Changeset 1554


Ignore:
Timestamp:
Mar 2, 2012, 4:16:57 PM (7 years ago)
Author:
mnot@…
Message:

Move cache-specific HEAD language to p6; fully specify effects on cache. Addresses #227.

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

Legend:

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

    r1552 r1554  
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    448 @page {
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    450        content: "Internet-Draft";
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    452   @top-right {
    453        content: "March 2012";
    454   }
    455   @top-center {
    456        content: "HTTP/1.1, Part 2";
    457   }
    458   @bottom-left {
    459        content: "Fielding, et al.";
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    461   @bottom-center {
    462        content: "Expires September 2012";
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    480 </style><link rel="Contents" href="#rfc.toc">
    481       <link rel="Author" href="#rfc.authors">
    482       <link rel="Copyright" href="#rfc.copyrightnotice">
    483       <link rel="Index" href="#rfc.index">
    484       <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
    485       <link rel="Chapter" title="2 Method" href="#rfc.section.2">
    486       <link rel="Chapter" title="3 Header Fields" href="#rfc.section.3">
    487       <link rel="Chapter" title="4 Status Code and Reason Phrase" href="#rfc.section.4">
    488       <link rel="Chapter" title="5 Representation" href="#rfc.section.5">
    489       <link rel="Chapter" title="6 Method Definitions" href="#rfc.section.6">
    490       <link rel="Chapter" title="7 Status Code Definitions" href="#rfc.section.7">
    491       <link rel="Chapter" title="8 Date/Time Formats" href="#rfc.section.8">
    492       <link rel="Chapter" title="9 Product Tokens" href="#rfc.section.9">
    493       <link rel="Chapter" title="10 Header Field Definitions" href="#rfc.section.10">
    494       <link rel="Chapter" title="11 IANA Considerations" href="#rfc.section.11">
    495       <link rel="Chapter" title="12 Security Considerations" href="#rfc.section.12">
    496       <link rel="Chapter" title="13 Acknowledgments" href="#rfc.section.13">
    497       <link rel="Chapter" href="#rfc.section.14" title="14 References">
    498       <link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A">
    499       <link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B">
    500       <link rel="Appendix" title="C Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.C">
    501       <link href="p1-messaging.html" rel="prev">
    502       <link href="p3-payload.html" rel="next">
    503       <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.570, 2012-02-13 19:17:35, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">
    504       <link rel="schema.dct" href="http://purl.org/dc/terms/">
    505       <meta name="dct.creator" content="Fielding, R.">
    506       <meta name="dct.creator" content="Gettys, J.">
    507       <meta name="dct.creator" content="Mogul, J.">
    508       <meta name="dct.creator" content="Frystyk, H.">
    509       <meta name="dct.creator" content="Masinter, L.">
    510       <meta name="dct.creator" content="Leach, P.">
    511       <meta name="dct.creator" content="Berners-Lee, T.">
    512       <meta name="dct.creator" content="Lafon, Y.">
    513       <meta name="dct.creator" content="Reschke, J. F.">
    514       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p2-semantics-latest">
    515       <meta name="dct.issued" scheme="ISO8601" content="2012-03">
    516       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
    517       <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 2 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 2 defines the semantics of HTTP messages as expressed by request methods, request header fields, response status codes, and response header fields.">
    518       <meta name="description" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 2 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 2 defines the semantics of HTTP messages as expressed by request methods, request header fields, response status codes, and response header fields.">
    519    </head>
    520    <body onload="init();">
    521       <table class="header">
    522          <tbody>
    523             <tr>
    524                <td class="left">HTTPbis Working Group</td>
    525                <td class="right">R. Fielding, Editor</td>
    526             </tr>
    527             <tr>
    528                <td class="left">Internet-Draft</td>
    529                <td class="right">Adobe</td>
    530             </tr>
    531             <tr>
    532                <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
    533                </td>
    534                <td class="right">J. Gettys</td>
    535             </tr>
    536             <tr>
    537                <td class="left">Updates: <a href="http://tools.ietf.org/html/rfc2817">2817</a> (if approved)
    538                </td>
    539                <td class="right">Alcatel-Lucent</td>
    540             </tr>
    541             <tr>
    542                <td class="left">Intended status: Standards Track</td>
    543                <td class="right">J. Mogul</td>
    544             </tr>
    545             <tr>
    546                <td class="left">Expires: September 2012</td>
    547                <td class="right">HP</td>
    548             </tr>
    549             <tr>
    550                <td class="left"></td>
    551                <td class="right">H. Frystyk</td>
    552             </tr>
    553             <tr>
    554                <td class="left"></td>
    555                <td class="right">Microsoft</td>
    556             </tr>
    557             <tr>
    558                <td class="left"></td>
    559                <td class="right">L. Masinter</td>
    560             </tr>
    561             <tr>
    562                <td class="left"></td>
    563                <td class="right">Adobe</td>
    564             </tr>
    565             <tr>
    566                <td class="left"></td>
    567                <td class="right">P. Leach</td>
    568             </tr>
    569             <tr>
    570                <td class="left"></td>
    571                <td class="right">Microsoft</td>
    572             </tr>
    573             <tr>
    574                <td class="left"></td>
    575                <td class="right">T. Berners-Lee</td>
    576             </tr>
    577             <tr>
    578                <td class="left"></td>
    579                <td class="right">W3C/MIT</td>
    580             </tr>
    581             <tr>
    582                <td class="left"></td>
    583                <td class="right">Y. Lafon, Editor</td>
    584             </tr>
    585             <tr>
    586                <td class="left"></td>
    587                <td class="right">W3C</td>
    588             </tr>
    589             <tr>
    590                <td class="left"></td>
    591                <td class="right">J. Reschke, Editor</td>
    592             </tr>
    593             <tr>
    594                <td class="left"></td>
    595                <td class="right">greenbytes</td>
    596             </tr>
    597             <tr>
    598                <td class="left"></td>
    599                <td class="right">March 2012</td>
    600             </tr>
    601          </tbody>
    602       </table>
    603       <p class="title">HTTP/1.1, part 2: Message Semantics<br><span class="filename">draft-ietf-httpbis-p2-semantics-latest</span></p>
    604       <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
    605       <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information
    606          systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 2 of the
    607          seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
    608       </p> 
    609       <p>Part 2 defines the semantics of HTTP messages as expressed by request methods, request header fields, response status codes,
    610          and response header fields.
    611       </p>
    612       <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1>
    613       <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived
    614          at &lt;<a href="http://lists.w3.org/Archives/Public/ietf-http-wg/">http://lists.w3.org/Archives/Public/ietf-http-wg/</a>&gt;.
    615       </p> 
    616       <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;.
    617       </p> 
    618       <p>The changes in this draft are summarized in <a href="#changes.since.18" title="Since draft-ietf-httpbis-p2-semantics-18">Appendix&nbsp;C.20</a>.
    619       </p>
    620       <h1><a id="rfc.status" href="#rfc.status">Status of This Memo</a></h1>
    621       <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p>
    622       <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute
    623          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>.
    624       </p>
    625       <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
    626          documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
    627          in progress”.
    628       </p>
    629       <p>This Internet-Draft will expire in September 2012.</p>
    630       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    631       <p>Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
    632       <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
    633          and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License
    634          text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified
    635          BSD License.
    636       </p>
    637       <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November
    638          10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to
    639          allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s)
    640          controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative
    641          works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate
    642          it into languages other than English.
    643       </p>
    644       <hr class="noprint">
    645       <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
    646       <ul class="toc">
    647          <li>1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
    648                <li>1.1&nbsp;&nbsp;&nbsp;<a href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></li>
    649                <li>1.2&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a><ul>
    650                      <li>1.2.1&nbsp;&nbsp;&nbsp;<a href="#core.rules">Core Rules</a></li>
    651                      <li>1.2.2&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
    652                   </ul>
    653                </li>
    654             </ul>
    655          </li>
    656          <li>2.&nbsp;&nbsp;&nbsp;<a href="#method">Method</a><ul>
    657                <li>2.1&nbsp;&nbsp;&nbsp;<a href="#overview.of.methods">Overview of Methods</a></li>
    658                <li>2.2&nbsp;&nbsp;&nbsp;<a href="#method.registry">Method Registry</a><ul>
    659                      <li>2.2.1&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.methods">Considerations for New Methods</a></li>
    660                   </ul>
    661                </li>
    662             </ul>
    663          </li>
    664          <li>3.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Fields</a><ul>
    665                <li>3.1&nbsp;&nbsp;&nbsp;<a href="#considerations.for.creating.header.fields">Considerations for Creating Header Fields</a></li>
    666                <li>3.2&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a></li>
    667                <li>3.3&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a></li>
    668             </ul>
    669          </li>
    670          <li>4.&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a><ul>
    671                <li>4.1&nbsp;&nbsp;&nbsp;<a href="#overview.of.status.codes">Overview of Status Codes</a></li>
    672                <li>4.2&nbsp;&nbsp;&nbsp;<a href="#status.code.registry">Status Code Registry</a><ul>
    673                      <li>4.2.1&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></li>
    674                   </ul>
    675                </li>
    676             </ul>
    677          </li>
    678          <li>5.&nbsp;&nbsp;&nbsp;<a href="#representation">Representation</a><ul>
    679                <li>5.1&nbsp;&nbsp;&nbsp;<a href="#identifying.response.associated.with.representation">Identifying the Resource Associated with a Representation</a></li>
    680             </ul>
    681          </li>
    682          <li>6.&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul>
    683                <li>6.1&nbsp;&nbsp;&nbsp;<a href="#safe.and.idempotent">Safe and Idempotent Methods</a><ul>
    684                      <li>6.1.1&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li>
    685                      <li>6.1.2&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li>
    686                   </ul>
    687                </li>
    688                <li>6.2&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li>
    689                <li>6.3&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li>
    690                <li>6.4&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li>
    691                <li>6.5&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li>
    692                <li>6.6&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li>
    693                <li>6.7&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li>
    694                <li>6.8&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li>
    695                <li>6.9&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a><ul>
    696                      <li>6.9.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.6.9.1">Establishing a Tunnel with CONNECT</a></li>
    697                   </ul>
    698                </li>
    699             </ul>
    700          </li>
    701          <li>7.&nbsp;&nbsp;&nbsp;<a href="#status.codes">Status Code Definitions</a><ul>
    702                <li>7.1&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul>
    703                      <li>7.1.1&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li>
    704                      <li>7.1.2&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li>
    705                   </ul>
    706                </li>
    707                <li>7.2&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul>
    708                      <li>7.2.1&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li>
    709                      <li>7.2.2&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li>
    710                      <li>7.2.3&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li>
    711                      <li>7.2.4&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li>
    712                      <li>7.2.5&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li>
    713                      <li>7.2.6&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li>
    714                   </ul>
    715                </li>
    716                <li>7.3&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul>
    717                      <li>7.3.1&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li>
    718                      <li>7.3.2&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li>
    719                      <li>7.3.3&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li>
    720                      <li>7.3.4&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li>
    721                      <li>7.3.5&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li>
    722                      <li>7.3.6&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li>
    723                      <li>7.3.7&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li>
    724                   </ul>
    725                </li>
    726                <li>7.4&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul>
    727                      <li>7.4.1&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li>
    728                      <li>7.4.2&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li>
    729                      <li>7.4.3&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li>
    730                      <li>7.4.4&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li>
    731                      <li>7.4.5&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li>
    732                      <li>7.4.6&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li>
    733                      <li>7.4.7&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li>
    734                      <li>7.4.8&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li>
    735                      <li>7.4.9&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li>
    736                      <li>7.4.10&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li>
    737                      <li>7.4.11&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Request Representation Too Large</a></li>
    738                      <li>7.4.12&nbsp;&nbsp;&nbsp;<a href="#status.414">414 URI Too Long</a></li>
    739                      <li>7.4.13&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li>
    740                      <li>7.4.14&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li>
    741                      <li>7.4.15&nbsp;&nbsp;&nbsp;<a href="#status.426">426 Upgrade Required</a></li>
    742                   </ul>
    743                </li>
    744                <li>7.5&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul>
    745                      <li>7.5.1&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li>
    746                      <li>7.5.2&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li>
    747                      <li>7.5.3&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li>
    748                      <li>7.5.4&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li>
    749                      <li>7.5.5&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li>
    750                      <li>7.5.6&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li>
    751                   </ul>
    752                </li>
    753             </ul>
    754          </li>
    755          <li>8.&nbsp;&nbsp;&nbsp;<a href="#http.date">Date/Time Formats</a></li>
    756          <li>9.&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
    757          <li>10.&nbsp;&nbsp;&nbsp;<a href="#header.field.definitions">Header Field Definitions</a><ul>
    758                <li>10.1&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li>
    759                <li>10.2&nbsp;&nbsp;&nbsp;<a href="#header.date">Date</a></li>
    760                <li>10.3&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li>
    761                <li>10.4&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li>
    762                <li>10.5&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li>
    763                <li>10.6&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li>
    764                <li>10.7&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li>
    765                <li>10.8&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li>
    766                <li>10.9&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li>
    767                <li>10.10&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li>
    768             </ul>
    769          </li>
    770          <li>11.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
    771                <li>11.1&nbsp;&nbsp;&nbsp;<a href="#method.registration">Method Registry</a></li>
    772                <li>11.2&nbsp;&nbsp;&nbsp;<a href="#status.code.registration">Status Code Registry</a></li>
    773                <li>11.3&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li>
    774             </ul>
    775          </li>
    776          <li>12.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
    777                <li>12.1&nbsp;&nbsp;&nbsp;<a href="#security.sensitive">Transfer of Sensitive Information</a></li>
    778                <li>12.2&nbsp;&nbsp;&nbsp;<a href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URIs</a></li>
    779                <li>12.3&nbsp;&nbsp;&nbsp;<a href="#location.spoofing-leakage">Location Header Fields: Spoofing and Information Leakage</a></li>
    780                <li>12.4&nbsp;&nbsp;&nbsp;<a href="#rfc.section.12.4">Security Considerations for CONNECT</a></li>
    781             </ul>
    782          </li>
    783          <li>13.&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li>
    784          <li>14.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
    785                <li>14.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
    786                <li>14.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
    787             </ul>
    788          </li>
    789          <li><a href="#rfc.authors">Authors' Addresses</a></li>
    790          <li>A.&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
    791          <li>B.&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li>
    792          <li>C.&nbsp;&nbsp;&nbsp;<a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul>
    793                <li>C.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.C.1">Since RFC 2616</a></li>
    794                <li>C.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.C.2">Since draft-ietf-httpbis-p2-semantics-00</a></li>
    795                <li>C.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.C.3">Since draft-ietf-httpbis-p2-semantics-01</a></li>
    796                <li>C.4&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p2-semantics-02</a></li>
    797                <li>C.5&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p2-semantics-03</a></li>
    798                <li>C.6&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p2-semantics-04</a></li>
    799                <li>C.7&nbsp;&nbsp;&nbsp;<a href="#changes.since.05">Since draft-ietf-httpbis-p2-semantics-05</a></li>
    800                <li>C.8&nbsp;&nbsp;&nbsp;<a href="#changes.since.06">Since draft-ietf-httpbis-p2-semantics-06</a></li>
    801                <li>C.9&nbsp;&nbsp;&nbsp;<a href="#changes.since.07">Since draft-ietf-httpbis-p2-semantics-07</a></li>
    802                <li>C.10&nbsp;&nbsp;&nbsp;<a href="#changes.since.08">Since draft-ietf-httpbis-p2-semantics-08</a></li>
    803                <li>C.11&nbsp;&nbsp;&nbsp;<a href="#changes.since.09">Since draft-ietf-httpbis-p2-semantics-09</a></li>
    804                <li>C.12&nbsp;&nbsp;&nbsp;<a href="#changes.since.10">Since draft-ietf-httpbis-p2-semantics-10</a></li>
    805                <li>C.13&nbsp;&nbsp;&nbsp;<a href="#changes.since.11">Since draft-ietf-httpbis-p2-semantics-11</a></li>
    806                <li>C.14&nbsp;&nbsp;&nbsp;<a href="#changes.since.12">Since draft-ietf-httpbis-p2-semantics-12</a></li>
    807                <li>C.15&nbsp;&nbsp;&nbsp;<a href="#changes.since.13">Since draft-ietf-httpbis-p2-semantics-13</a></li>
    808                <li>C.16&nbsp;&nbsp;&nbsp;<a href="#changes.since.14">Since draft-ietf-httpbis-p2-semantics-14</a></li>
    809                <li>C.17&nbsp;&nbsp;&nbsp;<a href="#changes.since.15">Since draft-ietf-httpbis-p2-semantics-15</a></li>
    810                <li>C.18&nbsp;&nbsp;&nbsp;<a href="#changes.since.16">Since draft-ietf-httpbis-p2-semantics-16</a></li>
    811                <li>C.19&nbsp;&nbsp;&nbsp;<a href="#changes.since.17">Since draft-ietf-httpbis-p2-semantics-17</a></li>
    812                <li>C.20&nbsp;&nbsp;&nbsp;<a href="#changes.since.18">Since draft-ietf-httpbis-p2-semantics-18</a></li>
    813             </ul>
    814          </li>
    815          <li><a href="#rfc.index">Index</a></li>
    816       </ul>
    817       <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
    818       <p id="rfc.section.1.p.1">This document defines HTTP/1.1 request and response semantics. Each HTTP message, as defined in <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, is in the form of either a request or a response. An HTTP server listens on a connection for HTTP requests and responds
    819          to each request, in the order received on that connection, with one or more HTTP response messages. This document defines
    820          the commonly agreed upon semantics of the HTTP uniform interface, the intentions defined by each request method, and the various
    821          response messages that might be expected as a result of applying that method to the target resource.
