Ignore:
Timestamp:
09/05/14 09:52:21 (6 years ago)
Author:
julian.reschke@…
Message:

min. fixes (reg names, punctuation, etc) (see #553)

File:
1 edited

Legend:

Unmodified
Added
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  • draft-ietf-httpbis/latest/p2-semantics.html

    r2662 r2663  
     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/">
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     6      <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title><script>
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     22  toggleButtonsToElementsByName("h3");
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     35function toggleButton(node) {
     36  if (! buttonsAdded) {
     37
     38    // docname
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     40
     41    var id = node.getAttribute("id");
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     57    if (id != "") {
     58      ref += "#" + id;
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     60
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     66    section = section.replace("\u00a0", " ");
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     70    uri = uri.replace("{section}", encodeURIComponent(section));
     71    uri = uri.replace("{ref}", encodeURIComponent(ref));
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     75    button.setAttribute("href", uri);
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     88}</script><style type="text/css" title="Xml2Rfc (sans serif)">
     89a {
     90  text-decoration: none;
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     92a.smpl {
     93  color: black;
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     95a:hover {
     96  text-decoration: underline;
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     98a:active {
     99  text-decoration: underline;
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     101address {
     102  margin-top: 1em;
     103  margin-left: 2em;
     104  font-style: normal;
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     108  font-family: cambria, helvetica, arial, sans-serif;
     109  font-size: 11pt;
     110  margin-right: 2em;
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     112cite {
     113  font-style: normal;
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     115div.note {
     116  margin-left: 2em;
     117}
     118dl {
     119  margin-left: 2em;
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     121ul.empty {
     122  list-style-type: none;
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     124ul.empty li {
     125  margin-top: .5em;
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     127dl p {
     128  margin-left: 0em;
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     131  margin-top: .5em;
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     151  page-break-after: avoid;
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     157  margin-left: 3em;
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     159li {
     160  margin-left: 2em;
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     163  margin-left: 2em;
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     172  margin-left: 0em;
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     174p {
     175  margin-left: 2em;
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     178  margin-left: 3em;
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     222table.full {
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     226table.tt td {
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     229table.all td {
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     233table.full td {
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     237table.tt th {
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     240table.all th {
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     255table.right {
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     272  font-size: 11pt;
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     275td.top {
     276  vertical-align: top;
     277}
     278td.topnowrap {
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     280  white-space: nowrap;
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     282table.header td {
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     286table.header a {
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     291  white-space: nowrap;
     292  padding-right: 1em;
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     294thead {
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     304  font-weight: bold;
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     309  font-weight: normal;
     310  font-size: 10pt;
     311  margin-left: 0em;
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     321}
     322samp, tt, code, pre {
     323  font: consolas, monospace;
     324}
     325ul.ind, ul.ind ul {
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     334  margin-left: 0em;
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     347  font-variant: small-caps;
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     419  a {
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     422  }
     423
     424  table.header {
     425    width: 90%;
     426  }
     427
     428  td.header {
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     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 {
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     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 10, 2014";
     466  }
     467  @bottom-right {
     468       content: "[Page " counter(page) "]";
     469  }
     470}
     471
     472@page:first {
     473    @top-left {
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     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      <meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP semantics, HTTP payload, HTTP content, HTTP method, HTTP status code">
     506      <link rel="schema.dct" href="http://purl.org/dc/terms/">
     507      <meta name="dct.creator" content="Fielding, R.">
     508      <meta name="dct.creator" content="Reschke, J. F.">
     509      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p2-semantics-latest">
     510      <meta name="dct.issued" scheme="ISO8601" content="2014-05-09">
     511      <meta name="dct.replaces" content="urn:ietf:rfc:2616">
     512      <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.">
     513      <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.">
     514   </head>
     515   <body onload="initFeedback();">
     516      <table class="header">
     517         <tbody>
     518            <tr>
     519               <td class="left">HTTPbis Working Group</td>
     520               <td class="right">R. Fielding, Editor</td>
     521            </tr>
     522            <tr>
     523               <td class="left">Internet-Draft</td>
     524               <td class="right">Adobe</td>
     525            </tr>
     526            <tr>
     527               <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
     528               </td>
     529               <td class="right">J. Reschke, Editor</td>
     530            </tr>
     531            <tr>
     532               <td class="left">Updates: <a href="http://tools.ietf.org/html/rfc2817">2817</a> (if approved)
     533               </td>
     534               <td class="right">greenbytes</td>
     535            </tr>
     536            <tr>
     537               <td class="left">Intended status: Standards Track</td>
     538               <td class="right">May 9, 2014</td>
     539            </tr>
     540            <tr>
     541               <td class="left">Expires: November 10, 2014</td>
     542               <td class="right"></td>
     543            </tr>
     544         </tbody>
     545      </table>
     546      <p class="title">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content<br><span class="filename">draft-ietf-httpbis-p2-semantics-latest</span></p>
     547      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
     548      <p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext
     549         information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header
     550         fields, response status codes, and response header fields, along with the payload of messages (metadata and body content)
     551         and mechanisms for content negotiation.
