.3"></div><pre class="text">  text/html;charset=utf-8
    908   text/html;charset=UTF-8
    909   Text/HTML;Charset="utf-8"
    910   text/html; charset="utf-8"
    911 </pre><p id="rfc.section.3.1.1.1.p.8">Internet media types ought to be registered with IANA according to the procedures defined in <a href="#BCP13" id="rfc.xref.BCP13.1"><cite title="Media Type Specifications and Registration Procedures">[BCP13]</cite></a>.
    912                   </p>
    913                   <div class="note" id="rfc.section.3.1.1.1.p.9">
    914                      <p><b>Note:</b> Unlike some similar constructs in other header fields, media type parameters do not allow whitespace (even "bad" whitespace)
    915                         around the "=" character.
    916                      </p>
    917                   </div>
    918                </div>
    919                <div id="charset">
    920                   <h4 id="rfc.section.3.1.1.2"><a href="#rfc.section.3.1.1.2">3.1.1.2</a>&nbsp;<a href="#charset">Charset</a></h4>
    921                   <p id="rfc.section.3.1.1.2.p.1">HTTP uses <dfn>charset</dfn> names to indicate or negotiate the character encoding scheme of a textual representation <a href="#RFC6365" id="rfc.xref.RFC6365.2"><cite title="Terminology Used in Internationalization in the IETF">[RFC6365]</cite></a>. A charset is identified by a case-insensitive token.
    922                   </p>
    923                   <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.5"></span>  <a href="#charset" class="smpl">charset</a> = <a href="#imported.abnf" class="smpl">token</a>
    924 </pre><p id="rfc.section.3.1.1.2.p.3">Charset names ought to be registered in the IANA Character Set registry (&lt;<a href="http://www.iana.org/assignments/character-sets">http://www.iana.org/assignments/character-sets</a>&gt;) according to the procedures defined in <a href="#RFC2978" id="rfc.xref.RFC2978.1"><cite title="IANA Charset Registration Procedures">[RFC2978]</cite></a>.
    925                   </p>
    926                </div>
    927                <div id="canonicalization.and.text.defaults">
    928                   <h4 id="rfc.section.3.1.1.3"><a href="#rfc.section.3.1.1.3">3.1.1.3</a>&nbsp;<a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></h4>
    929                   <p id="rfc.section.3.1.1.3.p.1">Internet media types are registered with a canonical form in order to be interoperable among systems with varying native encoding
    930                      formats. Representations selected or transferred via HTTP ought to be in canonical form, for many of the same reasons described
    931                      by the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. However, the performance characteristics of email deployments (i.e., store and forward messages to peers) are significantly
    932                      different from those common to HTTP and the Web (server-based information services). Furthermore, MIME's constraints for the
    933                      sake of compatibility with older mail transfer protocols do not apply to HTTP (see <a href="#differences.between.http.and.mime" title="Differences between HTTP and MIME">Appendix&nbsp;A</a>).
    934                   </p>
    935                   <p id="rfc.section.3.1.1.3.p.2">MIME's canonical form requires that media subtypes of the "text" type use CRLF as the text line break. HTTP allows the transfer
    936                      of text media with plain CR or LF alone representing a line break, when such line breaks are consistent for an entire representation.
    937                      An HTTP sender <em class="bcp14">MAY</em> generate, and a recipient <em class="bcp14">MUST</em> be able to parse, line breaks in text media that consist of CRLF, bare CR, or bare LF. In addition, text media in HTTP is
    938                      not limited to charsets that use octets 13 and 10 for CR and LF, respectively. This flexibility regarding line breaks applies
    939                      only to text within a representation that has been assigned a "text" media type; it does not apply to "multipart" types or
    940                      HTTP elements outside the payload body (e.g., header fields).
    941                   </p>
    942                   <p id="rfc.section.3.1.1.3.p.3">If a representation is encoded with a content-coding, the underlying data ought to be in a form defined above prior to being
    943                      encoded.
    944                   </p>
    945                </div>
    946                <div id="multipart.types">
    947                   <h4 id="rfc.section.3.1.1.4"><a href="#rfc.section.3.1.1.4">3.1.1.4</a>&nbsp;<a href="#multipart.types">Multipart Types</a></h4>
    948                   <p id="rfc.section.3.1.1.4.p.1">MIME provides for a number of "multipart" types — encapsulations of one or more representations within a single message body.
    949                      All multipart types share a common syntax, as defined in <a href="http://tools.ietf.org/html/rfc2046#section-5.1.1">Section 5.1.1</a> of <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, and include a boundary parameter as part of the media type value. The message body is itself a protocol element; a sender <em class="bcp14">MUST</em> generate only CRLF to represent line breaks between body parts.
    950                   </p>
    951                   <p id="rfc.section.3.1.1.4.p.2">HTTP message framing does not use the multipart boundary as an indicator of message body length, though it might be used by
    952                      implementations that generate or process the payload. For example, the "multipart/form-data" type is often used for carrying
    953                      form data in a request, as described in <a href="#RFC2388" id="rfc.xref.RFC2388.1"><cite title="Returning Values from Forms: multipart/form-data">[RFC2388]</cite></a>, and the "multipart/byteranges" type is defined by this specification for use in some <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> responses <a href="#RFC7233" id="rfc.xref.RFC7233.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>.
    954                   </p>
    955                </div>
    956                <div id="header.content-type">
    957                   <div id="rfc.iref.c.2"></div>
    958                   <h4 id="rfc.section.3.1.1.5"><a href="#rfc.section.3.1.1.5">3.1.1.5</a>&nbsp;<a href="#header.content-type">Content-Type</a></h4>
    959                   <p id="rfc.section.3.1.1.5.p.1">The "Content-Type" header field indicates the media type of the associated representation: either the representation enclosed
    960                      in the message payload or the <a href="#representations" class="smpl">selected representation</a>, as determined by the message semantics. The indicated media type defines both the data format and how that data is intended
    961                      to be processed by a recipient, within the scope of the received message semantics, after any content codings indicated by <a href="#header.content-encoding" class="smpl">Content-Encoding</a> are decoded.
    962                   </p>
    963                   <div id="rfc.figure.u.5"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  <a href="#header.content-type" class="smpl">Content-Type</a> = <a href="#media.type" class="smpl">media-type</a>
    964 </pre><p id="rfc.section.3.1.1.5.p.3">Media types are defined in <a href="#media.type" title="Media Type">Section&nbsp;3.1.1.1</a>. An example of the field is
    965                   </p>
    966                   <div id="rfc.figure.u.6"></div><pre class="text">  Content-Type: text/html; charset=ISO-8859-4
    967 </pre><p id="rfc.section.3.1.1.5.p.5">A sender that generates a message containing a payload body <em class="bcp14">SHOULD</em> generate a Content-Type header field in that message unless the intended media type of the enclosed representation is unknown
    968                      to the sender. If a Content-Type header field is not present, the recipient <em class="bcp14">MAY</em> either assume a media type of "application/octet-stream" (<a href="#RFC2046" id="rfc.xref.RFC2046.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, <a href="http://tools.ietf.org/html/rfc2046#section-4.5.1">Section 4.5.1</a>) or examine the data to determine its type.
    969                   </p>
    970                   <p id="rfc.section.3.1.1.5.p.6">In practice, resource owners do not always properly configure their origin server to provide the correct Content-Type for
    971                      a given representation, with the result that some clients will examine a payload's content and override the specified type.
    972                      Clients that do so risk drawing incorrect conclusions, which might expose additional security risks (e.g., "privilege escalation").
    973                      Furthermore, it is impossible to determine the sender's intent by examining the data format: many data formats match multiple
    974                      media types that differ only in processing semantics. Implementers are encouraged to provide a means of disabling such "content
    975                      sniffing" when it is used.
    976                   </p>
    977                </div>
    978             </div>
    979             <div id="data.encoding">
    980                <h3 id="rfc.section.3.1.2"><a href="#rfc.section.3.1.2">3.1.2</a>&nbsp;<a href="#data.encoding">Encoding for Compression or Integrity</a></h3>
    981                <div id="content.codings">
    982                   <div id="rfc.iref.c.3"></div>
    983                   <div id="rfc.iref.c.4"></div>
    984                   <div id="rfc.iref.x.1"></div>
    985                   <div id="rfc.iref.d.1"></div>
    986                   <div id="rfc.iref.g.7"></div>
    987                   <div id="rfc.iref.x.2"></div>
    988                   <h4 id="rfc.section.3.1.2.1"><a href="#rfc.section.3.1.2.1">3.1.2.1</a>&nbsp;<a href="#content.codings">Content Codings</a></h4>
    989                   <p id="rfc.section.3.1.2.1.p.1">Content coding values indicate an encoding transformation that has been or can be applied to a representation. Content codings
    990                      are primarily used to allow a representation to be compressed or otherwise usefully transformed without losing the identity
    991                      of its underlying media type and without loss of information. Frequently, the representation is stored in coded form, transmitted
    992                      directly, and only decoded by the final recipient.
    993                   </p>
    994                   <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.8"></span>  <a href="#content.codings" class="smpl">content-coding</a>   = <a href="#imported.abnf" class="smpl">token</a>
    995 </pre><p id="rfc.section.3.1.2.1.p.3">All content-coding values are case-insensitive and ought to be registered within the "HTTP Content Coding Registry", as defined
    996                      in <a href="#content.coding.registry" title="Content Coding Registry">Section&nbsp;8.4</a>. They are used in the <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.1" title="Accept-Encoding">Section&nbsp;5.3.4</a>) and <a href="#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.2" title="Content-Encoding">Section&nbsp;3.1.2.2</a>) header fields.
    997                   </p>
    998                   <p id="rfc.section.3.1.2.1.p.4">The following content-coding values are defined by this specification: </p>
    999                   <ul class="empty">
    1000                      <li>compress (and x-compress): See <a href="p1-messaging.html#compress.coding" title="Compress Coding">Section 4.2.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.
    1001                      </li>
    1002                      <li>deflate: See <a href="p1-messaging.html#deflate.coding" title="Deflate Coding">Section 4.2.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.
    1003                      </li>
    1004                      <li>gzip (and x-gzip): See <a href="p1-messaging.html#gzip.coding" title="Gzip Coding">Section 4.2.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.
    1005                      </li>
    1006                   </ul>
    1007                </div>
    1008                <div id="header.content-encoding">
    1009                   <div id="rfc.iref.c.5"></div>
    1010                   <h4 id="rfc.section.3.1.2.2"><a href="#rfc.section.3.1.2.2">3.1.2.2</a>&nbsp;<a href="#header.content-encoding">Content-Encoding</a></h4>
    1011                   <p id="rfc.section.3.1.2.2.p.1">The "Content-Encoding" header field indicates what content codings have been applied to the representation, beyond those inherent
    1012                      in the media type, and thus what decoding mechanisms have to be applied in order to obtain data in the media type referenced
    1013                      by the <a href="#header.content-type" class="smpl">Content-Type</a> header field. Content-Encoding is primarily used to allow a representation's data to be compressed without losing the identity
    1014                      of its underlying media type.
    1015                   </p>
    1016                   <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  <a href="#header.content-encoding" class="smpl">Content-Encoding</a> = 1#<a href="#content.codings" class="smpl">content-coding</a>
    1017 </pre><p id="rfc.section.3.1.2.2.p.3">An example of its use is</p>
    1018                   <div id="rfc.figure.u.9"></div><pre class="text">  Content-Encoding: gzip
    1019 </pre><p id="rfc.section.3.1.2.2.p.5">If one or more encodings have been applied to a representation, the sender that applied the encodings <em class="bcp14">MUST</em> generate a Content-Encoding header field that lists the content codings in the order in which they were applied. Additional
    1020                      information about the encoding parameters can be provided by other header fields not defined by this specification.
    1021                   </p>
    1022                   <p id="rfc.section.3.1.2.2.p.6">Unlike Transfer-Encoding (<a href="p1-messaging.html#header.transfer-encoding" title="Transfer-Encoding">Section 3.3.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), the codings listed in Content-Encoding are a characteristic of the representation; the representation is defined in terms
    1023                      of the coded form, and all other metadata about the representation is about the coded form unless otherwise noted in the metadata
    1024                      definition. Typically, the representation is only decoded just prior to rendering or analogous usage.
    1025                   </p>
    1026                   <p id="rfc.section.3.1.2.2.p.7">If the media type includes an inherent encoding, such as a data format that is always compressed, then that encoding would
    1027                      not be restated in Content-Encoding even if it happens to be the same algorithm as one of the content codings. Such a content
    1028                      coding would only be listed if, for some bizarre reason, it is applied a second time to form the representation. Likewise,
    1029                      an origin server might choose to publish the same data as multiple representations that differ only in whether the coding
    1030                      is defined as part of <a href="#header.content-type" class="smpl">Content-Type</a> or Content-Encoding, since some user agents will behave differently in their handling of each response (e.g., open a "Save
    1031                      as ..." dialog instead of automatic decompression and rendering of content).
    1032                   </p>
    1033                   <p id="rfc.section.3.1.2.2.p.8">An origin server <em class="bcp14">MAY</em> respond with a status code of <a href="#status.415" class="smpl">415 (Unsupported Media Type)</a> if a representation in the request message has a content coding that is not acceptable.
    1034                   </p>
    1035                </div>
    1036             </div>
    1037             <div id="audience.language">
    1038                <h3 id="rfc.section.3.1.3"><a href="#rfc.section.3.1.3">3.1.3</a>&nbsp;<a href="#audience.language">Audience Language</a></h3>
    1039                <div id="language.tags">
    1040                   <h4 id="rfc.section.3.1.3.1"><a href="#rfc.section.3.1.3.1">3.1.3.1</a>&nbsp;<a href="#language.tags">Language Tags</a></h4>
    1041                   <p id="rfc.section.3.1.3.1.p.1">A language tag, as defined in <a href="#RFC5646" id="rfc.xref.RFC5646.1"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a>, identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information to
    1042                      other human beings. Computer languages are explicitly excluded.
    1043                   </p>
    1044                   <p id="rfc.section.3.1.3.1.p.2">HTTP uses language tags within the <a href="#header.accept-language" class="smpl">Accept-Language</a> and <a href="#header.content-language" class="smpl">Content-Language</a> header fields. <a href="#header.accept-language" class="smpl">Accept-Language</a> uses the broader language-range production defined in <a href="#header.accept-language" id="rfc.xref.header.accept-language.1" title="Accept-Language">Section&nbsp;5.3.5</a>, whereas <a href="#header.content-language" class="smpl">Content-Language</a> uses the language-tag production defined below.
    1045                   </p>
    1046                   <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.10"></span>  <a href="#language.tags" class="smpl">language-tag</a> = &lt;Language-Tag, defined in <a href="#RFC5646" id="rfc.xref.RFC5646.2"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a>, <a href="http://tools.ietf.org/html/rfc5646#section-2.1">Section 2.1</a>&gt;
    1047 </pre><p id="rfc.section.3.1.3.1.p.4">A language tag is a sequence of one or more case-insensitive subtags, each separated by a hyphen character ("-", %x2D). In
    1048                      most cases, a language tag consists of a primary language subtag that identifies a broad family of related languages (e.g.,
    1049                      "en" = English), which is optionally followed by a series of subtags that refine or narrow that language's range (e.g., "en-CA"
    1050                      = the variety of English as communicated in Canada). Whitespace is not allowed within a language tag. Example tags include:
    1051                   </p>
    1052                   <div id="rfc.figure.u.11"></div><pre class="text">  fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
    1053 </pre><p id="rfc.section.3.1.3.1.p.6">See <a href="#RFC5646" id="rfc.xref.RFC5646.3"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a> for further information.
    1054                   </p>
    1055                </div>
    1056                <div id="header.content-language">
    1057                   <div id="rfc.iref.c.6"></div>
    1058                   <h4 id="rfc.section.3.1.3.2"><a href="#rfc.section.3.1.3.2">3.1.3.2</a>&nbsp;<a href="#header.content-language">Content-Language</a></h4>
    1059                   <p id="rfc.section.3.1.3.2.p.1">The "Content-Language" header field describes the natural language(s) of the intended audience for the representation. Note
    1060                      that this might not be equivalent to all the languages used within the representation.
    1061                   </p>
    1062                   <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.11"></span>  <a href="#header.content-language" class="smpl">Content-Language</a> = 1#<a href="#language.tags" class="smpl">language-tag</a>
    1063 </pre><p id="rfc.section.3.1.3.2.p.3">Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;3.1.3.1</a>. The primary purpose of Content-Language is to allow a user to identify and differentiate representations according to the
    1064                      users' own preferred language. Thus, if the content is intended only for a Danish-literate audience, the appropriate field
    1065                      is
    1066                   </p>
    1067                   <div id="rfc.figure.u.13"></div><pre class="text">  Content-Language: da
    1068 </pre><p id="rfc.section.3.1.3.2.p.5">If no Content-Language is specified, the default is that the content is intended for all language audiences. This might mean
    1069                      that the sender does not consider it to be specific to any natural language, or that the sender does not know for which language
    1070                      it is intended.
    1071                   </p>
    1072                   <p id="rfc.section.3.1.3.2.p.6">Multiple languages <em class="bcp14">MAY</em> be listed for content that is intended for multiple audiences. For example, a rendition of the "Treaty of Waitangi", presented
    1073                      simultaneously in the original Maori and English versions, would call for
    1074                   </p>
    1075                   <div id="rfc.figure.u.14"></div><pre class="text">  Content-Language: mi, en
    1076 </pre><p id="rfc.section.3.1.3.2.p.8">However, just because multiple languages are present within a representation does not mean that it is intended for multiple
    1077                      linguistic audiences. An example would be a beginner's language primer, such as "A First Lesson in Latin", which is clearly
    1078                      intended to be used by an English-literate audience. In this case, the Content-Language would properly only include "en".
    1079                   </p>
    1080                   <p id="rfc.section.3.1.3.2.p.9">Content-Language <em class="bcp14">MAY</em> be applied to any media type — it is not limited to textual documents.
    1081                   </p>
    1082                </div>
    1083             </div>
    1084             <div id="identification">
    1085                <h3 id="rfc.section.3.1.4"><a href="#rfc.section.3.1.4">3.1.4</a>&nbsp;<a href="#identification">Identification</a></h3>
    1086                <div id="identifying.payload">
    1087                   <h4 id="rfc.section.3.1.4.1"><a href="#rfc.section.3.1.4.1">3.1.4.1</a>&nbsp;<a href="#identifying.payload">Identifying a Representation</a></h4>
    1088                   <p id="rfc.section.3.1.4.1.p.1">When a complete or partial representation is transferred in a message payload, it is often desirable for the sender to supply,
    1089                      or the recipient to determine, an identifier for a resource corresponding to that representation.
    1090                   </p>
    1091                   <p id="rfc.section.3.1.4.1.p.2">For a request message: </p>
    1092                   <ul>
    1093                      <li>If the request has a <a href="#header.content-location" class="smpl">Content-Location</a> header field, then the sender asserts that the payload is a representation of the resource identified by the Content-Location
    1094                         field-value. However, such an assertion cannot be trusted unless it can be verified by other means (not defined by this specification).
    1095                         The information might still be useful for revision history links.
    1096                      </li>
    1097                      <li>Otherwise, the payload is unidentified.</li>
    1098                   </ul>
    1099                   <p id="rfc.section.3.1.4.1.p.3">For a response message, the following rules are applied in order until a match is found: </p>
    1100                   <ol>
    1101                      <li>If the request method is GET or HEAD and the response status code is <a href="#status.200" class="smpl">200 (OK)</a>, <a href="#status.204" class="smpl">204 (No Content)</a>, <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a>, or <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a>, the payload is a representation of the resource identified by the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    1102                      </li>
    1103                      <li>If the request method is GET or HEAD and the response status code is <a href="#status.203" class="smpl">203 (Non-Authoritative Information)</a>, the payload is a potentially modified or enhanced representation of the <a href="#resources" class="smpl">target resource</a> as provided by an intermediary.
    1104                      </li>
    1105                      <li>If the response has a <a href="#header.content-location" class="smpl">Content-Location</a> header field and its field-value is a reference to the same URI as the effective request URI, the payload is a representation
    1106                         of the resource identified by the effective request URI.
    1107                      </li>
    1108                      <li>If the response has a <a href="#header.content-location" class="smpl">Content-Location</a> header field and its field-value is a reference to a URI different from the effective request URI, then the sender asserts
    1109                         that the payload is a representation of the resource identified by the Content-Location field-value. However, such an assertion
    1110                         cannot be trusted unless it can be verified by other means (not defined by this specification).
    1111                      </li>
    1112                      <li>Otherwise, the payload is unidentified.</li>
    1113                   </ol>
    1114                </div>
    1115                <div id="header.content-location">
    1116                   <div id="rfc.iref.c.7"></div>
    1117                   <h4 id="rfc.section.3.1.4.2"><a href="#rfc.section.3.1.4.2">3.1.4.2</a>&nbsp;<a href="#header.content-location">Content-Location</a></h4>
    1118                   <p id="rfc.section.3.1.4.2.p.1">The "Content-Location" header field references a URI that can be used as an identifier for a specific resource corresponding
    1119                      to the representation in this message's payload. In other words, if one were to perform a GET request on this URI at the time
    1120                      of this message's generation, then a <a href="#status.200" class="smpl">200 (OK)</a> response would contain the same representation that is enclosed as payload in this message.
    1121                   </p>
    1122                   <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.12"></span>  <a href="#header.content-location" class="smpl">Content-Location</a> = <a href="#imported.abnf" class="smpl">absolute-URI</a> / <a href="#imported.abnf" class="smpl">partial-URI</a>
    1123 </pre><p id="rfc.section.3.1.4.2.p.3">The Content-Location value is not a replacement for the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.12"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). It is representation metadata. It has the same syntax and semantics as the header field of the same name defined for MIME
    1124                      body parts in <a href="http://tools.ietf.org/html/rfc2557#section-4">Section 4</a> of <a href="#RFC2557" id="rfc.xref.RFC2557.1"><cite title="MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)">[RFC2557]</cite></a>. However, its appearance in an HTTP message has some special implications for HTTP recipients.
    1125                   </p>
    1126                   <p id="rfc.section.3.1.4.2.p.4">If Content-Location is included in a <a href="#status.2xx" class="smpl">2xx (Successful)</a> response message and its value refers (after conversion to absolute form) to a URI that is the same as the effective request
    1127                      URI, then the recipient <em class="bcp14">MAY</em> consider the payload to be a current representation of that resource at the time indicated by the message origination date.
    1128                      For a GET (<a href="#GET" id="rfc.xref.GET.2" title="GET">Section&nbsp;4.3.1</a>) or HEAD (<a href="#HEAD" id="rfc.xref.HEAD.1" title="HEAD">Section&nbsp;4.3.2</a>) request, this is the same as the default semantics when no Content-Location is provided by the server. For a state-changing
    1129                      request like PUT (<a href="#PUT" id="rfc.xref.PUT.1" title="PUT">Section&nbsp;4.3.4</a>) or POST (<a href="#POST" id="rfc.xref.POST.1" title="POST">Section&nbsp;4.3.3</a>), it implies that the server's response contains the new representation of that resource, thereby distinguishing it from
    1130                      representations that might only report about the action (e.g., "It worked!"). This allows authoring applications to update
    1131                      their local copies without the need for a subsequent GET request.
    1132                   </p>
    1133                   <p id="rfc.section.3.1.4.2.p.5">If Content-Location is included in a <a href="#status.2xx" class="smpl">2xx (Successful)</a> response message and its field-value refers to a URI that differs from the effective request URI, then the origin server claims
    1134                      that the URI is an identifier for a different resource corresponding to the enclosed representation. Such a claim can only
    1135                      be trusted if both identifiers share the same resource owner, which cannot be programmatically determined via HTTP.
    1136                   </p>
    1137                   <ul>
    1138                      <li>For a response to a GET or HEAD request, this is an indication that the effective request URI refers to a resource that is
    1139                         subject to content negotiation and the Content-Location field-value is a more specific identifier for the <a href="#representations" class="smpl">selected representation</a>.
    1140                      </li>
    1141                      <li>For a <a href="#status.201" class="smpl">201 (Created)</a> response to a state-changing method, a Content-Location field-value that is identical to the <a href="#header.location" class="smpl">Location</a> field-value indicates that this payload is a current representation of the newly created resource.
    1142                      </li>
    1143                      <li>Otherwise, such a Content-Location indicates that this payload is a representation reporting on the requested action's status
    1144                         and that the same report is available (for future access with GET) at the given URI. For example, a purchase transaction made
    1145                         via a POST request might include a receipt document as the payload of the <a href="#status.200" class="smpl">200 (OK)</a> response; the Content-Location field-value provides an identifier for retrieving a copy of that same receipt in the future.
    1146                      </li>
    1147                   </ul>
    1148                   <p id="rfc.section.3.1.4.2.p.6">A user agent that sends Content-Location in a request message is stating that its value refers to where the user agent originally
    1149                      obtained the content of the enclosed representation (prior to any modifications made by that user agent). In other words,
    1150                      the user agent is providing a back link to the source of the original representation.
    1151                   </p>
    1152                   <p id="rfc.section.3.1.4.2.p.7">An origin server that receives a Content-Location field in a request message <em class="bcp14">MUST</em> treat the information as transitory request context rather than as metadata to be saved verbatim as part of the representation.
    1153                      An origin server <em class="bcp14">MAY</em> use that context to guide in processing the request or to save it for other uses, such as within source links or versioning
    1154                      metadata. However, an origin server <em class="bcp14">MUST NOT</em> use such context information to alter the request semantics.
    1155                   </p>
    1156                   <p id="rfc.section.3.1.4.2.p.8">For example, if a client makes a PUT request on a negotiated resource and the origin server accepts that PUT (without redirection),
    1157                      then the new state of that resource is expected to be consistent with the one representation supplied in that PUT; the Content-Location
    1158                      cannot be used as a form of reverse content selection identifier to update only one of the negotiated representations. If
    1159                      the user agent had wanted the latter semantics, it would have applied the PUT directly to the Content-Location URI.
    1160                   </p>
    1161                </div>
    1162             </div>
    1163          </div>
    1164          <div id="representation.data">
    1165             <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a href="#representation.data">Representation Data</a></h2>
    1166             <p id="rfc.section.3.2.p.1">The representation data associated with an HTTP message is either provided as the payload body of the message or referred
    1167                to by the message semantics and the effective request URI. The representation data is in a format and encoding defined by
    1168                the representation metadata header fields.
    1169             </p>
    1170             <p id="rfc.section.3.2.p.2">The data type of the representation data is determined via the header fields <a href="#header.content-type" class="smpl">Content-Type</a> and <a href="#header.content-encoding" class="smpl">Content-Encoding</a>. These define a two-layer, ordered encoding model:
    1171             </p>
    1172             <div id="rfc.figure.u.16"></div><pre class="text">  representation-data := Content-Encoding( Content-Type( bits ) )
    1173 </pre></div>
    1174          <div id="payload">
    1175             <div id="rfc.iref.p.1"></div>
    1176             <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a href="#payload">Payload Semantics</a></h2>
    1177             <p id="rfc.section.3.3.p.1">Some HTTP messages transfer a complete or partial representation as the message "<dfn>payload</dfn>". In some cases, a payload might contain only the associated representation's header fields (e.g., responses to HEAD) or
    1178                only some part(s) of the representation data (e.g., the <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> status code).
    1179             </p>
    1180             <p id="rfc.section.3.3.p.2">The purpose of a payload in a request is defined by the method semantics. For example, a representation in the payload of
    1181                a PUT request (<a href="#PUT" id="rfc.xref.PUT.2" title="PUT">Section&nbsp;4.3.4</a>) represents the desired state of the <a href="#resources" class="smpl">target resource</a> if the request is successfully applied, whereas a representation in the payload of a POST request (<a href="#POST" id="rfc.xref.POST.2" title="POST">Section&nbsp;4.3.3</a>) represents information to be processed by the target resource.
    1182             </p>
    1183             <p id="rfc.section.3.3.p.3">In a response, the payload's purpose is defined by both the request method and the response status code. For example, the
    1184                payload of a <a href="#status.200" class="smpl">200 (OK)</a> response to GET (<a href="#GET" id="rfc.xref.GET.3" title="GET">Section&nbsp;4.3.1</a>) represents the current state of the <a href="#resources" class="smpl">target resource</a>, as observed at the time of the message origination date (<a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section&nbsp;7.1.1.2</a>), whereas the payload of the same status code in a response to POST might represent either the processing result or the new
    1185                state of the target resource after applying the processing. Response messages with an error status code usually contain a
    1186                payload that represents the error condition, such that it describes the error state and what next steps are suggested for
    1187                resolving it.
    1188             </p>
    1189             <p id="rfc.section.3.3.p.4">Header fields that specifically describe the payload, rather than the associated representation, are referred to as "payload
    1190                header fields". Payload header fields are defined in other parts of this specification, due to their impact on message parsing.
    1191             </p>
    1192             <div id="rfc.table.u.2">
    1193                <table class="tt full left" cellpadding="3" cellspacing="0">
    1194                   <thead>
    1195                      <tr>
    1196                         <th>Header Field Name</th>
    1197                         <th>Defined in...</th>
    1198                      </tr>
    1199                   </thead>
    1200                   <tbody>
    1201                      <tr>
    1202                         <td class="left">Content-Length</td>
    1203                         <td class="left"><a href="p1-messaging.html#header.content-length" title="Content-Length">Section 3.3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.13"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a></td>
    1204                      </tr>
    1205                      <tr>
    1206                         <td class="left">Content-Range</td>
    1207                         <td class="left"><a href="p5-range.html#header.content-range" title="Content-Range">Section 4.2</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td>
    1208                      </tr>
    1209                      <tr>
    1210                         <td class="left">Trailer</td>
    1211                         <td class="left"><a href="p1-messaging.html#header.trailer" title="Trailer">Section 4.4</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.14"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a></td>
    1212                      </tr>
    1213                      <tr>
    1214                         <td class="left">Transfer-Encoding</td>
    1215                         <td class="left"><a href="p1-messaging.html#header.transfer-encoding" title="Transfer-Encoding">Section 3.3.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.15"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a></td>
    1216                      </tr>
    1217                   </tbody>
    1218                </table>
    1219             </div>
    1220          </div>
    1221          <div id="content.negotiation">
    1222             <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a href="#content.negotiation">Content Negotiation</a></h2>
    1223             <p id="rfc.section.3.4.p.1">When responses convey payload information, whether indicating a success or an error, the origin server often has different
    1224                ways of representing that information; for example, in different formats, languages, or encodings. Likewise, different users
    1225                or user agents might have differing capabilities, characteristics, or preferences that could influence which representation,
    1226                among those available, would be best to deliver. For this reason, HTTP provides mechanisms for <a href="#content.negotiation" class="smpl">content negotiation</a>.
    1227             </p>
    1228             <p id="rfc.section.3.4.p.2">This specification defines two patterns of content negotiation that can be made visible within the protocol: "proactive",
    1229                where the server selects the representation based upon the user agent's stated preferences, and "reactive" negotiation, where
    1230                the server provides a list of representations for the user agent to choose from. Other patterns of content negotiation include
    1231                "conditional content", where the representation consists of multiple parts that are selectively rendered based on user agent
    1232                parameters, "active content", where the representation contains a script that makes additional (more specific) requests based
    1233                on the user agent characteristics, and "Transparent Content Negotiation" (<a href="#RFC2295" id="rfc.xref.RFC2295.1"><cite title="Transparent Content Negotiation in HTTP">[RFC2295]</cite></a>), where content selection is performed by an intermediary. These patterns are not mutually exclusive, and each has trade-offs
    1234                in applicability and practicality.