    822       </p>
    823       <p id="rfc.section.1.p.2">This document is currently disorganized in order to minimize the changes between drafts and enable reviewers to see the smaller
    824          errata changes. A future draft will reorganize the sections to better reflect the content. In particular, the sections will
    825          be ordered according to the typical processing of an HTTP request message (after message parsing): resource mapping, methods,
    826          request modifying header fields, response status, status modifying header fields, and resource metadata. The current mess
    827          reflects how widely dispersed these topics and associated requirements had become in <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
    828       </p>
    829       <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a id="intro.conformance.and.error.handling" href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></h2>
    830       <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"
    831          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>.
    832       </p>
    833       <p id="rfc.section.1.1.p.2">This document defines conformance criteria for several roles in HTTP communication, including Senders, Recipients, Clients,
    834          Servers, User-Agents, Origin Servers, Intermediaries, Proxies and Gateways. See <a href="p1-messaging.html#architecture" title="Architecture">Section 2</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for definitions of these terms.
    835       </p>
    836       <p id="rfc.section.1.1.p.3">An implementation is considered conformant if it complies with all of the requirements associated with its role(s). Note that
    837          SHOULD-level requirements are relevant here, unless one of the documented exceptions is applicable.
    838       </p>
    839       <p id="rfc.section.1.1.p.4">This document also uses ABNF to define valid protocol elements (<a href="#notation" title="Syntax Notation">Section&nbsp;1.2</a>). In addition to the prose requirements placed upon them, Senders <em class="bcp14">MUST NOT</em> generate protocol elements that are invalid.
    840       </p>
    841       <p id="rfc.section.1.1.p.5">Unless noted otherwise, Recipients <em class="bcp14">MAY</em> take steps to recover a usable protocol element from an invalid construct. However, HTTP does not define specific error handling
    842          mechanisms, except in cases where it has direct impact on security. This is because different uses of the protocol require
    843          different error handling strategies; for example, a Web browser may wish to transparently recover from a response where the
    844          Location header field doesn't parse according to the ABNF, whereby in a systems control protocol using HTTP, this type of
    845          error recovery could lead to dangerous consequences.
    846       </p>
    847       <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a id="notation" href="#notation">Syntax Notation</a></h2>
    848       <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 the list rule extension defined in <a href="p1-messaging.html#notation" title="Syntax Notation">Section 1.2</a> of <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;B</a> shows the collected ABNF with the list rule expanded.
    849       </p>
    850       <p id="rfc.section.1.2.p.2">The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="http://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG
    851          (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR
    852          (any visible US-ASCII character).
    853       </p>
    854       <h3 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1</a>&nbsp;<a id="core.rules" href="#core.rules">Core Rules</a></h3>
    855       <p id="rfc.section.1.2.1.p.1">The core rules below are defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>:
    856       </p>
    857       <div id="rfc.figure.u.1"></div><pre class="inline">  <a href="#core.rules" class="smpl">BWS</a>           = &lt;BWS, defined in <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#whitespace" title="Whitespace">Section 3.2.1</a>&gt;
    858   <a href="#core.rules" class="smpl">OWS</a>           = &lt;OWS, defined in <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#whitespace" title="Whitespace">Section 3.2.1</a>&gt;
    859   <a href="#core.rules" class="smpl">RWS</a>           = &lt;RWS, defined in <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#whitespace" title="Whitespace">Section 3.2.1</a>&gt;
    860   <a href="#core.rules" class="smpl">obs-text</a>      = &lt;obs-text, defined in <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a>&gt;
    861   <a href="#core.rules" class="smpl">quoted-string</a> = &lt;quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.9"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a>&gt;
    862   <a href="#core.rules" class="smpl">token</a>         = &lt;token, defined in <a href="#Part1" id="rfc.xref.Part1.10"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a>&gt;
    863 </pre><h3 id="rfc.section.1.2.2"><a href="#rfc.section.1.2.2">1.2.2</a>&nbsp;<a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3>
    864       <p id="rfc.section.1.2.2.p.1">The ABNF rules below are defined in other parts:</p>
    865       <div id="rfc.figure.u.2"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">absolute-URI</a>  = &lt;absolute-URI, defined in <a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a>&gt;
    866   <a href="#abnf.dependencies" class="smpl">comment</a>       = &lt;comment, defined in <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a>&gt;
    867   <a href="#abnf.dependencies" class="smpl">partial-URI</a>   = &lt;partial-URI, defined in <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a>&gt;
    868   <a href="#abnf.dependencies" class="smpl">URI-reference</a> = &lt;URI-reference, defined in <a href="#Part1" id="rfc.xref.Part1.14"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a>&gt;
    869 </pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="method" href="#method">Method</a></h1>
    870       <p id="rfc.section.2.p.1">The Method token indicates the request method to be performed on the target resource (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.15"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). The method is case-sensitive.
    871       </p>
    872       <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.1"></span>  <a href="#method" class="smpl">Method</a>         = <a href="#core.rules" class="smpl">token</a>
    873 </pre><p id="rfc.section.2.p.3">The list of methods allowed by a resource can be specified in an Allow header field (<a href="#header.allow" id="rfc.xref.header.allow.1" title="Allow">Section&nbsp;10.1</a>). The status code of the response always notifies the client whether a method is currently allowed on a resource, since the
    874          set of allowed methods can change dynamically. An origin server <em class="bcp14">SHOULD</em> respond with the status code 405 (Method Not Allowed) if the method is known by the origin server but not allowed for the
    875          resource, and 501 (Not Implemented) if the method is unrecognized or not implemented by the origin server. The methods GET
    876          and HEAD <em class="bcp14">MUST</em> be supported by all general-purpose servers. All other methods are <em class="bcp14">OPTIONAL</em>; however, if the above methods are implemented, they <em class="bcp14">MUST</em> be implemented with the same semantics as those specified in <a href="#method.definitions" title="Method Definitions">Section&nbsp;6</a>.
    877       </p>
    878       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="overview.of.methods" href="#overview.of.methods">Overview of Methods</a></h2>
    879       <p id="rfc.section.2.1.p.1">The methods listed below are defined in <a href="#method.definitions" title="Method Definitions">Section&nbsp;6</a>.
    880       </p>
    881       <div id="rfc.table.u.1">
    882          <table class="tt full left" cellpadding="3" cellspacing="0">
    883             <thead>
    884                <tr>
    885                   <th>Method Name</th>
    886                   <th>Defined in...</th>
    887                </tr>
    888             </thead>
    889             <tbody>
    890                <tr>
    891                   <td class="left">OPTIONS</td>
    892                   <td class="left"><a href="#OPTIONS" id="rfc.xref.OPTIONS.1" title="OPTIONS">Section&nbsp;6.2</a></td>
    893                </tr>
    894                <tr>
    895                   <td class="left">GET</td>
    896                   <td class="left"><a href="#GET" id="rfc.xref.GET.1" title="GET">Section&nbsp;6.3</a></td>
    897                </tr>
    898                <tr>
    899                   <td class="left">HEAD</td>
    900                   <td class="left"><a href="#HEAD" id="rfc.xref.HEAD.1" title="HEAD">Section&nbsp;6.4</a></td>
    901                </tr>
    902                <tr>
    903                   <td class="left">POST</td>
    904                   <td class="left"><a href="#POST" id="rfc.xref.POST.1" title="POST">Section&nbsp;6.5</a></td>
    905                </tr>
    906                <tr>
    907                   <td class="left">PUT</td>
    908                   <td class="left"><a href="#PUT" id="rfc.xref.PUT.1" title="PUT">Section&nbsp;6.6</a></td>
    909                </tr>
    910                <tr>
    911                   <td class="left">DELETE</td>
    912                   <td class="left"><a href="#DELETE" id="rfc.xref.DELETE.1" title="DELETE">Section&nbsp;6.7</a></td>
    913                </tr>
    914                <tr>
    915                   <td class="left">TRACE</td>
    916                   <td class="left"><a href="#TRACE" id="rfc.xref.TRACE.1" title="TRACE">Section&nbsp;6.8</a></td>
    917                </tr>
    918                <tr>
    919                   <td class="left">CONNECT</td>
    920                   <td class="left"><a href="#CONNECT" id="rfc.xref.CONNECT.1" title="CONNECT">Section&nbsp;6.9</a></td>
    921                </tr>
    922             </tbody>
    923          </table>
    924       </div>
    925       <p id="rfc.section.2.1.p.2">Note that this list is not exhaustive — it does not include request methods defined in other specifications.</p>
    926       <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="method.registry" href="#method.registry">Method Registry</a></h2>
    927       <p id="rfc.section.2.2.p.1">The HTTP Method Registry defines the name space for the Method token in the Request line of an HTTP request.</p>
    928       <p id="rfc.section.2.2.p.2">Registrations <em class="bcp14">MUST</em> include the following fields:
    929       </p>
    930       <ul>
    931          <li>Method Name (see <a href="#method" title="Method">Section&nbsp;2</a>)
    932          </li>
    933          <li>Safe ("yes" or "no", see <a href="#safe.methods" title="Safe Methods">Section&nbsp;6.1.1</a>)
    934          </li>
    935          <li>Pointer to specification text</li>
    936       </ul>
    937       <p id="rfc.section.2.2.p.3">Values to be added to this name space are subject to IETF review (<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>).
    938       </p>
    939       <p id="rfc.section.2.2.p.4">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-methods">http://www.iana.org/assignments/http-methods</a>&gt;.
    940       </p>
    941       <h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a>&nbsp;<a id="considerations.for.new.methods" href="#considerations.for.new.methods">Considerations for New Methods</a></h3>
    942       <p id="rfc.section.2.2.1.p.1">When it is necessary to express new semantics for a HTTP request that aren't specific to a single application or media type,
    943          and currently defined methods are inadequate, it may be appropriate to register a new method.
    944       </p>
    945       <p id="rfc.section.2.2.1.p.2">HTTP methods are generic; that is, they are potentially applicable to any resource, not just one particular media type, "type"
    946          of resource, or application. As such, it is preferred that new HTTP methods be registered in a document that isn't specific
    947          to a single application, so that this is clear.
    948       </p>
    949       <p id="rfc.section.2.2.1.p.3">Due to the parsing rules defined in <a href="p1-messaging.html#message.body" title="Message Body">Section 3.3</a> of <a href="#Part1" id="rfc.xref.Part1.16"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, definitions of HTTP methods cannot prohibit the presence of a message body on either the request or the response message
    950          (with responses to HEAD requests being the single exception). Definitions of new methods cannot change this rule, but they
    951          can specify that only zero-length bodies (as opposed to absent bodies) are allowed.
    952       </p>
    953       <p id="rfc.section.2.2.1.p.4">New method definitions need to indicate whether they are safe (<a href="#safe.methods" title="Safe Methods">Section&nbsp;6.1.1</a>), what semantics (if any) the request body has, and whether they are idempotent (<a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;6.1.2</a>). They also need to state whether they can be cached (<a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>); in particular what conditions a cache may store the response, and under what conditions such a stored response may be used
    954          to satisfy a subsequent request.
    955       </p>
    956       <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Fields</a></h1>
    957       <p id="rfc.section.3.p.1">Header fields are key value pairs that can be used to communicate data about the message, its payload, the target resource,
    958          or about the connection itself (i.e., control data). See <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.17"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for a general definition of their syntax.
    959       </p>
    960       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="considerations.for.creating.header.fields" href="#considerations.for.creating.header.fields">Considerations for Creating Header Fields</a></h2>
    961       <p id="rfc.section.3.1.p.1">New header fields are registered using the procedures described in <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>.
    962       </p>
    963       <p id="rfc.section.3.1.p.2">The requirements for header field names are defined in <a href="http://tools.ietf.org/html/rfc3864#section-4.1">Section 4.1</a> of <a href="#RFC3864" id="rfc.xref.RFC3864.2"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>. Authors of specifications defining new fields are advised to keep the name as short as practical, and not to prefix them
    964          with "X-" if they are to be registered (either immediately or in the future).
    965       </p>
    966       <p id="rfc.section.3.1.p.3">New header field values typically have their syntax defined using ABNF (<a href="#RFC5234" id="rfc.xref.RFC5234.3"><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 3.2.5</a> of <a href="#Part1" id="rfc.xref.Part1.18"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> as necessary, and are usually constrained to the range of ASCII characters. Header fields needing a greater range of characters
    967          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>.
    968       </p>
    969       <p id="rfc.section.3.1.p.4">Because commas (",") are used as a generic delimiter between field-values, they need to be treated with care if they are allowed
    970          in the field-value's payload. Typically, components that might contain a comma are protected with double-quotes using the
    971          quoted-string ABNF production (<a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a> of <a href="#Part1" id="rfc.xref.Part1.19"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
    972       </p>
    973       <p id="rfc.section.3.1.p.5">For example, a textual date and a URI (either of which might contain a comma) could be safely carried in field-values like
    974          these:
    975       </p>
    976       <div id="rfc.figure.u.4"></div><pre class="text">  Example-URI-Field: "http://example.com/a.html,foo",
    977                      "http://without-a-comma.example.com/"
    978   Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
    979 </pre><p id="rfc.section.3.1.p.7">Note that double quote delimiters almost always are used with the quoted-string production; using a different syntax inside
    980          double quotes will likely cause unnecessary confusion.