     552      </p>
     553      <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1>
     554      <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;.
     555      </p>
     556      <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;.
     557      </p>
     558      <p><em>This is a temporary document for the purpose of tracking the editorial changes made during the AUTH48 (RFC publication) phase.</em>
     559      </p>
     560      <div id="rfc.status">
     561         <h1><a href="#rfc.status">Status of This Memo</a></h1>
     562         <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p>
     563         <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute
     564            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>.
     565         </p>
     566         <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
     567            documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
     568            in progress”.
     569         </p>
     570         <p>This Internet-Draft will expire on November 10, 2014.</p>
     571      </div>
     572      <div id="rfc.copyrightnotice">
     573         <h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1>
     574         <p>Copyright © 2014 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
     575         <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
     576            and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License
     577            text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified
     578            BSD License.
     579         </p>
     580         <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November
     581            10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to
     582            allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s)
     583            controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative
     584            works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate
     585            it into languages other than English.
     586         </p>
     587      </div>
     588      <hr class="noprint">
     589      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
     590      <ul class="toc">
     591         <li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
     592               <li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li>
     593               <li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li>
     594            </ul>
     595         </li>
     596         <li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#resources">Resources</a></li>
     597         <li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#representations">Representations</a><ul>
     598               <li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#representation.metadata">Representation Metadata</a><ul>
     599                     <li><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#data.type">Processing Representation Data</a></li>
     600                     <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>
     601                     <li><a href="#rfc.section.3.1.3">3.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#audience.language">Audience Language</a></li>
     602                     <li><a href="#rfc.section.3.1.4">3.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#identification">Identification</a></li>
     603                  </ul>
     604               </li>
     605               <li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#representation.data">Representation Data</a></li>
     606               <li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#payload">Payload Semantics</a></li>
     607               <li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul>
     608                     <li><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#proactive.negotiation">Proactive Negotiation</a></li>
     609                     <li><a href="#rfc.section.3.4.2">3.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#reactive.negotiation">Reactive Negotiation</a></li>
     610                  </ul>
     611               </li>
     612            </ul>
     613         </li>
     614         <li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#methods">Request Methods</a><ul>
     615               <li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.overview">Overview</a></li>
     616               <li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#method.properties">Common Method Properties</a><ul>
     617                     <li><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li>
     618                     <li><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li>
     619                     <li><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#cacheable.methods">Cacheable Methods</a></li>
     620                  </ul>
     621               </li>
     622               <li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul>
     623                     <li><a href="#rfc.section.4.3.1">4.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li>
     624                     <li><a href="#rfc.section.4.3.2">4.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li>
     625                     <li><a href="#rfc.section.4.3.3">4.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li>
     626                     <li><a href="#rfc.section.4.3.4">4.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li>
     627                     <li><a href="#rfc.section.4.3.5">4.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li>
     628                     <li><a href="#rfc.section.4.3.6">4.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li>
     629                     <li><a href="#rfc.section.4.3.7">4.3.7</a>&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li>
     630                     <li><a href="#rfc.section.4.3.8">4.3.8</a>&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li>
     631                  </ul>
     632               </li>
     633            </ul>
     634         </li>
     635         <li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a><ul>
     636               <li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#request.controls">Controls</a><ul>
     637                     <li><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li>
     638                     <li><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li>
     639                  </ul>
     640               </li>
     641               <li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#request.conditionals">Conditionals</a></li>
     642               <li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#request.conneg">Content Negotiation</a><ul>
     643                     <li><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li>
     644                     <li><a href="#rfc.section.5.3.2">5.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li>