    1235             </p>
    1236             <p id="rfc.section.3.4.p.3">Note that, in all cases, HTTP is not aware of the resource semantics. The consistency with which an origin server responds
    1237                to requests, over time and over the varying dimensions of content negotiation, and thus the "sameness" of a resource's observed
    1238                representations over time, is determined entirely by whatever entity or algorithm selects or generates those responses. HTTP
    1239                pays no attention to the man behind the curtain.
    1240             </p>
    1241             <div id="proactive.negotiation">
    1242                <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;<a href="#proactive.negotiation">Proactive Negotiation</a></h3>
    1243                <p id="rfc.section.3.4.1.p.1">When content negotiation preferences are sent by the user agent in a request to encourage an algorithm located at the server
    1244                   to select the preferred representation, it is called <dfn>proactive negotiation</dfn> (a.k.a., <dfn>server-driven negotiation</dfn>). Selection is based on the available representations for a response (the dimensions over which it might vary, such as language,
    1245                   content-coding, etc.) compared to various information supplied in the request, including both the explicit negotiation fields
    1246                   of <a href="#request.conneg" title="Content Negotiation">Section&nbsp;5.3</a> and implicit characteristics, such as the client's network address or parts of the <a href="#header.user-agent" class="smpl">User-Agent</a> field.
    1247                </p>
    1248                <p id="rfc.section.3.4.1.p.2">Proactive negotiation is advantageous when the algorithm for selecting from among the available representations is difficult
    1249                   to describe to a user agent, or when the server desires to send its "best guess" to the user agent along with the first response
    1250                   (hoping to avoid the round trip delay of a subsequent request if the "best guess" is good enough for the user). In order to
    1251                   improve the server's guess, a user agent <em class="bcp14">MAY</em> send request header fields that describe its preferences.
    1252                </p>
    1253                <p id="rfc.section.3.4.1.p.3">Proactive negotiation has serious disadvantages: </p>
    1254                <ul>
    1255                   <li>It is impossible for the server to accurately determine what might be "best" for any given user, since that would require
    1256                      complete knowledge of both the capabilities of the user agent and the intended use for the response (e.g., does the user want
    1257                      to view it on screen or print it on paper?);
    1258                   </li>
    1259                   <li>Having the user agent describe its capabilities in every request can be both very inefficient (given that only a small percentage
    1260                      of responses have multiple representations) and a potential risk to the user's privacy;
    1261                   </li>
    1262                   <li>It complicates the implementation of an origin server and the algorithms for generating responses to a request; and,</li>
    1263                   <li>It limits the reusability of responses for shared caching.</li>
    1264                </ul>
    1265                <p id="rfc.section.3.4.1.p.4">A user agent cannot rely on proactive negotiation preferences being consistently honored, since the origin server might not
    1266                   implement proactive negotiation for the requested resource or might decide that sending a response that doesn't conform to
    1267                   the user agent's preferences is better than sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response.
    1268                </p>
    1269                <p id="rfc.section.3.4.1.p.5">A <a href="#header.vary" class="smpl">Vary</a> header field (<a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section&nbsp;7.1.4</a>) is often sent in a response subject to proactive negotiation to indicate what parts of the request information were used
    1270                   in the selection algorithm.
    1271                </p>
    1272             </div>
    1273             <div id="reactive.negotiation">
    1274                <h3 id="rfc.section.3.4.2"><a href="#rfc.section.3.4.2">3.4.2</a>&nbsp;<a href="#reactive.negotiation">Reactive Negotiation</a></h3>
    1275                <p id="rfc.section.3.4.2.p.1">With <dfn>reactive negotiation</dfn> (a.k.a., <dfn>agent-driven negotiation</dfn>), selection of the best response representation (regardless of the status code) is performed by the user agent after receiving
    1276                   an initial response from the origin server that contains a list of resources for alternative representations. If the user
    1277                   agent is not satisfied by the initial response representation, it can perform a GET request on one or more of the alternative
    1278                   resources, selected based on metadata included in the list, to obtain a different form of representation for that response.
    1279                   Selection of alternatives might be performed automatically by the user agent or manually by the user selecting from a generated
    1280                   (possibly hypertext) menu.
    1281                </p>
    1282                <p id="rfc.section.3.4.2.p.2">Note that the above refers to representations of the response, in general, not representations of the resource. The alternative
    1283                   representations are only considered representations of the target resource if the response in which those alternatives are
    1284                   provided has the semantics of being a representation of the target resource (e.g., a <a href="#status.200" class="smpl">200 (OK)</a> response to a GET request) or has the semantics of providing links to alternative representations for the target resource
    1285                   (e.g., a <a href="#status.300" class="smpl">300 (Multiple Choices)</a> response to a GET request).
    1286                </p>
    1287                <p id="rfc.section.3.4.2.p.3">A server might choose not to send an initial representation, other than the list of alternatives, and thereby indicate that
    1288                   reactive negotiation by the user agent is preferred. For example, the alternatives listed in responses with the <a href="#status.300" class="smpl">300 (Multiple Choices)</a> and <a href="#status.406" class="smpl">406 (Not Acceptable)</a> status codes include information about the available representations so that the user or user agent can react by making a
    1289                   selection.
    1290                </p>
    1291                <p id="rfc.section.3.4.2.p.4">Reactive negotiation is advantageous when the response would vary over commonly used dimensions (such as type, language, or
    1292                   encoding), when the origin server is unable to determine a user agent's capabilities from examining the request, and generally
    1293                   when public caches are used to distribute server load and reduce network usage.
    1294                </p>
    1295                <p id="rfc.section.3.4.2.p.5">Reactive negotiation suffers from the disadvantages of transmitting a list of alternatives to the user agent, which degrades
    1296                   user-perceived latency if transmitted in the header section, and needing a second request to obtain an alternate representation.
    1297                   Furthermore, this specification does not define a mechanism for supporting automatic selection, though it does not prevent
    1298                   such a mechanism from being developed as an extension.
    1299                </p>
    1300             </div>
    1301          </div>
    1302       </div>
    1303       <div id="methods">
    1304          <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a href="#methods">Request Methods</a></h1>
    1305          <div id="method.overview">
    1306             <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a href="#method.overview">Overview</a></h2>
    1307             <p id="rfc.section.4.1.p.1">The request method token is the primary source of request semantics; it indicates the purpose for which the client has made
    1308                this request and what is expected by the client as a successful result.
    1309             </p>
    1310             <p id="rfc.section.4.1.p.2">The request method's semantics might be further specialized by the semantics of some header fields when present in a request
    1311                (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5</a>) if those additional semantics do not conflict with the method. For example, a client can send conditional request header
    1312                fields (<a href="#request.conditionals" title="Conditionals">Section&nbsp;5.2</a>) to make the requested action conditional on the current state of the target resource (<a href="#RFC7232" id="rfc.xref.RFC7232.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>).
    1313             </p>
    1314             <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.13"></span>  <a href="#method.overview" class="smpl">method</a> = <a href="#imported.abnf" class="smpl">token</a>
    1315 </pre><p id="rfc.section.4.1.p.4">HTTP was originally designed to be usable as an interface to distributed object systems. The request method was envisioned
    1316                as applying semantics to a <a href="#resources" class="smpl">target resource</a> in much the same way as invoking a defined method on an identified object would apply semantics. The method token is case-sensitive
    1317                because it might be used as a gateway to object-based systems with case-sensitive method names.
    1318             </p>
    1319             <p id="rfc.section.4.1.p.5">Unlike distributed objects, the standardized request methods in HTTP are not resource-specific, since uniform interfaces provide
    1320                for better visibility and reuse in network-based systems <a href="#REST" id="rfc.xref.REST.2"><cite title="Architectural Styles and the Design of Network-based Software Architectures">[REST]</cite></a>. Once defined, a standardized method ought to have the same semantics when applied to any resource, though each resource
    1321                determines for itself whether those semantics are implemented or allowed.
    1322             </p>
    1323             <p id="rfc.section.4.1.p.6">This specification defines a number of standardized methods that are commonly used in HTTP, as outlined by the following table.
    1324                By convention, standardized methods are defined in all-uppercase US-ASCII letters.
    1325             </p>
    1326             <div id="rfc.table.1">
    1327                <div id="table.of.methods"></div>
    1328                <table class="tt full left" cellpadding="3" cellspacing="0">
    1329                   <thead>
    1330                      <tr>
    1331                         <th>Method</th>
    1332                         <th>Description</th>
    1333                         <th>Sec.</th>
    1334                      </tr>
    1335                   </thead>
    1336                   <tbody>
    1337                      <tr>
    1338                         <td class="left">GET</td>
    1339                         <td class="left">Transfer a current representation of the target resource.</td>
    1340                         <td class="left"><a href="#GET" id="rfc.xref.GET.4" title="GET">4.3.1</a></td>
    1341                      </tr>
    1342                      <tr>
    1343                         <td class="left">HEAD</td>
    1344                         <td class="left">Same as GET, but only transfer the status line and header section.</td>
    1345                         <td class="left"><a href="#HEAD" id="rfc.xref.HEAD.2" title="HEAD">4.3.2</a></td>
    1346                      </tr>
    1347                      <tr>
    1348                         <td class="left">POST</td>
    1349                         <td class="left">Perform resource-specific processing on the request payload.</td>
    1350                         <td class="left"><a href="#POST" id="rfc.xref.POST.3" title="POST">4.3.3</a></td>
    1351                      </tr>
    1352                      <tr>
    1353                         <td class="left">PUT</td>
    1354                         <td class="left">Replace all current representations of the target resource with the request payload.</td>
    1355                         <td class="left"><a href="#PUT" id="rfc.xref.PUT.3" title="PUT">4.3.4</a></td>
    1356                      </tr>
    1357                      <tr>
    1358                         <td class="left">DELETE</td>
    1359                         <td class="left">Remove all current representations of the target resource.</td>
    1360                         <td class="left"><a href="#DELETE" id="rfc.xref.DELETE.1" title="DELETE">4.3.5</a></td>
    1361                      </tr>
    1362                      <tr>
    1363                         <td class="left">CONNECT</td>
    1364                         <td class="left">Establish a tunnel to the server identified by the target resource.</td>
    1365                         <td class="left"><a href="#CONNECT" id="rfc.xref.CONNECT.1" title="CONNECT">4.3.6</a></td>
    1366                      </tr>
    1367                      <tr>
    1368                         <td class="left">OPTIONS</td>
    1369                         <td class="left">Describe the communication options for the target resource.</td>
    1370                         <td class="left"><a href="#OPTIONS" id="rfc.xref.OPTIONS.1" title="OPTIONS">4.3.7</a></td>
    1371                      </tr>
    1372                      <tr>
    1373                         <td class="left">TRACE</td>
    1374                         <td class="left">Perform a message loop-back test along the path to the target resource.</td>
    1375                         <td class="left"><a href="#TRACE" id="rfc.xref.TRACE.1" title="TRACE">4.3.8</a></td>
    1376                      </tr>
    1377                   </tbody>
    1378                </table>
    1379             </div>
    1380             <p id="rfc.section.4.1.p.7">All general-purpose servers <em class="bcp14">MUST</em> support the methods GET and HEAD. All other methods are <em class="bcp14">OPTIONAL</em>.
    1381             </p>
    1382             <p id="rfc.section.4.1.p.8">Additional methods, outside the scope of this specification, have been standardized for use in HTTP. All such methods ought
    1383                to be registered within the "Hypertext Transfer Protocol (HTTP) Method Registry" maintained by IANA, as defined in <a href="#method.registry" title="Method Registry">Section&nbsp;8.1</a>.
    1384             </p>
    1385             <p id="rfc.section.4.1.p.9">The set of methods allowed by a target resource can be listed in an <a href="#header.allow" class="smpl">Allow</a> header field (<a href="#header.allow" id="rfc.xref.header.allow.1" title="Allow">Section&nbsp;7.4.1</a>). However, the set of allowed methods can change dynamically. When a request method is received that is unrecognized or not
    1386                implemented by an origin server, the origin server <em class="bcp14">SHOULD</em> respond with the <a href="#status.501" class="smpl">501 (Not Implemented)</a> status code. When a request method is received that is known by an origin server but not allowed for the target resource,
    1387                the origin server <em class="bcp14">SHOULD</em> respond with the <a href="#status.405" class="smpl">405 (Method Not Allowed)</a> status code.
    1388             </p>
    1389          </div>
    1390          <div id="method.properties">
    1391             <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a href="#method.properties">Common Method Properties</a></h2>
    1392             <div id="safe.methods">
    1393                <div id="rfc.iref.s.2"></div>
    1394                <h3 id="rfc.section.4.2.1"><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;<a href="#safe.methods">Safe Methods</a></h3>
    1395                <p id="rfc.section.4.2.1.p.1">Request methods are considered "<dfn>safe</dfn>" if their defined semantics are essentially read-only; i.e., the client does not request, and does not expect, any state
    1396                   change on the origin server as a result of applying a safe method to a target resource. Likewise, reasonable use of a safe
    1397                   method is not expected to cause any harm, loss of property, or unusual burden on the origin server.
    1398                </p>
    1399                <p id="rfc.section.4.2.1.p.2">This definition of safe methods does not prevent an implementation from including behavior that is potentially harmful, that
    1400                   is not entirely read-only, or that causes side effects while invoking a safe method. What is important, however, is that the
    1401                   client did not request that additional behavior and cannot be held accountable for it. For example, most servers append request
    1402                   information to access log files at the completion of every response, regardless of the method, and that is considered safe
    1403                   even though the log storage might become full and crash the server. Likewise, a safe request initiated by selecting an advertisement
    1404                   on the Web will often have the side effect of charging an advertising account.
    1405                </p>
    1406                <p id="rfc.section.4.2.1.p.3">Of the request methods defined by this specification, the GET, HEAD, OPTIONS, and TRACE methods are defined to be safe.</p>
    1407                <p id="rfc.section.4.2.1.p.4">The purpose of distinguishing between safe and unsafe methods is to allow automated retrieval processes (spiders) and cache
    1408                   performance optimization (pre-fetching) to work without fear of causing harm. In addition, it allows a user agent to apply
    1409                   appropriate constraints on the automated use of unsafe methods when processing potentially untrusted content.
    1410                </p>
    1411                <p id="rfc.section.4.2.1.p.5">A user agent <em class="bcp14">SHOULD</em> distinguish between safe and unsafe methods when presenting potential actions to a user, such that the user can be made aware
    1412                   of an unsafe action before it is requested.
    1413                </p>
    1414                <p id="rfc.section.4.2.1.p.6">When a resource is constructed such that parameters within the effective request URI have the effect of selecting an action,
    1415                   it is the resource owner's responsibility to ensure that the action is consistent with the request method semantics. For example,
    1416                   it is common for Web-based content editing software to use actions within query parameters, such as "page?do=delete". If the
    1417                   purpose of such a resource is to perform an unsafe action, then the resource owner <em class="bcp14">MUST</em> disable or disallow that action when it is accessed using a safe request method. Failure to do so will result in unfortunate
    1418                   side effects when automated processes perform a GET on every URI reference for the sake of link maintenance, pre-fetching,
    1419                   building a search index, etc.
    1420                </p>
    1421             </div>
    1422             <div id="idempotent.methods">
    1423                <div id="rfc.iref.i.1"></div>
    1424                <h3 id="rfc.section.4.2.2"><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></h3>
    1425                <p id="rfc.section.4.2.2.p.1">A request method is considered "<dfn id="idempotent">idempotent</dfn>" if the intended effect on the server of multiple identical requests with that method is the same as the effect for a single
    1426                   such request. Of the request methods defined by this specification, PUT, DELETE, and safe request methods are idempotent.
    1427                </p>
    1428                <p id="rfc.section.4.2.2.p.2">Like the definition of safe, the idempotent property only applies to what has been requested by the user; a server is free
    1429                   to log each request separately, retain a revision control history, or implement other non-idempotent side effects for each
    1430                   idempotent request.
    1431                </p>
    1432                <p id="rfc.section.4.2.2.p.3">Idempotent methods are distinguished because the request can be repeated automatically if a communication failure occurs before
    1433                   the client is able to read the server's response. For example, if a client sends a PUT request and the underlying connection
    1434                   is closed before any response is received, then the client can establish a new connection and retry the idempotent request.
    1435                   It knows that repeating the request will have the same intended effect, even if the original request succeeded, though the
    1436                   response might differ.
    1437                </p>
    1438             </div>
    1439             <div id="cacheable.methods">
    1440                <div id="rfc.iref.c.8"></div>
    1441                <h3 id="rfc.section.4.2.3"><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;<a href="#cacheable.methods">Cacheable Methods</a></h3>
    1442                <p id="rfc.section.4.2.3.p.1">Request methods can be defined as "<dfn id="cacheable">cacheable</dfn>" to indicate that responses to them are allowed to be stored for future reuse; for specific requirements see <a href="#RFC7234" id="rfc.xref.RFC7234.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>. In general, safe methods that do not depend on a current or authoritative response are defined as cacheable; this specification
    1443                   defines GET, HEAD, and POST as cacheable, although the overwhelming majority of cache implementations only support GET and
    1444                   HEAD.
    1445                </p>
    1446             </div>
    1447          </div>
    1448          <div id="method.definitions">
    1449             <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a href="#method.definitions">Method Definitions</a></h2>
    1450             <div id="GET">
    1451                <h3 id="rfc.section.4.3.1"><a href="#rfc.section.4.3.1">4.3.1</a>&nbsp;<a href="#GET">GET</a></h3>
    1452                <div id="rfc.iref.g.14"></div>
    1453                <p id="rfc.section.4.3.1.p.1">The GET method requests transfer of a current selected representation for the <a href="#resources" class="smpl">target resource</a>. GET is the primary mechanism of information retrieval and the focus of almost all performance optimizations. Hence, when
    1454                   people speak of retrieving some identifiable information via HTTP, they are generally referring to making a GET request.
    1455                </p>
    1456                <p id="rfc.section.4.3.1.p.2">It is tempting to think of resource identifiers as remote file system pathnames and of representations as being a copy of
    1457                   the contents of such files. In fact, that is how many resources are implemented (see <a href="#attack.pathname" title="Attacks Based on File and Path Names">Section&nbsp;9.1</a> for related security considerations). However, there are no such limitations in practice. The HTTP interface for a resource
    1458                   is just as likely to be implemented as a tree of content objects, a programmatic view on various database records, or a gateway
    1459                   to other information systems. Even when the URI mapping mechanism is tied to a file system, an origin server might be configured
    1460                   to execute the files with the request as input and send the output as the representation rather than transfer the files directly.
    1461                   Regardless, only the origin server needs to know how each of its resource identifiers corresponds to an implementation and
    1462                   how each implementation manages to select and send a current representation of the target resource in a response to GET.
    1463                </p>
    1464                <p id="rfc.section.4.3.1.p.3">A client can alter the semantics of GET to be a "range request", requesting transfer of only some part(s) of the selected
    1465                   representation, by sending a <a href="p5-range.html#header.range" class="smpl">Range</a> header field in the request (<a href="#RFC7233" id="rfc.xref.RFC7233.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>).
    1466                </p>
    1467                <p id="rfc.section.4.3.1.p.4">A payload within a GET request message has no defined semantics; sending a payload body on a GET request might cause some
    1468                   existing implementations to reject the request.
    1469                </p>
    1470                <p id="rfc.section.4.3.1.p.5">The response to a GET request is cacheable; a cache <em class="bcp14">MAY</em> use it to satisfy subsequent GET and HEAD requests unless otherwise indicated by the Cache-Control header field (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 5.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    1471                </p>
    1472             </div>
    1473             <div id="HEAD">
    1474                <h3 id="rfc.section.4.3.2"><a href="#rfc.section.4.3.2">4.3.2</a>&nbsp;<a href="#HEAD">HEAD</a></h3>
    1475                <div id="rfc.iref.h.1"></div>
    1476                <p id="rfc.section.4.3.2.p.1">The HEAD method is identical to GET except that the server <em class="bcp14">MUST NOT</em> send a message body in the response (i.e., the response terminates at the end of the header section). The server <em class="bcp14">SHOULD</em> send the same header fields in response to a HEAD request as it would have sent if the request had been a GET, except that
    1477                   the payload header fields (<a href="#payload" title="Payload Semantics">Section&nbsp;3.3</a>) <em class="bcp14">MAY</em> be omitted. This method can be used for obtaining metadata about the selected representation without transferring the representation
    1478                   data and is often used for testing hypertext links for validity, accessibility, and recent modification.
    1479                </p>
    1480                <p id="rfc.section.4.3.2.p.2">A payload within a HEAD request message has no defined semantics; sending a payload body on a HEAD request might cause some
    1481                   existing implementations to reject the request.
    1482                </p>
    1483                <p id="rfc.section.4.3.2.p.3">The response to a HEAD request is cacheable; a cache <em class="bcp14">MAY</em> use it to satisfy subsequent HEAD requests unless otherwise indicated by the Cache-Control header field (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 5.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>). A HEAD response might also have an effect on previously cached responses to GET; see <a href="p6-cache.html#head.effects" title="Freshening Responses via HEAD">Section 4.3.5</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>.
    1484                </p>
    1485             </div>
    1486             <div id="POST">
    1487                <div id="rfc.iref.p.2"></div>
    1488                <h3 id="rfc.section.4.3.3"><a href="#rfc.section.4.3.3">4.3.3</a>&nbsp;<a href="#POST">POST</a></h3>
    1489                <p id="rfc.section.4.3.3.p.1">The POST method requests that the <a href="#resources" class="smpl">target resource</a> process the representation enclosed in the request according to the resource's own specific semantics. For example, POST is
    1490                   used for the following functions (among others):
    1491                </p>
    1492                <ul>
    1493                   <li>Providing a block of data, such as the fields entered into an HTML form, to a data-handling process;</li>
    1494                   <li>Posting a message to a bulletin board, newsgroup, mailing list, blog, or similar group of articles;</li>
    1495                   <li>Creating a new resource that has yet to be identified by the origin server; and</li>
    1496                   <li>Appending data to a resource's existing representation(s).</li>
    1497                </ul>
    1498                <p id="rfc.section.4.3.3.p.2">An origin server indicates response semantics by choosing an appropriate status code depending on the result of processing
    1499                   the POST request; almost all of the status codes defined by this specification might be received in a response to POST (the
    1500                   exceptions being <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a>, <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a>, and <a href="p5-range.html#status.416" class="smpl">416 (Range Not Satisfiable)</a>).
    1501                </p>
    1502                <p id="rfc.section.4.3.3.p.3">If one or more resources has been created on the origin server as a result of successfully processing a POST request, the
    1503                   origin server <em class="bcp14">SHOULD</em> send a <a href="#status.201" class="smpl">201 (Created)</a> response containing a <a href="#header.location" class="smpl">Location</a> header field that provides an identifier for the primary resource created (<a href="#header.location" id="rfc.xref.header.location.1" title="Location">Section&nbsp;7.1.2</a>) and a representation that describes the status of the request while referring to the new resource(s).
    1504                </p>
    1505                <p id="rfc.section.4.3.3.p.4">Responses to POST requests are only cacheable when they include explicit freshness information (see <a href="p6-cache.html#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section 4.2.1</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>). However, POST caching is not widely implemented. For cases where an origin server wishes the client to be able to cache
    1506                   the result of a POST in a way that can be reused by a later GET, the origin server <em class="bcp14">MAY</em> send a <a href="#status.200" class="smpl">200 (OK)</a> response containing the result and a <a href="#header.content-location" class="smpl">Content-Location</a> header field that has the same value as the POST's effective request URI (<a href="#header.content-location" id="rfc.xref.header.content-location.2" title="Content-Location">Section&nbsp;3.1.4.2</a>).
    1507                </p>
    1508                <p id="rfc.section.4.3.3.p.5">If the result of processing a POST would be equivalent to a representation of an existing resource, an origin server <em class="bcp14">MAY</em> redirect the user agent to that resource by sending a <a href="#status.303" class="smpl">303 (See Other)</a> response with the existing resource's identifier in the <a href="#header.location" class="smpl">Location</a> field. This has the benefits of providing the user agent a resource identifier and transferring the representation via a method
    1509                   more amenable to shared caching, though at the cost of an extra request if the user agent does not already have the representation
    1510                   cached.
    1511                </p>
    1512             </div>
    1513             <div id="PUT">
    1514                <h3 id="rfc.section.4.3.4"><a href="#rfc.section.4.3.4">4.3.4</a>&nbsp;<a href="#PUT">PUT</a></h3>
    1515                <div id="rfc.iref.p.3"></div>
    1516                <p id="rfc.section.4.3.4.p.1">The PUT method requests that the state of the <a href="#resources" class="smpl">target resource</a> be created or replaced with the state defined by the representation enclosed in the request message payload. A successful
    1517                   PUT of a given representation would suggest that a subsequent GET on that same target resource will result in an equivalent
    1518                   representation being sent in a <a href="#status.200" class="smpl">200 (OK)</a> response. However, there is no guarantee that such a state change will be observable, since the target resource might be acted
    1519                   upon by other user agents in parallel, or might be subject to dynamic processing by the origin server, before any subsequent
    1520                   GET is received. A successful response only implies that the user agent's intent was achieved at the time of its processing
    1521                   by the origin server.
    1522                </p>
    1523                <p id="rfc.section.4.3.4.p.2">If the target resource does not have a current representation and the PUT successfully creates one, then the origin server <em class="bcp14">MUST</em> inform the user agent by sending a <a href="#status.201" class="smpl">201 (Created)</a> response. If the target resource does have a current representation and that representation is successfully modified in accordance
    1524                   with the state of the enclosed representation, then the origin server <em class="bcp14">MUST</em> send either a <a href="#status.200" class="smpl">200 (OK)</a> or a <a href="#status.204" class="smpl">204 (No Content)</a> response to indicate successful completion of the request.
    1525                </p>
    1526                <p id="rfc.section.4.3.4.p.3">An origin server <em class="bcp14">SHOULD</em> ignore unrecognized header fields received in a PUT request (i.e., do not save them as part of the resource state).
    1527                </p>
    1528                <p id="rfc.section.4.3.4.p.4">An origin server <em class="bcp14">SHOULD</em> verify that the PUT representation is consistent with any constraints the server has for the target resource that cannot or
    1529                   will not be changed by the PUT. This is particularly important when the origin server uses internal configuration information
    1530                   related to the URI in order to set the values for representation metadata on GET responses. When a PUT representation is inconsistent
    1531                   with the target resource, the origin server <em class="bcp14">SHOULD</em> either make them consistent, by transforming the representation or changing the resource configuration, or respond with an
    1532                   appropriate error message containing sufficient information to explain why the representation is unsuitable. The <a href="#status.409" class="smpl">409 (Conflict)</a> or <a href="#status.415" class="smpl">415 (Unsupported Media Type)</a> status codes are suggested, with the latter being specific to constraints on <a href="#header.content-type" class="smpl">Content-Type</a> values.
    1533                </p>
    1534                <p id="rfc.section.4.3.4.p.5">For example, if the target resource is configured to always have a <a href="#header.content-type" class="smpl">Content-Type</a> of "text/html" and the representation being PUT has a Content-Type of "image/jpeg", the origin server ought to do one of:
    1535                </p>
    1536                <ol class="la">
    1537                   <li>reconfigure the target resource to reflect the new media type;</li>
    1538                   <li>transform the PUT representation to a format consistent with that of the resource before saving it as the new resource state;
    1539                      or,
    1540                   </li>
    1541                   <li>reject the request with a <a href="#status.415" class="smpl">415 (Unsupported Media Type)</a> response indicating that the target resource is limited to "text/html", perhaps including a link to a different resource that
    1542                      would be a suitable target for the new representation.
    1543                   </li>
    1544                </ol>
    1545                <p id="rfc.section.4.3.4.p.6">HTTP does not define exactly how a PUT method affects the state of an origin server beyond what can be expressed by the intent
    1546                   of the user agent request and the semantics of the origin server response. It does not define what a resource might be, in
    1547                   any sense of that word, beyond the interface provided via HTTP. It does not define how resource state is "stored", nor how
    1548                   such storage might change as a result of a change in resource state, nor how the origin server translates resource state into
    1549                   representations. Generally speaking, all implementation details behind the resource interface are intentionally hidden by
    1550                   the server.
    1551                </p>
    1552                <p id="rfc.section.4.3.4.p.7">An origin server <em class="bcp14">MUST NOT</em> send a validator header field (<a href="#response.validator" title="Validator Header Fields">Section&nbsp;7.2</a>), such as an <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> or <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> field, in a successful response to PUT unless the request's representation data was saved without any transformation applied
    1553                   to the body (i.e., the resource's new representation data is identical to the representation data received in the PUT request)
    1554                   and the validator field value reflects the new representation. This requirement allows a user agent to know when the representation
    1555                   body it has in memory remains current as a result of the PUT, thus not in need of being retrieved again from the origin server,
    1556                   and that the new validator(s) received in the response can be used for future conditional requests in order to prevent accidental
    1557                   overwrites (<a href="#request.conditionals" title="Conditionals">Section&nbsp;5.2</a>).
    1558                </p>
    1559                <p id="rfc.section.4.3.4.p.8">The fundamental difference between the POST and PUT methods is highlighted by the different intent for the enclosed representation.
    1560                   The target resource in a POST request is intended to handle the enclosed representation according to the resource's own semantics,
    1561                   whereas the enclosed representation in a PUT request is defined as replacing the state of the target resource. Hence, the
    1562                   intent of PUT is idempotent and visible to intermediaries, even though the exact effect is only known by the origin server.
    1563                </p>
    1564                <p id="rfc.section.4.3.4.p.9">Proper interpretation of a PUT request presumes that the user agent knows which target resource is desired. A service that
    1565                   selects a proper URI on behalf of the client, after receiving a state-changing request, <em class="bcp14">SHOULD</em> be implemented using the POST method rather than PUT. If the origin server will not make the requested PUT state change to
    1566                   the target resource and instead wishes to have it applied to a different resource, such as when the resource has been moved
    1567                   to a different URI, then the origin server <em class="bcp14">MUST</em> send an appropriate <a href="#status.3xx" class="smpl">3xx (Redirection)</a> response; the user agent <em class="bcp14">MAY</em> then make its own decision regarding whether or not to redirect the request.
    1568                </p>
    1569                <p id="rfc.section.4.3.4.p.10">A PUT request applied to the target resource can have side effects on other resources. For example, an article might have
    1570                   a URI for identifying "the current version" (a resource) that is separate from the URIs identifying each particular version
    1571                   (different resources that at one point shared the same state as the current version resource). A successful PUT request on
    1572                   "the current version" URI might therefore create a new version resource in addition to changing the state of the target resource,
    1573                   and might also cause links to be added between the related resources.
    1574                </p>
    1575                <p id="rfc.section.4.3.4.p.11">An origin server that allows PUT on a given target resource <em class="bcp14">MUST</em> send a <a href="#status.400" class="smpl">400 (Bad Request)</a> response to a PUT request that contains a <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> header field (<a href="p5-range.html#header.content-range" title="Content-Range">Section 4.2</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>), since the payload is likely to be partial content that has been mistakenly PUT as a full representation. Partial content
    1576                   updates are possible by targeting a separately identified resource with state that overlaps a portion of the larger resource,
    1577                   or by using a different method that has been specifically defined for partial updates (for example, the PATCH method defined
    1578                   in <a href="#RFC5789" id="rfc.xref.RFC5789.1"><cite title="PATCH Method for HTTP">[RFC5789]</cite></a>).