    981       </p>
    982       <p id="rfc.section.3.1.p.8">Many header fields use a format including (case-insensitively) named parameters (for instance, Content-Type, defined in <a href="p3-payload.html#header.content-type" title="Content-Type">Section 6.8</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>). Allowing both unquoted (token) and quoted (quoted-string) syntax for the parameter value enables recipients to use existing
    983          parser components. When allowing both forms, the meaning of a parameter value ought to be independent of the syntax used for
    984          it (for an example, see the notes on parameter handling for media types in <a href="p3-payload.html#media.types" title="Media Types">Section 2.3</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>).
    985       </p>
    986       <p id="rfc.section.3.1.p.9">Authors of specifications defining new header fields are advised to consider documenting: </p>
    987       <ul>
    988          <li>
    989             <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="#Part1" id="rfc.xref.Part1.20"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
    990             </p>
    991             <p>If it does not use the list syntax, document how to treat messages where the header field occurs multiple times (a sensible
    992                default would be to ignore the header field, but this might not always be the right choice).
    993             </p>
    994             <p>Note that intermediaries and software libraries might combine multiple header field instances into a single one, despite the
    995                header field not allowing this. A robust format enables recipients to discover these situations (good example: "Content-Type",
    996                as the comma can only appear inside quoted strings; bad example: "Location", as a comma can occur inside a URI).
    997             </p>
    998          </li>
    999          <li>
    1000             <p>Under what conditions the header field can be used; e.g., only in responses or requests, in all messages, only on responses
    1001                to a particular request method.
    1002             </p>
    1003          </li>
    1004          <li>
    1005             <p>Whether it is appropriate to list the field-name in the Connection header (i.e., if the header is to be hop-by-hop, see <a href="p1-messaging.html#header.connection" title="Connection">Section 8.1</a> of <a href="#Part1" id="rfc.xref.Part1.21"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
    1006             </p>
    1007          </li>
    1008          <li>
    1009             <p>Under what conditions intermediaries are allowed to modify the header field's value, insert or delete it.</p>
    1010          </li>
    1011          <li>
    1012             <p>How the header might interact with caching (see <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
    1013             </p>
    1014          </li>
    1015          <li>
    1016             <p>Whether the header field is useful or allowable in trailers (see <a href="p1-messaging.html#chunked.encoding" title="Chunked Transfer Coding">Section 5.1</a> of <a href="#Part1" id="rfc.xref.Part1.22"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
    1017             </p>
    1018          </li>
    1019          <li>
    1020             <p>Whether the header field should be preserved across redirects.</p>
    1021          </li>
    1022       </ul>
    1023       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="request.header.fields" href="#request.header.fields">Request Header Fields</a></h2>
    1024       <p id="rfc.section.3.2.p.1">The request header fields allow the client to pass additional information about the request, and about the client itself,
    1025          to the server. These fields act as request modifiers, with semantics equivalent to the parameters on a programming language
    1026          method invocation.
    1027       </p>
    1028       <div id="rfc.table.u.2">
    1029          <table class="tt full left" cellpadding="3" cellspacing="0">
    1030             <thead>
    1031                <tr>
    1032                   <th>Header Field Name</th>
    1033                   <th>Defined in...</th>
    1034                </tr>
    1035             </thead>
    1036             <tbody>
    1037                <tr>
    1038                   <td class="left">Accept</td>
    1039                   <td class="left"><a href="p3-payload.html#header.accept" title="Accept">Section 6.1</a> of <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a></td>
    1040                </tr>
    1041                <tr>
    1042                   <td class="left">Accept-Charset</td>
    1043                   <td class="left"><a href="p3-payload.html#header.accept-charset" title="Accept-Charset">Section 6.2</a> of <a href="#Part3" id="rfc.xref.Part3.4"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a></td>
    1044                </tr>
    1045                <tr>
    1046                   <td class="left">Accept-Encoding</td>
    1047                   <td class="left"><a href="p3-payload.html#header.accept-encoding" title="Accept-Encoding">Section 6.3</a> of <a href="#Part3" id="rfc.xref.Part3.5"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a></td>
    1048                </tr>
    1049                <tr>
    1050                   <td class="left">Accept-Language</td>
    1051                   <td class="left"><a href="p3-payload.html#header.accept-language" title="Accept-Language">Section 6.4</a> of <a href="#Part3" id="rfc.xref.Part3.6"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a></td>
    1052                </tr>
    1053                <tr>
    1054                   <td class="left">Authorization</td>
    1055                   <td class="left"><a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.1"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a></td>
    1056                </tr>
    1057                <tr>
    1058                   <td class="left">Expect</td>
    1059                   <td class="left"><a href="#header.expect" id="rfc.xref.header.expect.1" title="Expect">Section&nbsp;10.3</a></td>
    1060                </tr>
    1061                <tr>
    1062                   <td class="left">From</td>
    1063                   <td class="left"><a href="#header.from" id="rfc.xref.header.from.1" title="From">Section&nbsp;10.4</a></td>
    1064                </tr>
    1065                <tr>
    1066                   <td class="left">Host</td>
    1067                   <td class="left"><a href="p1-messaging.html#header.host" title="Host">Section 8.2</a> of <a href="#Part1" id="rfc.xref.Part1.23"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a></td>
    1068                </tr>
    1069                <tr>
    1070                   <td class="left">If-Match</td>
    1071                   <td class="left"><a href="p4-conditional.html#header.if-match" title="If-Match">Section 3.1</a> of <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
    1072                </tr>
    1073                <tr>
    1074                   <td class="left">If-Modified-Since</td>
    1075                   <td class="left"><a href="p4-conditional.html#header.if-modified-since" title="If-Modified-Since">Section 3.3</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
    1076                </tr>
    1077                <tr>
    1078                   <td class="left">If-None-Match</td>
    1079                   <td class="left"><a href="p4-conditional.html#header.if-none-match" title="If-None-Match">Section 3.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
    1080                </tr>
    1081                <tr>
    1082                   <td class="left">If-Range</td>
    1083                   <td class="left"><a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a></td>
    1084                </tr>
    1085                <tr>
    1086                   <td class="left">If-Unmodified-Since</td>
    1087                   <td class="left"><a href="p4-conditional.html#header.if-unmodified-since" title="If-Unmodified-Since">Section 3.4</a> of <a href="#Part4" id="rfc.xref.Part4.4"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
    1088                </tr>
    1089                <tr>
    1090                   <td class="left">Max-Forwards</td>
    1091                   <td class="left"><a href="#header.max-forwards" id="rfc.xref.header.max-forwards.1" title="Max-Forwards">Section&nbsp;10.6</a></td>
    1092                </tr>
    1093                <tr>
    1094                   <td class="left">Proxy-Authorization</td>
    1095                   <td class="left"><a href="p7-auth.html#header.proxy-authorization" title="Proxy-Authorization">Section 4.3</a> of <a href="#Part7" id="rfc.xref.Part7.2"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a></td>
    1096                </tr>
    1097                <tr>
    1098                   <td class="left">Range</td>
    1099                   <td class="left"><a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a></td>
    1100                </tr>
    1101                <tr>
    1102                   <td class="left">Referer</td>
    1103                   <td class="left"><a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section&nbsp;10.7</a></td>
    1104                </tr>
    1105                <tr>
    1106                   <td class="left">TE</td>
    1107                   <td class="left"><a href="p1-messaging.html#header.te" title="TE">Section 5.4</a> of <a href="#Part1" id="rfc.xref.Part1.24"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a></td>
    1108                </tr>
    1109                <tr>
    1110                   <td class="left">User-Agent</td>
    1111                   <td class="left"><a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section&nbsp;10.10</a></td>
    1112                </tr>
    1113             </tbody>
    1114          </table>
    1115       </div>
    1116       <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a id="response.header.fields" href="#response.header.fields">Response Header Fields</a></h2>
    1117       <p id="rfc.section.3.3.p.1">The response header fields allow the server to pass additional information about the response which cannot be placed in the
    1118          Status-Line. These header fields give information about the server and about further access to the target resource (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.25"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
    1119       </p>
    1120       <div id="rfc.table.u.3">
    1121          <table class="tt full left" cellpadding="3" cellspacing="0">
    1122             <thead>
    1123                <tr>
    1124                   <th>Header Field Name</th>
    1125                   <th>Defined in...</th>
    1126                </tr>
    1127             </thead>
    1128             <tbody>
    1129                <tr>
    1130                   <td class="left">Accept-Ranges</td>
    1131                   <td class="left"><a href="p5-range.html#header.accept-ranges" title="Accept-Ranges">Section 5.1</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a></td>
    1132                </tr>
    1133                <tr>
    1134                   <td class="left">Age</td>
    1135                   <td class="left"><a href="p6-cache.html#header.age" title="Age">Section 3.1</a> of <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a></td>
    1136                </tr>
    1137                <tr>
    1138                   <td class="left">Allow</td>
    1139                   <td class="left"><a href="#header.allow" id="rfc.xref.header.allow.2" title="Allow">Section&nbsp;10.1</a></td>
    1140                </tr>
    1141                <tr>
    1142                   <td class="left">Date</td>
    1143                   <td class="left"><a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section&nbsp;10.2</a></td>
    1144                </tr>
    1145                <tr>
    1146                   <td class="left">ETag</td>
    1147                   <td class="left"><a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
    1148                </tr>
    1149                <tr>
    1150                   <td class="left">Location</td>
    1151                   <td class="left"><a href="#header.location" id="rfc.xref.header.location.1" title="Location">Section&nbsp;10.5</a></td>
    1152                </tr>
    1153                <tr>
    1154                   <td class="left">Proxy-Authenticate</td>
    1155                   <td class="left"><a href="p7-auth.html#header.proxy-authenticate" title="Proxy-Authenticate">Section 4.2</a> of <a href="#Part7" id="rfc.xref.Part7.3"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a></td>
    1156                </tr>
    1157                <tr>
    1158                   <td class="left">Retry-After</td>
    1159                   <td class="left"><a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section&nbsp;10.8</a></td>
    1160                </tr>
    1161                <tr>
    1162                   <td class="left">Server</td>
    1163                   <td class="left"><a href="#header.server" id="rfc.xref.header.server.1" title="Server">Section&nbsp;10.9</a></td>
    1164                </tr>
    1165                <tr>
    1166                   <td class="left">Vary</td>
    1167                   <td class="left"><a href="p6-cache.html#header.vary" title="Vary">Section 3.5</a> of <a href="#Part6" id="rfc.xref.Part6.4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a></td>
    1168                </tr>
    1169                <tr>
    1170                   <td class="left">WWW-Authenticate</td>
    1171                   <td class="left"><a href="p7-auth.html#header.www-authenticate" title="WWW-Authenticate">Section 4.4</a> of <a href="#Part7" id="rfc.xref.Part7.4"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a></td>
    1172                </tr>
    1173             </tbody>
    1174          </table>
    1175       </div>
    1176       <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="status.code.and.reason.phrase" href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h1>
    1177       <p id="rfc.section.4.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request.</p>
    1178       <p id="rfc.section.4.p.2">The Reason-Phrase is intended to give a short textual description of the Status-Code and is intended for a human user. The
    1179          client does not need to examine or display the Reason-Phrase.
    1180       </p>
    1181       <div id="rfc.figure.u.5"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span>  <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a>    = 3<a href="#notation" class="smpl">DIGIT</a>
    1182   <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a>  = *( <a href="#notation" class="smpl">HTAB</a> / <a href="#notation" class="smpl">SP</a> / <a href="#notation" class="smpl">VCHAR</a> / <a href="#core.rules" class="smpl">obs-text</a> )
    1183 </pre><p id="rfc.section.4.p.4">HTTP status codes are extensible. HTTP applications are not required to understand the meaning of all registered status codes,
    1184          though such understanding is obviously desirable. However, applications <em class="bcp14">MUST</em> understand the class of any status code, as indicated by the first digit, and treat any unrecognized response as being equivalent
    1185          to the x00 status code of that class, with the exception that an unrecognized response <em class="bcp14">MUST NOT</em> be cached. For example, if an unrecognized status code of 431 is received by the client, it can safely assume that there was
    1186          something wrong with its request and treat the response as if it had received a 400 status code. In such cases, user agents <em class="bcp14">SHOULD</em> present to the user the representation enclosed with the response, since that representation is likely to include human-readable
    1187          information which will explain the unusual status.
    1188       </p>
    1189       <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="overview.of.status.codes" href="#overview.of.status.codes">Overview of Status Codes</a></h2>
    1190       <p id="rfc.section.4.1.p.1">The status codes listed below are defined in <a href="#status.codes" title="Status Code Definitions">Section&nbsp;7</a> of this specification, <a href="p4-conditional.html#status.code.definitions" title="Status Code Definitions">Section 4</a> of <a href="#Part4" id="rfc.xref.Part4.6"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p5-range.html#status.code.definitions" title="Status Code Definitions">Section 3</a> of <a href="#Part5" id="rfc.xref.Part5.4"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>, and <a href="p7-auth.html#status.code.definitions" title="Status Code Definitions">Section 3</a> of <a href="#Part7" id="rfc.xref.Part7.5"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>. The reason phrases listed here are only recommendations — they can be replaced by local equivalents without affecting the
    1191          protocol.