     645                     <li><a href="#rfc.section.5.3.3">5.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li>
     646                     <li><a href="#rfc.section.5.3.4">5.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li>
     647                     <li><a href="#rfc.section.5.3.5">5.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li>
     648                  </ul>
     649               </li>
     650               <li><a href="#rfc.section.5.4">5.4</a>&nbsp;&nbsp;&nbsp;<a href="#request.auth">Authentication Credentials</a></li>
     651               <li><a href="#rfc.section.5.5">5.5</a>&nbsp;&nbsp;&nbsp;<a href="#request.context">Request Context</a><ul>
     652                     <li><a href="#rfc.section.5.5.1">5.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li>
     653                     <li><a href="#rfc.section.5.5.2">5.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li>
     654                     <li><a href="#rfc.section.5.5.3">5.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li>
     655                  </ul>
     656               </li>
     657            </ul>
     658         </li>
     659         <li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#status.codes">Response Status Codes</a><ul>
     660               <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>
     661               <li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul>
     662                     <li><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li>
     663                     <li><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li>
     664                  </ul>
     665               </li>
     666               <li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul>
     667                     <li><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li>
     668                     <li><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li>
     669                     <li><a href="#rfc.section.6.3.3">6.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li>
     670                     <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>
     671                     <li><a href="#rfc.section.6.3.5">6.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li>
     672                     <li><a href="#rfc.section.6.3.6">6.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li>
     673                  </ul>
     674               </li>
     675               <li><a href="#rfc.section.6.4">6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul>
     676                     <li><a href="#rfc.section.6.4.1">6.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li>
     677                     <li><a href="#rfc.section.6.4.2">6.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li>
     678                     <li><a href="#rfc.section.6.4.3">6.4.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li>
     679                     <li><a href="#rfc.section.6.4.4">6.4.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li>
     680                     <li><a href="#rfc.section.6.4.5">6.4.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li>
     681                     <li><a href="#rfc.section.6.4.6">6.4.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li>
     682                     <li><a href="#rfc.section.6.4.7">6.4.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li>
     683                  </ul>
     684               </li>
     685               <li><a href="#rfc.section.6.5">6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul>
     686                     <li><a href="#rfc.section.6.5.1">6.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li>
     687                     <li><a href="#rfc.section.6.5.2">6.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li>
     688                     <li><a href="#rfc.section.6.5.3">6.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li>
     689                     <li><a href="#rfc.section.6.5.4">6.5.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li>
     690                     <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>
     691                     <li><a href="#rfc.section.6.5.6">6.5.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li>
     692                     <li><a href="#rfc.section.6.5.7">6.5.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li>
     693                     <li><a href="#rfc.section.6.5.8">6.5.8</a>&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li>
     694                     <li><a href="#rfc.section.6.5.9">6.5.9</a>&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li>
     695                     <li><a href="#rfc.section.6.5.10">6.5.10</a>&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li>
     696                     <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>
     697                     <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>
     698                     <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>
     699                     <li><a href="#rfc.section.6.5.14">6.5.14</a>&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li>
     700                     <li><a href="#rfc.section.6.5.15">6.5.15</a>&nbsp;&nbsp;&nbsp;<a href="#status.426">426 Upgrade Required</a></li>
     701                  </ul>
     702               </li>
     703               <li><a href="#rfc.section.6.6">6.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul>
     704                     <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>
     705                     <li><a href="#rfc.section.6.6.2">6.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li>
     706                     <li><a href="#rfc.section.6.6.3">6.6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li>
     707                     <li><a href="#rfc.section.6.6.4">6.6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li>
     708                     <li><a href="#rfc.section.6.6.5">6.6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li>
     709                     <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>
     710                  </ul>
     711               </li>
     712            </ul>
     713         </li>
     714         <li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a><ul>
     715               <li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#response.control.data">Control Data</a><ul>
     716                     <li><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#origination.date">Origination Date</a></li>
     717                     <li><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li>
     718                     <li><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li>
     719                     <li><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
     720                  </ul>
     721               </li>
     722               <li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#response.validator">Validator Header Fields</a></li>