    1579                </p>
    1580                <p id="rfc.section.4.3.4.p.12">Responses to the PUT method are not cacheable. If a successful PUT request passes through a cache that has one or more stored
    1581                   responses for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation" title="Invalidation">Section 4.4</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    1582                </p>
    1583             </div>
    1584             <div id="DELETE">
    1585                <h3 id="rfc.section.4.3.5"><a href="#rfc.section.4.3.5">4.3.5</a>&nbsp;<a href="#DELETE">DELETE</a></h3>
    1586                <div id="rfc.iref.d.2"></div>
    1587                <p id="rfc.section.4.3.5.p.1">The DELETE method requests that the origin server remove the association between the <a href="#resources" class="smpl">target resource</a> and its current functionality. In effect, this method is similar to the rm command in UNIX: it expresses a deletion operation
    1588                   on the URI mapping of the origin server rather than an expectation that the previously associated information be deleted.
    1589                </p>
    1590                <p id="rfc.section.4.3.5.p.2">If the target resource has one or more current representations, they might or might not be destroyed by the origin server,
    1591                   and the associated storage might or might not be reclaimed, depending entirely on the nature of the resource and its implementation
    1592                   by the origin server (which are beyond the scope of this specification). Likewise, other implementation aspects of a resource
    1593                   might need to be deactivated or archived as a result of a DELETE, such as database or gateway connections. In general, it
    1594                   is assumed that the origin server will only allow DELETE on resources for which it has a prescribed mechanism for accomplishing
    1595                   the deletion.
    1596                </p>
    1597                <p id="rfc.section.4.3.5.p.3">Relatively few resources allow the DELETE method — its primary use is for remote authoring environments, where the user has
    1598                   some direction regarding its effect. For example, a resource that was previously created using a PUT request, or identified
    1599                   via the Location header field after a <a href="#status.201" class="smpl">201 (Created)</a> response to a POST request, might allow a corresponding DELETE request to undo those actions. Similarly, custom user agent
    1600                   implementations that implement an authoring function, such as revision control clients using HTTP for remote operations, might
    1601                   use DELETE based on an assumption that the server's URI space has been crafted to correspond to a version repository.
    1602                </p>
    1603                <p id="rfc.section.4.3.5.p.4">If a DELETE method is successfully applied, the origin server <em class="bcp14">SHOULD</em> send a <a href="#status.202" class="smpl">202 (Accepted)</a> status code if the action will likely succeed but has not yet been enacted, a <a href="#status.204" class="smpl">204 (No Content)</a> status code if the action has been enacted and no further information is to be supplied, or a <a href="#status.200" class="smpl">200 (OK)</a> status code if the action has been enacted and the response message includes a representation describing the status.
    1604                </p>
    1605                <p id="rfc.section.4.3.5.p.5">A payload within a DELETE request message has no defined semantics; sending a payload body on a DELETE request might cause
    1606                   some existing implementations to reject the request.
    1607                </p>
    1608                <p id="rfc.section.4.3.5.p.6">Responses to the DELETE method are not cacheable. If a DELETE request passes through a cache that has one or more stored responses
    1609                   for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation" title="Invalidation">Section 4.4</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    1610                </p>
    1611             </div>
    1612             <div id="CONNECT">
    1613                <div id="rfc.iref.c.9"></div>
    1614                <h3 id="rfc.section.4.3.6"><a href="#rfc.section.4.3.6">4.3.6</a>&nbsp;<a href="#CONNECT">CONNECT</a></h3>
    1615                <p id="rfc.section.4.3.6.p.1">The CONNECT method requests that the recipient establish a tunnel to the destination origin server identified by the request-target
    1616                   and, if successful, thereafter restrict its behavior to blind forwarding of packets, in both directions, until the tunnel
    1617                   is closed. Tunnels are commonly used to create an end-to-end virtual connection, through one or more proxies, which can then
    1618                   be secured using TLS (Transport Layer Security, <a href="#RFC5246" id="rfc.xref.RFC5246.1"><cite title="The Transport Layer Security (TLS) Protocol Version 1.2">[RFC5246]</cite></a>).
    1619                </p>
    1620                <p id="rfc.section.4.3.6.p.2">CONNECT is intended only for use in requests to a proxy. An origin server that receives a CONNECT request for itself <em class="bcp14">MAY</em> respond with a <a href="#status.2xx" class="smpl">2xx (Successful)</a> status code to indicate that a connection is established. However, most origin servers do not implement CONNECT.
    1621                </p>
    1622                <p id="rfc.section.4.3.6.p.3">A client sending a CONNECT request <em class="bcp14">MUST</em> send the authority form of request-target (<a href="p1-messaging.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.16"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>); i.e., the request-target consists of only the host name and port number of the tunnel destination, separated by a colon.
    1623                   For example,
    1624                </p>
    1625                <div id="rfc.figure.u.18"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.1
    1626 Host: server.example.com:80
    1627 
    1628 </pre><p id="rfc.section.4.3.6.p.5">The recipient proxy can establish a tunnel either by directly connecting to the request-target or, if configured to use another
    1629                   proxy, by forwarding the CONNECT request to the next inbound proxy. Any <a href="#status.2xx" class="smpl">2xx (Successful)</a> response indicates that the sender (and all inbound proxies) will switch to tunnel mode immediately after the blank line that
    1630                   concludes the successful response's header section; data received after that blank line is from the server identified by the
    1631                   request-target. Any response other than a successful response indicates that the tunnel has not yet been formed and that the
    1632                   connection remains governed by HTTP.
    1633                </p>
    1634                <p id="rfc.section.4.3.6.p.6">A tunnel is closed when a tunnel intermediary detects that either side has closed its connection: the intermediary <em class="bcp14">MUST</em> attempt to send any outstanding data that came from the closed side to the other side, close both connections, and then discard
    1635                   any remaining data left undelivered.
    1636                </p>
    1637                <p id="rfc.section.4.3.6.p.7">Proxy authentication might be used to establish the authority to create a tunnel. For example,</p>
    1638                <div id="rfc.figure.u.19"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.1
    1639 Host: server.example.com:80
    1640 Proxy-Authorization: basic aGVsbG86d29ybGQ=
    1641 
    1642 </pre><p id="rfc.section.4.3.6.p.9">There are significant risks in establishing a tunnel to arbitrary servers, particularly when the destination is a well-known
    1643                   or reserved TCP port that is not intended for Web traffic. For example, a CONNECT to a request-target of "example.com:25"
    1644                   would suggest that the proxy connect to the reserved port for SMTP traffic; if allowed, that could trick the proxy into relaying
    1645                   spam email. Proxies that support CONNECT <em class="bcp14">SHOULD</em> restrict its use to a limited set of known ports or a configurable whitelist of safe request targets.
    1646                </p>
    1647                <p id="rfc.section.4.3.6.p.10">A server <em class="bcp14">MUST NOT</em> send any <a href="p1-messaging.html#header.transfer-encoding" class="smpl">Transfer-Encoding</a> or <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a> header fields in a <a href="#status.2xx" class="smpl">2xx (Successful)</a> response to CONNECT. A client <em class="bcp14">MUST</em> ignore any Content-Length or Transfer-Encoding header fields received in a successful response to CONNECT.
    1648                </p>
    1649                <p id="rfc.section.4.3.6.p.11">A payload within a CONNECT request message has no defined semantics; sending a payload body on a CONNECT request might cause
    1650                   some existing implementations to reject the request.
    1651                </p>
    1652                <p id="rfc.section.4.3.6.p.12">Responses to the CONNECT method are not cacheable.</p>
    1653             </div>
    1654             <div id="OPTIONS">
    1655                <h3 id="rfc.section.4.3.7"><a href="#rfc.section.4.3.7">4.3.7</a>&nbsp;<a href="#OPTIONS">OPTIONS</a></h3>
    1656                <div id="rfc.iref.o.1"></div>
    1657                <p id="rfc.section.4.3.7.p.1">The OPTIONS method requests information about the communication options available for the target resource, at either the origin
    1658                   server or an intervening intermediary. This method allows a client to determine the options and/or requirements associated
    1659                   with a resource, or the capabilities of a server, without implying a resource action.
    1660                </p>
    1661                <p id="rfc.section.4.3.7.p.2">An OPTIONS request with an asterisk ("*") as the request-target (<a href="p1-messaging.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.17"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) applies to the server in general rather than to a specific resource. Since a server's communication options typically depend
    1662                   on the resource, the "*" request is only useful as a "ping" or "no-op" type of method; it does nothing beyond allowing the
    1663                   client to test the capabilities of the server. For example, this can be used to test a proxy for HTTP/1.1 conformance (or
    1664                   lack thereof).
    1665                </p>
    1666                <p id="rfc.section.4.3.7.p.3">If the request-target is not an asterisk, the OPTIONS request applies to the options that are available when communicating
    1667                   with the target resource.
    1668                </p>
    1669                <p id="rfc.section.4.3.7.p.4">A server generating a successful response to OPTIONS <em class="bcp14">SHOULD</em> send any header fields that might indicate optional features implemented by the server and applicable to the target resource
    1670                   (e.g., <a href="#header.allow" class="smpl">Allow</a>), including potential extensions not defined by this specification. The response payload, if any, might also describe the
    1671                   communication options in a machine or human-readable representation. A standard format for such a representation is not defined
    1672                   by this specification, but might be defined by future extensions to HTTP. A server <em class="bcp14">MUST</em> generate a <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a> field with a value of "0" if no payload body is to be sent in the response.
    1673                </p>
    1674                <p id="rfc.section.4.3.7.p.5">A client <em class="bcp14">MAY</em> send a <a href="#header.max-forwards" class="smpl">Max-Forwards</a> header field in an OPTIONS request to target a specific recipient in the request chain (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.1" title="Max-Forwards">Section&nbsp;5.1.2</a>). A proxy <em class="bcp14">MUST NOT</em> generate a Max-Forwards header field while forwarding a request unless that request was received with a Max-Forwards field.
    1675                </p>
    1676                <p id="rfc.section.4.3.7.p.6">A client that generates an OPTIONS request containing a payload body <em class="bcp14">MUST</em> send a valid <a href="#header.content-type" class="smpl">Content-Type</a> header field describing the representation media type. Although this specification does not define any use for such a payload,
    1677                   future extensions to HTTP might use the OPTIONS body to make more detailed queries about the target resource.
    1678                </p>
    1679                <p id="rfc.section.4.3.7.p.7">Responses to the OPTIONS method are not cacheable.</p>
    1680             </div>
    1681             <div id="TRACE">
    1682                <h3 id="rfc.section.4.3.8"><a href="#rfc.section.4.3.8">4.3.8</a>&nbsp;<a href="#TRACE">TRACE</a></h3>
    1683                <div id="rfc.iref.t.1"></div>
    1684                <p id="rfc.section.4.3.8.p.1">The TRACE method requests a remote, application-level loop-back of the request message. The final recipient of the request <em class="bcp14">SHOULD</em> reflect the message received, excluding some fields described below, back to the client as the message body of a <a href="#status.200" class="smpl">200 (OK)</a> response with a <a href="#header.content-type" class="smpl">Content-Type</a> of "message/http" (<a href="p1-messaging.html#internet.media.type.message.http" title="Internet Media Type message/http">Section 8.3.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.18"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). The final recipient is either the origin server or the first server to receive a <a href="#header.max-forwards" class="smpl">Max-Forwards</a> value of zero (0) in the request (<a href="#header.max-forwards" id="rfc.xref.header.max-forwards.2" title="Max-Forwards">Section&nbsp;5.1.2</a>).
    1685                </p>
    1686                <p id="rfc.section.4.3.8.p.2">A client <em class="bcp14">MUST NOT</em> generate header fields in a TRACE request containing sensitive data that might be disclosed by the response. For example,
    1687                   it would be foolish for a user agent to send stored user credentials <a href="#RFC7235" id="rfc.xref.RFC7235.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a> or cookies <a href="#RFC6265" id="rfc.xref.RFC6265.1"><cite title="HTTP State Management Mechanism">[RFC6265]</cite></a> in a TRACE request. The final recipient of the request <em class="bcp14">SHOULD</em> exclude any request header fields that are likely to contain sensitive data when that recipient generates the response body.
    1688                </p>
    1689                <p id="rfc.section.4.3.8.p.3">TRACE allows the client to see what is being received at the other end of the request chain and use that data for testing
    1690                   or diagnostic information. The value of the <a href="p1-messaging.html#header.via" class="smpl">Via</a> header field (<a href="p1-messaging.html#header.via" title="Via">Section 5.7.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.19"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) is of particular interest, since it acts as a trace of the request chain. Use of the <a href="#header.max-forwards" class="smpl">Max-Forwards</a> header field allows the client to limit the length of the request chain, which is useful for testing a chain of proxies forwarding
    1691                   messages in an infinite loop.
    1692                </p>
    1693                <p id="rfc.section.4.3.8.p.4">A client <em class="bcp14">MUST NOT</em> send a message body in a TRACE request.
    1694                </p>
    1695                <p id="rfc.section.4.3.8.p.5">Responses to the TRACE method are not cacheable.</p>
    1696             </div>
    1697          </div>
    1698       </div>
    1699       <div id="request.header.fields">
    1700          <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a href="#request.header.fields">Request Header Fields</a></h1>
    1701          <p id="rfc.section.5.p.1">A client sends request header fields to provide more information about the request context, make the request conditional based
    1702             on the target resource state, suggest preferred formats for the response, supply authentication credentials, or modify the
    1703             expected request processing. These fields act as request modifiers, similar to the parameters on a programming language method
    1704             invocation.
    1705          </p>
    1706          <div id="request.controls">
    1707             <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a href="#request.controls">Controls</a></h2>
    1708             <p id="rfc.section.5.1.p.1">Controls are request header fields that direct specific handling of the request.</p>
    1709             <div id="rfc.table.u.3">
    1710                <table class="tt full left" cellpadding="3" cellspacing="0">
    1711                   <thead>
    1712                      <tr>
    1713                         <th>Header Field Name</th>
    1714                         <th>Defined in...</th>
    1715                      </tr>
    1716                   </thead>
    1717                   <tbody>
    1718                      <tr>
    1719                         <td class="left">Cache-Control</td>
    1720                         <td class="left"><a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 5.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td>
    1721                      </tr>
    1722                      <tr>
    1723                         <td class="left">Expect</td>
    1724                         <td class="left"><a href="#header.expect" id="rfc.xref.header.expect.1" title="Expect">Section&nbsp;5.1.1</a></td>
    1725                      </tr>
    1726                      <tr>
    1727                         <td class="left">Host</td>
    1728                         <td class="left"><a href="p1-messaging.html#header.host" title="Host">Section 5.4</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.20"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a></td>
    1729                      </tr>
    1730                      <tr>
    1731                         <td class="left">Max-Forwards</td>
    1732                         <td class="left"><a href="#header.max-forwards" id="rfc.xref.header.max-forwards.3" title="Max-Forwards">Section&nbsp;5.1.2</a></td>
    1733                      </tr>
    1734                      <tr>
    1735                         <td class="left">Pragma</td>
    1736                         <td class="left"><a href="p6-cache.html#header.pragma" title="Pragma">Section 5.4</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td>
    1737                      </tr>
    1738                      <tr>
    1739                         <td class="left">Range</td>
    1740                         <td class="left"><a href="p5-range.html#header.range" title="Range">Section 3.1</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td>
    1741                      </tr>
    1742                      <tr>
    1743                         <td class="left">TE</td>
    1744                         <td class="left"><a href="p1-messaging.html#header.te" title="TE">Section 4.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.21"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a></td>
    1745                      </tr>
    1746                   </tbody>
    1747                </table>
    1748             </div>
    1749             <div id="header.expect">
    1750                <div id="rfc.iref.e.1"></div>
    1751                <div id="rfc.iref.38"></div>
    1752                <h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;<a href="#header.expect">Expect</a></h3>
    1753                <p id="rfc.section.5.1.1.p.1">The "Expect" header field in a request indicates a certain set of behaviors (expectations) that need to be supported by the
    1754                   server in order to properly handle this request. The only such expectation defined by this specification is <a href="#header.expect" class="smpl">100-continue</a>.
    1755                </p>
    1756                <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.15"></span>  <a href="#header.expect" class="smpl">Expect</a>  = "100-continue"
    1757 </pre><p id="rfc.section.5.1.1.p.3">The Expect field-value is case-insensitive.</p>
    1758                <p id="rfc.section.5.1.1.p.4">A server that receives an Expect field-value other than <a href="#header.expect" class="smpl">100-continue</a> <em class="bcp14">MAY</em> respond with a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status code to indicate that the unexpected expectation cannot be met.
    1759                </p>
    1760                <p id="rfc.section.5.1.1.p.5">A <dfn>100-continue</dfn> expectation informs recipients that the client is about to send a (presumably large) message body in this request and wishes
    1761                   to receive a <a href="#status.100" class="smpl">100 (Continue)</a> interim response if the request-line and header fields are not sufficient to cause an immediate success, redirect, or error
    1762                   response. This allows the client to wait for an indication that it is worthwhile to send the message body before actually
    1763                   doing so, which can improve efficiency when the message body is huge or when the client anticipates that an error is likely
    1764                   (e.g., when sending a state-changing method, for the first time, without previously verified authentication credentials).
    1765                </p>
    1766                <p id="rfc.section.5.1.1.p.6">For example, a request that begins with</p>
    1767                <div id="rfc.figure.u.21"></div><pre class="text2">PUT /somewhere/fun HTTP/1.1
    1768 Host: origin.example.com
    1769 Content-Type: video/h264
    1770 Content-Length: 1234567890987
    1771 Expect: 100-continue
    1772 
    1773 </pre><p id="rfc.section.5.1.1.p.8">allows the origin server to immediately respond with an error message, such as <a href="p7-auth.html#status.401" class="smpl">401 (Unauthorized)</a> or <a href="#status.405" class="smpl">405 (Method Not Allowed)</a>, before the client starts filling the pipes with an unnecessary data transfer.
    1774                </p>
    1775                <p id="rfc.section.5.1.1.p.9">Requirements for clients: </p>
    1776                <ul>
    1777                   <li>A client <em class="bcp14">MUST NOT</em> generate a 100-continue expectation in a request that does not include a message body.
    1778                   </li>
    1779                   <li>A client that will wait for a <a href="#status.100" class="smpl">100 (Continue)</a> response before sending the request message body <em class="bcp14">MUST</em> send an <a href="#header.expect" class="smpl">Expect</a> header field containing a 100-continue expectation.
    1780                   </li>
    1781                   <li>A client that sends a 100-continue expectation is not required to wait for any specific length of time; such a client <em class="bcp14">MAY</em> proceed to send the message body even if it has not yet received a response. Furthermore, since <a href="#status.100" class="smpl">100 (Continue)</a> responses cannot be sent through an HTTP/1.0 intermediary, such a client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the message body.
    1782                   </li>
    1783                   <li>A client that receives a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status code in response to a request containing a 100-continue expectation <em class="bcp14">SHOULD</em> repeat that request without a 100-continue expectation, since the 417 response merely indicates that the response chain does
    1784                      not support expectations (e.g., it passes through an HTTP/1.0 server).
    1785                   </li>
    1786                </ul>
    1787                <p id="rfc.section.5.1.1.p.10">Requirements for servers: </p>
    1788                <ul>
    1789                   <li>A server that receives a 100-continue expectation in an HTTP/1.0 request <em class="bcp14">MUST</em> ignore that expectation.
    1790                   </li>
    1791                   <li>A server <em class="bcp14">MAY</em> omit sending a <a href="#status.100" class="smpl">100 (Continue)</a> response if it has already received some or all of the message body for the corresponding request, or if the framing indicates
    1792                      that there is no message body.
    1793                   </li>
    1794                   <li>A server that sends a <a href="#status.100" class="smpl">100 (Continue)</a> response <em class="bcp14">MUST</em> ultimately send a final status code, once the message body is received and processed, unless the connection is closed prematurely.
    1795                   </li>
    1796                   <li>A server that responds with a final status code before reading the entire message body <em class="bcp14">SHOULD</em> indicate in that response whether it intends to close the connection or continue reading and discarding the request message
    1797                      (see <a href="p1-messaging.html#persistent.tear-down" title="Tear-down">Section 6.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.22"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    1798                   </li>
    1799                </ul>
    1800                <p id="rfc.section.5.1.1.p.11">An origin server <em class="bcp14">MUST</em>, upon receiving an HTTP/1.1 (or later) request-line and a complete header section that contains a 100-continue expectation
    1801                   and indicates a request message body will follow, either send an immediate response with a final status code, if that status
    1802                   can be determined by examining just the request-line and header fields, or send an immediate <a href="#status.100" class="smpl">100 (Continue)</a> response to encourage the client to send the request's message body. The origin server <em class="bcp14">MUST NOT</em> wait for the message body before sending the <a href="#status.100" class="smpl">100 (Continue)</a> response.
    1803                </p>
    1804                <p id="rfc.section.5.1.1.p.12">A proxy <em class="bcp14">MUST</em>, upon receiving an HTTP/1.1 (or later) request-line and a complete header section that contains a 100-continue expectation
    1805                   and indicates a request message body will follow, either send an immediate response with a final status code, if that status
    1806                   can be determined by examining just the request-line and header fields, or begin forwarding the request toward the origin
    1807                   server by sending a corresponding request-line and header section to the next inbound server. If the proxy believes (from
    1808                   configuration or past interaction) that the next inbound server only supports HTTP/1.0, the proxy <em class="bcp14">MAY</em> generate an immediate <a href="#status.100" class="smpl">100 (Continue)</a> response to encourage the client to begin sending the message body.
    1809                </p>
    1810                <div class="note" id="rfc.section.5.1.1.p.13">
    1811                   <p><b>Note:</b> The Expect header field was added after the original publication of HTTP/1.1 <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> as both the means to request an interim <a href="#status.100" class="smpl">100 (Continue)</a> response and the general mechanism for indicating must-understand extensions. However, the extension mechanism has not been
    1812                      used by clients and the must-understand requirements have not been implemented by many servers, rendering the extension mechanism
    1813                      useless. This specification has removed the extension mechanism in order to simplify the definition and processing of 100-continue.
    1814                   </p>
    1815                </div>
    1816             </div>
    1817             <div id="header.max-forwards">
    1818                <div id="rfc.iref.m.1"></div>
    1819                <h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;<a href="#header.max-forwards">Max-Forwards</a></h3>
    1820                <p id="rfc.section.5.1.2.p.1">The "Max-Forwards" header field provides a mechanism with the TRACE (<a href="#TRACE" id="rfc.xref.TRACE.2" title="TRACE">Section&nbsp;4.3.8</a>) and OPTIONS (<a href="#OPTIONS" id="rfc.xref.OPTIONS.2" title="OPTIONS">Section&nbsp;4.3.7</a>) request methods to limit the number of times that the request is forwarded by proxies. This can be useful when the client
    1821                   is attempting to trace a request that appears to be failing or looping mid-chain.
    1822                </p>
    1823                <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.16"></span>  <a href="#header.max-forwards" class="smpl">Max-Forwards</a> = 1*<a href="#imported.abnf" class="smpl">DIGIT</a>
    1824 </pre><p id="rfc.section.5.1.2.p.3">The Max-Forwards value is a decimal integer indicating the remaining number of times this request message can be forwarded.</p>
    1825                <p id="rfc.section.5.1.2.p.4">Each intermediary that receives a TRACE or OPTIONS request containing a Max-Forwards header field <em class="bcp14">MUST</em> check and update its value prior to forwarding the request. If the received value is zero (0), the intermediary <em class="bcp14">MUST NOT</em> forward the request; instead, the intermediary <em class="bcp14">MUST</em> respond as the final recipient. If the received Max-Forwards value is greater than zero, the intermediary <em class="bcp14">MUST</em> generate an updated Max-Forwards field in the forwarded message with a field-value that is the lesser of a) the received value
    1826                   decremented by one (1) or b) the recipient's maximum supported value for Max-Forwards.
    1827                </p>
    1828                <p id="rfc.section.5.1.2.p.5">A recipient <em class="bcp14">MAY</em> ignore a Max-Forwards header field received with any other request methods.
    1829                </p>
    1830             </div>
    1831          </div>
    1832          <div id="request.conditionals">
    1833             <div id="rfc.iref.c.10"></div>
    1834             <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a href="#request.conditionals">Conditionals</a></h2>
    1835             <p id="rfc.section.5.2.p.1">The HTTP conditional request header fields <a href="#RFC7232" id="rfc.xref.RFC7232.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a> allow a client to place a precondition on the state of the target resource, so that the action corresponding to the method
    1836                semantics will not be applied if the precondition evaluates to false. Each precondition defined by this specification consists
    1837                of a comparison between a set of validators obtained from prior representations of the target resource to the current state
    1838                of validators for the <a href="#representations" class="smpl">selected representation</a> (<a href="#response.validator" title="Validator Header Fields">Section&nbsp;7.2</a>). Hence, these preconditions evaluate whether the state of the target resource has changed since a given state known by the
    1839                client. The effect of such an evaluation depends on the method semantics and choice of conditional, as defined in <a href="p4-conditional.html#evaluation" title="Evaluation">Section 5</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>.
    1840             </p>
    1841             <div id="rfc.table.u.4">
    1842                <table class="tt full left" cellpadding="3" cellspacing="0">
    1843                   <thead>
    1844                      <tr>
    1845                         <th>Header Field Name</th>
    1846                         <th>Defined in...</th>
    1847                      </tr>
    1848                   </thead>
    1849                   <tbody>
    1850                      <tr>
    1851                         <td class="left">If-Match</td>
    1852                         <td class="left"><a href="p4-conditional.html#header.if-match" title="If-Match">Section 3.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    1853                      </tr>
    1854                      <tr>
    1855                         <td class="left">If-None-Match</td>
    1856                         <td class="left"><a href="p4-conditional.html#header.if-none-match" title="If-None-Match">Section 3.2</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    1857                      </tr>
    1858                      <tr>
    1859                         <td class="left">If-Modified-Since</td>
    1860                         <td class="left"><a href="p4-conditional.html#header.if-modified-since" title="If-Modified-Since">Section 3.3</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    1861                      </tr>
    1862                      <tr>
    1863                         <td class="left">If-Unmodified-Since</td>
    1864                         <td class="left"><a href="p4-conditional.html#header.if-unmodified-since" title="If-Unmodified-Since">Section 3.4</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    1865                      </tr>
    1866                      <tr>
    1867                         <td class="left">If-Range</td>
    1868                         <td class="left"><a href="p5-range.html#header.if-range" title="If-Range">Section 3.2</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td>
    1869                      </tr>
    1870                   </tbody>
    1871                </table>
    1872             </div>
    1873          </div>
    1874          <div id="request.conneg">
    1875             <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;<a href="#request.conneg">Content Negotiation</a></h2>
    1876             <p id="rfc.section.5.3.p.1">The following request header fields are sent by a user agent to engage in <a href="#proactive.negotiation" class="smpl">proactive negotiation</a> of the response content, as defined in <a href="#proactive.negotiation" title="Proactive Negotiation">Section&nbsp;3.4.1</a>. The preferences sent in these fields apply to any content in the response, including representations of the target resource,
    1877                representations of error or processing status, and potentially even the miscellaneous text strings that might appear within
    1878                the protocol.
    1879             </p>
    1880             <div id="rfc.table.u.5">
    1881                <table class="tt full left" cellpadding="3" cellspacing="0">
    1882                   <thead>
    1883                      <tr>
    1884                         <th>Header Field Name</th>
    1885                         <th>Defined in...</th>
    1886                      </tr>
    1887                   </thead>
    1888                   <tbody>
    1889                      <tr>
    1890                         <td class="left">Accept</td>
    1891                         <td class="left"><a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section&nbsp;5.3.2</a></td>
    1892                      </tr>
    1893                      <tr>
    1894                         <td class="left">Accept-Charset</td>
    1895                         <td class="left"><a href="#header.accept-charset" id="rfc.xref.header.accept-charset.1" title="Accept-Charset">Section&nbsp;5.3.3</a></td>
    1896                      </tr>
    1897                      <tr>
    1898                         <td class="left">Accept-Encoding</td>
    1899                         <td class="left"><a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.2" title="Accept-Encoding">Section&nbsp;5.3.4</a></td>
    1900                      </tr>
    1901                      <tr>
    1902                         <td class="left">Accept-Language</td>
    1903                         <td class="left"><a href="#header.accept-language" id="rfc.xref.header.accept-language.2" title="Accept-Language">Section&nbsp;5.3.5</a></td>
    1904                      </tr>
    1905                   </tbody>
    1906                </table>
    1907             </div>
    1908             <div id="quality.values">
    1909                <h3 id="rfc.section.5.3.1"><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;<a href="#quality.values">Quality Values</a></h3>
    1910                <p id="rfc.section.5.3.1.p.1">Many of the request header fields for <a href="#proactive.negotiation" class="smpl">proactive negotiation</a> use a common parameter, named "q" (case-insensitive), to assign a relative "weight" to the preference for that associated
    1911                   kind of content. This weight is referred to as a "quality value" (or "qvalue") because the same parameter name is often used
    1912                   within server configurations to assign a weight to the relative quality of the various representations that can be selected
    1913                   for a resource.
    1914                </p>
    1915                <p id="rfc.section.5.3.1.p.2">The weight is normalized to a real number in the range 0 through 1, where 0.001 is the least preferred and 1 is the most preferred;
    1916                   a value of 0 means "not acceptable". If no "q" parameter is present, the default weight is 1.
    1917                </p>
    1918                <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span>  <a href="#quality.values" class="smpl">weight</a> = <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> "q=" <a href="#quality.values" class="smpl">qvalue</a>
    1919   <a href="#quality.values" class="smpl">qvalue</a> = ( "0" [ "." 0*3<a href="#imported.abnf" class="smpl">DIGIT</a> ] )
    1920          / ( "1" [ "." 0*3("0") ] )
    1921 </pre><p id="rfc.section.5.3.1.p.4">A sender of qvalue <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values ought to be limited in the same
    1922                   fashion.
    1923                </p>
    1924             </div>
    1925             <div id="header.accept">
    1926                <div id="rfc.iref.a.1"></div>
    1927                <h3 id="rfc.section.5.3.2"><a href="#rfc.section.5.3.2">5.3.2</a>&nbsp;<a href="#header.accept">Accept</a></h3>
    1928                <p id="rfc.section.5.3.2.p.1">The "Accept" header field can be used by user agents to specify response media types that are acceptable. Accept header fields
    1929                   can be used to indicate that the request is specifically limited to a small set of desired types, as in the case of a request
    1930                   for an in-line image.
    1931                </p>
    1932                <div id="rfc.figure.u.24"></div><pre class="inline"><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span>  <a href="#header.accept" class="smpl">Accept</a> = #( <a href="#header.accept" class="smpl">media-range</a> [ <a href="#header.accept" class="smpl">accept-params</a> ] )
    1933  
    1934   <a href="#header.accept" class="smpl">media-range</a>    = ( "*/*"
    1935                    / ( <a href="#media.type" class="smpl">type</a> "/" "*" )
    1936                    / ( <a href="#media.type" class="smpl">type</a> "/" <a href="#media.type" class="smpl">subtype</a> )
    1937                    ) *( <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
    1938   <a href="#header.accept" class="smpl">accept-params</a>  = <a href="#quality.values" class="smpl">weight</a> *( <a href="#header.accept" class="smpl">accept-ext</a> )
    1939   <a href="#header.accept" class="smpl">accept-ext</a> = <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#imported.abnf" class="smpl">token</a> [ "=" ( <a href="#imported.abnf" class="smpl">token</a> / <a href="#imported.abnf" class="smpl">quoted-string</a> ) ]
    1940 </pre><p id="rfc.section.5.3.2.p.3">The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating
    1941                   all subtypes of that type. The media-range can include media type parameters that are applicable to that range.
    1942                </p>
    1943                <p id="rfc.section.5.3.2.p.4">Each media-range might be followed by zero or more applicable media type parameters (e.g., <a href="#charset" class="smpl">charset</a>), an optional "q" parameter for indicating a relative weight (<a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>), and then zero or more extension parameters. The "q" parameter is necessary if any extensions (accept-ext) are present,
    1944                   since it acts as a separator between the two parameter sets.