    1192       </p>
    1193       <div id="rfc.table.u.4">
    1194          <table class="tt full left" cellpadding="3" cellspacing="0">
    1195             <thead>
    1196                <tr>
    1197                   <th>Status-Code</th>
    1198                   <th>Reason-Phrase</th>
    1199                   <th>Defined in...</th>
    1200                </tr>
    1201             </thead>
    1202             <tbody>
    1203                <tr>
    1204                   <td class="left">100</td>
    1205                   <td class="left">Continue</td>
    1206                   <td class="left"><a href="#status.100" id="rfc.xref.status.100.1" title="100 Continue">Section&nbsp;7.1.1</a></td>
    1207                </tr>
    1208                <tr>
    1209                   <td class="left">101</td>
    1210                   <td class="left">Switching Protocols</td>
    1211                   <td class="left"><a href="#status.101" id="rfc.xref.status.101.1" title="101 Switching Protocols">Section&nbsp;7.1.2</a></td>
    1212                </tr>
    1213                <tr>
    1214                   <td class="left">200</td>
    1215                   <td class="left">OK</td>
    1216                   <td class="left"><a href="#status.200" id="rfc.xref.status.200.1" title="200 OK">Section&nbsp;7.2.1</a></td>
    1217                </tr>
    1218                <tr>
    1219                   <td class="left">201</td>
    1220                   <td class="left">Created</td>
    1221                   <td class="left"><a href="#status.201" id="rfc.xref.status.201.1" title="201 Created">Section&nbsp;7.2.2</a></td>
    1222                </tr>
    1223                <tr>
    1224                   <td class="left">202</td>
    1225                   <td class="left">Accepted</td>
    1226                   <td class="left"><a href="#status.202" id="rfc.xref.status.202.1" title="202 Accepted">Section&nbsp;7.2.3</a></td>
    1227                </tr>
    1228                <tr>
    1229                   <td class="left">203</td>
    1230                   <td class="left">Non-Authoritative Information</td>
    1231                   <td class="left"><a href="#status.203" id="rfc.xref.status.203.1" title="203 Non-Authoritative Information">Section&nbsp;7.2.4</a></td>
    1232                </tr>
    1233                <tr>
    1234                   <td class="left">204</td>
    1235                   <td class="left">No Content</td>
    1236                   <td class="left"><a href="#status.204" id="rfc.xref.status.204.1" title="204 No Content">Section&nbsp;7.2.5</a></td>
    1237                </tr>
    1238                <tr>
    1239                   <td class="left">205</td>
    1240                   <td class="left">Reset Content</td>
    1241                   <td class="left"><a href="#status.205" id="rfc.xref.status.205.1" title="205 Reset Content">Section&nbsp;7.2.6</a></td>
    1242                </tr>
    1243                <tr>
    1244                   <td class="left">206</td>
    1245                   <td class="left">Partial Content</td>
    1246                   <td id="status.206" class="left"><a href="p5-range.html#status.206" title="206 Partial Content">Section 3.1</a> of <a href="#Part5" id="rfc.xref.Part5.5"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a></td>
    1247                </tr>
    1248                <tr>
    1249                   <td class="left">300</td>
    1250                   <td class="left">Multiple Choices</td>
    1251                   <td class="left"><a href="#status.300" id="rfc.xref.status.300.1" title="300 Multiple Choices">Section&nbsp;7.3.1</a></td>
    1252                </tr>
    1253                <tr>
    1254                   <td class="left">301</td>
    1255                   <td class="left">Moved Permanently</td>
    1256                   <td class="left"><a href="#status.301" id="rfc.xref.status.301.1" title="301 Moved Permanently">Section&nbsp;7.3.2</a></td>
    1257                </tr>
    1258                <tr>
    1259                   <td class="left">302</td>
    1260                   <td class="left">Found</td>
    1261                   <td class="left"><a href="#status.302" id="rfc.xref.status.302.1" title="302 Found">Section&nbsp;7.3.3</a></td>
    1262                </tr>
    1263                <tr>
    1264                   <td class="left">303</td>
    1265                   <td class="left">See Other</td>
    1266                   <td class="left"><a href="#status.303" id="rfc.xref.status.303.1" title="303 See Other">Section&nbsp;7.3.4</a></td>
    1267                </tr>
    1268                <tr>
    1269                   <td class="left">304</td>
    1270                   <td class="left">Not Modified</td>
    1271                   <td id="status.304" class="left"><a href="p4-conditional.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#Part4" id="rfc.xref.Part4.7"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
    1272                </tr>
    1273                <tr>
    1274                   <td class="left">305</td>
    1275                   <td class="left">Use Proxy</td>
    1276                   <td class="left"><a href="#status.305" id="rfc.xref.status.305.1" title="305 Use Proxy">Section&nbsp;7.3.5</a></td>
    1277                </tr>
    1278                <tr>
    1279                   <td class="left">307</td>
    1280                   <td class="left">Temporary Redirect</td>
    1281                   <td class="left"><a href="#status.307" id="rfc.xref.status.307.1" title="307 Temporary Redirect">Section&nbsp;7.3.7</a></td>
    1282                </tr>
    1283                <tr>
    1284                   <td class="left">400</td>
    1285                   <td class="left">Bad Request</td>
    1286                   <td class="left"><a href="#status.400" id="rfc.xref.status.400.1" title="400 Bad Request">Section&nbsp;7.4.1</a></td>
    1287                </tr>
    1288                <tr>
    1289                   <td class="left">401</td>
    1290                   <td class="left">Unauthorized</td>
    1291                   <td id="status.401" class="left"><a href="p7-auth.html#status.401" title="401 Unauthorized">Section 3.1</a> of <a href="#Part7" id="rfc.xref.Part7.6"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a></td>
    1292                </tr>
    1293                <tr>
    1294                   <td class="left">402</td>
    1295                   <td class="left">Payment Required</td>
    1296                   <td class="left"><a href="#status.402" id="rfc.xref.status.402.1" title="402 Payment Required">Section&nbsp;7.4.2</a></td>
    1297                </tr>
    1298                <tr>
    1299                   <td class="left">403</td>
    1300                   <td class="left">Forbidden</td>
    1301                   <td class="left"><a href="#status.403" id="rfc.xref.status.403.1" title="403 Forbidden">Section&nbsp;7.4.3</a></td>
    1302                </tr>
    1303                <tr>
    1304                   <td class="left">404</td>
    1305                   <td class="left">Not Found</td>
    1306                   <td class="left"><a href="#status.404" id="rfc.xref.status.404.1" title="404 Not Found">Section&nbsp;7.4.4</a></td>
    1307                </tr>
    1308                <tr>
    1309                   <td class="left">405</td>
    1310                   <td class="left">Method Not Allowed</td>
    1311                   <td class="left"><a href="#status.405" id="rfc.xref.status.405.1" title="405 Method Not Allowed">Section&nbsp;7.4.5</a></td>
    1312                </tr>
    1313                <tr>
    1314                   <td class="left">406</td>
    1315                   <td class="left">Not Acceptable</td>
    1316                   <td class="left"><a href="#status.406" id="rfc.xref.status.406.1" title="406 Not Acceptable">Section&nbsp;7.4.6</a></td>
    1317                </tr>
    1318                <tr>
    1319                   <td class="left">407</td>
    1320                   <td class="left">Proxy Authentication Required</td>
    1321                   <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="#Part7" id="rfc.xref.Part7.7"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a></td>
    1322                </tr>
    1323                <tr>
    1324                   <td class="left">408</td>
    1325                   <td class="left">Request Time-out</td>
    1326                   <td class="left"><a href="#status.408" id="rfc.xref.status.408.1" title="408 Request Timeout">Section&nbsp;7.4.7</a></td>
    1327                </tr>
    1328                <tr>
    1329                   <td class="left">409</td>
    1330                   <td class="left">Conflict</td>
    1331                   <td class="left"><a href="#status.409" id="rfc.xref.status.409.1" title="409 Conflict">Section&nbsp;7.4.8</a></td>
    1332                </tr>
    1333                <tr>
    1334                   <td class="left">410</td>
    1335                   <td class="left">Gone</td>
    1336                   <td class="left"><a href="#status.410" id="rfc.xref.status.410.1" title="410 Gone">Section&nbsp;7.4.9</a></td>
    1337                </tr>
    1338                <tr>
    1339                   <td class="left">411</td>
    1340                   <td class="left">Length Required</td>
    1341                   <td class="left"><a href="#status.411" id="rfc.xref.status.411.1" title="411 Length Required">Section&nbsp;7.4.10</a></td>
    1342                </tr>
    1343                <tr>
    1344                   <td class="left">412</td>
    1345                   <td class="left">Precondition Failed</td>
    1346                   <td id="status.412" class="left"><a href="p4-conditional.html#status.412" title="412 Precondition Failed">Section 4.2</a> of <a href="#Part4" id="rfc.xref.Part4.8"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
    1347                </tr>
    1348                <tr>
    1349                   <td class="left">413</td>
    1350                   <td class="left">Request Representation Too Large</td>
    1351                   <td class="left"><a href="#status.413" id="rfc.xref.status.413.1" title="413 Request Representation Too Large">Section&nbsp;7.4.11</a></td>
    1352                </tr>
    1353                <tr>
    1354                   <td class="left">414</td>
    1355                   <td class="left">URI Too Long</td>
    1356                   <td class="left"><a href="#status.414" id="rfc.xref.status.414.1" title="414 URI Too Long">Section&nbsp;7.4.12</a></td>
    1357                </tr>
    1358                <tr>
    1359                   <td class="left">415</td>
    1360                   <td class="left">Unsupported Media Type</td>
    1361                   <td class="left"><a href="#status.415" id="rfc.xref.status.415.1" title="415 Unsupported Media Type">Section&nbsp;7.4.13</a></td>
    1362                </tr>
    1363                <tr>
    1364                   <td class="left">416</td>
    1365                   <td class="left">Requested range not satisfiable</td>
    1366                   <td id="status.416" class="left"><a href="p5-range.html#status.416" title="416 Requested Range Not Satisfiable">Section 3.2</a> of <a href="#Part5" id="rfc.xref.Part5.6"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a></td>
    1367                </tr>
    1368                <tr>
    1369                   <td class="left">417</td>
    1370                   <td class="left">Expectation Failed</td>
    1371                   <td class="left"><a href="#status.417" id="rfc.xref.status.417.1" title="417 Expectation Failed">Section&nbsp;7.4.14</a></td>
    1372                </tr>
    1373                <tr>
    1374                   <td class="left">426</td>
    1375                   <td class="left">Upgrade Required</td>
    1376                   <td class="left"><a href="#status.426" id="rfc.xref.status.426.1" title="426 Upgrade Required">Section&nbsp;7.4.15</a></td>
    1377                </tr>
    1378                <tr>
    1379                   <td class="left">500</td>
    1380                   <td class="left">Internal Server Error</td>
    1381                   <td class="left"><a href="#status.500" id="rfc.xref.status.500.1" title="500 Internal Server Error">Section&nbsp;7.5.1</a></td>
    1382                </tr>
    1383                <tr>
    1384                   <td class="left">501</td>
    1385                   <td class="left">Not Implemented</td>
    1386                   <td class="left"><a href="#status.501" id="rfc.xref.status.501.1" title="501 Not Implemented">Section&nbsp;7.5.2</a></td>
    1387                </tr>
    1388                <tr>
    1389                   <td class="left">502</td>
    1390                   <td class="left">Bad Gateway</td>
    1391                   <td class="left"><a href="#status.502" id="rfc.xref.status.502.1" title="502 Bad Gateway">Section&nbsp;7.5.3</a></td>
    1392                </tr>
    1393                <tr>
    1394                   <td class="left">503</td>
    1395                   <td class="left">Service Unavailable</td>
    1396                   <td class="left"><a href="#status.503" id="rfc.xref.status.503.1" title="503 Service Unavailable">Section&nbsp;7.5.4</a></td>
    1397                </tr>
    1398                <tr>
    1399                   <td class="left">504</td>
    1400                   <td class="left">Gateway Time-out</td>
    1401                   <td class="left"><a href="#status.504" id="rfc.xref.status.504.1" title="504 Gateway Timeout">Section&nbsp;7.5.5</a></td>
    1402                </tr>
    1403                <tr>
    1404                   <td class="left">505</td>
    1405                   <td class="left">HTTP Version not supported</td>
    1406                   <td class="left"><a href="#status.505" id="rfc.xref.status.505.1" title="505 HTTP Version Not Supported">Section&nbsp;7.5.6</a></td>
    1407                </tr>
    1408             </tbody>
    1409          </table>
    1410       </div>
    1411       <p id="rfc.section.4.1.p.2">Note that this list is not exhaustive — it does not include extension status codes defined in other specifications.</p>
    1412       <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="status.code.registry" href="#status.code.registry">Status Code Registry</a></h2>
    1413       <p id="rfc.section.4.2.p.1">The HTTP Status Code Registry defines the name space for the Status-Code token in the Status-Line of an HTTP response.</p>
    1414       <p id="rfc.section.4.2.p.2">Values to be added to this name space are subject to IETF review (<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>).
    1415       </p>
    1416       <p id="rfc.section.4.2.p.3">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>&gt;.
    1417       </p>
    1418       <h3 id="rfc.section.4.2.1"><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;<a id="considerations.for.new.status.codes" href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></h3>
    1419       <p id="rfc.section.4.2.1.p.1">When it is necessary to express new semantics for a HTTP response that aren't specific to a single application or media type,
    1420          and currently defined status codes are inadequate, a new status code can be registered.
    1421       </p>
    1422       <p id="rfc.section.4.2.1.p.2">HTTP status codes are generic; that is, they are potentially applicable to any resource, not just one particular media type,
    1423          "type" of resource, or application. As such, it is preferred that new HTTP status codes be registered in a document that isn't
    1424          specific to a single application, so that this is clear.
    1425       </p>
    1426       <p id="rfc.section.4.2.1.p.3">Definitions of new HTTP status codes typically explain the request conditions that produce a response containing the status
    1427          code (e.g., combinations of request headers and/or method(s)), along with any interactions with response headers (e.g., those
    1428          that are required, those that modify the semantics of the response).
    1429       </p>
    1430       <p id="rfc.section.4.2.1.p.4">New HTTP status codes are required to fall under one of the categories defined in <a href="#status.codes" title="Status Code Definitions">Section&nbsp;7</a>. To allow existing parsers to properly handle them, new status codes cannot disallow a response body, although they can mandate
    1431          a zero-length response body. They can require the presence of one or more particular HTTP response header(s).
    1432       </p>
    1433       <p id="rfc.section.4.2.1.p.5">Likewise, their definitions can specify that caches are allowed to use heuristics to determine their freshness (see <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>; by default, it is not allowed), and can define how to determine the resource which they carry a representation for (see <a href="#identifying.response.associated.with.representation" title="Identifying the Resource Associated with a Representation">Section&nbsp;5.1</a>; by default, it is anonymous).
    1434       </p>
    1435       <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="representation" href="#representation">Representation</a></h1>
    1436       <p id="rfc.section.5.p.1">Request and Response messages <em class="bcp14">MAY</em> transfer a representation if not otherwise restricted by the request method or response status code. A representation consists
    1437          of metadata (representation header fields) and data (representation body). When a complete or partial representation is enclosed
    1438          in an HTTP message, it is referred to as the payload of the message. HTTP representations are defined in <a href="#Part3" id="rfc.xref.Part3.7"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
    1439       </p>
    1440       <p id="rfc.section.5.p.2">A representation body is only present in a message when a message body is present, as described in <a href="p1-messaging.html#message.body" title="Message Body">Section 3.3</a> of <a href="#Part1" id="rfc.xref.Part1.26"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. The representation body is obtained from the message body by decoding any Transfer-Encoding that might have been applied
    1441          to ensure safe and proper transfer of the message.
    1442       </p>
    1443       <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="identifying.response.associated.with.representation" href="#identifying.response.associated.with.representation">Identifying the Resource Associated with a Representation</a></h2>
    1444       <p id="rfc.section.5.1.p.1">It is sometimes necessary to determine an identifier for the resource associated with a representation.</p>
    1445       <p id="rfc.section.5.1.p.2">An HTTP request representation, when present, is always associated with an anonymous (i.e., unidentified) resource.</p>
    1446       <p id="rfc.section.5.1.p.3">In the common case, an HTTP response is a representation of the target resource (see <a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.27"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). However, this is not always the case. To determine the URI of the resource a response is associated with, the following
    1447          rules are used (with the first applicable one being selected):
    1448       </p>
    1449       <ol>
    1450          <li>If the response status code is 200 or 203 and the request method was GET, the response payload is a representation of the
    1451             target resource.
    1452          </li>
    1453          <li>If the response status code is 204, 206, or 304 and the request method was GET or HEAD, the response payload is a partial
    1454             representation of the target resource.
    1455          </li>
    1456          <li>If the response has a Content-Location header field, and that URI is the same as the effective request URI, the response payload
    1457             is a representation of the target resource.
    1458          </li>
    1459          <li>If the response has a Content-Location header field, and that URI is not the same as the effective request URI, then the response
    1460             asserts that its payload is a representation of the resource identified by the Content-Location URI. However, such an assertion
    1461             cannot be trusted unless it can be verified by other means (not defined by HTTP).