     723               <li><a href="#rfc.section.7.3">7.3</a>&nbsp;&nbsp;&nbsp;<a href="#response.auth">Authentication Challenges</a></li>
     724               <li><a href="#rfc.section.7.4">7.4</a>&nbsp;&nbsp;&nbsp;<a href="#response.context">Response Context</a><ul>
     725                     <li><a href="#rfc.section.7.4.1">7.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li>
     726                     <li><a href="#rfc.section.7.4.2">7.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li>
     727                  </ul>
     728               </li>
     729            </ul>
     730         </li>
     731         <li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
     732               <li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry">Method Registry</a><ul>
     733                     <li><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry.procedure">Procedure</a></li>
     734                     <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>
     735                     <li><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.registration">Registrations</a></li>
     736                  </ul>
     737               </li>
     738               <li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry">Status Code Registry</a><ul>
     739                     <li><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry.procedure">Procedure</a></li>
     740                     <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>
     741                     <li><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registration">Registrations</a></li>
     742                  </ul>
     743               </li>
     744               <li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registry">Header Field Registry</a><ul>
     745                     <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>
     746                     <li><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Registrations</a></li>
     747                  </ul>
     748               </li>
     749               <li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registry">Content Coding Registry</a><ul>
     750                     <li><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.procedure">Procedure</a></li>
     751                     <li><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registration">Registrations</a></li>
     752                  </ul>
     753               </li>
     754            </ul>
     755         </li>
     756         <li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
     757               <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>
     758               <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>
     759               <li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#personal.information">Disclosure of Personal Information</a></li>
     760               <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>
     761               <li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#fragment.disclosure">Disclosure of Fragment after Redirects</a></li>
     762               <li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#disclosure.product.information">Disclosure of Product Information</a></li>
     763               <li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#fingerprinting">Browser Fingerprinting</a></li>
     764            </ul>
     765         </li>
     766         <li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li>
     767         <li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
     768               <li><a href="#rfc.section.11.1">11.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
     769               <li><a href="#rfc.section.11.2">11.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
     770            </ul>
     771         </li>
     772         <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>
     773               <li><a href="#rfc.section.A.1">A.1</a>&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li>
     774               <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>
     775               <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>
     776               <li><a href="#rfc.section.A.4">A.4</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.content-encoding">Conversion of Content-Encoding</a></li>
     777               <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>
     778               <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>
     779            </ul>
     780         </li>
     781         <li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
     782         <li><a href="#rfc.section.C">C.</a>&nbsp;&nbsp;&nbsp;<a href="#imported.abnf">Imported ABNF</a></li>
     783         <li><a href="#rfc.section.D">D.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li>
     784         <li><a href="#rfc.index">Index</a></li>
     785         <li><a href="#rfc.authors">Authors' Addresses</a></li>
     786      </ul>
     787      <div id="introduction">
     788         <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1>
     789         <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
     790            request, parses each message received, interprets the message semantics in relation to the identified request target, and
     791            responds to that request with one or more response messages. A client constructs request messages to communicate specific
     792            intentions, examines received responses to see if the intentions were carried out, and determines how to interpret the results.
     793            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>.
     794         </p>
     795         <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>).
     796         </p>
     797         <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>).
     798         </p>
     799         <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,
     800            the request header fields that might influence content selection, and the various selection algorithms that are collectively
     801            referred to as "<dfn>content negotiation</dfn>" (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;3.4</a>).
     802         </p>
     803         <div id="conformance">
     804            <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>
     805            <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"
     806               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>.
     807            </p>
     808            <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>.
     809            </p>
     810         </div>
     811         <div id="notation">
     812            <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2>
     813            <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
     814               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.