    1945                </p>
    1946                <div class="note" id="rfc.section.5.3.2.p.5">
    1947                   <p><b>Note:</b> Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to historical practice.
    1948                      Although this prevents any media type parameter named "q" from being used with a media range, such an event is believed to
    1949                      be unlikely given the lack of any "q" parameters in the IANA media type registry and the rare usage of any media type parameters
    1950                      in Accept. Future media types are discouraged from registering any parameter named "q".
    1951                   </p>
    1952                </div>
    1953                <p id="rfc.section.5.3.2.p.6">The example</p>
    1954                <div id="rfc.figure.u.25"></div><pre class="text">  Accept: audio/*; q=0.2, audio/basic
    1955 </pre><p id="rfc.section.5.3.2.p.8">is interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80% markdown in quality".</p>
    1956                <p id="rfc.section.5.3.2.p.9">A request without any Accept header field implies that the user agent will accept any media type in response. If the header
    1957                   field is present in a request and none of the available representations for the response have a media type that is listed
    1958                   as acceptable, the origin server can either honor the header field by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response or disregard the header field by treating the response as if it is not subject to content negotiation.
    1959                </p>
    1960                <p id="rfc.section.5.3.2.p.10">A more elaborate example is</p>
    1961                <div id="rfc.figure.u.26"></div><pre class="text">  Accept: text/plain; q=0.5, text/html,
    1962           text/x-dvi; q=0.8, text/x-c
    1963 </pre><p id="rfc.section.5.3.2.p.12">Verbally, this would be interpreted as "text/html and text/x-c are the equally preferred media types, but if they do not exist,
    1964                   then send the text/x-dvi representation, and if that does not exist, send the text/plain representation".
    1965                </p>
    1966                <p id="rfc.section.5.3.2.p.13">Media ranges can be overridden by more specific media ranges or specific media types. If more than one media range applies
    1967                   to a given type, the most specific reference has precedence. For example,
    1968                </p>
    1969                <div id="rfc.figure.u.27"></div><pre class="text">  Accept: text/*, text/plain, text/plain;format=flowed, */*
    1970 </pre><p id="rfc.section.5.3.2.p.15">have the following precedence: </p>
    1971                <ol>
    1972                   <li>text/plain;format=flowed</li>
    1973                   <li>text/plain</li>
    1974                   <li>text/*</li>
    1975                   <li>*/*</li>
    1976                </ol>
    1977                <p id="rfc.section.5.3.2.p.16">The media type quality factor associated with a given type is determined by finding the media range with the highest precedence
    1978                   that matches the type. For example,
    1979                </p>
    1980                <div id="rfc.figure.u.28"></div><pre class="text">  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
    1981           text/html;level=2;q=0.4, */*;q=0.5
    1982 </pre><p id="rfc.section.5.3.2.p.18">would cause the following values to be associated:</p>
    1983                <div id="rfc.table.u.6">
    1984                   <table class="tt full left" cellpadding="3" cellspacing="0">
    1985                      <thead>
    1986                         <tr>
    1987                            <th>Media Type</th>
    1988                            <th>Quality Value</th>
    1989                         </tr>
    1990                      </thead>
    1991                      <tbody>
    1992                         <tr>
    1993                            <td class="left">text/html;level=1</td>
    1994                            <td class="left">1</td>
    1995                         </tr>
    1996                         <tr>
    1997                            <td class="left">text/html</td>
    1998                            <td class="left">0.7</td>
    1999                         </tr>
    2000                         <tr>
    2001                            <td class="left">text/plain</td>
    2002                            <td class="left">0.3</td>
    2003                         </tr>
    2004                         <tr>
    2005                            <td class="left">image/jpeg</td>
    2006                            <td class="left">0.5</td>
    2007                         </tr>
    2008                         <tr>
    2009                            <td class="left">text/html;level=2</td>
    2010                            <td class="left">0.4</td>
    2011                         </tr>
    2012                         <tr>
    2013                            <td class="left">text/html;level=3</td>
    2014                            <td class="left">0.7</td>
    2015                         </tr>
    2016                      </tbody>
    2017                   </table>
    2018                </div>
    2019                <p id="rfc.section.5.3.2.p.19"><b>Note:</b> A user agent might be provided with a default set of quality values for certain media ranges. However, unless the user agent
    2020                   is a closed system that cannot interact with other rendering agents, this default set ought to be configurable by the user.
    2021                </p>
    2022             </div>
    2023             <div id="header.accept-charset">
    2024                <div id="rfc.iref.a.2"></div>
    2025                <h3 id="rfc.section.5.3.3"><a href="#rfc.section.5.3.3">5.3.3</a>&nbsp;<a href="#header.accept-charset">Accept-Charset</a></h3>
    2026                <p id="rfc.section.5.3.3.p.1">The "Accept-Charset" header field can be sent by a user agent to indicate what charsets are acceptable in textual response
    2027                   content. This field allows user agents capable of understanding more comprehensive or special-purpose charsets to signal that
    2028                   capability to an origin server that is capable of representing information in those charsets.
    2029                </p>
    2030                <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.23"></span>  <a href="#header.accept-charset" class="smpl">Accept-Charset</a> = 1#( ( <a href="#charset" class="smpl">charset</a> / "*" ) [ <a href="#quality.values" class="smpl">weight</a> ] )
    2031 </pre><p id="rfc.section.5.3.3.p.3">Charset names are defined in <a href="#charset" title="Charset">Section&nbsp;3.1.1.2</a>. A user agent <em class="bcp14">MAY</em> associate a quality value with each charset to indicate the user's relative preference for that charset, as defined in <a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>. An example is
    2032                </p>
    2033                <div id="rfc.figure.u.30"></div><pre class="text">  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
    2034 </pre><p id="rfc.section.5.3.3.p.5">The special value "*", if present in the Accept-Charset field, matches every charset that is not mentioned elsewhere in the
    2035                   Accept-Charset field. If no "*" is present in an Accept-Charset field, then any charsets not explicitly mentioned in the field
    2036                   are considered "not acceptable" to the client.
    2037                </p>
    2038                <p id="rfc.section.5.3.3.p.6">A request without any Accept-Charset header field implies that the user agent will accept any charset in response. Most general-purpose
    2039                   user agents do not send Accept-Charset, unless specifically configured to do so, because a detailed list of supported charsets
    2040                   makes it easier for a server to identify an individual by virtue of the user agent's request characteristics (<a href="#fingerprinting" title="Browser Fingerprinting">Section&nbsp;9.7</a>).
    2041                </p>
    2042                <p id="rfc.section.5.3.3.p.7">If an Accept-Charset header field is present in a request and none of the available representations for the response has a
    2043                   charset that is listed as acceptable, the origin server can either honor the header field, by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response, or disregard the header field by treating the resource as if it is not subject to content negotiation.
    2044                </p>
    2045             </div>
    2046             <div id="header.accept-encoding">
    2047                <div id="rfc.iref.a.3"></div>
    2048                <h3 id="rfc.section.5.3.4"><a href="#rfc.section.5.3.4">5.3.4</a>&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></h3>
    2049                <p id="rfc.section.5.3.4.p.1">The "Accept-Encoding" header field can be used by user agents to indicate what response content-codings (<a href="#content.codings" title="Content Codings">Section&nbsp;3.1.2.1</a>) are acceptable in the response. An "identity" token is used as a synonym for "no encoding" in order to communicate when
    2050                   no encoding is preferred.
    2051                </p>
    2052                <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.24"></span><span id="rfc.iref.g.25"></span>  <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a>  = #( <a href="#header.accept-encoding" class="smpl">codings</a> [ <a href="#quality.values" class="smpl">weight</a> ] )
    2053   <a href="#header.accept-encoding" class="smpl">codings</a>          = <a href="#content.codings" class="smpl">content-coding</a> / "identity" / "*"
    2054 </pre><p id="rfc.section.5.3.4.p.3">Each codings value <em class="bcp14">MAY</em> be given an associated quality value representing the preference for that encoding, as defined in <a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>. The asterisk "*" symbol in an Accept-Encoding field matches any available content-coding not explicitly listed in the header
    2055                   field.
    2056                </p>
    2057                <p id="rfc.section.5.3.4.p.4">For example,</p>
    2058                <div id="rfc.figure.u.32"></div><pre class="text">  Accept-Encoding: compress, gzip
    2059   Accept-Encoding:
    2060   Accept-Encoding: *
    2061   Accept-Encoding: compress;q=0.5, gzip;q=1.0
    2062   Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
    2063 </pre><p id="rfc.section.5.3.4.p.6">A request without an Accept-Encoding header field implies that the user agent has no preferences regarding content-codings.
    2064                   Although this allows the server to use any content-coding in a response, it does not imply that the user agent will be able
    2065                   to correctly process all encodings.
    2066                </p>
    2067                <p id="rfc.section.5.3.4.p.7">A server tests whether a content-coding for a given representation is acceptable using these rules: </p>
    2068                <ol>
    2069                   <li>If no Accept-Encoding field is in the request, any content-coding is considered acceptable by the user agent.</li>
    2070                   <li>If the representation has no content-coding, then it is acceptable by default unless specifically excluded by the Accept-Encoding
    2071                      field stating either "identity;q=0" or "*;q=0" without a more specific entry for "identity".
    2072                   </li>
    2073                   <li>If the representation's content-coding is one of the content-codings listed in the Accept-Encoding field, then it is acceptable
    2074                      unless it is accompanied by a qvalue of 0. (As defined in <a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>, a qvalue of 0 means "not acceptable".)
    2075                   </li>
    2076                   <li>If multiple content-codings are acceptable, then the acceptable content-coding with the highest non-zero qvalue is preferred.</li>
    2077                </ol>
    2078                <p id="rfc.section.5.3.4.p.8">An Accept-Encoding header field with a combined field-value that is empty implies that the user agent does not want any content-coding
    2079                   in response. If an Accept-Encoding header field is present in a request and none of the available representations for the
    2080                   response have a content-coding that is listed as acceptable, the origin server <em class="bcp14">SHOULD</em> send a response without any content-coding.
    2081                </p>
    2082                <div class="note" id="rfc.section.5.3.4.p.9">
    2083                   <p><b>Note:</b> Most HTTP/1.0 applications do not recognize or obey qvalues associated with content-codings. This means that qvalues might
    2084                      not work and are not permitted with x-gzip or x-compress.
    2085                   </p>
    2086                </div>
    2087             </div>
    2088             <div id="header.accept-language">
    2089                <div id="rfc.iref.a.4"></div>
    2090                <h3 id="rfc.section.5.3.5"><a href="#rfc.section.5.3.5">5.3.5</a>&nbsp;<a href="#header.accept-language">Accept-Language</a></h3>
    2091                <p id="rfc.section.5.3.5.p.1">The "Accept-Language" header field can be used by user agents to indicate the set of natural languages that are preferred
    2092                   in the response. Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;3.1.3.1</a>.
    2093                </p>
    2094                <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span>  <a href="#header.accept-language" class="smpl">Accept-Language</a> = 1#( <a href="#header.accept-language" class="smpl">language-range</a> [ <a href="#quality.values" class="smpl">weight</a> ] )
    2095   <a href="#header.accept-language" class="smpl">language-range</a>  =
    2096             &lt;language-range, defined in <a href="#RFC4647" id="rfc.xref.RFC4647.1"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-2.1">Section 2.1</a>&gt;
    2097 </pre><p id="rfc.section.5.3.5.p.3">Each language-range can be given an associated quality value representing an estimate of the user's preference for the languages
    2098                   specified by that range, as defined in <a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>. For example,
    2099                </p>
    2100                <div id="rfc.figure.u.34"></div><pre class="text">  Accept-Language: da, en-gb;q=0.8, en;q=0.7
    2101 </pre><p id="rfc.section.5.3.5.p.5">would mean: "I prefer Danish, but will accept British English and other types of English".</p>
    2102                <p id="rfc.section.5.3.5.p.6">A request without any Accept-Language header field implies that the user agent will accept any language in response. If the
    2103                   header field is present in a request and none of the available representations for the response have a matching language tag,
    2104                   the origin server can either disregard the header field by treating the response as if it is not subject to content negotiation
    2105                   or honor the header field by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response. However, the latter is not encouraged, as doing so can prevent users from accessing content that they might be able
    2106                   to use (with translation software, for example).
    2107                </p>
    2108                <p id="rfc.section.5.3.5.p.7">Note that some recipients treat the order in which language tags are listed as an indication of descending priority, particularly
    2109                   for tags that are assigned equal quality values (no value is the same as q=1). However, this behavior cannot be relied upon.
    2110                   For consistency and to maximize interoperability, many user agents assign each language tag a unique quality value while also
    2111                   listing them in order of decreasing quality. Additional discussion of language priority lists can be found in <a href="http://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>.
    2112                </p>
    2113                <p id="rfc.section.5.3.5.p.8">For matching, <a href="http://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements. The
    2114                   "Basic Filtering" scheme (<a href="#RFC4647" id="rfc.xref.RFC4647.4"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-3.3.1">Section 3.3.1</a>) is identical to the matching scheme that was previously defined for HTTP in <a href="http://tools.ietf.org/html/rfc2616#section-14.4">Section 14.4</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
    2115                </p>
    2116                <p id="rfc.section.5.3.5.p.9">It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic
    2117                   preferences of the user in every request (<a href="#fingerprinting" title="Browser Fingerprinting">Section&nbsp;9.7</a>).
    2118                </p>
    2119                <p id="rfc.section.5.3.5.p.10">Since intelligibility is highly dependent on the individual user, user agents need to allow user control over the linguistic
    2120                   preference (either through configuration of the user agent itself or by defaulting to a user controllable system setting).
    2121                   A user agent that does not provide such control to the user <em class="bcp14">MUST NOT</em> send an Accept-Language header field.
    2122                </p>
    2123                <div class="note" id="rfc.section.5.3.5.p.11">
    2124                   <p><b>Note:</b> User agents ought to provide guidance to users when setting a preference, since users are rarely familiar with the details
    2125                      of language matching as described above. For example, users might assume that on selecting "en-gb", they will be served any
    2126                      kind of English document if British English is not available. A user agent might suggest, in such a case, to add "en" to the
    2127                      list for better matching behavior.
    2128                   </p>
    2129                </div>
    2130             </div>
    2131          </div>
    2132          <div id="request.auth">
    2133             <h2 id="rfc.section.5.4"><a href="#rfc.section.5.4">5.4</a>&nbsp;<a href="#request.auth">Authentication Credentials</a></h2>
    2134             <p id="rfc.section.5.4.p.1">Two header fields are used for carrying authentication credentials, as defined in <a href="#RFC7235" id="rfc.xref.RFC7235.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a>. Note that various custom mechanisms for user authentication use the Cookie header field for this purpose, as defined in <a href="#RFC6265" id="rfc.xref.RFC6265.2"><cite title="HTTP State Management Mechanism">[RFC6265]</cite></a>.
    2135             </p>
    2136             <div id="rfc.table.u.7">
    2137                <table class="tt full left" cellpadding="3" cellspacing="0">
    2138                   <thead>
    2139                      <tr>
    2140                         <th>Header Field Name</th>
    2141                         <th>Defined in...</th>
    2142                      </tr>
    2143                   </thead>
    2144                   <tbody>
    2145                      <tr>
    2146                         <td class="left">Authorization</td>
    2147                         <td class="left"><a href="p7-auth.html#header.authorization" title="Authorization">Section 4.2</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td>
    2148                      </tr>
    2149                      <tr>
    2150                         <td class="left">Proxy-Authorization</td>
    2151                         <td class="left"><a href="p7-auth.html#header.proxy-authorization" title="Proxy-Authorization">Section 4.4</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td>
    2152                      </tr>
    2153                   </tbody>
    2154                </table>
    2155             </div>
    2156          </div>
    2157          <div id="request.context">
    2158             <h2 id="rfc.section.5.5"><a href="#rfc.section.5.5">5.5</a>&nbsp;<a href="#request.context">Request Context</a></h2>
    2159             <p id="rfc.section.5.5.p.1">The following request header fields provide additional information about the request context, including information about
    2160                the user, user agent, and resource behind the request.
    2161             </p>
    2162             <div id="rfc.table.u.8">
    2163                <table class="tt full left" cellpadding="3" cellspacing="0">
    2164                   <thead>
    2165                      <tr>
    2166                         <th>Header Field Name</th>
    2167                         <th>Defined in...</th>
    2168                      </tr>
    2169                   </thead>
    2170                   <tbody>
    2171                      <tr>
    2172                         <td class="left">From</td>
    2173                         <td class="left"><a href="#header.from" id="rfc.xref.header.from.1" title="From">Section&nbsp;5.5.1</a></td>
    2174                      </tr>
    2175                      <tr>
    2176                         <td class="left">Referer</td>
    2177                         <td class="left"><a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section&nbsp;5.5.2</a></td>
    2178                      </tr>
    2179                      <tr>
    2180                         <td class="left">User-Agent</td>
    2181                         <td class="left"><a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section&nbsp;5.5.3</a></td>
    2182                      </tr>
    2183                   </tbody>
    2184                </table>
    2185             </div>
    2186             <div id="header.from">
    2187                <div id="rfc.iref.f.1"></div>
    2188                <h3 id="rfc.section.5.5.1"><a href="#rfc.section.5.5.1">5.5.1</a>&nbsp;<a href="#header.from">From</a></h3>
    2189                <p id="rfc.section.5.5.1.p.1">The "From" header field contains an Internet email address for a human user who controls the requesting user agent. The address
    2190                   ought to be machine-usable, as defined by "mailbox" in <a href="http://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a>:
    2191                </p>
    2192                <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.28"></span>  <a href="#header.from" class="smpl">From</a>    = <a href="#header.from" class="smpl">mailbox</a>
    2193  
    2194   <a href="#header.from" class="smpl">mailbox</a> = &lt;mailbox, defined in <a href="#RFC5322" id="rfc.xref.RFC5322.2"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="http://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a>&gt;
    2195 </pre><p id="rfc.section.5.5.1.p.3">An example is:</p>
    2196                <div id="rfc.figure.u.36"></div><pre class="text">  From: webmaster@example.org
    2197 </pre><p id="rfc.section.5.5.1.p.5">The From header field is rarely sent by non-robotic user agents. A user agent <em class="bcp14">SHOULD NOT</em> send a From header field without explicit configuration by the user, since that might conflict with the user's privacy interests
    2198                   or their site's security policy.
    2199                </p>
    2200                <p id="rfc.section.5.5.1.p.6">A robotic user agent <em class="bcp14">SHOULD</em> send a valid From header field so that the person responsible for running the robot can be contacted if problems occur on
    2201                   servers, such as if the robot is sending excessive, unwanted, or invalid requests.
    2202                </p>
    2203                <p id="rfc.section.5.5.1.p.7">A server <em class="bcp14">SHOULD NOT</em> use the From header field for access control or authentication, since most recipients will assume that the field value is
    2204                   public information.
    2205                </p>
    2206             </div>
    2207             <div id="header.referer">
    2208                <div id="rfc.iref.r.2"></div>
    2209                <h3 id="rfc.section.5.5.2"><a href="#rfc.section.5.5.2">5.5.2</a>&nbsp;<a href="#header.referer">Referer</a></h3>
    2210                <p id="rfc.section.5.5.2.p.1">The "Referer" [sic] header field allows the user agent to specify a URI reference for the resource from which the <a href="p1-messaging.html#target-resource" class="smpl">target URI</a> was obtained (i.e., the "referrer", though the field name is misspelled). A user agent <em class="bcp14">MUST NOT</em> include the fragment and userinfo components of the URI reference <a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, if any, when generating the Referer field value.
    2211                </p>
    2212                <div id="rfc.figure.u.37"></div><pre class="inline"><span id="rfc.iref.g.29"></span>  <a href="#header.referer" class="smpl">Referer</a> = <a href="#imported.abnf" class="smpl">absolute-URI</a> / <a href="#imported.abnf" class="smpl">partial-URI</a>
    2213 </pre><p id="rfc.section.5.5.2.p.3">The Referer header field allows servers to generate back-links to other resources for simple analytics, logging, optimized
    2214                   caching, etc. It also allows obsolete or mistyped links to be found for maintenance. Some servers use the Referer header field
    2215                   as a means of denying links from other sites (so-called "deep linking") or restricting cross-site request forgery (CSRF),
    2216                   but not all requests contain it.
    2217                </p>
    2218                <p id="rfc.section.5.5.2.p.4">Example:</p>
    2219                <div id="rfc.figure.u.38"></div><pre class="text">  Referer: http://www.example.org/hypertext/Overview.html
    2220 </pre><p id="rfc.section.5.5.2.p.6">If the target URI was obtained from a source that does not have its own URI (e.g., input from the user keyboard, or an entry
    2221                   within the user's bookmarks/favorites), the user agent <em class="bcp14">MUST</em> either exclude Referer or send it with a value of "about:blank".
    2222                </p>
    2223                <p id="rfc.section.5.5.2.p.7">The Referer field has the potential to reveal information about the request context or browsing history of the user, which
    2224                   is a privacy concern if the referring resource's identifier reveals personal information (such as an account name) or a resource
    2225                   that is supposed to be confidential (such as behind a firewall or internal to a secured service). Most general-purpose user
    2226                   agents do not send the Referer header field when the referring resource is a local "file" or "data" URI. A user agent <em class="bcp14">MUST NOT</em> send a <a href="#header.referer" class="smpl">Referer</a> header field in an unsecured HTTP request if the referring page was received with a secure protocol. See <a href="#sensitive.information.in.uris" title="Disclosure of Sensitive Information in URIs">Section&nbsp;9.4</a> for additional security considerations.
    2227                </p>
    2228                <p id="rfc.section.5.5.2.p.8">Some intermediaries have been known to indiscriminately remove Referer header fields from outgoing requests. This has the
    2229                   unfortunate side effect of interfering with protection against CSRF attacks, which can be far more harmful to their users.
    2230                   Intermediaries and user agent extensions that wish to limit information disclosure in Referer ought to restrict their changes
    2231                   to specific edits, such as replacing internal domain names with pseudonyms or truncating the query and/or path components.
    2232                   An intermediary <em class="bcp14">SHOULD NOT</em> modify or delete the Referer header field when the field value shares the same scheme and host as the request target.
    2233                </p>
    2234             </div>
    2235             <div id="header.user-agent">
    2236                <div id="rfc.iref.u.1"></div>
    2237                <h3 id="rfc.section.5.5.3"><a href="#rfc.section.5.5.3">5.5.3</a>&nbsp;<a href="#header.user-agent">User-Agent</a></h3>
    2238                <p id="rfc.section.5.5.3.p.1">The "User-Agent" header field contains information about the user agent originating the request, which is often used by servers
    2239                   to help identify the scope of reported interoperability problems, to work around or tailor responses to avoid particular user
    2240                   agent limitations, and for analytics regarding browser or operating system use. A user agent <em class="bcp14">SHOULD</em> send a User-Agent field in each request unless specifically configured not to do so.
    2241                </p>
    2242                <div id="rfc.figure.u.39"></div><pre class="inline"><span id="rfc.iref.g.30"></span>  <a href="#header.user-agent" class="smpl">User-Agent</a> = <a href="#header.user-agent" class="smpl">product</a> *( <a href="#imported.abnf" class="smpl">RWS</a> ( <a href="#header.user-agent" class="smpl">product</a> / <a href="#imported.abnf" class="smpl">comment</a> ) )
    2243 </pre><p id="rfc.section.5.5.3.p.3">The User-Agent field-value consists of one or more product identifiers, each followed by zero or more comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.23"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), which together identify the user agent software and its significant subproducts. By convention, the product identifiers
    2244                   are listed in decreasing order of their significance for identifying the user agent software. Each product identifier consists
    2245                   of a name and optional version.
    2246                </p>
    2247                <div id="rfc.figure.u.40"></div><pre class="inline"><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span>  <a href="#header.user-agent" class="smpl">product</a>         = <a href="#imported.abnf" class="smpl">token</a> ["/" <a href="#header.user-agent" class="smpl">product-version</a>]
    2248   <a href="#header.user-agent" class="smpl">product-version</a> = <a href="#imported.abnf" class="smpl">token</a>
    2249 </pre><p id="rfc.section.5.5.3.p.5">A sender <em class="bcp14">SHOULD</em> limit generated product identifiers to what is necessary to identify the product; a sender <em class="bcp14">MUST NOT</em> generate advertising or other nonessential information within the product identifier. A sender <em class="bcp14">SHOULD NOT</em> generate information in <a href="#header.user-agent" class="smpl">product-version</a> that is not a version identifier (i.e., successive versions of the same product name ought only to differ in the product-version
    2250                   portion of the product identifier).
    2251                </p>
    2252                <p id="rfc.section.5.5.3.p.6">Example:</p>
    2253                <div id="rfc.figure.u.41"></div><pre class="text">  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
    2254 </pre><p id="rfc.section.5.5.3.p.8">A user agent <em class="bcp14">SHOULD NOT</em> generate a User-Agent field containing needlessly fine-grained detail and <em class="bcp14">SHOULD</em> limit the addition of subproducts by third parties. Overly long and detailed User-Agent field values increase request latency
    2255                   and the risk of a user being identified against their wishes ("fingerprinting").
    2256                </p>
    2257                <p id="rfc.section.5.5.3.p.9">Likewise, implementations are encouraged not to use the product tokens of other implementations in order to declare compatibility
    2258                   with them, as this circumvents the purpose of the field. If a user agent masquerades as a different user agent, recipients
    2259                   can assume that the user intentionally desires to see responses tailored for that identified user agent, even if they might
    2260                   not work as well for the actual user agent being used.
    2261                </p>
    2262             </div>
    2263          </div>
    2264       </div>
    2265       <div id="status.codes">
    2266          <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a href="#status.codes">Response Status Codes</a></h1>
    2267          <p id="rfc.section.6.p.1">The status-code element is a three-digit integer code giving the result of the attempt to understand and satisfy the request.</p>
    2268          <p id="rfc.section.6.p.2">HTTP status codes are extensible. HTTP clients are not required to understand the meaning of all registered status codes,
    2269             though such understanding is obviously desirable. However, a client <em class="bcp14">MUST</em> understand the class of any status code, as indicated by the first digit, and treat an unrecognized status code as being equivalent
    2270             to the x00 status code of that class, with the exception that a recipient <em class="bcp14">MUST NOT</em> cache a response with an unrecognized status code.
    2271          </p>
    2272          <p id="rfc.section.6.p.3">For example, if an unrecognized status code of 471 is received by a client, the client can assume that there was something
    2273             wrong with its request and treat the response as if it had received a <a href="#status.400" class="smpl">400 (Bad Request)</a> status code. The response message will usually contain a representation that explains the status.
    2274          </p>
    2275          <p id="rfc.section.6.p.4">The first digit of the status-code defines the class of response. The last two digits do not have any categorization role.
    2276             There are five values for the first digit:
    2277          </p>
    2278          <ul>
    2279             <li><a href="#status.1xx" class="smpl">1xx (Informational)</a>: The request was received, continuing process
    2280             </li>
    2281             <li><a href="#status.2xx" class="smpl">2xx (Successful)</a>: The request was successfully received, understood, and accepted
    2282             </li>
    2283             <li><a href="#status.3xx" class="smpl">3xx (Redirection)</a>: Further action needs to be taken in order to complete the request
    2284             </li>
    2285             <li><a href="#status.4xx" class="smpl">4xx (Client Error)</a>: The request contains bad syntax or cannot be fulfilled
    2286             </li>
    2287             <li><a href="#status.5xx" class="smpl">5xx (Server Error)</a>: The server failed to fulfill an apparently valid request
    2288             </li>
    2289          </ul>
    2290          <div id="overview.of.status.codes">
    2291             <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a href="#overview.of.status.codes">Overview of Status Codes</a></h2>
    2292             <p id="rfc.section.6.1.p.1">The status codes listed below are defined in this specification, <a href="p4-conditional.html#status.code.definitions" title="Status Code Definitions">Section 4</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>, <a href="p5-range.html#range.response" title="Responses to a Range Request">Section 4</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>, and <a href="p7-auth.html#status.code.definitions" title="Status Code Definitions">Section 3</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a>. The reason phrases listed here are only recommendations — they can be replaced by local equivalents without affecting the
    2293                protocol.
    2294             </p>
    2295             <p id="rfc.section.6.1.p.2">Responses with status codes that are defined as cacheable by default (e.g., 200, 203, 204, 206, 300, 301, 404, 405, 410, 414,
    2296                and 501 in this specification) can be reused by a cache with heuristic expiration unless otherwise indicated by the method
    2297                definition or explicit cache controls <a href="#RFC7234" id="rfc.xref.RFC7234.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>; all other status codes are not cacheable by default.