    1462          </li>
    1463          <li>Otherwise, the response is a representation of an anonymous (i.e., unidentified) resource.</li>
    1464       </ol>
    1465       <p id="rfc.section.5.1.p.5"> <span class="comment" id="TODO-req-uri">[<a href="#TODO-req-uri" class="smpl">TODO-req-uri</a>: The comparison function is going to have to be defined somewhere, because we already need to compare URIs for things like
    1466             cache invalidation.]</span>
    1467       </p>
    1468       <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="method.definitions" href="#method.definitions">Method Definitions</a></h1>
    1469       <p id="rfc.section.6.p.1">The set of common request methods for HTTP/1.1 is defined below. Although this set can be expanded, additional methods cannot
    1470          be assumed to share the same semantics for separately extended clients and servers.
    1471       </p>
    1472       <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="safe.and.idempotent" href="#safe.and.idempotent">Safe and Idempotent Methods</a></h2>
    1473       <div id="rfc.iref.s.1"></div>
    1474       <h3 id="rfc.section.6.1.1"><a href="#rfc.section.6.1.1">6.1.1</a>&nbsp;<a id="safe.methods" href="#safe.methods">Safe Methods</a></h3>
    1475       <p id="rfc.section.6.1.1.p.1">Implementors need to be aware that the software represents the user in their interactions over the Internet, and need to allow
    1476          the user to be aware of any actions they take which might have an unexpected significance to themselves or others.
    1477       </p>
    1478       <p id="rfc.section.6.1.1.p.2">In particular, the convention has been established that the GET, HEAD, OPTIONS, and TRACE request methods <em class="bcp14">SHOULD NOT</em> have the significance of taking an action other than retrieval. These request methods ought to be considered "<dfn id="safe">safe</dfn>". This allows user agents to represent other methods, such as POST, PUT and DELETE, in a special way, so that the user is
    1479          made aware of the fact that a possibly unsafe action is being requested.
    1480       </p>
    1481       <p id="rfc.section.6.1.1.p.3">Naturally, it is not possible to ensure that the server does not generate side-effects as a result of performing a GET request;
    1482          in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the
    1483          side-effects, so therefore cannot be held accountable for them.
    1484       </p>
    1485       <div id="rfc.iref.i.1"></div>
    1486       <h3 id="rfc.section.6.1.2"><a href="#rfc.section.6.1.2">6.1.2</a>&nbsp;<a id="idempotent.methods" href="#idempotent.methods">Idempotent Methods</a></h3>
    1487       <p id="rfc.section.6.1.2.p.1">Request methods can also have the property of "idempotence" in that, aside from error or expiration issues, the intended effect
    1488          of multiple identical requests is the same as for a single request. PUT, DELETE, and all safe request methods are idempotent.
    1489          It is important to note that idempotence refers only to changes requested by the client: a server is free to change its state
    1490          due to multiple requests for the purpose of tracking those requests, versioning of results, etc.
    1491       </p>
    1492       <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a id="OPTIONS" href="#OPTIONS">OPTIONS</a></h2>
    1493       <div id="rfc.iref.o.1"></div>
    1494       <div id="rfc.iref.m.1"></div>
    1495       <p id="rfc.section.6.2.p.1">The OPTIONS method requests information about the communication options available on the request/response chain identified
    1496          by the effective request URI. This method allows a client to determine the options and/or requirements associated with a resource,
    1497          or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
    1498       </p>
    1499       <p id="rfc.section.6.2.p.2">Responses to the OPTIONS method are not cacheable.</p>
    1500       <p id="rfc.section.6.2.p.3">If the OPTIONS request includes a message body (as indicated by the presence of Content-Length or Transfer-Encoding), then
    1501          the media type <em class="bcp14">MUST</em> be indicated by a Content-Type field. Although this specification does not define any use for such a body, future extensions
    1502          to HTTP might use the OPTIONS body to make more detailed queries on the server.
    1503       </p>
    1504       <p id="rfc.section.6.2.p.4">If the request-target is an asterisk ("*"), the OPTIONS request is intended to apply to the server in general rather than
    1505          to a specific resource. Since a server's communication options typically depend on the resource, the "*" request is only useful
    1506          as a "ping" or "no-op" type of method; it does nothing beyond allowing the client to test the capabilities of the server.
    1507          For example, this can be used to test a proxy for HTTP/1.1 conformance (or lack thereof).
    1508       </p>
    1509       <p id="rfc.section.6.2.p.5">If the request-target is not an asterisk, the OPTIONS request applies only to the options that are available when communicating
    1510          with that resource.
    1511       </p>
    1512       <p id="rfc.section.6.2.p.6">A 200 response <em class="bcp14">SHOULD</em> include any header fields that indicate optional features implemented by the server and applicable to that resource (e.g.,
    1513          Allow), possibly including extensions not defined by this specification. The response body, if any, <em class="bcp14">SHOULD</em> also include information about the communication options. The format for such a body is not defined by this specification,
    1514          but might be defined by future extensions to HTTP. Content negotiation <em class="bcp14">MAY</em> be used to select the appropriate response format. If no response body is included, the response <em class="bcp14">MUST</em> include a Content-Length field with a field-value of "0".
    1515       </p>
    1516       <p id="rfc.section.6.2.p.7">The Max-Forwards header field <em class="bcp14">MAY</em> be used to target a specific proxy in the request chain (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.2" title="Max-Forwards">Section&nbsp;10.6</a>). If no Max-Forwards field is present in the request, then the forwarded request <em class="bcp14">MUST NOT</em> include a Max-Forwards field.
    1517       </p>
    1518       <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a id="GET" href="#GET">GET</a></h2>
    1519       <div id="rfc.iref.g.5"></div>
    1520       <div id="rfc.iref.m.2"></div>
    1521       <p id="rfc.section.6.3.p.1">The GET method requests transfer of a current representation of the target resource.</p>
    1522       <p id="rfc.section.6.3.p.2">If the target resource is a data-producing process, it is the produced data which shall be returned as the representation
    1523          in the response and not the source text of the process, unless that text happens to be the output of the process.
    1524       </p>
    1525       <p id="rfc.section.6.3.p.3">The semantics of the GET method change to a "conditional GET" if the request message includes an If-Modified-Since, If-Unmodified-Since,
    1526          If-Match, If-None-Match, or If-Range header field. A conditional GET requests that the representation be transferred only
    1527          under the circumstances described by the conditional header field(s). The conditional GET request is intended to reduce unnecessary
    1528          network usage by allowing cached representations to be refreshed without requiring multiple requests or transferring data
    1529          already held by the client.
    1530       </p>
    1531       <p id="rfc.section.6.3.p.4">The semantics of the GET method change to a "partial GET" if the request message includes a Range header field. A partial
    1532          GET requests that only part of the representation be transferred, as described in <a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.7"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. The partial GET request is intended to reduce unnecessary network usage by allowing partially-retrieved representations
    1533          to be completed without transferring data already held by the client.
    1534       </p>
    1535       <p id="rfc.section.6.3.p.5">Bodies on GET requests have no defined semantics. Note that sending a body on a GET request might cause some existing implementations
    1536          to reject the request.
    1537       </p>
    1538       <p id="rfc.section.6.3.p.6">The response to a GET request is cacheable and <em class="bcp14">MAY</em> be used to satisfy subsequent GET and HEAD requests (see <a href="#Part6" id="rfc.xref.Part6.6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
    1539       </p>
    1540       <p id="rfc.section.6.3.p.7">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URIs">Section&nbsp;12.2</a> for security considerations when used for forms.
    1541       </p>
    1542       <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a id="HEAD" href="#HEAD">HEAD</a></h2>
    1543       <div id="rfc.iref.h.1"></div>
    1544       <div id="rfc.iref.m.3"></div>
    1545       <p id="rfc.section.6.4.p.1">The HEAD method is identical to GET except that the server <em class="bcp14">MUST NOT</em> return a message body in the response. The metadata contained in the HTTP header fields in response to a HEAD request <em class="bcp14">SHOULD</em> be identical to the information sent in response to a GET request. This method can be used for obtaining metadata about the
    1546          representation implied by the request without transferring the representation body. This method is often used for testing
    1547          hypertext links for validity, accessibility, and recent modification.
    1548       </p>
    1549       <p id="rfc.section.6.4.p.2">The response to a HEAD request is cacheable and <em class="bcp14">MAY</em> be used to satisfy a subsequent HEAD request; see <a href="#Part6" id="rfc.xref.Part6.7"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. It also <em class="bcp14">MAY</em> be used to update a previously cached representation from that resource; if the new field values indicate that the cached
    1550          representation differs from the current representation (as would be indicated by a change in Content-Length, ETag or Last-Modified),
    1551          then the cache <em class="bcp14">MUST</em> treat the cache entry as stale.
    1552       </p>
    1553       <p id="rfc.section.6.4.p.3">Bodies on HEAD requests have no defined semantics. Note that sending a body on a HEAD request might cause some existing implementations
    1554          to reject the request.
    1555       </p>
    1556       <div id="rfc.iref.p.1"></div>
    1557       <div id="rfc.iref.m.4"></div>
    1558       <h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a>&nbsp;<a id="POST" href="#POST">POST</a></h2>
    1559       <p id="rfc.section.6.5.p.1">The POST method requests that the origin server accept the representation enclosed in the request as data to be processed
    1560          by the target resource. POST is designed to allow a uniform method to cover the following functions:
    1561       </p>
    1562       <ul>
    1563          <li>Annotation of existing resources;</li>
    1564          <li>Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles;</li>
    1565          <li>Providing a block of data, such as the result of submitting a form, to a data-handling process;</li>
    1566          <li>Extending a database through an append operation.</li>
    1567       </ul>
    1568       <p id="rfc.section.6.5.p.2">The actual function performed by the POST method is determined by the server and is usually dependent on the effective request
    1569          URI.
    1570       </p>
    1571       <p id="rfc.section.6.5.p.3">The action performed by the POST method might not result in a resource that can be identified by a URI. In this case, either
    1572          200 (OK) or 204 (No Content) is the appropriate response status code, depending on whether or not the response includes a
    1573          representation that describes the result.
    1574       </p>
    1575       <p id="rfc.section.6.5.p.4">If a resource has been created on the origin server, the response <em class="bcp14">SHOULD</em> be 201 (Created) and contain a representation which describes the status of the request and refers to the new resource, and
    1576          a Location header field (see <a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;10.5</a>).
    1577       </p>
    1578       <p id="rfc.section.6.5.p.5">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 2.3.1</a> of <a href="#Part6" id="rfc.xref.Part6.8"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). A cached POST response with a Content-Location header field (see <a href="p3-payload.html#header.content-location" title="Content-Location">Section 6.7</a> of <a href="#Part3" id="rfc.xref.Part3.8"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) whose value is the effective Request URI <em class="bcp14">MAY</em> be used to satisfy subsequent GET and HEAD requests.
    1579       </p>
    1580       <p id="rfc.section.6.5.p.6">Note that POST caching is not widely implemented. However, the 303 (See Other) response can be used to direct the user agent
    1581          to retrieve a cacheable resource.
    1582       </p>
    1583       <div id="rfc.iref.p.2"></div>
    1584       <div id="rfc.iref.m.5"></div>
    1585       <h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a>&nbsp;<a id="PUT" href="#PUT">PUT</a></h2>
    1586       <p id="rfc.section.6.6.p.1">The PUT method requests that the state of the target resource be created or replaced with the state defined by the representation
    1587          enclosed in the request message payload. A successful PUT of a given representation would suggest that a subsequent GET on
    1588          that same target resource will result in an equivalent representation being returned in a 200 (OK) response. However, there
    1589          is no guarantee that such a state change will be observable, since the target resource might be acted upon by other user agents
    1590          in parallel, or might be subject to dynamic processing by the origin server, before any subsequent GET is received. A successful
    1591          response only implies that the user agent's intent was achieved at the time of its processing by the origin server.
    1592       </p>
    1593       <p id="rfc.section.6.6.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 201 (Created) response. If the target resource does have a current representation and that
    1594          representation is successfully modified in accordance with the state of the enclosed representation, then either a 200 (OK)
    1595          or 204 (No Content) response <em class="bcp14">SHOULD</em> be sent to indicate successful completion of the request.
    1596       </p>
    1597       <p id="rfc.section.6.6.p.3">Unrecognized header fields <em class="bcp14">SHOULD</em> be ignored (i.e., not saved as part of the resource state).
    1598       </p>
    1599       <p id="rfc.section.6.6.p.4">An origin server <em class="bcp14">SHOULD</em> verify that the PUT representation is consistent with any constraints which the server has for the target resource that cannot
    1600          or will not be changed by the PUT. This is particularly important when the origin server uses internal configuration information
    1601          related to the URI in order to set the values for representation metadata on GET responses. When a PUT representation is inconsistent
    1602          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
    1603          appropriate error message containing sufficient information to explain why the representation is unsuitable. The 409 (Conflict)
    1604          or 415 (Unsupported Media Type) status codes are suggested, with the latter being specific to constraints on Content-Type
    1605          values.
    1606       </p>
    1607       <p id="rfc.section.6.6.p.5">For example, if the target resource is configured to always have a Content-Type of "text/html" and the representation being
    1608          PUT has a Content-Type of "image/jpeg", then the origin server <em class="bcp14">SHOULD</em> do one of: (a) reconfigure the target resource to reflect the new media type; (b) transform the PUT representation to a format
    1609          consistent with that of the resource before saving it as the new resource state; or, (c) reject the request with a 415 response
    1610          indicating that the target resource is limited to "text/html", perhaps including a link to a different resource that would
    1611          be a suitable target for the new representation.
    1612       </p>
    1613       <p id="rfc.section.6.6.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
    1614          of the user agent request and the semantics of the origin server response. It does not define what a resource might be, in
    1615          any sense of that word, beyond the interface provided via HTTP. It does not define how resource state is "stored", nor how
    1616          such storage might change as a result of a change in resource state, nor how the origin server translates resource state into
    1617          representations. Generally speaking, all implementation details behind the resource interface are intentionally hidden by
    1618          the server.
    1619       </p>
    1620       <p id="rfc.section.6.6.p.7">The fundamental difference between the POST and PUT methods is highlighted by the different intent for the target resource.
    1621          The target resource in a POST request is intended to handle the enclosed representation as a data-accepting process, such
    1622          as for a gateway to some other protocol or a document that accepts annotations. In contrast, the target resource in a PUT
    1623          request is intended to take the enclosed representation as a new or replacement value. Hence, the intent of PUT is idempotent
    1624          and visible to intermediaries, even though the exact effect is only known by the origin server.
    1625       </p>
    1626       <p id="rfc.section.6.6.p.8">Proper interpretation of a PUT request presumes that the user agent knows what target resource is desired. A service that
    1627          is intended to select 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
    1628          the target resource and instead wishes to have it applied to a different resource, such as when the resource has been moved
    1629          to a different URI, then the origin server <em class="bcp14">MUST</em> send a 301 (Moved Permanently) response; the user agent <em class="bcp14">MAY</em> then make its own decision regarding whether or not to redirect the request.
    1630       </p>
    1631       <p id="rfc.section.6.6.p.9">A PUT request applied to the target resource <em class="bcp14">MAY</em> have side-effects on other resources. For example, an article might have a URI for identifying "the current version" (a resource)
    1632          which is separate from the URIs identifying each particular version (different resources that at one point shared the same
    1633          state as the current version resource). A successful PUT request on "the current version" URI might therefore create a new
    1634          version resource in addition to changing the state of the target resource, and might also cause links to be added between
    1635          the related resources.