     815            </p>
     816            <p id="rfc.section.1.2.p.2">This specification uses the terms "character", "character encoding scheme", "charset", and "protocol element" as they are
     817               defined in <a href="#RFC6365" id="rfc.xref.RFC6365.1"><cite title="Terminology Used in Internationalization in the IETF">[RFC6365]</cite></a>.
     818            </p>
     819         </div>
     820      </div>
     821      <div id="resources">
     822         <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#resources">Resources</a></h1>
     823         <p id="rfc.section.2.p.1">The target of an HTTP request is called a "<dfn>resource</dfn>". HTTP does not limit the nature of a resource; it merely defines an interface that might be used to interact with resources.
     824            Each resource is identified by a Uniform Resource Identifier (URI), as described 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 Sets" 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
     1626Host: 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
     1639Host: server.example.com:80
     1640Proxy-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
     1768Host: origin.example.com
     1769Content-Type: video/h264
     1770Content-Length: 1234567890987
     1771Expect: 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 the Referer field 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
     2960Upgrade: HTTP/3.0
     2961Connection: Upgrade
     2962Content-Length: 53
     2963Content-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
     3099Sun 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, information providers, and users of known security concerns relevant to HTTP semantics
     4123            and its use for transferring information over the Internet. Considerations related to message syntax, parsing, and routing
     4124            are discussed in <a href="p1-messaging.html#security.considerations" title="Security Considerations">Section 9</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.43"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.
     4125         </p>
     4126         <p id="rfc.section.9.p.2">The list of considerations below is not exhaustive. Most security concerns related to HTTP semantics are about securing server-side
     4127            applications (code behind the HTTP interface), securing user agent processing of payloads received via HTTP, or secure use
     4128            of the Internet in general, rather than security of the protocol. Various organizations maintain topical information and links
     4129            to current research on Web application security (e.g., <a href="#OWASP" id="rfc.xref.OWASP.1"><cite title="A Guide to Building Secure Web Applications and Web Services">[OWASP]</cite></a>).
     4130         </p>
     4131         <div id="attack.pathname">
     4132            <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a href="#attack.pathname">Attacks Based on File and Path Names</a></h2>
     4133            <p id="rfc.section.9.1.p.1">Origin servers frequently make use of their local file system to manage the mapping from effective request URI to resource
     4134               representations. Implementers need to be aware that most file systems are not designed to protect against malicious file or
     4135               path names and, thus, depend on the origin server to avoid mapping to file names, folders, or directories that have special
     4136               significance to the system.
     4137            </p>
     4138            <p id="rfc.section.9.1.p.2">For example, UNIX, Microsoft Windows, and other operating systems use ".." as a path component to indicate a directory level
     4139               above the current one, and they use specially named paths or file names to send data to system devices. Similar naming conventions
     4140               might exist within other types of storage systems. Likewise, local storage systems have an annoying tendency to prefer user-friendliness
     4141               over security when handling invalid or unexpected characters, recomposition of decomposed characters, and case-normalization
     4142               of case-insensitive names.
     4143            </p>
     4144            <p id="rfc.section.9.1.p.3">Attacks based on such special names tend to focus on either denial-of-service (e.g., telling the server to read from a COM
     4145               port) or disclosure of configuration and source files that are not meant to be served.
     4146            </p>
     4147         </div>
     4148         <div id="attack.injection">
     4149            <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a href="#attack.injection">Attacks Based on Command, Code, or Query Injection</a></h2>
     4150            <p id="rfc.section.9.2.p.1">Origin servers often use parameters within the URI as a means of identifying system services, selecting database entries,
     4151               or choosing a data source. However, data received in a request cannot be trusted. An attacker could construct any of the request
     4152               data elements (method, request-target, header fields, or body) to contain data that might be misinterpreted as a command,
     4153               code, or query when passed through a command invocation, language interpreter, or database interface.
     4154            </p>
     4155            <p id="rfc.section.9.2.p.2">For example, SQL injection is a common attack wherein additional query language is inserted within some part of the request-target
     4156               or header fields (e.g., <a href="p1-messaging.html#header.host" class=