    2298             </p>
    2299             <div id="rfc.table.u.9">
    2300                <table class="tt full left" cellpadding="3" cellspacing="0">
    2301                   <thead>
    2302                      <tr>
    2303                         <th>Code</th>
    2304                         <th>Reason-Phrase</th>
    2305                         <th>Defined in...</th>
    2306                      </tr>
    2307                   </thead>
    2308                   <tbody>
    2309                      <tr>
    2310                         <td class="left">100</td>
    2311                         <td class="left">Continue</td>
    2312                         <td class="left"><a href="#status.100" id="rfc.xref.status.100.1" title="100 Continue">Section&nbsp;6.2.1</a></td>
    2313                      </tr>
    2314                      <tr>
    2315                         <td class="left">101</td>
    2316                         <td class="left">Switching Protocols</td>
    2317                         <td class="left"><a href="#status.101" id="rfc.xref.status.101.1" title="101 Switching Protocols">Section&nbsp;6.2.2</a></td>
    2318                      </tr>
    2319                      <tr>
    2320                         <td class="left">200</td>
    2321                         <td class="left">OK</td>
    2322                         <td class="left"><a href="#status.200" id="rfc.xref.status.200.1" title="200 OK">Section&nbsp;6.3.1</a></td>
    2323                      </tr>
    2324                      <tr>
    2325                         <td class="left">201</td>
    2326                         <td class="left">Created</td>
    2327                         <td class="left"><a href="#status.201" id="rfc.xref.status.201.1" title="201 Created">Section&nbsp;6.3.2</a></td>
    2328                      </tr>
    2329                      <tr>
    2330                         <td class="left">202</td>
    2331                         <td class="left">Accepted</td>
    2332                         <td class="left"><a href="#status.202" id="rfc.xref.status.202.1" title="202 Accepted">Section&nbsp;6.3.3</a></td>
    2333                      </tr>
    2334                      <tr>
    2335                         <td class="left">203</td>
    2336                         <td class="left">Non-Authoritative Information</td>
    2337                         <td class="left"><a href="#status.203" id="rfc.xref.status.203.1" title="203 Non-Authoritative Information">Section&nbsp;6.3.4</a></td>
    2338                      </tr>
    2339                      <tr>
    2340                         <td class="left">204</td>
    2341                         <td class="left">No Content</td>
    2342                         <td class="left"><a href="#status.204" id="rfc.xref.status.204.1" title="204 No Content">Section&nbsp;6.3.5</a></td>
    2343                      </tr>
    2344                      <tr>
    2345                         <td class="left">205</td>
    2346                         <td class="left">Reset Content</td>
    2347                         <td class="left"><a href="#status.205" id="rfc.xref.status.205.1" title="205 Reset Content">Section&nbsp;6.3.6</a></td>
    2348                      </tr>
    2349                      <tr>
    2350                         <td class="left">206</td>
    2351                         <td class="left">Partial Content</td>
    2352                         <td id="status.206" class="left"><a href="p5-range.html#status.206" title="206 Partial Content">Section 4.1</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td>
    2353                      </tr>
    2354                      <tr>
    2355                         <td class="left">300</td>
    2356                         <td class="left">Multiple Choices</td>
    2357                         <td class="left"><a href="#status.300" id="rfc.xref.status.300.1" title="300 Multiple Choices">Section&nbsp;6.4.1</a></td>
    2358                      </tr>
    2359                      <tr>
    2360                         <td class="left">301</td>
    2361                         <td class="left">Moved Permanently</td>
    2362                         <td class="left"><a href="#status.301" id="rfc.xref.status.301.1" title="301 Moved Permanently">Section&nbsp;6.4.2</a></td>
    2363                      </tr>
    2364                      <tr>
    2365                         <td class="left">302</td>
    2366                         <td class="left">Found</td>
    2367                         <td class="left"><a href="#status.302" id="rfc.xref.status.302.1" title="302 Found">Section&nbsp;6.4.3</a></td>
    2368                      </tr>
    2369                      <tr>
    2370                         <td class="left">303</td>
    2371                         <td class="left">See Other</td>
    2372                         <td class="left"><a href="#status.303" id="rfc.xref.status.303.1" title="303 See Other">Section&nbsp;6.4.4</a></td>
    2373                      </tr>
    2374                      <tr>
    2375                         <td class="left">304</td>
    2376                         <td class="left">Not Modified</td>
    2377                         <td id="status.304" class="left"><a href="p4-conditional.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    2378                      </tr>
    2379                      <tr>
    2380                         <td class="left">305</td>
    2381                         <td class="left">Use Proxy</td>
    2382                         <td class="left"><a href="#status.305" id="rfc.xref.status.305.1" title="305 Use Proxy">Section&nbsp;6.4.5</a></td>
    2383                      </tr>
    2384                      <tr>
    2385                         <td class="left">307</td>
    2386                         <td class="left">Temporary Redirect</td>
    2387                         <td class="left"><a href="#status.307" id="rfc.xref.status.307.1" title="307 Temporary Redirect">Section&nbsp;6.4.7</a></td>
    2388                      </tr>
    2389                      <tr>
    2390                         <td class="left">400</td>
    2391                         <td class="left">Bad Request</td>
    2392                         <td class="left"><a href="#status.400" id="rfc.xref.status.400.1" title="400 Bad Request">Section&nbsp;6.5.1</a></td>
    2393                      </tr>
    2394                      <tr>
    2395                         <td class="left">401</td>
    2396                         <td class="left">Unauthorized</td>
    2397                         <td id="status.401" class="left"><a href="p7-auth.html#status.401" title="401 Unauthorized">Section 3.1</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td>
    2398                      </tr>
    2399                      <tr>
    2400                         <td class="left">402</td>
    2401                         <td class="left">Payment Required</td>
    2402                         <td class="left"><a href="#status.402" id="rfc.xref.status.402.1" title="402 Payment Required">Section&nbsp;6.5.2</a></td>
    2403                      </tr>
    2404                      <tr>
    2405                         <td class="left">403</td>
    2406                         <td class="left">Forbidden</td>
    2407                         <td class="left"><a href="#status.403" id="rfc.xref.status.403.1" title="403 Forbidden">Section&nbsp;6.5.3</a></td>
    2408                      </tr>
    2409                      <tr>
    2410                         <td class="left">404</td>
    2411                         <td class="left">Not Found</td>
    2412                         <td class="left"><a href="#status.404" id="rfc.xref.status.404.1" title="404 Not Found">Section&nbsp;6.5.4</a></td>
    2413                      </tr>
    2414                      <tr>
    2415                         <td class="left">405</td>
    2416                         <td class="left">Method Not Allowed</td>
    2417                         <td class="left"><a href="#status.405" id="rfc.xref.status.405.1" title="405 Method Not Allowed">Section&nbsp;6.5.5</a></td>
    2418                      </tr>
    2419                      <tr>
    2420                         <td class="left">406</td>
    2421                         <td class="left">Not Acceptable</td>
    2422                         <td class="left"><a href="#status.406" id="rfc.xref.status.406.1" title="406 Not Acceptable">Section&nbsp;6.5.6</a></td>
    2423                      </tr>
    2424                      <tr>
    2425                         <td class="left">407</td>
    2426                         <td class="left">Proxy Authentication Required</td>
    2427                         <td id="status.407" class="left"><a href="p7-auth.html#status.407" title="407 Proxy Authentication Required">Section 3.2</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td>
    2428                      </tr>
    2429                      <tr>
    2430                         <td class="left">408</td>
    2431                         <td class="left">Request Time-out</td>
    2432                         <td class="left"><a href="#status.408" id="rfc.xref.status.408.1" title="408 Request Timeout">Section&nbsp;6.5.7</a></td>
    2433                      </tr>
    2434                      <tr>
    2435                         <td class="left">409</td>
    2436                         <td class="left">Conflict</td>
    2437                         <td class="left"><a href="#status.409" id="rfc.xref.status.409.1" title="409 Conflict">Section&nbsp;6.5.8</a></td>
    2438                      </tr>
    2439                      <tr>
    2440                         <td class="left">410</td>
    2441                         <td class="left">Gone</td>
    2442                         <td class="left"><a href="#status.410" id="rfc.xref.status.410.1" title="410 Gone">Section&nbsp;6.5.9</a></td>
    2443                      </tr>
    2444                      <tr>
    2445                         <td class="left">411</td>
    2446                         <td class="left">Length Required</td>
    2447                         <td class="left"><a href="#status.411" id="rfc.xref.status.411.1" title="411 Length Required">Section&nbsp;6.5.10</a></td>
    2448                      </tr>
    2449                      <tr>
    2450                         <td class="left">412</td>
    2451                         <td class="left">Precondition Failed</td>
    2452                         <td id="status.412" class="left"><a href="p4-conditional.html#status.412" title="412 Precondition Failed">Section 4.2</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    2453                      </tr>
    2454                      <tr>
    2455                         <td class="left">413</td>
    2456                         <td class="left">Payload Too Large</td>
    2457                         <td class="left"><a href="#status.413" id="rfc.xref.status.413.1" title="413 Payload Too Large">Section&nbsp;6.5.11</a></td>
    2458                      </tr>
    2459                      <tr>
    2460                         <td class="left">414</td>
    2461                         <td class="left">URI Too Long</td>
    2462                         <td class="left"><a href="#status.414" id="rfc.xref.status.414.1" title="414 URI Too Long">Section&nbsp;6.5.12</a></td>
    2463                      </tr>
    2464                      <tr>
    2465                         <td class="left">415</td>
    2466                         <td class="left">Unsupported Media Type</td>
    2467                         <td class="left"><a href="#status.415" id="rfc.xref.status.415.1" title="415 Unsupported Media Type">Section&nbsp;6.5.13</a></td>
    2468                      </tr>
    2469                      <tr>
    2470                         <td class="left">416</td>
    2471                         <td class="left">Range Not Satisfiable</td>
    2472                         <td id="status.416" class="left"><a href="p5-range.html#status.416" title="416 Range Not Satisfiable">Section 4.4</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td>
    2473                      </tr>
    2474                      <tr>
    2475                         <td class="left">417</td>
    2476                         <td class="left">Expectation Failed</td>
    2477                         <td class="left"><a href="#status.417" id="rfc.xref.status.417.1" title="417 Expectation Failed">Section&nbsp;6.5.14</a></td>
    2478                      </tr>
    2479                      <tr>
    2480                         <td class="left">426</td>
    2481                         <td class="left">Upgrade Required</td>
    2482                         <td class="left"><a href="#status.426" id="rfc.xref.status.426.1" title="426 Upgrade Required">Section&nbsp;6.5.15</a></td>
    2483                      </tr>
    2484                      <tr>
    2485                         <td class="left">500</td>
    2486                         <td class="left">Internal Server Error</td>
    2487                         <td class="left"><a href="#status.500" id="rfc.xref.status.500.1" title="500 Internal Server Error">Section&nbsp;6.6.1</a></td>
    2488                      </tr>
    2489                      <tr>
    2490                         <td class="left">501</td>
    2491                         <td class="left">Not Implemented</td>
    2492                         <td class="left"><a href="#status.501" id="rfc.xref.status.501.1" title="501 Not Implemented">Section&nbsp;6.6.2</a></td>
    2493                      </tr>
    2494                      <tr>
    2495                         <td class="left">502</td>
    2496                         <td class="left">Bad Gateway</td>
    2497                         <td class="left"><a href="#status.502" id="rfc.xref.status.502.1" title="502 Bad Gateway">Section&nbsp;6.6.3</a></td>
    2498                      </tr>
    2499                      <tr>
    2500                         <td class="left">503</td>
    2501                         <td class="left">Service Unavailable</td>
    2502                         <td class="left"><a href="#status.503" id="rfc.xref.status.503.1" title="503 Service Unavailable">Section&nbsp;6.6.4</a></td>
    2503                      </tr>
    2504                      <tr>
    2505                         <td class="left">504</td>
    2506                         <td class="left">Gateway Time-out</td>
    2507                         <td class="left"><a href="#status.504" id="rfc.xref.status.504.1" title="504 Gateway Timeout">Section&nbsp;6.6.5</a></td>
    2508                      </tr>
    2509                      <tr>
    2510                         <td class="left">505</td>
    2511                         <td class="left">HTTP Version Not Supported</td>
    2512                         <td class="left"><a href="#status.505" id="rfc.xref.status.505.1" title="505 HTTP Version Not Supported">Section&nbsp;6.6.6</a></td>
    2513                      </tr>
    2514                   </tbody>
    2515                </table>
    2516             </div>
    2517             <p id="rfc.section.6.1.p.3">Note that this list is not exhaustive — it does not include extension status codes defined in other specifications. The complete
    2518                list of status codes is maintained by IANA. See <a href="#status.code.registry" title="Status Code Registry">Section&nbsp;8.2</a> for details.
    2519             </p>
    2520          </div>
    2521          <div id="status.1xx">
    2522             <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a href="#status.1xx">Informational 1xx</a></h2>
    2523             <div id="rfc.iref.65"></div>
    2524             <div id="rfc.iref.s.3"></div>
    2525             <p id="rfc.section.6.2.p.1">The <dfn>1xx (Informational)</dfn> class of status code indicates an interim response for communicating connection status or request progress prior to completing
    2526                the requested action and sending a final response. All 1xx responses consist of only the status-line and optional header fields
    2527                and, thus, are terminated by the empty line at the end of the header section. Since HTTP/1.0 did not define any 1xx status
    2528                codes, a server <em class="bcp14">MUST NOT</em> send a 1xx response to an HTTP/1.0 client.
    2529             </p>
    2530             <p id="rfc.section.6.2.p.2">A client <em class="bcp14">MUST</em> be able to parse one or more 1xx responses received prior to a final response, even if the client does not expect one. A user
    2531                agent <em class="bcp14">MAY</em> ignore unexpected 1xx responses.
    2532             </p>
    2533             <p id="rfc.section.6.2.p.3">A proxy <em class="bcp14">MUST</em> forward 1xx responses unless the proxy itself requested the generation of the 1xx response. For example, if a proxy adds an
    2534                "Expect: 100-continue" field when it forwards a request, then it need not forward the corresponding <a href="#status.100" class="smpl">100 (Continue)</a> response(s).
    2535             </p>
    2536             <div id="status.100">
    2537                <div id="rfc.iref.66"></div>
    2538                <h3 id="rfc.section.6.2.1"><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;<a href="#status.100">100 Continue</a></h3>
    2539                <p id="rfc.section.6.2.1.p.1">The <dfn>100 (Continue)</dfn> status code indicates that the initial part of a request has been received and has not yet been rejected by the server. The
    2540                   server intends to send a final response after the request has been fully received and acted upon.
    2541                </p>
    2542                <p id="rfc.section.6.2.1.p.2">When the request contains an <a href="#header.expect" class="smpl">Expect</a> header field that includes a <a href="#header.expect" class="smpl">100-continue</a> expectation, the 100 response indicates that the server wishes to receive the request payload body, as described in <a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section&nbsp;5.1.1</a>. The client ought to continue sending the request and discard the 100 response.
    2543                </p>
    2544                <p id="rfc.section.6.2.1.p.3">If the request did not contain an <a href="#header.expect" class="smpl">Expect</a> header field containing the <a href="#header.expect" class="smpl">100-continue</a> expectation, the client can simply discard this interim response.
    2545                </p>
    2546             </div>
    2547             <div id="status.101">
    2548                <div id="rfc.iref.66"></div>
    2549                <h3 id="rfc.section.6.2.2"><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;<a href="#status.101">101 Switching Protocols</a></h3>
    2550                <p id="rfc.section.6.2.2.p.1">The <dfn>101 (Switching Protocols)</dfn> status code indicates that the server understands and is willing to comply with the client's request, via the <a href="p1-messaging.html#header.upgrade" class="smpl">Upgrade</a> header field (<a href="p1-messaging.html#header.upgrade" title="Upgrade">Section 6.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.24"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), for a change in the application protocol being used on this connection. The server <em class="bcp14">MUST</em> generate an Upgrade header field in the response that indicates which protocol(s) will be switched to immediately after the
    2551                   empty line that terminates the 101 response.
    2552                </p>
    2553                <p id="rfc.section.6.2.2.p.2">It is assumed that the server will only agree to switch protocols when it is advantageous to do so. For example, switching
    2554                   to a newer version of HTTP might be advantageous over older versions, and switching to a real-time, synchronous protocol might
    2555                   be advantageous when delivering resources that use such features.
    2556                </p>
    2557             </div>
    2558          </div>
    2559          <div id="status.2xx">
    2560             <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a href="#status.2xx">Successful 2xx</a></h2>
    2561             <div id="rfc.iref.66"></div>
    2562             <div id="rfc.iref.s.4"></div>
    2563             <p id="rfc.section.6.3.p.1">The <dfn>2xx (Successful)</dfn> class of status code indicates that the client's request was successfully received, understood, and accepted.
    2564             </p>
    2565             <div id="status.200">
    2566                <div id="rfc.iref.67"></div>
    2567                <h3 id="rfc.section.6.3.1"><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;<a href="#status.200">200 OK</a></h3>
    2568                <p id="rfc.section.6.3.1.p.1">The <dfn>200 (OK)</dfn> status code indicates that the request has succeeded. The payload sent in a 200 response depends on the request method. For
    2569                   the methods defined by this specification, the intended meaning of the payload can be summarized as:
    2570                </p>
    2571                <dl>
    2572                   <dt>GET</dt>
    2573                   <dd>a representation of the <a href="#resources" class="smpl">target resource</a>;
    2574                   </dd>
    2575                   <dt>HEAD</dt>
    2576                   <dd>the same representation as GET, but without the representation data;</dd>
    2577                   <dt>POST</dt>
    2578                   <dd>a representation of the status of, or results obtained from, the action;</dd>
    2579                   <dt>PUT, DELETE</dt>
    2580                   <dd>a representation of the status of the action;</dd>
    2581                   <dt>OPTIONS</dt>
    2582                   <dd>a representation of the communications options;</dd>
    2583                   <dt>TRACE</dt>
    2584                   <dd>a representation of the request message as received by the end server.</dd>
    2585                </dl>
    2586                <p id="rfc.section.6.3.1.p.2">Aside from responses to CONNECT, a 200 response always has a payload, though an origin server <em class="bcp14">MAY</em> generate a payload body of zero length. If no payload is desired, an origin server ought to send <dfn>204 (No Content)</dfn> instead. For CONNECT, no payload is allowed because the successful result is a tunnel, which begins immediately after the
    2587                   200 response header section.
    2588                </p>
    2589                <p id="rfc.section.6.3.1.p.3">A 200 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2590                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2591                </p>
    2592             </div>
    2593             <div id="status.201">
    2594                <div id="rfc.iref.67"></div>
    2595                <h3 id="rfc.section.6.3.2"><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;<a href="#status.201">201 Created</a></h3>
    2596                <p id="rfc.section.6.3.2.p.1">The <dfn>201 (Created)</dfn> status code indicates that the request has been fulfilled and has resulted in one or more new resources being created. The
    2597                   primary resource created by the request is identified by either a <a href="#header.location" class="smpl">Location</a> header field in the response or, if no <a href="#header.location" class="smpl">Location</a> field is received, by the effective request URI.
    2598                </p>
    2599                <p id="rfc.section.6.3.2.p.2">The 201 response payload typically describes and links to the resource(s) created. See <a href="#response.validator" title="Validator Header Fields">Section&nbsp;7.2</a> for a discussion of the meaning and purpose of validator header fields, such as <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> and <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a>, in a 201 response.
    2600                </p>
    2601             </div>
    2602             <div id="status.202">
    2603                <div id="rfc.iref.67"></div>
    2604                <h3 id="rfc.section.6.3.3"><a href="#rfc.section.6.3.3">6.3.3</a>&nbsp;<a href="#status.202">202 Accepted</a></h3>
    2605                <p id="rfc.section.6.3.3.p.1">The <dfn>202 (Accepted)</dfn> status code indicates that the request has been accepted for processing, but the processing has not been completed. The request
    2606                   might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility
    2607                   in HTTP for re-sending a status code from an asynchronous operation.
    2608                </p>
    2609                <p id="rfc.section.6.3.3.p.2">The 202 response is intentionally noncommittal. Its purpose is to allow a server to accept a request for some other process
    2610                   (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the
    2611                   server persist until the process is completed. The representation sent with this response ought to describe the request's
    2612                   current status and point to (or embed) a status monitor that can provide the user with an estimate of when the request will
    2613                   be fulfilled.
    2614                </p>
    2615             </div>
    2616             <div id="status.203">
    2617                <div id="rfc.iref.67"></div>
    2618                <h3 id="rfc.section.6.3.4"><a href="#rfc.section.6.3.4">6.3.4</a>&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></h3>
    2619                <p id="rfc.section.6.3.4.p.1">The <dfn>203 (Non-Authoritative Information)</dfn> status code indicates that the request was successful but the enclosed payload has been modified from that of the origin server's <a href="#status.200" class="smpl">200 (OK)</a> response by a transforming proxy (<a href="p1-messaging.html#message.transformations" title="Transformations">Section 5.7.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.25"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). This status code allows the proxy to notify recipients when a transformation has been applied, since that knowledge might
    2620                   impact later decisions regarding the content. For example, future cache validation requests for the content might only be
    2621                   applicable along the same request path (through the same proxies).
    2622                </p>
    2623                <p id="rfc.section.6.3.4.p.2">The 203 response is similar to the Warning code of 214 Transformation Applied (<a href="p6-cache.html#header.warning" title="Warning">Section 5.5</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.12"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>), which has the advantage of being applicable to responses with any status code.
    2624                </p>
    2625                <p id="rfc.section.6.3.4.p.3">A 203 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2626                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.13"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2627                </p>
    2628             </div>
    2629             <div id="status.204">
    2630                <div id="rfc.iref.67"></div>
    2631                <h3 id="rfc.section.6.3.5"><a href="#rfc.section.6.3.5">6.3.5</a>&nbsp;<a href="#status.204">204 No Content</a></h3>
    2632                <p id="rfc.section.6.3.5.p.1">The <dfn>204 (No Content)</dfn> status code indicates that the server has successfully fulfilled the request and that there is no additional content to send
    2633                   in the response payload body. Metadata in the response header fields refer to the <a href="#resources" class="smpl">target resource</a> and its <a href="#representations" class="smpl">selected representation</a> after the requested action was applied.
    2634                </p>
    2635                <p id="rfc.section.6.3.5.p.2">For example, if a 204 status code is received in response to a PUT request and the response contains an <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> header field, then the PUT was successful and the ETag field-value contains the entity-tag for the new representation of that
    2636                   target resource.
    2637                </p>
    2638                <p id="rfc.section.6.3.5.p.3">The 204 response allows a server to indicate that the action has been successfully applied to the target resource, while implying
    2639                   that the user agent does not need to traverse away from its current "document view" (if any). The server assumes that the
    2640                   user agent will provide some indication of the success to its user, in accord with its own interface, and apply any new or
    2641                   updated metadata in the response to its active representation.
    2642                </p>
    2643                <p id="rfc.section.6.3.5.p.4">For example, a 204 status code is commonly used with document editing interfaces corresponding to a "save" action, such that
    2644                   the document being saved remains available to the user for editing. It is also frequently used with interfaces that expect
    2645                   automated data transfers to be prevalent, such as within distributed version control systems.
    2646                </p>
    2647                <p id="rfc.section.6.3.5.p.5">A 204 response is terminated by the first empty line after the header fields because it cannot contain a message body.</p>
    2648                <p id="rfc.section.6.3.5.p.6">A 204 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2649                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.14"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2650                </p>
    2651             </div>
    2652             <div id="status.205">
    2653                <div id="rfc.iref.67"></div>
    2654                <h3 id="rfc.section.6.3.6"><a href="#rfc.section.6.3.6">6.3.6</a>&nbsp;<a href="#status.205">205 Reset Content</a></h3>
    2655                <p id="rfc.section.6.3.6.p.1">The <dfn>205 (Reset Content)</dfn> status code indicates that the server has fulfilled the request and desires that the user agent reset the "document view",
    2656                   which caused the request to be sent, to its original state as received from the origin server.
    2657                </p>
    2658                <p id="rfc.section.6.3.6.p.2">This response is intended to support a common data entry use case where the user receives content that supports data entry
    2659                   (a form, notepad, canvas, etc.), enters or manipulates data in that space, causes the entered data to be submitted in a request,
    2660                   and then the data entry mechanism is reset for the next entry so that the user can easily initiate another input action.
    2661                </p>
    2662                <p id="rfc.section.6.3.6.p.3">Since the 205 status code implies that no additional content will be provided, a server <em class="bcp14">MUST NOT</em> generate a payload in a 205 response. In other words, a server <em class="bcp14">MUST</em> do one of the following for a 205 response: a) indicate a zero-length body for the response by including a <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a> header field with a value of 0; b) indicate a zero-length payload for the response by including a <a href="p1-messaging.html#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field with a value of chunked and a message body consisting of a single chunk of zero-length; or, c) close the connection
    2663                   immediately after sending the blank line terminating the header section.
    2664                </p>
    2665             </div>
    2666          </div>
    2667          <div id="status.3xx">
    2668             <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a href="#status.3xx">Redirection 3xx</a></h2>
    2669             <div id="rfc.iref.67"></div>
    2670             <div id="rfc.iref.s.5"></div>
    2671             <p id="rfc.section.6.4.p.1">The <dfn>3xx (Redirection)</dfn> class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. If
    2672                a <a href="#header.location" class="smpl">Location</a> header field (<a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;7.1.2</a>) is provided, the user agent <em class="bcp14">MAY</em> automatically redirect its request to the URI referenced by the Location field value, even if the specific status code is
    2673                not understood. Automatic redirection needs to done with care for methods not known to be <a href="#safe.methods" class="smpl">safe</a>, as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>, since the user might not wish to redirect an unsafe request.
    2674             </p>
    2675             <p id="rfc.section.6.4.p.2">There are several types of redirects: </p>
    2676             <ol>
    2677                <li>
    2678                   <p>Redirects that indicate the resource might be available at a different URI, as provided by the <a href="#header.location" class="smpl">Location</a> field, as in the status codes <a href="#status.301" class="smpl">301 (Moved Permanently)</a>, <a href="#status.302" class="smpl">302 (Found)</a>, and <a href="#status.307" class="smpl">307 (Temporary Redirect)</a>.
    2679                   </p>
    2680                </li>
    2681                <li>
    2682                   <p>Redirection that offers a choice of matching resources, each capable of representing the original request target, as in the <a href="#status.300" class="smpl">300 (Multiple Choices)</a> status code.
    2683                   </p>
    2684                </li>
    2685                <li>
    2686                   <p>Redirection to a different resource, identified by the <a href="#header.location" class="smpl">Location</a> field, that can represent an indirect response to the request, as in the <a href="#status.303" class="smpl">303 (See Other)</a> status code.
    2687                   </p>
    2688                </li>
    2689                <li>
    2690                   <p>Redirection to a previously cached result, as in the <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> status code.
    2691                   </p>
    2692                </li>
    2693             </ol>
    2694             <div class="note" id="rfc.section.6.4.p.3">
    2695                <p><b>Note:</b> In HTTP/1.0, the status codes <a href="#status.301" class="smpl">301 (Moved Permanently)</a> and <a href="#status.302" class="smpl">302 (Found)</a> were defined for the first type of redirect (<a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, <a href="http://tools.ietf.org/html/rfc1945#section-9.3">Section 9.3</a>). Early user agents split on whether the method applied to the redirect target would be the same as the original request
    2696                   or would be rewritten as GET. Although HTTP originally defined the former semantics for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a> (to match its original implementation at CERN), and defined <a href="#status.303" class="smpl">303 (See Other)</a> to match the latter semantics, prevailing practice gradually converged on the latter semantics for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a> as well. The first revision of HTTP/1.1 added <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> to indicate the former semantics without being impacted by divergent practice. Over 10 years later, most user agents still
    2697                   do method rewriting for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a>; therefore, this specification makes that behavior conformant when the original request is POST.
    2698                </p>
    2699             </div>
    2700             <p id="rfc.section.6.4.p.4">A client <em class="bcp14">SHOULD</em> detect and intervene in cyclical redirections (i.e., "infinite" redirection loops).
    2701             </p>
    2702             <div class="note" id="rfc.section.6.4.p.5">
    2703                <p><b>Note:</b> An earlier version of this specification recommended a maximum of five redirections (<a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, <a href="http://tools.ietf.org/html/rfc2068#section-10.3">Section 10.3</a>). Content developers need to be aware that some clients might implement such a fixed limitation.
    2704                </p>
    2705             </div>
    2706             <div id="status.300">
    2707                <div id="rfc.iref.68"></div>
    2708                <h3 id="rfc.section.6.4.1"><a href="#rfc.section.6.4.1">6.4.1</a>&nbsp;<a href="#status.300">300 Multiple Choices</a></h3>
    2709                <p id="rfc.section.6.4.1.p.1">The <dfn>300 (Multiple Choices)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> has more than one representation, each with its own more specific identifier, and information about the alternatives is being
    2710                   provided so that the user (or user agent) can select a preferred representation by redirecting its request to one or more
    2711                   of those identifiers. In other words, the server desires that the user agent engage in reactive negotiation to select the
    2712                   most appropriate representation(s) for its needs (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;3.4</a>).
    2713                </p>
    2714                <p id="rfc.section.6.4.1.p.2">If the server has a preferred choice, the server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field containing a preferred choice's URI reference. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection.
    2715                </p>
    2716                <p id="rfc.section.6.4.1.p.3">For request methods other than HEAD, the server <em class="bcp14">SHOULD</em> generate a payload in the 300 response containing a list of representation metadata and URI reference(s) from which the user
    2717                   or user agent can choose the one most preferred. The user agent <em class="bcp14">MAY</em> make a selection from that list automatically if it understands the provided media type. A specific format for automatic selection
    2718                   is not defined by this specification because HTTP tries to remain orthogonal to the definition of its payloads. In practice,
    2719                   the representation is provided in some easily parsed format believed to be acceptable to the user agent, as determined by
    2720                   shared design or content negotiation, or in some commonly accepted hypertext format.
    2721                </p>
    2722                <p id="rfc.section.6.4.1.p.4">A 300 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2723                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.15"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2724                </p>
    2725                <div class="note" id="rfc.section.6.4.1.p.5">
    2726                   <p><b>Note:</b> The original proposal for the 300 status code defined the URI header field as providing a list of alternative representations,
    2727                      such that it would be usable for 200, 300, and 406 responses and be transferred in responses to the HEAD method. However,
    2728                      lack of deployment and disagreement over syntax led to both URI and Alternates (a subsequent proposal) being dropped from
    2729                      this specification. It is possible to communicate the list using a set of Link header fields <a href="#RFC5988" id="rfc.xref.RFC5988.1"><cite title="Web Linking">[RFC5988]</cite></a>, each with a relationship of "alternate", though deployment is a chicken-and-egg problem.
    2730                   </p>
    2731                </div>
    2732             </div>
    2733             <div id="status.301">
    2734                <div id="rfc.iref.68"></div>
    2735                <h3 id="rfc.section.6.4.2"><a href="#rfc.section.6.4.2">6.4.2</a>&nbsp;<a href="#status.301">301 Moved Permanently</a></h3>
    2736                <p id="rfc.section.6.4.2.p.1">The <dfn>301 (Moved Permanently)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> has been assigned a new permanent URI and any future references to this resource ought to use one of the enclosed URIs. Clients
    2737                   with link-editing capabilities ought to automatically re-link references to the effective request URI to one or more of the
    2738                   new references sent by the server, where possible.
    2739                </p>
    2740                <p id="rfc.section.6.4.2.p.2">The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a preferred URI reference for the new permanent URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note
    2741                   with a hyperlink to the new URI(s).
    2742                </p>
    2743                <div class="note" id="rfc.section.6.4.2.p.3">
    2744                   <p><b>Note:</b> For historical reasons, a user agent <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, the <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> status code can be used instead.
    2745                   </p>
    2746                </div>
    2747                <p id="rfc.section.6.4.2.p.4">A 301 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2748                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.16"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2749                </p>
    2750             </div>
    2751             <div id="status.302">
    2752                <div id="rfc.iref.68"></div>
    2753                <h3 id="rfc.section.6.4.3"><a href="#rfc.section.6.4.3">6.4.3</a>&nbsp;<a href="#status.302">302 Found</a></h3>
    2754                <p id="rfc.section.6.4.3.p.1">The <dfn>302 (Found)</dfn> status code indicates that the target resource resides temporarily under a different URI. Since the redirection might be altered
    2755                   on occasion, the client ought to continue to use the effective request URI for future requests.
    2756                </p>
    2757                <p id="rfc.section.6.4.3.p.2">The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a URI reference for the different URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note
    2758                   with a hyperlink to the different URI(s).
    2759                </p>
    2760                <div class="note" id="rfc.section.6.4.3.p.3">
    2761                   <p><b>Note:</b> For historical reasons, a user agent <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, the <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> status code can be used instead.
    2762                   </p>
    2763                </div>
    2764             </div>
    2765             <div id="status.303">
    2766                <div id="rfc.iref.68"></div>
    2767                <h3 id="rfc.section.6.4.4"><a href="#rfc.section.6.4.4">6.4.4</a>&nbsp;<a href="#status.303">303 See Other</a></h3>
    2768                <p id="rfc.section.6.4.4.p.1">The <dfn>303 (See Other)</dfn> status code indicates that the server is redirecting the user agent to a different resource, as indicated by a URI in the <a href="#header.location" class="smpl">Location</a> header field, which is intended to provide an indirect response to the original request. A user agent can perform a retrieval
    2769                   request targeting that URI (a GET or HEAD request if using HTTP), which might also be redirected, and present the eventual
    2770                   result as an answer to the original request. Note that the new URI in the Location header field is not considered equivalent
    2771                   to the effective request URI.
    2772                </p>
    2773                <p id="rfc.section.6.4.4.p.2">This status code is applicable to any HTTP method. It is primarily used to allow the output of a POST action to redirect the
    2774                   user agent to a selected resource, since doing so provides the information corresponding to the POST response in a form that
    2775                   can be separately identified, bookmarked, and cached, independent of the original request.
    2776                </p>
    2777                <p id="rfc.section.6.4.4.p.3">A 303 response to a GET request indicates that the origin server does not have a representation of the <a href="#resources" class="smpl">target resource</a> that can be transferred by the server over HTTP. However, the <a href="#header.location" class="smpl">Location</a> field value refers to a resource that is descriptive of the target resource, such that making a retrieval request on that
    2778                   other resource might result in a representation that is useful to recipients without implying that it represents the original
    2779                   target resource. Note that answers to the questions of what can be represented, what representations are adequate, and what
    2780                   might be a useful description are outside the scope of HTTP.