    1636       </p>
    1637       <p id="rfc.section.6.6.p.10">An origin server <em class="bcp14">SHOULD</em> reject any PUT request that contains a Content-Range header field, since it might be misinterpreted as partial content (or
    1638          might be partial content that is being mistakenly PUT as a full representation). Partial content updates are possible by targeting
    1639          a separately identified resource with state that overlaps a portion of the larger resource, or by using a different method
    1640          that has been specifically defined for partial updates (for example, the PATCH method defined in <a href="#RFC5789" id="rfc.xref.RFC5789.1"><cite title="PATCH Method for HTTP">[RFC5789]</cite></a>).
    1641       </p>
    1642       <p id="rfc.section.6.6.p.11">Responses to the PUT method are not cacheable. If a PUT request passes through a cache that has one or more stored responses
    1643          for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 2.5</a> of <a href="#Part6" id="rfc.xref.Part6.9"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
    1644       </p>
    1645       <div id="rfc.iref.d.1"></div>
    1646       <div id="rfc.iref.m.6"></div>
    1647       <h2 id="rfc.section.6.7"><a href="#rfc.section.6.7">6.7</a>&nbsp;<a id="DELETE" href="#DELETE">DELETE</a></h2>
    1648       <p id="rfc.section.6.7.p.1">The DELETE method requests that the origin server delete the target resource. This method <em class="bcp14">MAY</em> be overridden by human intervention (or other means) on the origin server. The client cannot be guaranteed that the operation
    1649          has been carried out, even if the status code returned from the origin server indicates that the action has been completed
    1650          successfully. However, the server <em class="bcp14">SHOULD NOT</em> indicate success unless, at the time the response is given, it intends to delete the resource or move it to an inaccessible
    1651          location.
    1652       </p>
    1653       <p id="rfc.section.6.7.p.2">A successful response <em class="bcp14">SHOULD</em> be 200 (OK) if the response includes an representation describing the status, 202 (Accepted) if the action has not yet been
    1654          enacted, or 204 (No Content) if the action has been enacted but the response does not include a representation.
    1655       </p>
    1656       <p id="rfc.section.6.7.p.3">Bodies on DELETE requests have no defined semantics. Note that sending a body on a DELETE request might cause some existing
    1657          implementations to reject the request.
    1658       </p>
    1659       <p id="rfc.section.6.7.p.4">Responses to the DELETE method are not cacheable. If a DELETE request passes through a cache that has one or more stored responses
    1660          for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 2.5</a> of <a href="#Part6" id="rfc.xref.Part6.10"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
    1661       </p>
    1662       <h2 id="rfc.section.6.8"><a href="#rfc.section.6.8">6.8</a>&nbsp;<a id="TRACE" href="#TRACE">TRACE</a></h2>
    1663       <div id="rfc.iref.t.1"></div>
    1664       <div id="rfc.iref.m.7"></div>
    1665       <p id="rfc.section.6.8.p.1">The TRACE method requests a remote, application-layer loop-back of the request message. The final recipient of the request <em class="bcp14">SHOULD</em> reflect the message received back to the client as the message body of a 200 (OK) response. The final recipient is either
    1666          the origin server or the first proxy to receive a Max-Forwards value of zero (0) in the request (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.3" title="Max-Forwards">Section&nbsp;10.6</a>). A TRACE request <em class="bcp14">MUST NOT</em> include a message body.
    1667       </p>
    1668       <p id="rfc.section.6.8.p.2">TRACE allows the client to see what is being received at the other end of the request chain and use that data for testing
    1669          or diagnostic information. The value of the Via header field (<a href="p1-messaging.html#header.via" title="Via">Section 8.4</a> of <a href="#Part1" id="rfc.xref.Part1.28"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) is of particular interest, since it acts as a trace of the request chain. Use of the Max-Forwards header field allows the
    1670          client to limit the length of the request chain, which is useful for testing a chain of proxies forwarding messages in an
    1671          infinite loop.
    1672       </p>
    1673       <p id="rfc.section.6.8.p.3">If the request is valid, the response <em class="bcp14">SHOULD</em> have a Content-Type of "message/http" (see <a href="p1-messaging.html#internet.media.type.message.http" title="Internet Media Type message/http">Section 9.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.29"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) and contain a message body that encloses a copy of the entire request message. Responses to the TRACE method are not cacheable.
    1674       </p>
    1675       <div id="rfc.iref.c.1"></div>
    1676       <div id="rfc.iref.m.8"></div>
    1677       <h2 id="rfc.section.6.9"><a href="#rfc.section.6.9">6.9</a>&nbsp;<a id="CONNECT" href="#CONNECT">CONNECT</a></h2>
    1678       <p id="rfc.section.6.9.p.1">The CONNECT method requests that the proxy establish a tunnel to the request-target and then restrict its behavior to blind
    1679          forwarding of packets until the connection is closed.
    1680       </p>
    1681       <p id="rfc.section.6.9.p.2">When using CONNECT, the request-target <em class="bcp14">MUST</em> use the authority form (<a href="p1-messaging.html#request-target" title="request-target">Section 3.1.1.2</a> of <a href="#Part1" id="rfc.xref.Part1.30"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>); i.e., the request-target consists of only the host name and port number of the tunnel destination, separated by a colon.
    1682          For example,
    1683       </p>
    1684       <div id="rfc.figure.u.6"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.1
    1685 Host: server.example.com:80
    1686 
    1687 </pre><p id="rfc.section.6.9.p.4">Other HTTP mechanisms can be used normally with the CONNECT method — except end-to-end protocol Upgrade requests, since the
    1688          tunnel must be established first.
    1689       </p>
    1690       <p id="rfc.section.6.9.p.5">For example, proxy authentication might be used to establish the authority to create a tunnel:</p>
    1691       <div id="rfc.figure.u.7"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.1
    1692 Host: server.example.com:80
    1693 Proxy-Authorization: basic aGVsbG86d29ybGQ=
    1694 
    1695 </pre><p id="rfc.section.6.9.p.7">Bodies on CONNECT requests have no defined semantics. Note that sending a body on a CONNECT request might cause some existing
    1696          implementations to reject the request.
    1697       </p>
    1698       <p id="rfc.section.6.9.p.8">Like any other pipelined HTTP/1.1 request, data to be tunnel may be sent immediately after the blank line. The usual caveats
    1699          also apply: data may be discarded if the eventual response is negative, and the connection may be reset with no response if
    1700          more than one TCP segment is outstanding.
    1701       </p>
    1702       <h3 id="rfc.section.6.9.1"><a href="#rfc.section.6.9.1">6.9.1</a>&nbsp;Establishing a Tunnel with CONNECT
    1703       </h3>
    1704       <p id="rfc.section.6.9.1.p.1">Any successful (2xx) response to a CONNECT request indicates that the proxy has established a connection to the requested
    1705          host and port, and has switched to tunneling the current connection to that server connection.
    1706       </p>
    1707       <p id="rfc.section.6.9.1.p.2">It may be the case that the proxy itself can only reach the requested origin server through another proxy. In this case, the
    1708          first proxy <em class="bcp14">SHOULD</em> make a CONNECT request of that next proxy, requesting a tunnel to the authority. A proxy <em class="bcp14">MUST NOT</em> respond with any 2xx status code unless it has either a direct or tunnel connection established to the authority.
    1709       </p>
    1710       <p id="rfc.section.6.9.1.p.3">An origin server which receives a CONNECT request for itself <em class="bcp14">MAY</em> respond with a 2xx status code to indicate that a connection is established.
    1711       </p>
    1712       <p id="rfc.section.6.9.1.p.4">If at any point either one of the peers gets disconnected, any outstanding data that came from that peer will be passed to
    1713          the other one, and after that also the other connection will be terminated by the proxy. If there is outstanding data to that
    1714          peer undelivered, that data will be discarded.
    1715       </p>
    1716       <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="status.codes" href="#status.codes">Status Code Definitions</a></h1>
    1717       <p id="rfc.section.7.p.1">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role.
    1718          There are 5 values for the first digit:
    1719       </p>
    1720       <ul>
    1721          <li>1xx: Informational - Request received, continuing process</li>
    1722          <li>2xx: Success - The action was successfully received, understood, and accepted</li>
    1723          <li>3xx: Redirection - Further action must be taken in order to complete the request</li>
    1724          <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li>
    1725          <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li>
    1726       </ul>
    1727       <p id="rfc.section.7.p.2">Each Status-Code is described below, including any metadata required in the response.</p>
    1728       <p id="rfc.section.7.p.3">For most status codes the response can carry a payload, in which case a Content-Type header field indicates the payload's
    1729          media type (<a href="p3-payload.html#header.content-type" title="Content-Type">Section 6.8</a> of <a href="#Part3" id="rfc.xref.Part3.9"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>).
    1730       </p>
    1731       <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="status.1xx" href="#status.1xx">Informational 1xx</a></h2>
    1732       <p id="rfc.section.7.1.p.1">This class of status code indicates a provisional response, consisting only of the Status-Line and optional header fields,
    1733          and is terminated by an empty line. There are no required header fields for this class of status code. Since HTTP/1.0 did
    1734          not define any 1xx status codes, servers <em class="bcp14">MUST NOT</em> send a 1xx response to an HTTP/1.0 client except under experimental conditions.
    1735       </p>
    1736       <p id="rfc.section.7.1.p.2">A client <em class="bcp14">MUST</em> be prepared to accept one or more 1xx status responses prior to a regular response, even if the client does not expect a 100
    1737          (Continue) status message. Unexpected 1xx status responses <em class="bcp14">MAY</em> be ignored by a user agent.
    1738       </p>
    1739       <p id="rfc.section.7.1.p.3">Proxies <em class="bcp14">MUST</em> forward 1xx responses, unless the connection between the proxy and its client has been closed, or unless the proxy itself
    1740          requested the generation of the 1xx response. (For example, if a proxy adds a "Expect: 100-continue" field when it forwards
    1741          a request, then it need not forward the corresponding 100 (Continue) response(s).)
    1742       </p>
    1743       <div id="rfc.iref.22"></div>
    1744       <div id="rfc.iref.s.2"></div>
    1745       <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a id="status.100" href="#status.100">100 Continue</a></h3>
    1746       <p id="rfc.section.7.1.1.p.1">The client <em class="bcp14">SHOULD</em> continue with its request. This interim response is used to inform the client that the initial part of the request has been
    1747          received and has not yet been rejected by the server. The client <em class="bcp14">SHOULD</em> continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The
    1748          server <em class="bcp14">MUST</em> send a final response after the request has been completed. See <a href="p1-messaging.html#use.of.the.100.status" title="Use of the 100 (Continue) Status">Section 6.2.3</a> of <a href="#Part1" id="rfc.xref.Part1.31"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for detailed discussion of the use and handling of this status code.
    1749       </p>
    1750       <div id="rfc.iref.23"></div>
    1751       <div id="rfc.iref.s.3"></div>
    1752       <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;<a id="status.101" href="#status.101">101 Switching Protocols</a></h3>
    1753       <p id="rfc.section.7.1.2.p.1">The server understands and is willing to comply with the client's request, via the Upgrade message header field (<a href="p1-messaging.html#header.upgrade" title="Upgrade">Section 8.3</a> of <a href="#Part1" id="rfc.xref.Part1.32"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>), for a change in the application protocol being used on this connection. The server will switch protocols to those defined
    1754          by the response's Upgrade header field immediately after the empty line which terminates the 101 response.
    1755       </p>
    1756       <p id="rfc.section.7.1.2.p.2">The protocol <em class="bcp14">SHOULD</em> be switched only when it is advantageous to do so. For example, switching to a newer version of HTTP is advantageous over
    1757          older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use
    1758          such features.
    1759       </p>
    1760       <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="status.2xx" href="#status.2xx">Successful 2xx</a></h2>
    1761       <p id="rfc.section.7.2.p.1">This class of status code indicates that the client's request was successfully received, understood, and accepted.</p>
    1762       <div id="rfc.iref.24"></div>
    1763       <div id="rfc.iref.s.4"></div>
    1764       <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a id="status.200" href="#status.200">200 OK</a></h3>
    1765       <p id="rfc.section.7.2.1.p.1">The request has succeeded. The payload returned with the response is dependent on the method used in the request, for example: </p>
    1766       <dl>
    1767          <dt>GET</dt>
    1768          <dd>a representation of the target resource is sent in the response;</dd>
    1769          <dt>HEAD</dt>
    1770          <dd>the same representation as GET, except without the message body;</dd>
    1771          <dt>POST</dt>
    1772          <dd>a representation describing or containing the result of the action;</dd>
    1773          <dt>TRACE</dt>
    1774          <dd>a representation containing the request message as received by the end server.</dd>
    1775       </dl>
    1776       <p id="rfc.section.7.2.1.p.2">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 2.3.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.11"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 200 responses.
    1777       </p>
    1778       <div id="rfc.iref.25"></div>
    1779       <div id="rfc.iref.s.5"></div>
    1780       <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a id="status.201" href="#status.201">201 Created</a></h3>
    1781       <p id="rfc.section.7.2.2.p.1">The request has been fulfilled and has resulted in a new resource being created. The newly created resource can be referenced
    1782          by the URI(s) returned in the payload of the response, with the most specific URI for the resource given by a Location header
    1783          field. The response can include a payload containing a list of resource characteristics and location(s) from which the user
    1784          or user agent can choose the one most appropriate.
    1785       </p>
    1786       <p id="rfc.section.7.2.2.p.2">The origin server <em class="bcp14">MUST</em> create the resource before returning the 201 status code. If the action cannot be carried out immediately, the server <em class="bcp14">SHOULD</em> respond with 202 (Accepted) response instead.
    1787       </p>
    1788       <p id="rfc.section.7.2.2.p.3">A 201 response <em class="bcp14">MAY</em> contain an ETag response header field indicating the current value of the entity-tag for the representation of the resource
    1789          just created (see <a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.9"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
    1790       </p>
    1791       <div id="rfc.iref.26"></div>
    1792       <div id="rfc.iref.s.6"></div>
    1793       <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;<a id="status.202" href="#status.202">202 Accepted</a></h3>
    1794       <p id="rfc.section.7.2.3.p.1">The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually
    1795          be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status
    1796          code from an asynchronous operation such as this.
    1797       </p>
    1798       <p id="rfc.section.7.2.3.p.2">The 202 response is intentionally non-committal. Its purpose is to allow a server to accept a request for some other process
    1799          (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the
    1800          server persist until the process is completed. The representation returned with this response <em class="bcp14">SHOULD</em> include an indication of the request's current status and either a pointer to a status monitor or some estimate of when the
    1801          user can expect the request to be fulfilled.
    1802       </p>
    1803       <div id="rfc.iref.27"></div>
    1804       <div id="rfc.iref.s.7"></div>
    1805       <h3 id="rfc.section.7.2.4"><a href="#rfc.section.7.2.4">7.2.4</a>&nbsp;<a id="status.203" href="#status.203">203 Non-Authoritative Information</a></h3>
    1806       <p id="rfc.section.7.2.4.p.1">The representation in the response has been transformed or otherwise modified by a transforming proxy (<a href="p1-messaging.html#intermediaries" title="Intermediaries">Section 2.3</a> of <a href="#Part1" id="rfc.xref.Part1.33"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). Note that the behavior of transforming intermediaries is controlled by the no-transform Cache-Control directive (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 3.2</a> of <a href="#Part6" id="rfc.xref.Part6.12"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
    1807       </p>
    1808       <p id="rfc.section.7.2.4.p.2">This status code is only appropriate when the response status code would have been 200 (OK) otherwise. When the status code
    1809          before transformation would have been different, the 214 Transformation Applied warn-code (<a href="p6-cache.html#header.warning" title="Warning">Section 3.6</a> of <a href="#Part6" id="rfc.xref.Part6.13"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) is appropriate.