    2781                </p>
    2782                <p id="rfc.section.6.4.4.p.4">Except for responses to a HEAD request, the representation of a 303 response ought to contain a short hypertext note with
    2783                   a hyperlink to the same URI reference provided in the <a href="#header.location" class="smpl">Location</a> header field.
    2784                </p>
    2785             </div>
    2786             <div id="status.305">
    2787                <div id="rfc.iref.68"></div>
    2788                <h3 id="rfc.section.6.4.5"><a href="#rfc.section.6.4.5">6.4.5</a>&nbsp;<a href="#status.305">305 Use Proxy</a></h3>
    2789                <p id="rfc.section.6.4.5.p.1">The <dfn>305 (Use Proxy)</dfn> status code was defined in a previous version of this specification and is now deprecated (<a href="#changes.from.rfc.2616" title="Changes from RFC 2616">Appendix&nbsp;B</a>).
    2790                </p>
    2791             </div>
    2792             <div id="status.306">
    2793                <div id="rfc.iref.68"></div>
    2794                <h3 id="rfc.section.6.4.6"><a href="#rfc.section.6.4.6">6.4.6</a>&nbsp;<a href="#status.306">306 (Unused)</a></h3>
    2795                <p id="rfc.section.6.4.6.p.1">The 306 status code was defined in a previous version of this specification, is no longer used, and the code is reserved.</p>
    2796             </div>
    2797             <div id="status.307">
    2798                <div id="rfc.iref.68"></div>
    2799                <h3 id="rfc.section.6.4.7"><a href="#rfc.section.6.4.7">6.4.7</a>&nbsp;<a href="#status.307">307 Temporary Redirect</a></h3>
    2800                <p id="rfc.section.6.4.7.p.1">The <dfn>307 (Temporary Redirect)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> resides temporarily under a different URI and the user agent <em class="bcp14">MUST NOT</em> change the request method if it performs an automatic redirection to that URI. Since the redirection can change over time,
    2801                   the client ought to continue using the original effective request URI for future requests.
    2802                </p>
    2803                <p id="rfc.section.6.4.7.p.2">The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a URI reference for the different URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note
    2804                   with a hyperlink to the different URI(s).
    2805                </p>
    2806                <div class="note" id="rfc.section.6.4.7.p.3">
    2807                   <p><b>Note:</b> This status code is similar to <a href="#status.302" class="smpl">302 (Found)</a>, except that it does not allow changing the request method from POST to GET. This specification defines no equivalent counterpart
    2808                      for <a href="#status.301" class="smpl">301 (Moved
    2809                         Permanently)</a> (<a href="#RFC7238" id="rfc.xref.RFC7238.1"><cite title="The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)">[RFC7238]</cite></a>, however, defines the status code 308 (Permanent Redirect) for this purpose).
    2810                   </p>
    2811                </div>
    2812             </div>
    2813          </div>
    2814          <div id="status.4xx">
    2815             <h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a>&nbsp;<a href="#status.4xx">Client Error 4xx</a></h2>
    2816             <div id="rfc.iref.68"></div>
    2817             <div id="rfc.iref.s.6"></div>
    2818             <p id="rfc.section.6.5.p.1">The <dfn>4xx (Client Error)</dfn> class of status code indicates that the client seems to have erred. Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition.
    2819                These status codes are applicable to any request method. User agents <em class="bcp14">SHOULD</em> display any included representation to the user.
    2820             </p>
    2821             <div id="status.400">
    2822                <div id="rfc.iref.69"></div>
    2823                <h3 id="rfc.section.6.5.1"><a href="#rfc.section.6.5.1">6.5.1</a>&nbsp;<a href="#status.400">400 Bad Request</a></h3>
    2824                <p id="rfc.section.6.5.1.p.1">The <dfn>400 (Bad Request)</dfn> status code indicates that the server cannot or will not process the request due to something that is perceived to be a client
    2825                   error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).
    2826                </p>
    2827             </div>
    2828             <div id="status.402">
    2829                <div id="rfc.iref.69"></div>
    2830                <h3 id="rfc.section.6.5.2"><a href="#rfc.section.6.5.2">6.5.2</a>&nbsp;<a href="#status.402">402 Payment Required</a></h3>
    2831                <p id="rfc.section.6.5.2.p.1">The <dfn>402 (Payment Required)</dfn> status code is reserved for future use.
    2832                </p>
    2833             </div>
    2834             <div id="status.403">
    2835                <div id="rfc.iref.69"></div>
    2836                <h3 id="rfc.section.6.5.3"><a href="#rfc.section.6.5.3">6.5.3</a>&nbsp;<a href="#status.403">403 Forbidden</a></h3>
    2837                <p id="rfc.section.6.5.3.p.1">The <dfn>403 (Forbidden)</dfn> status code indicates that the server understood the request but refuses to authorize it. A server that wishes to make public
    2838                   why the request has been forbidden can describe that reason in the response payload (if any).
    2839                </p>
    2840                <p id="rfc.section.6.5.3.p.2">If authentication credentials were provided in the request, the server considers them insufficient to grant access. The client <em class="bcp14">SHOULD NOT</em> automatically repeat the request with the same credentials. The client <em class="bcp14">MAY</em> repeat the request with new or different credentials. However, a request might be forbidden for reasons unrelated to the credentials.
    2841                </p>
    2842                <p id="rfc.section.6.5.3.p.3">An origin server that wishes to "hide" the current existence of a forbidden <a href="#resources" class="smpl">target resource</a> <em class="bcp14">MAY</em> instead respond with a status code of <a href="#status.404" class="smpl">404 (Not Found)</a>.
    2843                </p>
    2844             </div>
    2845             <div id="status.404">
    2846                <div id="rfc.iref.69"></div>
    2847                <h3 id="rfc.section.6.5.4"><a href="#rfc.section.6.5.4">6.5.4</a>&nbsp;<a href="#status.404">404 Not Found</a></h3>
    2848                <p id="rfc.section.6.5.4.p.1">The <dfn>404 (Not Found)</dfn> status code indicates that the origin server did not find a current representation for the <a href="#resources" class="smpl">target resource</a> or is not willing to disclose that one exists. A 404 status code does not indicate whether this lack of representation is
    2849                   temporary or permanent; the <a href="#status.410" class="smpl">410 (Gone)</a> status code is preferred over 404 if the origin server knows, presumably through some configurable means, that the condition
    2850                   is likely to be permanent.
    2851                </p>
    2852                <p id="rfc.section.6.5.4.p.2">A 404 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2853                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.17"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2854                </p>
    2855             </div>
    2856             <div id="status.405">
    2857                <div id="rfc.iref.69"></div>
    2858                <h3 id="rfc.section.6.5.5"><a href="#rfc.section.6.5.5">6.5.5</a>&nbsp;<a href="#status.405">405 Method Not Allowed</a></h3>
    2859                <p id="rfc.section.6.5.5.p.1">The <dfn>405 (Method Not Allowed)</dfn> status code indicates that the method received in the request-line is known by the origin server but not supported by the <a href="#resources" class="smpl">target resource</a>. The origin server <em class="bcp14">MUST</em> generate an <a href="#header.allow" class="smpl">Allow</a> header field in a 405 response containing a list of the target resource's currently supported methods.
    2860                </p>
    2861                <p id="rfc.section.6.5.5.p.2">A 405 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2862                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.18"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2863                </p>
    2864             </div>
    2865             <div id="status.406">
    2866                <div id="rfc.iref.69"></div>
    2867                <h3 id="rfc.section.6.5.6"><a href="#rfc.section.6.5.6">6.5.6</a>&nbsp;<a href="#status.406">406 Not Acceptable</a></h3>
    2868                <p id="rfc.section.6.5.6.p.1">The <dfn>406 (Not Acceptable)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> does not have a current representation that would be acceptable to the user agent, according to the <a href="#proactive.negotiation" class="smpl">proactive negotiation</a> header fields received in the request (<a href="#request.conneg" title="Content Negotiation">Section&nbsp;5.3</a>), and the server is unwilling to supply a default representation.
    2869                </p>
    2870                <p id="rfc.section.6.5.6.p.2">The server <em class="bcp14">SHOULD</em> generate a payload containing a list of available representation characteristics and corresponding resource identifiers from
    2871                   which the user or user agent can choose the one most appropriate. A user agent <em class="bcp14">MAY</em> automatically select the most appropriate choice from that list. However, this specification does not define any standard
    2872                   for such automatic selection, as described in <a href="#status.300" id="rfc.xref.status.300.2" title="300 Multiple Choices">Section&nbsp;6.4.1</a>.
    2873                </p>
    2874             </div>
    2875             <div id="status.408">
    2876                <div id="rfc.iref.69"></div>
    2877                <h3 id="rfc.section.6.5.7"><a href="#rfc.section.6.5.7">6.5.7</a>&nbsp;<a href="#status.408">408 Request Timeout</a></h3>
    2878                <p id="rfc.section.6.5.7.p.1">The <dfn>408 (Request Timeout)</dfn> status code indicates that the server did not receive a complete request message within the time that it was prepared to wait.
    2879                   A server <em class="bcp14">SHOULD</em> send the "<a href="p1-messaging.html#header.connection" class="smpl">close</a>" connection option (<a href="p1-messaging.html#header.connection" title="Connection">Section 6.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.26"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) in the response, since 408 implies that the server has decided to close the connection rather than continue waiting. If
    2880                   the client has an outstanding request in transit, the client <em class="bcp14">MAY</em> repeat that request on a new connection.
    2881                </p>
    2882             </div>
    2883             <div id="status.409">
    2884                <div id="rfc.iref.69"></div>
    2885                <h3 id="rfc.section.6.5.8"><a href="#rfc.section.6.5.8">6.5.8</a>&nbsp;<a href="#status.409">409 Conflict</a></h3>
    2886                <p id="rfc.section.6.5.8.p.1">The <dfn>409 (Conflict)</dfn> status code indicates that the request could not be completed due to a conflict with the current state of the target resource.
    2887                   This code is used in situations where the user might be able to resolve the conflict and resubmit the request. The server <em class="bcp14">SHOULD</em> generate a payload that includes enough information for a user to recognize the source of the conflict.
    2888                </p>
    2889                <p id="rfc.section.6.5.8.p.2">Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the representation
    2890                   being PUT included changes to a resource that conflict with those made by an earlier (third-party) request, the origin server
    2891                   might use a 409 response to indicate that it can't complete the request. In this case, the response representation would likely
    2892                   contain information useful for merging the differences based on the revision history.
    2893                </p>
    2894             </div>
    2895             <div id="status.410">
    2896                <div id="rfc.iref.69"></div>
    2897                <h3 id="rfc.section.6.5.9"><a href="#rfc.section.6.5.9">6.5.9</a>&nbsp;<a href="#status.410">410 Gone</a></h3>
    2898                <p id="rfc.section.6.5.9.p.1">The <dfn>410 (Gone)</dfn> status code indicates that access to the <a href="#resources" class="smpl">target resource</a> is no longer available at the origin server and that this condition is likely to be permanent. If the origin server does not
    2899                   know, or has no facility to determine, whether or not the condition is permanent, the status code <a href="#status.404" class="smpl">404 (Not Found)</a> ought to be used instead.
    2900                </p>
    2901                <p id="rfc.section.6.5.9.p.2">The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource
    2902                   is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event
    2903                   is common for limited-time, promotional services and for resources belonging to individuals no longer associated with the
    2904                   origin server's site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for
    2905                   any length of time — that is left to the discretion of the server owner.
    2906                </p>
    2907                <p id="rfc.section.6.5.9.p.3">A 410 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2908                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.19"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2909                </p>
    2910             </div>
    2911             <div id="status.411">
    2912                <div id="rfc.iref.69"></div>
    2913                <h3 id="rfc.section.6.5.10"><a href="#rfc.section.6.5.10">6.5.10</a>&nbsp;<a href="#status.411">411 Length Required</a></h3>
    2914                <p id="rfc.section.6.5.10.p.1">The <dfn>411 (Length Required)</dfn> status code indicates that the server refuses to accept the request without a defined <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a> (<a href="p1-messaging.html#header.content-length" title="Content-Length">Section 3.3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.27"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). The client <em class="bcp14">MAY</em> repeat the request if it adds a valid Content-Length header field containing the length of the message body in the request
    2915                   message.
    2916                </p>
    2917             </div>
    2918             <div id="status.413">
    2919                <div id="rfc.iref.69"></div>
    2920                <h3 id="rfc.section.6.5.11"><a href="#rfc.section.6.5.11">6.5.11</a>&nbsp;<a href="#status.413">413 Payload Too Large</a></h3>
    2921                <p id="rfc.section.6.5.11.p.1">The <dfn>413 (Payload Too Large)</dfn> status code indicates that the server is refusing to process a request because the request payload is larger than the server
    2922                   is willing or able to process. The server <em class="bcp14">MAY</em> close the connection to prevent the client from continuing the request.
    2923                </p>
    2924                <p id="rfc.section.6.5.11.p.2">If the condition is temporary, the server <em class="bcp14">SHOULD</em> generate a <a href="#header.retry-after" class="smpl">Retry-After</a> header field to indicate that it is temporary and after what time the client <em class="bcp14">MAY</em> try again.
    2925                </p>
    2926             </div>
    2927             <div id="status.414">
    2928                <div id="rfc.iref.69"></div>
    2929                <h3 id="rfc.section.6.5.12"><a href="#rfc.section.6.5.12">6.5.12</a>&nbsp;<a href="#status.414">414 URI Too Long</a></h3>
    2930                <p id="rfc.section.6.5.12.p.1">The <dfn>414 (URI Too Long)</dfn> status code indicates that the server is refusing to service the request because the request-target (<a href="p1-messaging.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.28"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly
    2931                   converted a POST request to a GET request with long query information, when the client has descended into a "black hole" of
    2932                   redirection (e.g., a redirected URI prefix that points to a suffix of itself) or when the server is under attack by a client
    2933                   attempting to exploit potential security holes.
    2934                </p>
    2935                <p id="rfc.section.6.5.12.p.2">A 414 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2936                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.20"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2937                </p>
    2938             </div>
    2939             <div id="status.415">
    2940                <div id="rfc.iref.69"></div>
    2941                <h3 id="rfc.section.6.5.13"><a href="#rfc.section.6.5.13">6.5.13</a>&nbsp;<a href="#status.415">415 Unsupported Media Type</a></h3>
    2942                <p id="rfc.section.6.5.13.p.1">The <dfn>415 (Unsupported Media Type)</dfn> status code indicates that the origin server is refusing to service the request because the payload is in a format not supported
    2943                   by this method on the <a href="#resources" class="smpl">target resource</a>. The format problem might be due to the request's indicated <a href="#header.content-type" class="smpl">Content-Type</a> or <a href="#header.content-encoding" class="smpl">Content-Encoding</a>, or as a result of inspecting the data directly.
    2944                </p>
    2945             </div>
    2946             <div id="status.417">
    2947                <div id="rfc.iref.69"></div>
    2948                <h3 id="rfc.section.6.5.14"><a href="#rfc.section.6.5.14">6.5.14</a>&nbsp;<a href="#status.417">417 Expectation Failed</a></h3>
    2949                <p id="rfc.section.6.5.14.p.1">The <dfn>417 (Expectation Failed)</dfn> status code indicates that the expectation given in the request's <a href="#header.expect" class="smpl">Expect</a> header field (<a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section&nbsp;5.1.1</a>) could not be met by at least one of the inbound servers.
    2950                </p>
    2951             </div>
    2952             <div id="status.426">
    2953                <div id="rfc.iref.69"></div>
    2954                <h3 id="rfc.section.6.5.15"><a href="#rfc.section.6.5.15">6.5.15</a>&nbsp;<a href="#status.426">426 Upgrade Required</a></h3>
    2955                <p id="rfc.section.6.5.15.p.1">The <dfn>426 (Upgrade Required)</dfn> status code indicates that the server refuses to perform the request using the current protocol but might be willing to do
    2956                   so after the client upgrades to a different protocol. The server <em class="bcp14">MUST</em> send an <a href="p1-messaging.html#header.upgrade" class="smpl">Upgrade</a> header field in a 426 response to indicate the required protocol(s) (<a href="p1-messaging.html#header.upgrade" title="Upgrade">Section 6.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.29"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    2957                </p>
    2958                <div id="rfc.figure.u.42"></div>
    2959                <p>Example:</p><pre class="text">HTTP/1.1 426 Upgrade Required
    2960 Upgrade: HTTP/3.0
    2961 Connection: Upgrade
    2962 Content-Length: 53
    2963 Content-Type: text/plain
    2964 
    2965 <span id="s426body">This service requires use of the HTTP/3.0 protocol.
    2966 </span></pre></div>
    2967          </div>
    2968          <div id="status.5xx">
    2969             <h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a>&nbsp;<a href="#status.5xx">Server Error 5xx</a></h2>
    2970             <div id="rfc.iref.69"></div>
    2971             <div id="rfc.iref.s.7"></div>
    2972             <p id="rfc.section.6.6.p.1">The <dfn>5xx (Server Error)</dfn> class of status code indicates that the server is aware that it has erred or is incapable of performing the requested method.
    2973                Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition.
    2974                A user agent <em class="bcp14">SHOULD</em> display any included representation to the user. These response codes are applicable to any request method.
    2975             </p>
    2976             <div id="status.500">
    2977                <div id="rfc.iref.70"></div>
    2978                <h3 id="rfc.section.6.6.1"><a href="#rfc.section.6.6.1">6.6.1</a>&nbsp;<a href="#status.500">500 Internal Server Error</a></h3>
    2979                <p id="rfc.section.6.6.1.p.1">The <dfn>500 (Internal Server Error)</dfn> status code indicates that the server encountered an unexpected condition that prevented it from fulfilling the request.
    2980                </p>
    2981             </div>
    2982             <div id="status.501">
    2983                <div id="rfc.iref.70"></div>
    2984                <h3 id="rfc.section.6.6.2"><a href="#rfc.section.6.6.2">6.6.2</a>&nbsp;<a href="#status.501">501 Not Implemented</a></h3>
    2985                <p id="rfc.section.6.6.2.p.1">The <dfn>501 (Not Implemented)</dfn> status code indicates that the server does not support the functionality required to fulfill the request. This is the appropriate
    2986                   response when the server does not recognize the request method and is not capable of supporting it for any resource.
    2987                </p>
    2988                <p id="rfc.section.6.6.2.p.2">A 501 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls
    2989                   (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.21"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).
    2990                </p>
    2991             </div>
    2992             <div id="status.502">
    2993                <div id="rfc.iref.70"></div>
    2994                <h3 id="rfc.section.6.6.3"><a href="#rfc.section.6.6.3">6.6.3</a>&nbsp;<a href="#status.502">502 Bad Gateway</a></h3>
    2995                <p id="rfc.section.6.6.3.p.1">The <dfn>502 (Bad Gateway)</dfn> status code indicates that the server, while acting as a gateway or proxy, received an invalid response from an inbound server
    2996                   it accessed while attempting to fulfill the request.
    2997                </p>
    2998             </div>
    2999             <div id="status.503">
    3000                <div id="rfc.iref.70"></div>
    3001                <h3 id="rfc.section.6.6.4"><a href="#rfc.section.6.6.4">6.6.4</a>&nbsp;<a href="#status.503">503 Service Unavailable</a></h3>
    3002                <p id="rfc.section.6.6.4.p.1">The <dfn>503 (Service Unavailable)</dfn> status code indicates that the server is currently unable to handle the request due to a temporary overload or scheduled maintenance,
    3003                   which will likely be alleviated after some delay. The server <em class="bcp14">MAY</em> send a <a href="#header.retry-after" class="smpl">Retry-After</a> header field (<a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section&nbsp;7.1.3</a>) to suggest an appropriate amount of time for the client to wait before retrying the request.
    3004                </p>
    3005                <div class="note" id="rfc.section.6.6.4.p.2">
    3006                   <p><b>Note:</b> The existence of the 503 status code does not imply that a server has to use it when becoming overloaded. Some servers might
    3007                      simply refuse the connection.
    3008                   </p>
    3009                </div>
    3010             </div>
    3011             <div id="status.504">
    3012                <div id="rfc.iref.70"></div>
    3013                <h3 id="rfc.section.6.6.5"><a href="#rfc.section.6.6.5">6.6.5</a>&nbsp;<a href="#status.504">504 Gateway Timeout</a></h3>
    3014                <p id="rfc.section.6.6.5.p.1">The <dfn>504 (Gateway Timeout)</dfn> status code indicates that the server, while acting as a gateway or proxy, did not receive a timely response from an upstream
    3015                   server it needed to access in order to complete the request.
    3016                </p>
    3017             </div>
    3018             <div id="status.505">
    3019                <div id="rfc.iref.70"></div>
    3020                <h3 id="rfc.section.6.6.6"><a href="#rfc.section.6.6.6">6.6.6</a>&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></h3>
    3021                <p id="rfc.section.6.6.6.p.1">The <dfn>505 (HTTP Version Not Supported)</dfn> status code indicates that the server does not support, or refuses to support, the major version of HTTP that was used in
    3022                   the request message. The server is indicating that it is unable or unwilling to complete the request using the same major
    3023                   version as the client, as described in <a href="p1-messaging.html#http.version" title="Protocol Versioning">Section 2.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.30"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>, other than with this error message. The server <em class="bcp14">SHOULD</em> generate a representation for the 505 response that describes why that version is not supported and what other protocols are
    3024                   supported by that server.
    3025                </p>
    3026             </div>
    3027          </div>
    3028       </div>
    3029       <div id="response.header.fields">
    3030          <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a href="#response.header.fields">Response Header Fields</a></h1>
    3031          <p id="rfc.section.7.p.1">The response header fields allow the server to pass additional information about the response beyond what is placed in the
    3032             status-line. These header fields give information about the server, about further access to the <a href="#resources" class="smpl">target resource</a>, or about related resources.
    3033          </p>
    3034          <p id="rfc.section.7.p.2">Although each response header field has a defined meaning, in general, the precise semantics might be further refined by the
    3035             semantics of the request method and/or response status code.
    3036          </p>
    3037          <div id="response.control.data">
    3038             <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a href="#response.control.data">Control Data</a></h2>
    3039             <p id="rfc.section.7.1.p.1">Response header fields can supply control data that supplements the status code, directs caching, or instructs the client
    3040                where to go next.
    3041             </p>
    3042             <div id="rfc.table.u.10">
    3043                <table class="tt full left" cellpadding="3" cellspacing="0">
    3044                   <thead>
    3045                      <tr>
    3046                         <th>Header Field Name</th>
    3047                         <th>Defined in...</th>
    3048                      </tr>
    3049                   </thead>
    3050                   <tbody>
    3051                      <tr>
    3052                         <td class="left">Age</td>
    3053                         <td class="left"><a href="p6-cache.html#header.age" title="Age">Section 5.1</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.22"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td>
    3054                      </tr>
    3055                      <tr>
    3056                         <td class="left">Cache-Control</td>
    3057                         <td class="left"><a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 5.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.23"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td>
    3058                      </tr>
    3059                      <tr>
    3060                         <td class="left">Expires</td>
    3061                         <td class="left"><a href="p6-cache.html#header.expires" title="Expires">Section 5.3</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.24"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td>
    3062                      </tr>
    3063                      <tr>
    3064                         <td class="left">Date</td>
    3065                         <td class="left"><a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section&nbsp;7.1.1.2</a></td>
    3066                      </tr>
    3067                      <tr>
    3068                         <td class="left">Location</td>
    3069                         <td class="left"><a href="#header.location" id="rfc.xref.header.location.3" title="Location">Section&nbsp;7.1.2</a></td>
    3070                      </tr>
    3071                      <tr>
    3072                         <td class="left">Retry-After</td>
    3073                         <td class="left"><a href="#header.retry-after" id="rfc.xref.header.retry-after.2" title="Retry-After">Section&nbsp;7.1.3</a></td>
    3074                      </tr>
    3075                      <tr>
    3076                         <td class="left">Vary</td>
    3077                         <td class="left"><a href="#header.vary" id="rfc.xref.header.vary.2" title="Vary">Section&nbsp;7.1.4</a></td>
    3078                      </tr>
    3079                      <tr>
    3080                         <td class="left">Warning</td>
    3081                         <td class="left"><a href="p6-cache.html#header.warning" title="Warning">Section 5.5</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.25"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td>
    3082                      </tr>
    3083                   </tbody>
    3084                </table>
    3085             </div>
    3086             <div id="origination.date">
    3087                <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a href="#origination.date">Origination Date</a></h3>
    3088                <div id="http.date">
    3089                   <h4 id="rfc.section.7.1.1.1"><a href="#rfc.section.7.1.1.1">7.1.1.1</a>&nbsp;<a href="#http.date">Date/Time Formats</a></h4>
    3090                   <p id="rfc.section.7.1.1.1.p.1">Prior to 1995, there were three different formats commonly used by servers to communicate timestamps. For compatibility with
    3091                      old implementations, all three are defined here. The preferred format is a fixed-length and single-zone subset of the date
    3092                      and time specification used by the Internet Message Format <a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>.
    3093                   </p>
    3094                   <div id="rfc.figure.u.43"></div><pre class="inline"><span id="rfc.iref.g.33"></span>  <a href="#http.date" class="smpl">HTTP-date</a>    = <a href="#preferred.date.format" class="smpl">IMF-fixdate</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a>
    3095 </pre><div id="rfc.figure.u.44"></div>
    3096                   <p>An example of the preferred format is</p><pre class="text">Sun, 06 Nov 1994 08:49:37 GMT    ; IMF-fixdate
    3097 </pre><div id="rfc.figure.u.45"></div>
    3098                   <p>Examples of the two obsolete formats are</p><pre class="text">Sunday, 06-Nov-94 08:49:37 GMT   ; obsolete RFC 850 format
    3099 Sun Nov  6 08:49:37 1994         ; ANSI C's asctime() format
    3100 </pre><p id="rfc.section.7.1.1.1.p.5">A recipient that parses a timestamp value in an HTTP header field <em class="bcp14">MUST</em> accept all three HTTP-date formats. When a sender generates a header field that contains one or more timestamps defined as
    3101                      HTTP-date, the sender <em class="bcp14">MUST</em> generate those timestamps in the IMF-fixdate format.
    3102                   </p>
    3103                   <p id="rfc.section.7.1.1.1.p.6">An HTTP-date value represents time as an instance of Coordinated Universal Time (UTC). The first two formats indicate UTC
    3104                      by the three-letter abbreviation for Greenwich Mean Time, "GMT", a predecessor of the UTC name; values in the asctime format
    3105                      are assumed to be in UTC. A sender that generates HTTP-date values from a local clock ought to use NTP (<a href="#RFC5905" id="rfc.xref.RFC5905.1"><cite title="Network Time Protocol Version 4: Protocol and Algorithms Specification">[RFC5905]</cite></a>) or some similar protocol to synchronize its clock to UTC.
    3106                   </p>
    3107                   <div id="preferred.date.format">
    3108                      <p id="rfc.section.7.1.1.1.p.7">          Preferred format:</p>
    3109                   </div>
    3110                   <div id="rfc.figure.u.46"></div><pre class="inline"><span id="rfc.iref.g.34"></span><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span>  <a href="#preferred.date.format" class="smpl">IMF-fixdate</a>  = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#imported.abnf" class="smpl">SP</a> date1 <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    3111   ; fixed length/zone/capitalization subset of the format
    3112   ; defined in <a href="http://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>
    3113  
    3114   <a href="#preferred.date.format" class="smpl">day-name</a>     = %x4D.6F.6E ; "Mon", case-sensitive
    3115                / %x54.75.65 ; "Tue", case-sensitive
    3116                / %x57.65.64 ; "Wed", case-sensitive
    3117                / %x54.68.75 ; "Thu", case-sensitive
    3118                / %x46.72.69 ; "Fri", case-sensitive
    3119                / %x53.61.74 ; "Sat", case-sensitive
    3120                / %x53.75.6E ; "Sun", case-sensitive
    3121                
    3122   <a href="#obsolete.date.formats" class="smpl">date1</a>        = <a href="#preferred.date.format" class="smpl">day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">month</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">year</a>
    3123                ; e.g., 02 Jun 1982
    3124 
    3125   <a href="#preferred.date.format" class="smpl">day</a>          = 2<a href="#imported.abnf" class="smpl">DIGIT</a>
    3126   <a href="#preferred.date.format" class="smpl">month</a>        = %x4A.61.6E ; "Jan", case-sensitive
    3127                / %x46.65.62 ; "Feb", case-sensitive
    3128                / %x4D.61.72 ; "Mar", case-sensitive
    3129                / %x41.70.72 ; "Apr", case-sensitive
    3130                / %x4D.61.79 ; "May", case-sensitive
    3131                / %x4A.75.6E ; "Jun", case-sensitive
    3132                / %x4A.75.6C ; "Jul", case-sensitive
    3133                / %x41.75.67 ; "Aug", case-sensitive
    3134                / %x53.65.70 ; "Sep", case-sensitive
    3135                / %x4F.63.74 ; "Oct", case-sensitive
    3136                / %x4E.6F.76 ; "Nov", case-sensitive
    3137                / %x44.65.63 ; "Dec", case-sensitive
    3138   <a href="#preferred.date.format" class="smpl">year</a>         = 4<a href="#imported.abnf" class="smpl">DIGIT</a>
    3139 
    3140   <a href="#preferred.date.format" class="smpl">GMT</a>          = %x47.4D.54 ; "GMT", case-sensitive
    3141 
    3142   <a href="#preferred.date.format" class="smpl">time-of-day</a>  = <a href="#preferred.date.format" class="smpl">hour</a> ":" <a href="#preferred.date.format" class="smpl">minute</a> ":" <a href="#preferred.date.format" class="smpl">second</a>
    3143                ; 00:00:00 - 23:59:60 (leap second)
    3144                  
    3145   <a href="#preferred.date.format" class="smpl">hour</a>         = 2<a href="#imported.abnf" class="smpl">DIGIT</a>               
    3146   <a href="#preferred.date.format" class="smpl">minute</a>       = 2<a href="#imported.abnf" class="smpl">DIGIT</a>               
    3147   <a href="#preferred.date.format" class="smpl">second</a>       = 2<a href="#imported.abnf" class="smpl">DIGIT</a>               
    3148 </pre><div id="obsolete.date.formats">
    3149                      <p id="rfc.section.7.1.1.1.p.9">       Obsolete formats:</p>
    3150                   </div>
    3151                   <div id="rfc.figure.u.47"></div><pre class="inline"><span id="rfc.iref.g.46"></span>  <a href="#obsolete.date.formats" class="smpl">obs-date</a>     = <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> / <a href="#obsolete.date.formats" class="smpl">asctime-date</a>
    3152 </pre><div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.47"></span>  <a href="#obsolete.date.formats" class="smpl">rfc850-date</a>  = <a href="#obsolete.date.formats" class="smpl">day-name-l</a> "," <a href="#imported.abnf" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date2</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    3153   <a href="#obsolete.date.formats" class="smpl">date2</a>        = <a href="#preferred.date.format" class="smpl">day</a> "-" <a href="#preferred.date.format" class="smpl">month</a> "-" 2<a href="#imported.abnf" class="smpl">DIGIT</a>
    3154                ; e.g., 02-Jun-82
    3155 
    3156   <a href="#obsolete.date.formats" class="smpl">day-name-l</a>   = %x4D.6F.6E.64.61.79    ; "Monday", case-sensitive
    3157          / %x54.75.65.73.64.61.79       ; "Tuesday", case-sensitive
    3158          / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
    3159          / %x54.68.75.72.73.64.61.79    ; "Thursday", case-sensitive
    3160          / %x46.72.69.64.61.79          ; "Friday", case-sensitive
    3161          / %x53.61.74.75.72.64.61.79    ; "Saturday", case-sensitive
    3162          / %x53.75.6E.64.61.79          ; "Sunday", case-sensitive
    3163 </pre><div id="rfc.figure.u.49"></div><pre class="inline"><span id="rfc.iref.g.48"></span>  <a href="#obsolete.date.formats" class="smpl">asctime-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date3</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">year</a>
    3164   <a href="#obsolete.date.formats" class="smpl">date3</a>        = <a href="#preferred.date.format" class="smpl">month</a> <a href="#imported.abnf" class="smpl">SP</a> ( 2<a href="#imported.abnf" class="smpl">DIGIT</a> / ( <a href="#imported.abnf" class="smpl">SP</a> 1<a href="#imported.abnf" class="smpl">DIGIT</a> ))
    3165                ; e.g., Jun  2
    3166 </pre><p id="rfc.section.7.1.1.1.p.13">HTTP-date is case sensitive. A sender <em class="bcp14">MUST NOT</em> generate additional whitespace in an HTTP-date beyond that specifically included as SP in the grammar. The semantics of <a href="#preferred.date.format" class="smpl">day-name</a>, <a href="#preferred.date.format" class="smpl">day</a>, <a href="#preferred.date.format" class="smpl">month</a>, <a href="#preferred.date.format" class="smpl">year</a>, and <a href="#preferred.date.format" class="smpl">time-of-day</a> are the same as those defined for the Internet Message Format constructs with the corresponding name (<a href="#RFC5322" id="rfc.xref.RFC5322.5"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="http://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a>).
    3167                   </p>
    3168                   <p id="rfc.section.7.1.1.1.p.14">Recipients of a timestamp value in rfc850-date format, which uses a two-digit year, <em class="bcp14">MUST</em> interpret a timestamp that appears to be more than 50 years in the future as representing the most recent year in the past
    3169                      that had the same last two digits.
    3170                   </p>
    3171                   <p id="rfc.section.7.1.1.1.p.15">Recipients of timestamp values are encouraged to be robust in parsing timestamps unless otherwise restricted by the field
    3172                      definition. For example, messages are occasionally forwarded over HTTP from a non-HTTP source that might generate any of the
    3173                      date and time specifications defined by the Internet Message Format.
    3174                   </p>
    3175                   <div class="note" id="rfc.section.7.1.1.1.p.16">
    3176                      <p><b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Implementations are
    3177                         not required to use these formats for user presentation, request logging, etc.
    3178                      </p>
    3179                   </div>
    3180                </div>
    3181                <div id="header.date">
    3182                   <div id="rfc.iref.d.3"></div>
    3183                   <h4 id="rfc.section.7.1.1.2"><a href="#rfc.section.7.1.1.2">7.1.1.2</a>&nbsp;<a href="#header.date">Date</a></h4>
    3184                   <p id="rfc.section.7.1.1.2.p.1">The "Date" header field represents the date and time at which the message was originated, having the same semantics as the
    3185                      Origination Date Field (orig-date) defined in <a href="http://tools.ietf.org/html/rfc5322#section-3.6.1">Section 3.6.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.6"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as defined in <a href="#http.date" title="Date/Time Formats">Section&nbsp;7.1.1.1</a>.
    3186                   </p>
    3187                   <div id="rfc.figure.u.50"></div><pre class="inline"><span id="rfc.iref.g.49"></span>  <a href="#header.date" class="smpl">Date</a> = <a href="#http.date" class="smpl">HTTP-date</a>
    3188 </pre><p id="rfc.section.7.1.1.2.p.3">An example is</p>
    3189                   <div id="rfc.figure.u.51"></div><pre class="text">  Date: Tue, 15 Nov 1994 08:12:31 GMT
    3190 </pre><p id="rfc.section.7.1.1.2.p.5">When a Date header field is generated, the sender <em class="bcp14">SHOULD</em> generate its field value as the best available approximation of the date and time of message generation. In theory, the date
    3191                      ought to represent the moment just before the payload is generated. In practice, the date can be generated at any time during
    3192                      message origination.
    3193                   </p>
    3194                   <p id="rfc.section.7.1.1.2.p.6">An origin server <em class="bcp14">MUST NOT</em> send a Date header field if it does not have a clock capable of providing a reasonable approximation of the current instance
    3195                      in Coordinated Universal Time. An origin server <em class="bcp14">MAY</em> send a Date header field if the response is in the <a href="#status.1xx" class="smpl">1xx (Informational)</a> or <a href="#status.5xx" class="smpl">5xx (Server Error)</a> class of status codes. An origin server <em class="bcp14">MUST</em> send a Date header field in all other cases.
    3196                   </p>
    3197                   <p id="rfc.section.7.1.1.2.p.7">A recipient with a clock that receives a response message without a Date header field <em class="bcp14">MUST</em> record the time it was received and append a corresponding Date header field to the message's header section if it is cached
    3198                      or forwarded downstream.
    3199                   </p>
    3200                   <p id="rfc.section.7.1.1.2.p.8">A user agent <em class="bcp14">MAY</em> send a Date header field in a request, though generally will not do so unless it is believed to convey useful information
    3201                      to the server. For example, custom applications of HTTP might convey a Date if the server is expected to adjust its interpretation
    3202                      of the user's request based on differences between the user agent and server clocks.
    3203                   </p>
    3204                </div>
    3205             </div>
    3206             <div id="header.location">
    3207                <div id="rfc.iref.l.1"></div>
    3208                <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;<a href="#header.location">Location</a></h3>
    3209                <p id="rfc.section.7.1.2.p.1">The "Location" header field is used in some responses to refer to a specific resource in relation to the response. The type
    3210                   of relationship is defined by the combination of request method and status code semantics.
    3211                </p>
    3212                <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.50"></span>  <a href="#header.location" class="smpl">Location</a> = <a href="#imported.abnf" class="smpl">URI-reference</a>
    3213 </pre><p id="rfc.section.7.1.2.p.3">The field value consists of a single URI-reference. When it has the form of a relative reference (<a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.2">Section 4.2</a>), the final value is computed by resolving it against the effective request URI (<a href="#RFC3986" id="rfc.xref.RFC3986.3"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-5">Section 5</a>).
    3214                </p>
    3215                <p id="rfc.section.7.1.2.p.4">For <a href="#status.201" class="smpl">201 (Created)</a> responses, the Location value refers to the primary resource created by the request. For <a href="#status.3xx" class="smpl">3xx (Redirection)</a> responses, the Location value refers to the preferred target resource for automatically redirecting the request.
    3216                </p>
    3217                <p id="rfc.section.7.1.2.p.5">If the Location value provided in a <a href="#status.3xx" class="smpl">3xx (Redirection)</a> response does not have a fragment component, a user agent <em class="bcp14">MUST</em> process the redirection as if the value inherits the fragment component of the URI reference used to generate the request
    3218                   target (i.e., the redirection inherits the original reference's fragment, if any).
    3219                </p>
    3220                <div id="rfc.figure.u.53"></div>
    3221                <p>For example, a GET request generated for the URI reference "http://www.example.org/~tim" might result in a <a href="#status.303" class="smpl">303 (See Other)</a> response containing the header field:
    3222                </p><pre class="text">  Location: /People.html#tim
    3223 </pre><p>which suggests that the user agent redirect to "http://www.example.org/People.html#tim"</p>
    3224                <div id="rfc.figure.u.54"></div>
    3225                <p>Likewise, a GET request generated for the URI reference "http://www.example.org/index.html#larry" might result in a <a href="#status.301" class="smpl">301 (Moved Permanently)</a> response containing the header field:
    3226                </p><pre class="text">  Location: http://www.example.net/index.html
    3227 </pre><p>which suggests that the user agent redirect to "http://www.example.net/index.html#larry", preserving the original fragment
    3228                   identifier.
    3229                </p>
    3230                <p id="rfc.section.7.1.2.p.8">There are circumstances in which a fragment identifier in a Location value would not be appropriate. For example, the Location
    3231                   header field in a <a href="#status.201" class="smpl">201 (Created)</a> response is supposed to provide a URI that is specific to the created resource.
    3232                </p>
    3233                <div class="note" id="rfc.section.7.1.2.p.9">
    3234                   <p><b>Note:</b> Some recipients attempt to recover from Location fields that are not valid URI references. This specification does not mandate
    3235                      or define such processing, but does allow it for the sake of robustness.
    3236                   </p>
    3237                </div>
    3238                <div class="note" id="rfc.section.7.1.2.p.10">
    3239                   <p><b>Note:</b> The <a href="#header.content-location" class="smpl">Content-Location</a> header field (<a href="#header.content-location" id="rfc.xref.header.content-location.3" title="Content-Location">Section&nbsp;3.1.4.2</a>) differs from Location in that the Content-Location refers to the most specific resource corresponding to the enclosed representation.
    3240                      It is therefore possible for a response to contain both the Location and Content-Location header fields.
    3241                   </p>
    3242                </div>
    3243             </div>
    3244             <div id="header.retry-after">
    3245                <div id="rfc.iref.r.3"></div>
    3246                <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;<a href="#header.retry-after">Retry-After</a></h3>
    3247                <p id="rfc.section.7.1.3.p.1">Servers send the "Retry-After" header field to indicate how long the user agent ought to wait before making a follow-up request.
    3248                   When sent with a <a href="#status.503" class="smpl">503 (Service Unavailable)</a> response, Retry-After indicates how long the service is expected to be unavailable to the client. When sent with any <a href="#status.3xx" class="smpl">3xx (Redirection)</a> response, Retry-After indicates the minimum time that the user agent is asked to wait before issuing the redirected request.
    3249                </p>
    3250                <p id="rfc.section.7.1.3.p.2">The value of this field can be either an HTTP-date or a number of seconds to delay after the response is received.</p>
    3251                <div id="rfc.figure.u.55"></div><pre class="inline"><span id="rfc.iref.g.51"></span>  <a href="#header.retry-after" class="smpl">Retry-After</a> = <a href="#http.date" class="smpl">HTTP-date</a> / <a href="#rule.delay-seconds" class="smpl">delay-seconds</a>
    3252 </pre><div id="rule.delay-seconds">
    3253                   <p id="rfc.section.7.1.3.p.4"> A delay-seconds value is a non-negative decimal integer, representing time in seconds.</p>
    3254                </div>
    3255                <div id="rfc.figure.u.56"></div><pre class="inline"><span id="rfc.iref.g.52"></span>  <a href="#rule.delay-seconds" class="smpl">delay-seconds</a>  = 1*<a href="#imported.abnf" class="smpl">DIGIT</a>
    3256 </pre><p id="rfc.section.7.1.3.p.6">Two examples of its use are</p>
    3257                <div id="rfc.figure.u.57"></div><pre class="text">  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
    3258   Retry-After: 120
    3259 </pre><p id="rfc.section.7.1.3.p.8">In the latter example, the delay is 2 minutes.</p>
    3260             </div>
    3261             <div id="header.vary">
    3262                <div id="rfc.iref.v.1"></div>
    3263                <h3 id="rfc.section.7.1.4"><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;<a href="#header.vary">Vary</a></h3>
    3264                <p id="rfc.section.7.1.4.p.1">The "Vary" header field in a response describes what parts of a request message, aside from the method, Host header field,
    3265                   and request target, might influence the origin server's process for selecting and representing this response. The value consists
    3266                   of either a single asterisk ("*") or a list of header field names (case-insensitive).
    3267                </p>
    3268                <div id="rfc.figure.u.58"></div><pre class="inline"><span id="rfc.iref.g.53"></span>  <a href="#header.vary" class="smpl">Vary</a> = "*" / 1#<a href="#imported.abnf" class="smpl">field-name</a>
    3269 </pre><p id="rfc.section.7.1.4.p.3">A Vary field value of "*" signals that anything about the request might play a role in selecting the response representation,
    3270                   possibly including elements outside the message syntax (e.g., the client's network address). A recipient will not be able
    3271                   to determine whether this response is appropriate for a later request without forwarding the request to the origin server.
    3272                   A proxy <em class="bcp14">MUST NOT</em> generate a Vary field with a "*" value.
    3273                </p>
    3274                <p id="rfc.section.7.1.4.p.4">A Vary field value consisting of a comma-separated list of names indicates that the named request header fields, known as
    3275                   the selecting header fields, might have a role in selecting the representation. The potential selecting header fields are
    3276                   not limited to those defined by this specification.
    3277                </p>
    3278                <div id="rfc.figure.u.59"></div>
    3279                <p>For example, a response that contains</p><pre class="text">  Vary: accept-encoding, accept-language
    3280 </pre><p>indicates that the origin server might have used the request's <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> and <a href="#header.accept-language" class="smpl">Accept-Language</a> fields (or lack thereof) as determining factors while choosing the content for this response.
    3281                </p>
    3282                <p id="rfc.section.7.1.4.p.6">An origin server might send Vary with a list of fields for two purposes: </p>
    3283                <ol>
    3284                   <li>
    3285                      <p>To inform cache recipients that they <em class="bcp14">MUST NOT</em> use this response to satisfy a later request unless the later request has the same values for the listed fields as the original
    3286                         request (<a href="p6-cache.html#caching.negotiated.responses" title="Calculating Secondary Keys with Vary">Section 4.1</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.26"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>). In other words, Vary expands the cache key required to match a new request to the stored cache entry.
    3287                      </p>
    3288                   </li>
    3289                   <li>
    3290                      <p>To inform user agent recipients that this response is subject to content negotiation (<a href="#request.conneg" title="Content Negotiation">Section&nbsp;5.3</a>) and that a different representation might be sent in a subsequent request if additional parameters are provided in the listed
    3291                         header fields (<a href="#proactive.negotiation" class="smpl">proactive negotiation</a>).
    3292                      </p>
    3293                   </li>
    3294                </ol>
    3295                <p id="rfc.section.7.1.4.p.7">An origin server <em class="bcp14">SHOULD</em> send a Vary header field when its algorithm for selecting a representation varies based on aspects of the request message
    3296                   other than the method and request target, unless the variance cannot be crossed or the origin server has been deliberately
    3297                   configured to prevent cache transparency. For example, there is no need to send the Authorization field name in Vary because
    3298                   reuse across users is constrained by the field definition (<a href="p7-auth.html#header.authorization" title="Authorization">Section 4.2</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a>). Likewise, an origin server might use Cache-Control directives (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 5.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.27"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>) to supplant Vary if it considers the variance less significant than the performance cost of Vary's impact on caching.
    3299                </p>
    3300             </div>
    3301          </div>
    3302          <div id="response.validator">
    3303             <div id="rfc.iref.s.8"></div>
    3304             <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a href="#response.validator">Validator Header Fields</a></h2>
    3305             <p id="rfc.section.7.2.p.1">Validator header fields convey metadata about the <a href="#representations" class="smpl">selected representation</a> (<a href="#representations" title="Representations">Section&nbsp;3</a>). In responses to safe requests, validator fields describe the selected representation chosen by the origin server while
    3306                handling the response. Note that, depending on the status code semantics, the <a href="#representations" class="smpl">selected representation</a> for a given response is not necessarily the same as the representation enclosed as response payload.
    3307             </p>
    3308             <p id="rfc.section.7.2.p.2">In a successful response to a state-changing request, validator fields describe the new representation that has replaced the
    3309                prior <a href="#representations" class="smpl">selected representation</a> as a result of processing the request.
    3310             </p>
    3311             <p id="rfc.section.7.2.p.3">For example, an ETag header field in a <a href="#status.201" class="smpl">201 (Created)</a> response communicates the entity-tag of the newly created resource's representation, so that it can be used in later conditional
    3312                requests to prevent the "lost update" problem <a href="#RFC7232" id="rfc.xref.RFC7232.12"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>.
    3313             </p>
    3314             <div id="rfc.table.u.11">
    3315                <table class="tt full left" cellpadding="3" cellspacing="0">
    3316                   <thead>
    3317                      <tr>
    3318                         <th>Header Field Name</th>
    3319                         <th>Defined in...</th>
    3320                      </tr>
    3321                   </thead>
    3322                   <tbody>
    3323                      <tr>
    3324                         <td class="left">ETag</td>
    3325                         <td class="left"><a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.13"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    3326                      </tr>
    3327                      <tr>
    3328                         <td class="left">Last-Modified</td>
    3329                         <td class="left"><a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.14"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td>
    3330                      </tr>
    3331                   </tbody>
    3332                </table>
    3333             </div>
    3334          </div>
    3335          <div id="response.auth">
    3336             <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a>&nbsp;<a href="#response.auth">Authentication Challenges</a></h2>
    3337             <p id="rfc.section.7.3.p.1">Authentication challenges indicate what mechanisms are available for the client to provide authentication credentials in future
    3338                requests.
    3339             </p>
    3340             <div id="rfc.table.u.12">
    3341                <table class="tt full left" cellpadding="3" cellspacing="0">
    3342                   <thead>
    3343                      <tr>
    3344                         <th>Header Field Name</th>
    3345                         <th>Defined in...</th>
    3346                      </tr>
    3347                   </thead>
    3348                   <tbody>
    3349                      <tr>
    3350                         <td class="left">WWW-Authenticate</td>
    3351                         <td class="left"><a href="p7-auth.html#header.www-authenticate" title="WWW-Authenticate">Section 4.1</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td>
    3352                      </tr>
    3353                      <tr>
    3354                         <td class="left">Proxy-Authenticate</td>
    3355                         <td class="left"><a href="p7-auth.html#header.proxy-authenticate" title="Proxy-Authenticate">Section 4.3</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td>
    3356                      </tr>
    3357                   </tbody>
    3358                </table>
    3359             </div>
    3360          </div>
    3361          <div id="response.context">
    3362             <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a>&nbsp;<a href="#response.context">Response Context</a></h2>
    3363             <p id="rfc.section.7.4.p.1">The remaining response header fields provide more information about the <a href="#resources" class="smpl">target resource</a> for potential use in later requests.
    3364             </p>
    3365             <div id="rfc.table.u.13">
    3366                <table class="tt full left" cellpadding="3" cellspacing="0">
    3367                   <thead>
    3368                      <tr>
    3369                         <th>Header Field Name</th>
    3370                         <th>Defined in...</th>
    3371                      </tr>
    3372                   </thead>
    3373                   <tbody>
    3374                      <tr>
    3375                         <td class="left">Accept-Ranges</td>
    3376                         <td class="left"><a href="p5-range.html#header.accept-ranges" title="Accept-Ranges">Section 2.3</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td>
    3377                      </tr>
    3378                      <tr>
    3379                         <td class="left">Allow</td>
    3380                         <td class="left"><a href="#header.allow" id="rfc.xref.header.allow.2" title="Allow">Section&nbsp;7.4.1</a></td>
    3381                      </tr>
    3382                      <tr>
    3383                         <td class="left">Server</td>
    3384                         <td class="left"><a href="#header.server" id="rfc.xref.header.server.1" title="Server">Section&nbsp;7.4.2</a></td>
    3385                      </tr>
    3386                   </tbody>
    3387                </table>
    3388             </div>
    3389             <div id="header.allow">
    3390                <div id="rfc.iref.a.5"></div>
    3391                <h3 id="rfc.section.7.4.1"><a href="#rfc.section.7.4.1">7.4.1</a>&nbsp;<a href="#header.allow">Allow</a></h3>
    3392                <p id="rfc.section.7.4.1.p.1">The "Allow" header field lists the set of methods advertised as supported by the <a href="#resources" class="smpl">target resource</a>. The purpose of this field is strictly to inform the recipient of valid request methods associated with the resource.
    3393                </p>
    3394                <div id="rfc.figure.u.60"></div><pre class="inline"><span id="rfc.iref.g.54"></span>  <a href="#header.allow" class="smpl">Allow</a> = #<a href="#method.overview" class="smpl">method</a>
    3395 </pre><p id="rfc.section.7.4.1.p.3">Example of use:</p>
    3396                <div id="rfc.figure.u.61"></div><pre class="text">  Allow: GET, HEAD, PUT
    3397 </pre><p id="rfc.section.7.4.1.p.5">The actual set of allowed methods is defined by the origin server at the time of each request. An origin server <em class="bcp14">MUST</em> generate an Allow field in a <a href="#status.405" class="smpl">405 (Method Not Allowed)</a> response and <em class="bcp14">MAY</em> do so in any other response. An empty Allow field value indicates that the resource allows no methods, which might occur in
    3398                   a 405 response if the resource has been temporarily disabled by configuration.
    3399                </p>
    3400                <p id="rfc.section.7.4.1.p.6">A proxy <em class="bcp14">MUST NOT</em> modify the Allow header field — it does not need to understand all of the indicated methods in order to handle them according
    3401                   to the generic message handling rules.
    3402                </p>
    3403             </div>
    3404             <div id="header.server">
    3405                <div id="rfc.iref.s.9"></div>
    3406                <h3 id="rfc.section.7.4.2"><a href="#rfc.section.7.4.2">7.4.2</a>&nbsp;<a href="#header.server">Server</a></h3>
    3407                <p id="rfc.section.7.4.2.p.1">The "Server" header field contains information about the software used by the origin server to handle the request, which is
    3408                   often used by clients to help identify the scope of reported interoperability problems, to work around or tailor requests
    3409                   to avoid particular server limitations, and for analytics regarding server or operating system use. An origin server <em class="bcp14">MAY</em> generate a Server field in its responses.
    3410                </p>
    3411                <div id="rfc.figure.u.62"></div><pre class="inline"><span id="rfc.iref.g.55"></span>  <a href="#header.server" class="smpl">Server</a> = <a href="#header.user-agent" class="smpl">product</a> *( <a href="#imported.abnf" class="smpl">RWS</a> ( <a href="#header.user-agent" class="smpl">product</a> / <a href="#imported.abnf" class="smpl">comment</a> ) )
    3412 </pre><p id="rfc.section.7.4.2.p.3">The Server field-value consists of one or more product identifiers, each followed by zero or more comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.31"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), which together identify the origin server software and its significant subproducts. By convention, the product identifiers
    3413                   are listed in decreasing order of their significance for identifying the origin server software. Each product identifier consists
    3414                   of a name and optional version, as defined in <a href="#header.user-agent" id="rfc.xref.header.user-agent.2" title="User-Agent">Section&nbsp;5.5.3</a>.
    3415                </p>
    3416                <p id="rfc.section.7.4.2.p.4">Example:</p>
    3417                <div id="rfc.figure.u.63"></div><pre class="text">  Server: CERN/3.0 libwww/2.17
    3418 </pre><p id="rfc.section.7.4.2.p.6">An origin server <em class="bcp14">SHOULD NOT</em> generate a Server field containing needlessly fine-grained detail and <em class="bcp14">SHOULD</em> limit the addition of subproducts by third parties. Overly long and detailed Server field values increase response latency
    3419                   and potentially reveal internal implementation details that might make it (slightly) easier for attackers to find and exploit
    3420                   known security holes.
    3421                </p>
    3422             </div>
    3423          </div>
    3424       </div>
    3425       <div id="IANA.considerations">
    3426          <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#IANA.considerations">IANA Considerations</a></h1>
    3427          <div id="method.registry">
    3428             <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#method.registry">Method Registry</a></h2>
    3429             <p id="rfc.section.8.1.p.1">The "Hypertext Transfer Protocol (HTTP) Method Registry" defines the namespace for the request method token (<a href="#methods" title="Request Methods">Section&nbsp;4</a>). The method registry has been created and is now maintained at &lt;<a href="http://www.iana.org/assignments/http-methods">http://www.iana.org/assignments/http-methods</a>&gt;.
    3430             </p>
    3431             <div id="method.registry.procedure">
    3432                <h3 id="rfc.section.8.1.1"><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;<a href="#method.registry.procedure">Procedure</a></h3>
    3433                <p id="rfc.section.8.1.1.p.1">HTTP method registrations <em class="bcp14">MUST</em> include the following fields:
    3434                </p>
    3435                <ul>
    3436                   <li>Method Name (see <a href="#methods" title="Request Methods">Section&nbsp;4</a>)
    3437                   </li>
    3438                   <li>Safe ("yes" or "no", see <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>)
    3439                   </li>
    3440                   <li>Idempotent ("yes" or "no", see <a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;4.2.2</a>)
    3441                   </li>
    3442                   <li>Pointer to specification text</li>
    3443                </ul>
    3444                <p id="rfc.section.8.1.1.p.2">Values to be added to this namespace require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).
    3445                </p>
    3446             </div>
    3447             <div id="considerations.for.new.methods">
    3448                <h3 id="rfc.section.8.1.2"><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;<a href="#considerations.for.new.methods">Considerations for New Methods</a></h3>
    3449                <p id="rfc.section.8.1.2.p.1">Standardized methods are generic; that is, they are potentially applicable to any resource, not just one particular media
    3450                   type, kind of resource, or application. As such, it is preferred that new methods be registered in a document that isn't specific
    3451                   to a single application or data format, since orthogonal technologies deserve orthogonal specification.
    3452                </p>
    3453                <p id="rfc.section.8.1.2.p.2">Since message parsing (<a href="p1-messaging.html#message.body" title="Message Body">Section 3.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.32"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) needs to be independent of method semantics (aside from responses to HEAD), definitions of new methods cannot change the
    3454                   parsing algorithm or prohibit the presence of a message body on either the request or the response message. Definitions of
    3455                   new methods can specify that only a zero-length message body is allowed by requiring a Content-Length header field with a
    3456                   value of "0".
    3457                </p>
    3458                <p id="rfc.section.8.1.2.p.3">A new method definition needs to indicate whether it is safe (<a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>), idempotent (<a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;4.2.2</a>), cacheable (<a href="#cacheable.methods" title="Cacheable Methods">Section&nbsp;4.2.3</a>), what semantics are to be associated with the payload body if any is present in the request and what refinements the method
    3459                   makes to header field or status code semantics. If the new method is cacheable, its definition ought to describe how, and
    3460                   under what conditions, a cache can store a response and use it to satisfy a subsequent request. The new method ought to describe
    3461                   whether it can be made conditional (<a href="#request.conditionals" title="Conditionals">Section&nbsp;5.2</a>) and, if so, how a server responds when the condition is false. Likewise, if the new method might have some use for partial
    3462                   response semantics (<a href="#RFC7233" id="rfc.xref.RFC7233.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>), it ought to document this, too.
    3463                </p>
    3464                <div class="note" id="rfc.section.8.1.2.p.4">
    3465                   <p><b>Note:</b> Avoid defining a method name that starts with "M-", since that prefix might be misinterpreted as having the semantics assigned
    3466                      to it by <a href="#RFC2774" id="rfc.xref.RFC2774.1"><cite title="An HTTP Extension Framework">[RFC2774]</cite></a>.
    3467                   </p>
    3468                </div>
    3469             </div>
    3470             <div id="method.registration">
    3471                <h3 id="rfc.section.8.1.3"><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;<a href="#method.registration">Registrations</a></h3>
    3472                <p id="rfc.section.8.1.3.p.1">The "Hypertext Transfer Protocol (HTTP) Method Registry" has been populated with the registrations below:</p>
    3473                <div id="rfc.table.2">
    3474                   <div id="iana.method.registration.table"></div>
    3475                   <table class="tt full left" cellpadding="3" cellspacing="0">
    3476                      <thead>
    3477                         <tr>
    3478                            <th>Method</th>
    3479                            <th>Safe</th>
    3480                            <th>Idempotent</th>
    3481                            <th>Reference</th>
    3482                         </tr>
    3483                      </thead>
    3484                      <tbody>
    3485                         <tr>
    3486                            <td class="left">CONNECT</td>
    3487                            <td class="left">no</td>
    3488                            <td class="left">no</td>
    3489                            <td class="left"><a href="#CONNECT" id="rfc.xref.CONNECT.2" title="CONNECT">Section&nbsp;4.3.6</a>
    3490                            </td>
    3491                         </tr>
    3492                         <tr>
    3493                            <td class="left">DELETE</td>
    3494                            <td class="left">no</td>
    3495                            <td class="left">yes</td>
    3496                            <td class="left"><a href="#DELETE" id="rfc.xref.DELETE.2" title="DELETE">Section&nbsp;4.3.5</a>
    3497                            </td>
    3498                         </tr>
    3499                         <tr>
    3500                            <td class="left">GET</td>
    3501                            <td class="left">yes</td>
    3502                            <td class="left">yes</td>
    3503                            <td class="left"><a href="#GET" id="rfc.xref.GET.5" title="GET">Section&nbsp;4.3.1</a>
    3504                            </td>
    3505                         </tr>
    3506                         <tr>
    3507                            <td class="left">HEAD</td>
    3508                            <td class="left">yes</td>
    3509                            <td class="left">yes</td>
    3510                            <td class="left"><a href="#HEAD" id="rfc.xref.HEAD.3" title="HEAD">Section&nbsp;4.3.2</a>
    3511                            </td>
    3512                         </tr>
    3513                         <tr>
    3514                            <td class="left">OPTIONS</td>
    3515                            <td class="left">yes</td>
    3516                            <td class="left">yes</td>
    3517                            <td class="left"><a href="#OPTIONS" id="rfc.xref.OPTIONS.3" title="OPTIONS">Section&nbsp;4.3.7</a>
    3518                            </td>
    3519                         </tr>
    3520                         <tr>
    3521                            <td class="left">POST</td>
    3522                            <td class="left">no</td>
    3523                            <td class="left">no</td>
    3524                            <td class="left"><a href="#POST" id="rfc.xref.POST.4" title="POST">Section&nbsp;4.3.3</a>
    3525                            </td>
    3526                         </tr>
    3527                         <tr>
    3528                            <td class="left">PUT</td>
    3529                            <td class="left">no</td>
    3530                            <td class="left">yes</td>
    3531                            <td class="left"><a href="#PUT" id="rfc.xref.PUT.4" title="PUT">Section&nbsp;4.3.4</a>
    3532                            </td>
    3533                         </tr>
    3534                         <tr>
    3535                            <td class="left">TRACE</td>
    3536                            <td class="left">yes</td>
    3537                            <td class="left">yes</td>
    3538                            <td class="left"><a href="#TRACE" id="rfc.xref.TRACE.3" title="TRACE">Section&nbsp;4.3.8</a>
    3539                            </td>
    3540                         </tr>
    3541                      </tbody>
    3542                   </table>
    3543                </div>
    3544             </div>
    3545          </div>
    3546          <div id="status.code.registry">
    3547             <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#status.code.registry">Status Code Registry</a></h2>
    3548             <p id="rfc.section.8.2.p.1">The "Hypertext Transfer Protocol (HTTP) Status Code Registry" defines the namespace for the response status-code token (<a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>). The status code registry is maintained at &lt;<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>&gt;.
    3549             </p>
    3550             <p id="rfc.section.8.2.p.2">This section replaces the registration procedure for HTTP Status Codes previously defined in <a href="http://tools.ietf.org/html/rfc2817#section-7.1">Section 7.1</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.1"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>.
    3551             </p>
    3552             <div id="status.code.registry.procedure">
    3553                <h3 id="rfc.section.8.2.1"><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;<a href="#status.code.registry.procedure">Procedure</a></h3>
    3554                <p id="rfc.section.8.2.1.p.1">A registration <em class="bcp14">MUST</em> include the following fields:
    3555                </p>
    3556                <ul>
    3557                   <li>Status Code (3 digits)</li>
    3558                   <li>Short Description</li>
    3559                   <li>Pointer to specification text</li>
    3560                </ul>
    3561                <p id="rfc.section.8.2.1.p.2">Values to be added to the HTTP status code namespace require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).
    3562                </p>
    3563             </div>
    3564             <div id="considerations.for.new.status.codes">
    3565                <h3 id="rfc.section.8.2.2"><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;<a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></h3>
    3566                <p id="rfc.section.8.2.2.p.1">When it is necessary to express semantics for a response that are not defined by current status codes, a new status code can
    3567                   be registered. Status codes are generic; they are potentially applicable to any resource, not just one particular media type,
    3568                   kind of resource, or application of HTTP. As such, it is preferred that new status codes be registered in a document that
    3569                   isn't specific to a single application.