    1810       </p>
    1811       <p id="rfc.section.7.2.4.p.3">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 2.3.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.14"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 203 responses.
    1812       </p>
    1813       <div id="rfc.iref.28"></div>
    1814       <div id="rfc.iref.s.8"></div>
    1815       <h3 id="rfc.section.7.2.5"><a href="#rfc.section.7.2.5">7.2.5</a>&nbsp;<a id="status.204" href="#status.204">204 No Content</a></h3>
    1816       <p id="rfc.section.7.2.5.p.1">The 204 (No Content) status code indicates that the server has successfully fulfilled the request and that there is no additional
    1817          content to return in the response payload body. Metadata in the response header fields refer to the target resource and its
    1818          current representation after the requested action.
    1819       </p>
    1820       <p id="rfc.section.7.2.5.p.2">For example, if a 204 status code is received in response to a PUT request and the response contains an ETag header field,
    1821          then the PUT was successful and the ETag field-value contains the entity-tag for the new representation of that target resource.
    1822       </p>
    1823       <p id="rfc.section.7.2.5.p.3">The 204 response allows a server to indicate that the action has been successfully applied to the target resource while implying
    1824          that the user agent <em class="bcp14">SHOULD NOT</em> traverse away from its current "document view" (if any). The server assumes that the user agent will provide some indication
    1825          of the success to its user, in accord with its own interface, and apply any new or updated metadata in the response to the
    1826          active representation.
    1827       </p>
    1828       <p id="rfc.section.7.2.5.p.4">For example, a 204 status code is commonly used with document editing interfaces corresponding to a "save" action, such that
    1829          the document being saved remains available to the user for editing. It is also frequently used with interfaces that expect
    1830          automated data transfers to be prevalent, such as within distributed version control systems.
    1831       </p>
    1832       <p id="rfc.section.7.2.5.p.5">The 204 response <em class="bcp14">MUST NOT</em> include a message body, and thus is always terminated by the first empty line after the header fields.
    1833       </p>
    1834       <div id="rfc.iref.29"></div>
    1835       <div id="rfc.iref.s.9"></div>
    1836       <h3 id="rfc.section.7.2.6"><a href="#rfc.section.7.2.6">7.2.6</a>&nbsp;<a id="status.205" href="#status.205">205 Reset Content</a></h3>
    1837       <p id="rfc.section.7.2.6.p.1">The server has fulfilled the request and the user agent <em class="bcp14">SHOULD</em> reset the document view which caused the request to be sent. This response is primarily intended to allow input for actions
    1838          to take place via user input, followed by a clearing of the form in which the input is given so that the user can easily initiate
    1839          another input action.
    1840       </p>
    1841       <p id="rfc.section.7.2.6.p.2">The message body included with the response <em class="bcp14">MUST</em> be empty. Note that receivers still need to parse the response according to the algorithm defined in <a href="p1-messaging.html#message.body" title="Message Body">Section 3.3</a> of <a href="#Part1" id="rfc.xref.Part1.34"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
    1842       </p>
    1843       <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a>&nbsp;<a id="status.3xx" href="#status.3xx">Redirection 3xx</a></h2>
    1844       <p id="rfc.section.7.3.p.1">This class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request.
    1845          If the required action involves a subsequent HTTP request, it <em class="bcp14">MAY</em> be carried out by the user agent without interaction with the user if and only if the method used in the second request is
    1846          known to be "safe", as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;6.1.1</a>.
    1847       </p>
    1848       <p id="rfc.section.7.3.p.2">There are several types of redirects: </p>
    1849       <ol>
    1850          <li>
    1851             <p>Redirects of the request to another URI, either temporarily or permanently. The new URI is specified in the Location header
    1852                field. In this specification, the status codes 301 (Moved Permanently), 302 (Found), and 307 (Temporary Redirect) fall under
    1853                this category.
    1854             </p>
    1855          </li>
    1856          <li>
    1857             <p>Redirection to a new location that represents an indirect response to the request, such as the result of a POST operation
    1858                to be retrieved with a subsequent GET request. This is status code 303 (See Other).
    1859             </p>
    1860          </li>
    1861          <li>
    1862             <p>Redirection offering a choice of matching resources for use by agent-driven content negotiation (<a href="p3-payload.html#agent-driven.negotiation" title="Agent-driven Negotiation">Section 5.2</a> of <a href="#Part3" id="rfc.xref.Part3.10"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>). This is status code 300 (Multiple Choices).
    1863             </p>
    1864          </li>
    1865          <li>
    1866             <p>Other kinds of redirection, such as to a cached result (status code 304 (Not Modified), see <a href="p4-conditional.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#Part4" id="rfc.xref.Part4.10"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
    1867             </p>
    1868          </li>
    1869       </ol>
    1870       <div class="note" id="rfc.section.7.3.p.3">
    1871          <p> <b>Note:</b> In HTTP/1.0, only the status codes 301 (Moved Permanently) and 302 (Found) were defined for the first type of redirect, and
    1872             the second type did not exist at all (<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>). However it turned out that web forms using POST expected redirects to change the operation for the subsequent request to
    1873             retrieval (GET). To address this use case, HTTP/1.1 introduced the second type of redirect with the status code 303 (See Other)
    1874             (<a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, <a href="http://tools.ietf.org/html/rfc2068#section-10.3.4">Section 10.3.4</a>). As user agents did not change their behavior to maintain backwards compatibility, the first revision of HTTP/1.1 added
    1875             yet another status code, 307 (Temporary Redirect), for which the backwards compatibility problems did not apply (<a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>, <a href="http://tools.ietf.org/html/rfc2616#section-10.3.8">Section 10.3.8</a>). Over 10 years later, most user agents still do method rewriting for status codes 301 and 302, therefore this specification
    1876             makes that behavior conformant in case the original request was POST.
    1877          </p>
    1878       </div>
    1879       <p id="rfc.section.7.3.p.4">A Location header field on a 3xx response indicates that a client <em class="bcp14">MAY</em> automatically redirect to the URI provided; see <a href="#header.location" id="rfc.xref.header.location.3" title="Location">Section&nbsp;10.5</a>.
    1880       </p>
    1881       <p id="rfc.section.7.3.p.5">Note that for methods not known to be "safe", as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;6.1.1</a>, automatic redirection needs to done with care, since the redirect might change the conditions under which the request was
    1882          issued.
    1883       </p>
    1884       <p id="rfc.section.7.3.p.6">Clients <em class="bcp14">SHOULD</em> detect and intervene in cyclical redirections (i.e., "infinite" redirection loops).
    1885       </p>
    1886       <div class="note" id="rfc.section.7.3.p.7">
    1887          <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.
    1888          </p>
    1889       </div>
    1890       <div id="rfc.iref.30"></div>
    1891       <div id="rfc.iref.s.10"></div>
    1892       <h3 id="rfc.section.7.3.1"><a href="#rfc.section.7.3.1">7.3.1</a>&nbsp;<a id="status.300" href="#status.300">300 Multiple Choices</a></h3>
    1893       <p id="rfc.section.7.3.1.p.1">The target resource has more than one representation, each with its own specific location, and agent-driven negotiation information
    1894          (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.11"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) is being provided so that the user (or user agent) can select a preferred representation by redirecting its request to that
    1895          location.
    1896       </p>
    1897       <p id="rfc.section.7.3.1.p.2">Unless it was a HEAD request, the response <em class="bcp14">SHOULD</em> include a representation containing a list of representation metadata and location(s) from which the user or user agent can
    1898          choose the one most appropriate. Depending upon the format and the capabilities of the user agent, selection of the most appropriate
    1899          choice <em class="bcp14">MAY</em> be performed automatically. However, this specification does not define any standard for such automatic selection.
    1900       </p>
    1901       <p id="rfc.section.7.3.1.p.3">If the server has a preferred choice of representation, it <em class="bcp14">SHOULD</em> include the specific URI for that representation in the Location field; user agents <em class="bcp14">MAY</em> use the Location field value for automatic redirection.
    1902       </p>
    1903       <p id="rfc.section.7.3.1.p.4">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 2.3.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.15"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 300 responses.
    1904       </p>
    1905       <div id="rfc.iref.31"></div>
    1906       <div id="rfc.iref.s.11"></div>
    1907       <h3 id="rfc.section.7.3.2"><a href="#rfc.section.7.3.2">7.3.2</a>&nbsp;<a id="status.301" href="#status.301">301 Moved Permanently</a></h3>
    1908       <p id="rfc.section.7.3.2.p.1">The target resource has been assigned a new permanent URI and any future references to this resource <em class="bcp14">SHOULD</em> use one of the returned URIs. Clients with link editing capabilities ought to automatically re-link references to the effective
    1909          request URI to one or more of the new references returned by the server, where possible.
    1910       </p>
    1911       <p id="rfc.section.7.3.2.p.2">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 2.3.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.16"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 301 responses.
    1912       </p>
    1913       <p id="rfc.section.7.3.2.p.3">The new permanent URI <em class="bcp14">SHOULD</em> be given by the Location field in the response. A response payload can contain a short hypertext note with a hyperlink to
    1914          the new URI(s).
    1915       </p>
    1916       <div class="note" id="rfc.section.7.3.2.p.4">
    1917          <p> <b>Note:</b> For historic reasons, user agents <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, status code 307 (Temporary
    1918             Redirect) can be used instead.
    1919          </p>
    1920       </div>
    1921       <div id="rfc.iref.32"></div>
    1922       <div id="rfc.iref.s.12"></div>
    1923       <h3 id="rfc.section.7.3.3"><a href="#rfc.section.7.3.3">7.3.3</a>&nbsp;<a id="status.302" href="#status.302">302 Found</a></h3>
    1924       <p id="rfc.section.7.3.3.p.1">The target resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client <em class="bcp14">SHOULD</em> continue to use the effective request URI for future requests.
    1925       </p>
    1926       <p id="rfc.section.7.3.3.p.2">The temporary URI <em class="bcp14">SHOULD</em> be given by the Location field in the response. A response payload can contain a short hypertext note with a hyperlink to
    1927          the new URI(s).
    1928       </p>
    1929       <div class="note" id="rfc.section.7.3.3.p.3">
    1930          <p> <b>Note:</b> For historic reasons, user agents <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, status code 307 (Temporary
    1931             Redirect) can be used instead.
    1932          </p>
    1933       </div>
    1934       <div id="rfc.iref.33"></div>
    1935       <div id="rfc.iref.s.13"></div>
    1936       <h3 id="rfc.section.7.3.4"><a href="#rfc.section.7.3.4">7.3.4</a>&nbsp;<a id="status.303" href="#status.303">303 See Other</a></h3>
    1937       <p id="rfc.section.7.3.4.p.1">The 303 status code indicates that the server is redirecting the user agent to a different resource, as indicated by a URI
    1938          in the Location header field, that is intended to provide an indirect response to the original request. In order to satisfy
    1939          the original request, a user agent <em class="bcp14">SHOULD</em> perform a retrieval request using the Location URI (a GET or HEAD request if using HTTP), which may itself be redirected further,
    1940          and present the eventual result as an answer to the original request. Note that the new URI in the Location header field is
    1941          not considered equivalent to the effective request URI.
    1942       </p>
    1943       <p id="rfc.section.7.3.4.p.2">This status code is generally applicable to any HTTP method. It is primarily used to allow the output of a POST action to
    1944          redirect the user agent to a selected resource, since doing so provides the information corresponding to the POST response
    1945          in a form that can be separately identified, bookmarked, and cached independent of the original request.
    1946       </p>
    1947       <p id="rfc.section.7.3.4.p.3">A 303 response to a GET request indicates that the requested resource does not have a representation of its own that can be
    1948          transferred by the server over HTTP. The Location URI indicates a resource that is descriptive of the target resource, such
    1949          that the follow-on representation might be useful to recipients without implying that it adequately represents the target
    1950          resource. Note that answers to the questions of what can be represented, what representations are adequate, and what might
    1951          be a useful description are outside the scope of HTTP and thus entirely determined by the URI owner(s).
    1952       </p>
    1953       <p id="rfc.section.7.3.4.p.4">Except for responses to a HEAD request, the representation of a 303 response <em class="bcp14">SHOULD</em> contain a short hypertext note with a hyperlink to the Location URI.
    1954       </p>
    1955       <div id="rfc.iref.34"></div>
    1956       <div id="rfc.iref.s.14"></div>
    1957       <h3 id="rfc.section.7.3.5"><a href="#rfc.section.7.3.5">7.3.5</a>&nbsp;<a id="status.305" href="#status.305">305 Use Proxy</a></h3>
    1958       <p id="rfc.section.7.3.5.p.1">The 305 status code was defined in a previous version of this specification (see <a href="#changes.from.rfc.2616" title="Changes from RFC 2616">Appendix&nbsp;A</a>), and is now deprecated.
    1959       </p>
    1960       <div id="rfc.iref.35"></div>
    1961       <div id="rfc.iref.s.15"></div>
    1962       <h3 id="rfc.section.7.3.6"><a href="#rfc.section.7.3.6">7.3.6</a>&nbsp;<a id="status.306" href="#status.306">306 (Unused)</a></h3>
    1963       <p id="rfc.section.7.3.6.p.1">The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.</p>
    1964       <div id="rfc.iref.36"></div>
    1965       <div id="rfc.iref.s.16"></div>
    1966       <h3 id="rfc.section.7.3.7"><a href="#rfc.section.7.3.7">7.3.7</a>&nbsp;<a id="status.307" href="#status.307">307 Temporary Redirect</a></h3>
    1967       <p id="rfc.section.7.3.7.p.1">The target resource resides temporarily under a different URI. Since the redirection can change over time, the client <em class="bcp14">SHOULD</em> continue to use the effective request URI for future requests.
    1968       </p>
    1969       <p id="rfc.section.7.3.7.p.2">The temporary URI <em class="bcp14">SHOULD</em> be given by the Location field in the response. A response payload can contain a short hypertext note with a hyperlink to
    1970          the new URI(s).
    1971       </p>
    1972       <div class="note" id="rfc.section.7.3.7.p.3">
    1973          <p> <b>Note:</b> This status code is similar to 302 Found, except that it does not allow rewriting the request method from POST to GET. This
    1974             specification defines no equivalent counterpart for 301 Moved Permanently.
    1975          </p>
    1976       </div>
    1977       <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a>&nbsp;<a id="status.4xx" href="#status.4xx">Client Error 4xx</a></h2>
    1978       <p id="rfc.section.7.4.p.1">The 4xx class of status code is intended for cases in which the client seems to have erred. Except when responding to a HEAD
    1979          request, the server <em class="bcp14">SHOULD</em> include a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition.
    1980          These status codes are applicable to any request method. User agents <em class="bcp14">SHOULD</em> display any included representation to the user.