    3570                </p>
    3571                <p id="rfc.section.8.2.2.p.2">New status codes are required to fall under one of the categories defined in <a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>. To allow existing parsers to process the response message, new status codes cannot disallow a payload, although they can
    3572                   mandate a zero-length payload body.
    3573                </p>
    3574                <p id="rfc.section.8.2.2.p.3">Proposals for new status codes that are not yet widely deployed ought to avoid allocating a specific number for the code until
    3575                   there is clear consensus that it will be registered; instead, early drafts can use a notation such as "4NN", or "3N0" .. "3N9",
    3576                   to indicate the class of the proposed status code(s) without consuming a number prematurely.
    3577                </p>
    3578                <p id="rfc.section.8.2.2.p.4">The definition of a new status code ought to explain the request conditions that would cause a response containing that status
    3579                   code (e.g., combinations of request header fields and/or method(s)) along with any dependencies on response header fields
    3580                   (e.g., what fields are required, what fields can modify the semantics, and what header field semantics are further refined
    3581                   when used with the new status code).
    3582                </p>
    3583                <p id="rfc.section.8.2.2.p.5">The definition of a new status code ought to specify whether or not it is cacheable. Note that all status codes can be cached
    3584                   if the response they occur in has explicit freshness information; however, status codes that are defined as being cacheable
    3585                   are allowed to be cached without explicit freshness information. Likewise, the definition of a status code can place constraints
    3586                   upon cache behavior. See <a href="#RFC7234" id="rfc.xref.RFC7234.28"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a> for more information.
    3587                </p>
    3588                <p id="rfc.section.8.2.2.p.6">Finally, the definition of a new status code ought to indicate whether the payload has any implied association with an identified
    3589                   resource (<a href="#identifying.payload" title="Identifying a Representation">Section&nbsp;3.1.4.1</a>).
    3590                </p>
    3591             </div>
    3592             <div id="status.code.registration">
    3593                <h3 id="rfc.section.8.2.3"><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;<a href="#status.code.registration">Registrations</a></h3>
    3594                <p id="rfc.section.8.2.3.p.1">The status code registry has been updated with the registrations below:</p>
    3595                <div id="rfc.table.3">
    3596                   <div id="iana.status.code.registration.table"></div>
    3597                   <table class="tt full left" cellpadding="3" cellspacing="0">
    3598                      <thead>
    3599                         <tr>
    3600                            <th>Value</th>
    3601                            <th>Description</th>
    3602                            <th>Reference</th>
    3603                         </tr>
    3604                      </thead>
    3605                      <tbody>
    3606                         <tr>
    3607                            <td class="left">100</td>
    3608                            <td class="left">Continue</td>
    3609                            <td class="left"><a href="#status.100" id="rfc.xref.status.100.2" title="100 Continue">Section&nbsp;6.2.1</a>
    3610                            </td>
    3611                         </tr>
    3612                         <tr>
    3613                            <td class="left">101</td>
    3614                            <td class="left">Switching Protocols</td>
    3615                            <td class="left"><a href="#status.101" id="rfc.xref.status.101.2" title="101 Switching Protocols">Section&nbsp;6.2.2</a>
    3616                            </td>
    3617                         </tr>
    3618                         <tr>
    3619                            <td class="left">200</td>
    3620                            <td class="left">OK</td>
    3621                            <td class="left"><a href="#status.200" id="rfc.xref.status.200.2" title="200 OK">Section&nbsp;6.3.1</a>
    3622                            </td>
    3623                         </tr>
    3624                         <tr>
    3625                            <td class="left">201</td>
    3626                            <td class="left">Created</td>
    3627                            <td class="left"><a href="#status.201" id="rfc.xref.status.201.2" title="201 Created">Section&nbsp;6.3.2</a>
    3628                            </td>
    3629                         </tr>
    3630                         <tr>
    3631                            <td class="left">202</td>
    3632                            <td class="left">Accepted</td>
    3633                            <td class="left"><a href="#status.202" id="rfc.xref.status.202.2" title="202 Accepted">Section&nbsp;6.3.3</a>
    3634                            </td>
    3635                         </tr>
    3636                         <tr>
    3637                            <td class="left">203</td>
    3638                            <td class="left">Non-Authoritative Information</td>
    3639                            <td class="left"><a href="#status.203" id="rfc.xref.status.203.2" title="203 Non-Authoritative Information">Section&nbsp;6.3.4</a>
    3640                            </td>
    3641                         </tr>
    3642                         <tr>
    3643                            <td class="left">204</td>
    3644                            <td class="left">No Content</td>
    3645                            <td class="left"><a href="#status.204" id="rfc.xref.status.204.2" title="204 No Content">Section&nbsp;6.3.5</a>
    3646                            </td>
    3647                         </tr>
    3648                         <tr>
    3649                            <td class="left">205</td>
    3650                            <td class="left">Reset Content</td>
    3651                            <td class="left"><a href="#status.205" id="rfc.xref.status.205.2" title="205 Reset Content">Section&nbsp;6.3.6</a>
    3652                            </td>
    3653                         </tr>
    3654                         <tr>
    3655                            <td class="left">300</td>
    3656                            <td class="left">Multiple Choices</td>
    3657                            <td class="left"><a href="#status.300" id="rfc.xref.status.300.3" title="300 Multiple Choices">Section&nbsp;6.4.1</a>
    3658                            </td>
    3659                         </tr>
    3660                         <tr>
    3661                            <td class="left">301</td>
    3662                            <td class="left">Moved Permanently</td>
    3663                            <td class="left"><a href="#status.301" id="rfc.xref.status.301.2" title="301 Moved Permanently">Section&nbsp;6.4.2</a>
    3664                            </td>
    3665                         </tr>
    3666                         <tr>
    3667                            <td class="left">302</td>
    3668                            <td class="left">Found</td>
    3669                            <td class="left"><a href="#status.302" id="rfc.xref.status.302.2" title="302 Found">Section&nbsp;6.4.3</a>
    3670                            </td>
    3671                         </tr>
    3672                         <tr>
    3673                            <td class="left">303</td>
    3674                            <td class="left">See Other</td>
    3675                            <td class="left"><a href="#status.303" id="rfc.xref.status.303.2" title="303 See Other">Section&nbsp;6.4.4</a>
    3676                            </td>
    3677                         </tr>
    3678                         <tr>
    3679                            <td class="left">305</td>
    3680                            <td class="left">Use Proxy</td>
    3681                            <td class="left"><a href="#status.305" id="rfc.xref.status.305.2" title="305 Use Proxy">Section&nbsp;6.4.5</a>
    3682                            </td>
    3683                         </tr>
    3684                         <tr>
    3685                            <td class="left">306</td>
    3686                            <td class="left">(Unused)</td>
    3687                            <td class="left"><a href="#status.306" id="rfc.xref.status.306.1" title="306 (Unused)">Section&nbsp;6.4.6</a>
    3688                            </td>
    3689                         </tr>
    3690                         <tr>
    3691                            <td class="left">307</td>
    3692                            <td class="left">Temporary Redirect</td>
    3693                            <td class="left"><a href="#status.307" id="rfc.xref.status.307.2" title="307 Temporary Redirect">Section&nbsp;6.4.7</a>
    3694                            </td>
    3695                         </tr>
    3696                         <tr>
    3697                            <td class="left">400</td>
    3698                            <td class="left">Bad Request</td>
    3699                            <td class="left"><a href="#status.400" id="rfc.xref.status.400.2" title="400 Bad Request">Section&nbsp;6.5.1</a>
    3700                            </td>
    3701                         </tr>
    3702                         <tr>
    3703                            <td class="left">402</td>
    3704                            <td class="left">Payment Required</td>
    3705                            <td class="left"><a href="#status.402" id="rfc.xref.status.402.2" title="402 Payment Required">Section&nbsp;6.5.2</a>
    3706                            </td>
    3707                         </tr>
    3708                         <tr>
    3709                            <td class="left">403</td>
    3710                            <td class="left">Forbidden</td>
    3711                            <td class="left"><a href="#status.403" id="rfc.xref.status.403.2" title="403 Forbidden">Section&nbsp;6.5.3</a>
    3712                            </td>
    3713                         </tr>
    3714                         <tr>
    3715                            <td class="left">404</td>
    3716                            <td class="left">Not Found</td>
    3717                            <td class="left"><a href="#status.404" id="rfc.xref.status.404.2" title="404 Not Found">Section&nbsp;6.5.4</a>
    3718                            </td>
    3719                         </tr>
    3720                         <tr>
    3721                            <td class="left">405</td>
    3722                            <td class="left">Method Not Allowed</td>
    3723                            <td class="left"><a href="#status.405" id="rfc.xref.status.405.2" title="405 Method Not Allowed">Section&nbsp;6.5.5</a>
    3724                            </td>
    3725                         </tr>
    3726                         <tr>
    3727                            <td class="left">406</td>
    3728                            <td class="left">Not Acceptable</td>
    3729                            <td class="left"><a href="#status.406" id="rfc.xref.status.406.2" title="406 Not Acceptable">Section&nbsp;6.5.6</a>
    3730                            </td>
    3731                         </tr>
    3732                         <tr>
    3733                            <td class="left">408</td>
    3734                            <td class="left">Request Timeout</td>
    3735                            <td class="left"><a href="#status.408" id="rfc.xref.status.408.2" title="408 Request Timeout">Section&nbsp;6.5.7</a>
    3736                            </td>
    3737                         </tr>
    3738                         <tr>
    3739                            <td class="left">409</td>
    3740                            <td class="left">Conflict</td>
    3741                            <td class="left"><a href="#status.409" id="rfc.xref.status.409.2" title="409 Conflict">Section&nbsp;6.5.8</a>
    3742                            </td>
    3743                         </tr>
    3744                         <tr>
    3745                            <td class="left">410</td>
    3746                            <td class="left">Gone</td>
    3747                            <td class="left"><a href="#status.410" id="rfc.xref.status.410.2" title="410 Gone">Section&nbsp;6.5.9</a>
    3748                            </td>
    3749                         </tr>
    3750                         <tr>
    3751                            <td class="left">411</td>
    3752                            <td class="left">Length Required</td>
    3753                            <td class="left"><a href="#status.411" id="rfc.xref.status.411.2" title="411 Length Required">Section&nbsp;6.5.10</a>
    3754                            </td>
    3755                         </tr>
    3756                         <tr>
    3757                            <td class="left">413</td>
    3758                            <td class="left">Payload Too Large</td>
    3759                            <td class="left"><a href="#status.413" id="rfc.xref.status.413.2" title="413 Payload Too Large">Section&nbsp;6.5.11</a>
    3760                            </td>
    3761                         </tr>
    3762                         <tr>
    3763                            <td class="left">414</td>
    3764                            <td class="left">URI Too Long</td>
    3765                            <td class="left"><a href="#status.414" id="rfc.xref.status.414.2" title="414 URI Too Long">Section&nbsp;6.5.12</a>
    3766                            </td>
    3767                         </tr>
    3768                         <tr>
    3769                            <td class="left">415</td>
    3770                            <td class="left">Unsupported Media Type</td>
    3771                            <td class="left"><a href="#status.415" id="rfc.xref.status.415.2" title="415 Unsupported Media Type">Section&nbsp;6.5.13</a>
    3772                            </td>
    3773                         </tr>
    3774                         <tr>
    3775                            <td class="left">417</td>
    3776                            <td class="left">Expectation Failed</td>
    3777                            <td class="left"><a href="#status.417" id="rfc.xref.status.417.2" title="417 Expectation Failed">Section&nbsp;6.5.14</a>
    3778                            </td>
    3779                         </tr>
    3780                         <tr>
    3781                            <td class="left">426</td>
    3782                            <td class="left">Upgrade Required</td>
    3783                            <td class="left"><a href="#status.426" id="rfc.xref.status.426.2" title="426 Upgrade Required">Section&nbsp;6.5.15</a>
    3784                            </td>
    3785                         </tr>
    3786                         <tr>
    3787                            <td class="left">500</td>
    3788                            <td class="left">Internal Server Error</td>
    3789                            <td class="left"><a href="#status.500" id="rfc.xref.status.500.2" title="500 Internal Server Error">Section&nbsp;6.6.1</a>
    3790                            </td>
    3791                         </tr>
    3792                         <tr>
    3793                            <td class="left">501</td>
    3794                            <td class="left">Not Implemented</td>
    3795                            <td class="left"><a href="#status.501" id="rfc.xref.status.501.2" title="501 Not Implemented">Section&nbsp;6.6.2</a>
    3796                            </td>
    3797                         </tr>
    3798                         <tr>
    3799                            <td class="left">502</td>
    3800                            <td class="left">Bad Gateway</td>
    3801                            <td class="left"><a href="#status.502" id="rfc.xref.status.502.2" title="502 Bad Gateway">Section&nbsp;6.6.3</a>
    3802                            </td>
    3803                         </tr>
    3804                         <tr>
    3805                            <td class="left">503</td>
    3806                            <td class="left">Service Unavailable</td>
    3807                            <td class="left"><a href="#status.503" id="rfc.xref.status.503.2" title="503 Service Unavailable">Section&nbsp;6.6.4</a>
    3808                            </td>
    3809                         </tr>
    3810                         <tr>
    3811                            <td class="left">504</td>
    3812                            <td class="left">Gateway Timeout</td>
    3813                            <td class="left"><a href="#status.504" id="rfc.xref.status.504.2" title="504 Gateway Timeout">Section&nbsp;6.6.5</a>
    3814                            </td>
    3815                         </tr>
    3816                         <tr>
    3817                            <td class="left">505</td>
    3818                            <td class="left">HTTP Version Not Supported</td>
    3819                            <td class="left"><a href="#status.505" id="rfc.xref.status.505.2" title="505 HTTP Version Not Supported">Section&nbsp;6.6.6</a>
    3820                            </td>
    3821                         </tr>
    3822                      </tbody>
    3823                   </table>
    3824                </div>
    3825             </div>
    3826          </div>
    3827          <div id="header.field.registry">
    3828             <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a href="#header.field.registry">Header Field Registry</a></h2>
    3829             <p id="rfc.section.8.3.p.1">HTTP header fields are registered within the "Message Headers" registry located at &lt;<a href="http://www.iana.org/assignments/message-headers">http://www.iana.org/assignments/message-headers</a>&gt;, as defined by <a href="#BCP90" id="rfc.xref.BCP90.1"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>.
    3830             </p>
    3831             <div id="considerations.for.new.header.fields">
    3832                <h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;<a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></h3>
    3833                <p id="rfc.section.8.3.1.p.1">Header fields are key:value pairs that can be used to communicate data about the message, its payload, the target resource,
    3834                   or the connection (i.e., control data). See <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.33"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a> for a general definition of header field syntax in HTTP messages.
    3835                </p>
    3836                <p id="rfc.section.8.3.1.p.2">The requirements for header field names are defined in <a href="#BCP90" id="rfc.xref.BCP90.2"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>.
    3837                </p>
    3838                <p id="rfc.section.8.3.1.p.3">Authors of specifications defining new fields are advised to keep the name as short as practical and not to prefix the name
    3839                   with "X-" unless the header field will never be used on the Internet. (The "X-" prefix idiom has been extensively misused
    3840                   in practice; it was intended to only be used as a mechanism for avoiding name collisions inside proprietary software or intranet
    3841                   processing, since the prefix would ensure that private names never collide with a newly registered Internet name; see <a href="#BCP178" id="rfc.xref.BCP178.1"><cite title="Deprecating the &#34;X-&#34; Prefix and Similar Constructs in Application Protocols">[BCP178]</cite></a> for further information).
    3842                </p>
    3843                <p id="rfc.section.8.3.1.p.4">New header field values typically have their syntax defined using ABNF (<a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>), using the extension defined in <a href="p1-messaging.html#abnf.extension" title="ABNF List Extension: #rule">Section 7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.34"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a> as necessary, and are usually constrained to the range of US-ASCII characters. Header fields needing a greater range of characters
    3844                   can use an encoding such as the one defined in <a href="#RFC5987" id="rfc.xref.RFC5987.1"><cite title="Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters">[RFC5987]</cite></a>.
    3845                </p>
    3846                <p id="rfc.section.8.3.1.p.5">Leading and trailing whitespace in raw field values is removed upon field parsing (<a href="p1-messaging.html#field.parsing" title="Field Parsing">Section 3.2.4</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.35"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). Field definitions where leading or trailing whitespace in values is significant will have to use a container syntax such
    3847                   as quoted-string (<a href="p1-messaging.html#field.components" title="Field Value Components">Section 3.2.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.36"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    3848                </p>
    3849                <p id="rfc.section.8.3.1.p.6">Because commas (",") are used as a generic delimiter between field-values, they need to be treated with care if they are allowed
    3850                   in the field-value. Typically, components that might contain a comma are protected with double-quotes using the quoted-string
    3851                   ABNF production.
    3852                </p>
    3853                <p id="rfc.section.8.3.1.p.7">For example, a textual date and a URI (either of which might contain a comma) could be safely carried in field-values like
    3854                   these:
    3855                </p>
    3856                <div id="rfc.figure.u.64"></div><pre class="text">  Example-URI-Field: "http://example.com/a.html,foo",
    3857                      "http://without-a-comma.example.com/"
    3858   Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
    3859 </pre><p id="rfc.section.8.3.1.p.9">Note that double-quote delimiters almost always are used with the quoted-string production; using a different syntax inside
    3860                   double-quotes will likely cause unnecessary confusion.
    3861                </p>
    3862                <p id="rfc.section.8.3.1.p.10">Many header fields use a format including (case-insensitively) named parameters (for instance, <a href="#header.content-type" class="smpl">Content-Type</a>, defined in <a href="#header.content-type" id="rfc.xref.header.content-type.3" title="Content-Type">Section&nbsp;3.1.1.5</a>). Allowing both unquoted (token) and quoted (quoted-string) syntax for the parameter value enables recipients to use existing
    3863                   parser components. When allowing both forms, the meaning of a parameter value ought to be independent of the syntax used for
    3864                   it (for an example, see the notes on parameter handling for media types in <a href="#media.type" title="Media Type">Section&nbsp;3.1.1.1</a>).
    3865                </p>
    3866                <p id="rfc.section.8.3.1.p.11">Authors of specifications defining new header fields are advised to consider documenting: </p>
    3867                <ul>
    3868                   <li>
    3869                      <p>Whether the field is a single value or whether it can be a list (delimited by commas; see <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.37"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    3870                      </p>
    3871                      <p>If it does not use the list syntax, document how to treat messages where the field occurs multiple times (a sensible default
    3872                         would be to ignore the field, but this might not always be the right choice).
    3873                      </p>
    3874                      <p>Note that intermediaries and software libraries might combine multiple header field instances into a single one, despite the
    3875                         field's definition not allowing the list syntax. A robust format enables recipients to discover these situations (good example:
    3876                         "Content-Type", as the comma can only appear inside quoted strings; bad example: "Location", as a comma can occur inside a
    3877                         URI).
    3878                      </p>
    3879                   </li>
    3880                   <li>
    3881                      <p>Under what conditions the header field can be used; e.g., only in responses or requests, in all messages, only on responses
    3882                         to a particular request method, etc.
    3883                      </p>
    3884                   </li>
    3885                   <li>
    3886                      <p>Whether the field should be stored by origin servers that understand it upon a PUT request.</p>
    3887                   </li>
    3888                   <li>
    3889                      <p>Whether the field semantics are further refined by the context, such as by existing request methods or status codes.</p>
    3890                   </li>
    3891                   <li>
    3892                      <p>Whether it is appropriate to list the field-name in the <a href="p1-messaging.html#header.connection" class="smpl">Connection</a> header field (i.e., if the header field is to be hop-by-hop; see <a href="p1-messaging.html#header.connection" title="Connection">Section 6.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.38"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    3893                      </p>
    3894                   </li>
    3895                   <li>
    3896                      <p>Under what conditions intermediaries are allowed to insert, delete, or modify the field's value.</p>
    3897                   </li>
    3898                   <li>
    3899                      <p>Whether it is appropriate to list the field-name in a <a href="#header.vary" class="smpl">Vary</a> response header field (e.g., when the request header field is used by an origin server's content selection algorithm; see <a href="#header.vary" id="rfc.xref.header.vary.3" title="Vary">Section&nbsp;7.1.4</a>).
    3900                      </p>
    3901                   </li>
    3902                   <li>
    3903                      <p>Whether the header field is useful or allowable in trailers (see <a href="p1-messaging.html#chunked.encoding" title="Chunked Transfer Coding">Section 4.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.39"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    3904                      </p>
    3905                   </li>
    3906                   <li>
    3907                      <p>Whether the header field ought to be preserved across redirects.</p>
    3908                   </li>
    3909                   <li>
    3910                      <p>Whether it introduces any additional security considerations, such as disclosure of privacy-related data.</p>
    3911                   </li>
    3912                </ul>
    3913             </div>
    3914             <div id="header.field.registration">
    3915                <h3 id="rfc.section.8.3.2"><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;<a href="#header.field.registration">Registrations</a></h3>
    3916                <p id="rfc.section.8.3.2.p.1">The "Message Headers" registry has been updated with the following permanent registrations:</p>
    3917                <div id="rfc.table.4">
    3918                   <div id="iana.header.registration.table"></div>
    3919                   <table class="tt full left" cellpadding="3" cellspacing="0">
    3920                      <thead>
    3921                         <tr>
    3922                            <th>Header Field Name</th>
    3923                            <th>Protocol</th>
    3924                            <th>Status</th>
    3925                            <th>Reference</th>
    3926                         </tr>
    3927                      </thead>
    3928                      <tbody>
    3929                         <tr>
    3930                            <td class="left">Accept</td>
    3931                            <td class="left">http</td>
    3932                            <td class="left">standard</td>
    3933                            <td class="left"><a href="#header.accept" id="rfc.xref.header.accept.3" title="Accept">Section&nbsp;5.3.2</a>
    3934                            </td>
    3935                         </tr>
    3936                         <tr>
    3937                            <td class="left">Accept-Charset</td>
    3938                            <td class="left">http</td>
    3939                            <td class="left">standard</td>
    3940                            <td class="left"><a href="#header.accept-charset" id="rfc.xref.header.accept-charset.2" title="Accept-Charset">Section&nbsp;5.3.3</a>
    3941                            </td>
    3942                         </tr>
    3943                         <tr>
    3944                            <td class="left">Accept-Encoding</td>
    3945                            <td class="left">http</td>
    3946                            <td class="left">standard</td>
    3947                            <td class="left"><a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.3" title="Accept-Encoding">Section&nbsp;5.3.4</a>
    3948                            </td>
    3949                         </tr>
    3950                         <tr>
    3951                            <td class="left">Accept-Language</td>
    3952                            <td class="left">http</td>
    3953                            <td class="left">standard</td>
    3954                            <td class="left"><a href="#header.accept-language" id="rfc.xref.header.accept-language.3" title="Accept-Language">Section&nbsp;5.3.5</a>
    3955                            </td>
    3956                         </tr>
    3957                         <tr>
    3958                            <td class="left">Allow</td>
    3959                            <td class="left">http</td>
    3960                            <td class="left">standard</td>
    3961                            <td class="left"><a href="#header.allow" id="rfc.xref.header.allow.3" title="Allow">Section&nbsp;7.4.1</a>
    3962                            </td>
    3963                         </tr>
    3964                         <tr>
    3965                            <td class="left">Content-Encoding</td>
    3966                            <td class="left">http</td>
    3967                            <td class="left">standard</td>
    3968                            <td class="left"><a href="#header.content-encoding" id="rfc.xref.header.content-encoding.3" title="Content-Encoding">Section&nbsp;3.1.2.2</a>
    3969                            </td>
    3970                         </tr>
    3971                         <tr>
    3972                            <td class="left">Content-Language</td>
    3973                            <td class="left">http</td>
    3974                            <td class="left">standard</td>
    3975                            <td class="left"><a href="#header.content-language" id="rfc.xref.header.content-language.2" title="Content-Language">Section&nbsp;3.1.3.2</a>
    3976                            </td>
    3977                         </tr>
    3978                         <tr>
    3979                            <td class="left">Content-Location</td>
    3980                            <td class="left">http</td>
    3981                            <td class="left">standard</td>
    3982                            <td class="left"><a href="#header.content-location" id="rfc.xref.header.content-location.4" title="Content-Location">Section&nbsp;3.1.4.2</a>
    3983                            </td>
    3984                         </tr>
    3985                         <tr>
    3986                            <td class="left">Content-Type</td>
    3987                            <td class="left">http</td>
    3988                            <td class="left">standard</td>
    3989                            <td class="left"><a href="#header.content-type" id="rfc.xref.header.content-type.4" title="Content-Type">Section&nbsp;3.1.1.5</a>
    3990                            </td>
    3991                         </tr>
    3992                         <tr>
    3993                            <td class="left">Date</td>
    3994                            <td class="left">http</td>
    3995                            <td class="left">standard</td>
    3996                            <td class="left"><a href="#header.date" id="rfc.xref.header.date.3" title="Date">Section&nbsp;7.1.1.2</a>
    3997                            </td>
    3998                         </tr>
    3999                         <tr>
    4000                            <td class="left">Expect</td>
    4001                            <td class="left">http</td>
    4002                            <td class="left">standard</td>
    4003                            <td class="left"><a href="#header.expect" id="rfc.xref.header.expect.4" title="Expect">Section&nbsp;5.1.1</a>
    4004                            </td>
    4005                         </tr>
    4006                         <tr>
    4007                            <td class="left">From</td>
    4008                            <td class="left">http</td>
    4009                            <td class="left">standard</td>
    4010                            <td class="left"><a href="#header.from" id="rfc.xref.header.from.2" title="From">Section&nbsp;5.5.1</a>
    4011                            </td>
    4012                         </tr>
    4013                         <tr>
    4014                            <td class="left">Location</td>
    4015                            <td class="left">http</td>
    4016                            <td class="left">standard</td>
    4017                            <td class="left"><a href="#header.location" id="rfc.xref.header.location.4" title="Location">Section&nbsp;7.1.2</a>
    4018                            </td>
    4019                         </tr>
    4020                         <tr>
    4021                            <td class="left">Max-Forwards</td>
    4022                            <td class="left">http</td>
    4023                            <td class="left">standard</td>
    4024                            <td class="left"><a href="#header.max-forwards" id="rfc.xref.header.max-forwards.4" title="Max-Forwards">Section&nbsp;5.1.2</a>
    4025                            </td>
    4026                         </tr>
    4027                         <tr>
    4028                            <td class="left">MIME-Version</td>
    4029                            <td class="left">http</td>
    4030                            <td class="left">standard</td>
    4031                            <td class="left"><a href="#mime-version" id="rfc.xref.mime-version.1" title="MIME-Version">Appendix&nbsp;A.1</a>
    4032                            </td>
    4033                         </tr>
    4034                         <tr>
    4035                            <td class="left">Referer</td>
    4036                            <td class="left">http</td>
    4037                            <td class="left">standard</td>
    4038                            <td class="left"><a href="#header.referer" id="rfc.xref.header.referer.2" title="Referer">Section&nbsp;5.5.2</a>
    4039                            </td>
    4040                         </tr>
    4041                         <tr>
    4042                            <td class="left">Retry-After</td>
    4043                            <td class="left">http</td>
    4044                            <td class="left">standard</td>
    4045                            <td class="left"><a href="#header.retry-after" id="rfc.xref.header.retry-after.3" title="Retry-After">Section&nbsp;7.1.3</a>
    4046                            </td>
    4047                         </tr>
    4048                         <tr>
    4049                            <td class="left">Server</td>
    4050                            <td class="left">http</td>
    4051                            <td class="left">standard</td>
    4052                            <td class="left"><a href="#header.server" id="rfc.xref.header.server.2" title="Server">Section&nbsp;7.4.2</a>
    4053                            </td>
    4054                         </tr>
    4055                         <tr>
    4056                            <td class="left">User-Agent</td>
    4057                            <td class="left">http</td>
    4058                            <td class="left">standard</td>
    4059                            <td class="left"><a href="#header.user-agent" id="rfc.xref.header.user-agent.3" title="User-Agent">Section&nbsp;5.5.3</a>
    4060                            </td>
    4061                         </tr>
    4062                         <tr>
    4063                            <td class="left">Vary</td>
    4064                            <td class="left">http</td>
    4065                            <td class="left">standard</td>
    4066                            <td class="left"><a href="#header.vary" id="rfc.xref.header.vary.4" title="Vary">Section&nbsp;7.1.4</a>
    4067                            </td>
    4068                         </tr>
    4069                      </tbody>
    4070                   </table>
    4071                </div>
    4072                <p id="rfc.section.8.3.2.p.2">The change controller for the above registrations is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
    4073             </div>
    4074          </div>
    4075          <div id="content.coding.registry">
    4076             <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a href="#content.coding.registry">Content Coding Registry</a></h2>
    4077             <p id="rfc.section.8.4.p.1">The "HTTP Content Coding Registry" defines the namespace for content coding names (<a href="p1-messaging.html#compression.codings" title="Compression Codings">Section 4.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.40"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). The content coding registry is maintained at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.
    4078             </p>
    4079             <div id="content.coding.procedure">
    4080                <h3 id="rfc.section.8.4.1"><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;<a href="#content.coding.procedure">Procedure</a></h3>
    4081                <p id="rfc.section.8.4.1.p.1">Content Coding registrations <em class="bcp14">MUST</em> include the following fields:
    4082                </p>
    4083                <ul>
    4084                   <li>Name</li>
    4085                   <li>Description</li>
    4086                   <li>Pointer to specification text</li>
    4087                </ul>
    4088                <p id="rfc.section.8.4.1.p.2">Names of content codings <em class="bcp14">MUST NOT</em> overlap with names of transfer codings (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 4</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.41"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), unless the encoding transformation is identical (as is the case for the compression codings defined in <a href="p1-messaging.html#compression.codings" title="Compression Codings">Section 4.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.42"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).
    4089                </p>
    4090                <p id="rfc.section.8.4.1.p.3">Values to be added to this namespace require IETF Review (see <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.3"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>), and <em class="bcp14">MUST</em> conform to the purpose of content coding defined in this section.
    4091                </p>
    4092             </div>
    4093             <div id="content.coding.registration">
    4094                <h3 id="rfc.section.8.4.2"><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;<a href="#content.coding.registration">Registrations</a></h3>
    4095                <p id="rfc.section.8.4.2.p.1">The "HTTP Content Coding Registry" has been updated with the registrations below:</p>
    4096                <div id="rfc.table.5">
    4097                   <div id="iana.content.coding.registration.table"></div>
    4098                   <table class="tt full left" cellpadding="3" cellspacing="0">
    4099                      <thead>
    4100                         <tr>
    4101                            <th>Name</th>
    4102                            <th>Description</th>
    4103                            <th>Reference</th>
    4104                         </tr>
    4105                      </thead>
    4106                      <tbody>
    4107                         <tr>
    4108                            <td class="left">identity</td>
    4109                            <td class="left">Reserved (synonym for "no encoding" in <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a>)
    4110                            </td>
    4111                            <td class="left"><a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.4" title="Accept-Encoding">Section&nbsp;5.3.4</a>
    4112                            </td>
    4113                         </tr>
    4114                      </tbody>
    4115                   </table>
    4116                </div>
    4117             </div>
    4118          </div>
    4119       </div>
    4120       <div id="security.considerations">
    4121          <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a href="#security.considerations">Security Considerations</a></h1>
    4122          <p id="rfc.section.9.p.1">This section is meant to inform developers, info