    1981       </p>
    1982       <div id="rfc.iref.37"></div>
    1983       <div id="rfc.iref.s.17"></div>
    1984       <h3 id="rfc.section.7.4.1"><a href="#rfc.section.7.4.1">7.4.1</a>&nbsp;<a id="status.400" href="#status.400">400 Bad Request</a></h3>
    1985       <p id="rfc.section.7.4.1.p.1">The server cannot or will not process the request, due to a client error (e.g., malformed syntax).</p>
    1986       <div id="rfc.iref.38"></div>
    1987       <div id="rfc.iref.s.18"></div>
    1988       <h3 id="rfc.section.7.4.2"><a href="#rfc.section.7.4.2">7.4.2</a>&nbsp;<a id="status.402" href="#status.402">402 Payment Required</a></h3>
    1989       <p id="rfc.section.7.4.2.p.1">This code is reserved for future use.</p>
    1990       <div id="rfc.iref.39"></div>
    1991       <div id="rfc.iref.s.19"></div>
    1992       <h3 id="rfc.section.7.4.3"><a href="#rfc.section.7.4.3">7.4.3</a>&nbsp;<a id="status.403" href="#status.403">403 Forbidden</a></h3>
    1993       <p id="rfc.section.7.4.3.p.1">The server understood the request, but refuses to authorize it. Providing different user authentication credentials might
    1994          be successful, but any credentials that were provided in the request are insufficient. The request <em class="bcp14">SHOULD NOT</em> be repeated with the same credentials.
    1995       </p>
    1996       <p id="rfc.section.7.4.3.p.2">If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it <em class="bcp14">SHOULD</em> describe the reason for the refusal in the representation. If the server does not wish to make this information available
    1997          to the client, the status code 404 (Not Found) <em class="bcp14">MAY</em> be used instead.
    1998       </p>
    1999       <div id="rfc.iref.40"></div>
    2000       <div id="rfc.iref.s.20"></div>
    2001       <h3 id="rfc.section.7.4.4"><a href="#rfc.section.7.4.4">7.4.4</a>&nbsp;<a id="status.404" href="#status.404">404 Not Found</a></h3>
    2002       <p id="rfc.section.7.4.4.p.1">The server has not found anything matching the effective request URI. No indication is given of whether the condition is temporary
    2003          or permanent. The 410 (Gone) status code <em class="bcp14">SHOULD</em> be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable
    2004          and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request
    2005          has been refused, or when no other response is applicable.
    2006       </p>
    2007       <div id="rfc.iref.41"></div>
    2008       <div id="rfc.iref.s.21"></div>
    2009       <h3 id="rfc.section.7.4.5"><a href="#rfc.section.7.4.5">7.4.5</a>&nbsp;<a id="status.405" href="#status.405">405 Method Not Allowed</a></h3>
    2010       <p id="rfc.section.7.4.5.p.1">The method specified in the Request-Line is not allowed for the target resource. The response <em class="bcp14">MUST</em> include an Allow header field containing a list of valid methods for the requested resource.
    2011       </p>
    2012       <div id="rfc.iref.42"></div>
    2013       <div id="rfc.iref.s.22"></div>
    2014       <h3 id="rfc.section.7.4.6"><a href="#rfc.section.7.4.6">7.4.6</a>&nbsp;<a id="status.406" href="#status.406">406 Not Acceptable</a></h3>
    2015       <p id="rfc.section.7.4.6.p.1">The resource identified by the request is only capable of generating response representations which have content characteristics
    2016          not acceptable according to the Accept and Accept-* header fields sent in the request (see <a href="p3-payload.html#header.field.definitions" title="Header Field Definitions">Section 6</a> of <a href="#Part3" id="rfc.xref.Part3.12"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>).
    2017       </p>
    2018       <p id="rfc.section.7.4.6.p.2">Unless it was a HEAD request, the response <em class="bcp14">SHOULD</em> include a representation containing a list of available representation characteristics and location(s) from which the user
    2019          or user agent can choose the one most appropriate. Depending upon the format and the capabilities of the user agent, selection
    2020          of the most appropriate choice <em class="bcp14">MAY</em> be performed automatically. However, this specification does not define any standard for such automatic selection.
    2021       </p>
    2022       <div class="note" id="rfc.section.7.4.6.p.3">
    2023          <p> <b>Note:</b> HTTP/1.1 servers are allowed to return responses which are not acceptable according to the accept header fields sent in the
    2024             request. In some cases, this might even be preferable to sending a 406 response. User agents are encouraged to inspect the
    2025             header fields of an incoming response to determine if it is acceptable.
    2026          </p>
    2027       </div>
    2028       <p id="rfc.section.7.4.6.p.4">If the response could be unacceptable, a user agent <em class="bcp14">SHOULD</em> temporarily stop receipt of more data and query the user for a decision on further actions.
    2029       </p>
    2030       <div id="rfc.iref.43"></div>
    2031       <div id="rfc.iref.s.23"></div>
    2032       <h3 id="rfc.section.7.4.7"><a href="#rfc.section.7.4.7">7.4.7</a>&nbsp;<a id="status.408" href="#status.408">408 Request Timeout</a></h3>
    2033       <p id="rfc.section.7.4.7.p.1">The client did not produce a request within the time that the server was prepared to wait. The client <em class="bcp14">MAY</em> repeat the request without modifications at any later time.
    2034       </p>
    2035       <div id="rfc.iref.44"></div>
    2036       <div id="rfc.iref.s.24"></div>
    2037       <h3 id="rfc.section.7.4.8"><a href="#rfc.section.7.4.8">7.4.8</a>&nbsp;<a id="status.409" href="#status.409">409 Conflict</a></h3>
    2038       <p id="rfc.section.7.4.8.p.1">The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in
    2039          situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response
    2040          body <em class="bcp14">SHOULD</em> include enough information for the user to recognize the source of the conflict. Ideally, the response representation would
    2041          include enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.
    2042       </p>
    2043       <p id="rfc.section.7.4.8.p.2">Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the representation
    2044          being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might
    2045          use the 409 response to indicate that it can't complete the request. In this case, the response representation would likely
    2046          contain a list of the differences between the two versions.
    2047       </p>
    2048       <div id="rfc.iref.45"></div>
    2049       <div id="rfc.iref.s.25"></div>
    2050       <h3 id="rfc.section.7.4.9"><a href="#rfc.section.7.4.9">7.4.9</a>&nbsp;<a id="status.410" href="#status.410">410 Gone</a></h3>
    2051       <p id="rfc.section.7.4.9.p.1">The target resource is no longer available at the server and no forwarding address is known. This condition is expected to
    2052          be considered permanent. Clients with link editing capabilities <em class="bcp14">SHOULD</em> delete references to the effective request URI after user approval. If the server does not know, or has no facility to determine,
    2053          whether or not the condition is permanent, the status code 404 (Not Found) <em class="bcp14">SHOULD</em> be used instead.
    2054       </p>
    2055       <p id="rfc.section.7.4.9.p.2">The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource
    2056          is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event
    2057          is common for limited-time, promotional services and for resources belonging to individuals no longer working at the server's
    2058          site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time
    2059          — that is left to the discretion of the server owner.
    2060       </p>
    2061       <p id="rfc.section.7.4.9.p.3">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 2.3.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.17"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 410 responses.
    2062       </p>
    2063       <div id="rfc.iref.46"></div>
    2064       <div id="rfc.iref.s.26"></div>
    2065       <h3 id="rfc.section.7.4.10"><a href="#rfc.section.7.4.10">7.4.10</a>&nbsp;<a id="status.411" href="#status.411">411 Length Required</a></h3>
    2066       <p id="rfc.section.7.4.10.p.1">The server refuses to accept the request without a defined Content-Length. 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
    2067          message.
    2068       </p>
    2069       <div id="rfc.iref.47"></div>
    2070       <div id="rfc.iref.s.27"></div>
    2071       <h3 id="rfc.section.7.4.11"><a href="#rfc.section.7.4.11">7.4.11</a>&nbsp;<a id="status.413" href="#status.413">413 Request Representation Too Large</a></h3>
    2072       <p id="rfc.section.7.4.11.p.1">The server is refusing to process a request because the request representation is larger than the server is willing or able
    2073          to process. The server <em class="bcp14">MAY</em> close the connection to prevent the client from continuing the request.
    2074       </p>
    2075       <p id="rfc.section.7.4.11.p.2">If the condition is temporary, the server <em class="bcp14">SHOULD</em> include a Retry-After header field to indicate that it is temporary and after what time the client <em class="bcp14">MAY</em> try again.
    2076       </p>
    2077       <div id="rfc.iref.48"></div>
    2078       <div id="rfc.iref.s.28"></div>
    2079       <h3 id="rfc.section.7.4.12"><a href="#rfc.section.7.4.12">7.4.12</a>&nbsp;<a id="status.414" href="#status.414">414 URI Too Long</a></h3>
    2080       <p id="rfc.section.7.4.12.p.1">The server is refusing to service the request because the effective request URI is longer than the server is willing to interpret.
    2081          This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long
    2082          query information, when the client has descended into a URI "black hole" of redirection (e.g., a redirected URI prefix that
    2083          points to a suffix of itself), or when the server is under attack by a client attempting to exploit security holes present
    2084          in some servers using fixed-length buffers for reading or manipulating the effective request URI.
    2085       </p>
    2086       <div id="rfc.iref.49"></div>
    2087       <div id="rfc.iref.s.29"></div>
    2088       <h3 id="rfc.section.7.4.13"><a href="#rfc.section.7.4.13">7.4.13</a>&nbsp;<a id="status.415" href="#status.415">415 Unsupported Media Type</a></h3>
    2089       <p id="rfc.section.7.4.13.p.1">The server is refusing to service the request because the request payload is in a format not supported by this request method
    2090          on the target resource.
    2091       </p>
    2092       <div id="rfc.iref.50"></div>
    2093       <div id="rfc.iref.s.30"></div>
    2094       <h3 id="rfc.section.7.4.14"><a href="#rfc.section.7.4.14">7.4.14</a>&nbsp;<a id="status.417" href="#status.417">417 Expectation Failed</a></h3>
    2095       <p id="rfc.section.7.4.14.p.1">The expectation given in an Expect header field (see <a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section&nbsp;10.3</a>) could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could
    2096          not be met by the next-hop server.
    2097       </p>
    2098       <div id="rfc.iref.51"></div>
    2099       <div id="rfc.iref.s.31"></div>
    2100       <h3 id="rfc.section.7.4.15"><a href="#rfc.section.7.4.15">7.4.15</a>&nbsp;<a id="status.426" href="#status.426">426 Upgrade Required</a></h3>
    2101       <p id="rfc.section.7.4.15.p.1">The request can not be completed without a prior protocol upgrade. This response <em class="bcp14">MUST</em> include an Upgrade header field (<a href="p1-messaging.html#header.upgrade" title="Upgrade">Section 8.3</a> of <a href="#Part1" id="rfc.xref.Part1.35"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) specifying the required protocols.
    2102       </p>
    2103       <div id="rfc.figure.u.8"></div>
    2104       <p>Example:</p>  <pre class="text">HTTP/1.1 426 Upgrade Required
    2105 Upgrade: HTTP/3.0
    2106 Connection: Upgrade
    2107 Content-Length: 53
    2108 Content-Type: text/plain
    2109 
    2110 <span id="s426body">This service requires use of the HTTP/3.0 protocol.
    2111 </span></pre><p id="rfc.section.7.4.15.p.3">The server <em class="bcp14">SHOULD</em> include a message body in the 426 response which indicates in human readable form the reason for the error and describes any
    2112          alternative courses which may be available to the user.
    2113       </p>
    2114       <h2 id="rfc.section.7.5"><a href="#rfc.section.7.5">7.5</a>&nbsp;<a id="status.5xx" href="#status.5xx">Server Error 5xx</a></h2>
    2115       <p id="rfc.section.7.5.p.1">Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has erred or is incapable
    2116          of performing the request. Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> include a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition.
    2117          User agents <em class="bcp14">SHOULD</em> display any included representation to the user. These response codes are applicable to any request method.
    2118       </p>
    2119       <div id="rfc.iref.52"></div>
    2120       <div id="rfc.iref.s.32"></div>
    2121       <h3 id="rfc.section.7.5.1"><a href="#rfc.section.7.5.1">7.5.1</a>&nbsp;<a id="status.500" href="#status.500">500 Internal Server Error</a></h3>
    2122       <p id="rfc.section.7.5.1.p.1">The server encountered an unexpected condition which prevented it from fulfilling the request.</p>
    2123       <div id="rfc.iref.53"></div>
    2124       <div id="rfc.iref.s.33"></div>
    2125       <h3 id="rfc.section.7.5.2"><a href="#rfc.section.7.5.2">7.5.2</a>&nbsp;<a id="status.501" href="#status.501">501 Not Implemented</a></h3>
    2126       <p id="rfc.section.7.5.2.p.1">The server does not support the functionality required to fulfill the request. This is the appropriate response when the server
    2127          does not recognize the request method and is not capable of supporting it for any resource.
    2128       </p>
    2129       <div id="rfc.iref.54"></div>
    2130       <div id="rfc.iref.s.34"></div>
    2131       <h3 id="rfc.section.7.5.3"><a href="#rfc.section.7.5.3">7.5.3</a>&nbsp;<a id="status.502" href="#status.502">502 Bad Gateway</a></h3>
    2132       <p id="rfc.section.7.5.3.p.1">The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting
    2133          to fulfill the request.
    2134       </p>
    2135       <div id="rfc.iref.55"></div>
    2136       <div id="rfc.iref.s.35"></div>
    2137       <h3 id="rfc.section.7.5.4"><a href="#rfc.section.7.5.4">7.5.4</a>&nbsp;<a id="status.503" href="#status.503">503 Service Unavailable</a></h3>
    2138       <p id="rfc.section.7.5.4.p.1">The server is currently unable to handle the request due to a temporary overloading or maintenance of the server.</p>
    2139       <p id="rfc.section.7.5.4.p.2">The implication is that this is a temporary condition which will be alleviated after some delay. If known, the length of the
    2140          delay <em class="bcp14">MAY</em> be indicated in a Retry-After header field (<a href="#header.retry-after" id="rfc.xref.header.retry-after.2" title="Retry-After">Section&nbsp;10.8</a>). If no Retry-After is given, the client <em class="bcp14">SHOULD</em> handle the response as it would for a 500 response.
    2141       </p>
    2142       <div class="note" id="rfc.section.7.5.4.p.3">
    2143          <p> <b>Note:</b> The existence of the 503 status code does not imply that a server must use it when becoming overloaded. Some servers might
    2144             wish to simply refuse the connection.
    2145          </p>
    2146       </div>
    2147       <div id="rfc.iref.56"></div>
    2148       <div id="rfc.iref.s.36"></div>
    2149       <h3 id="rfc.section.7.5.5"><a href="#rfc.section.7.5.5">7.5.5</a>&nbsp;<a id="status.504" href="#status.504">504 Gateway Timeout</a></h3>
    2150       <p id="rfc.section.7.5.5.p.1">The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server specified by the
    2151          URI (e.g., HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed to access in attempting to complete the request.
    2152       </p>
    2153       <div class="note" id="rfc.section.7.5.5.p.2">
    2154          <p> <b>Note</b> to implementors: some deployed proxies are known to return 400 or 500 when DNS lookups time out.
    2155          </p>
    2156       </div>
    2157       <div id="rfc.iref.57"></div>
    2158       <div id="rfc.iref.s.37"></div>
    2159       <h3 id="rfc.section.7.5.6"><a href="#rfc.section.7.5.6">7.5.6</a>&nbsp;<a id="status.505" href="#status.505">505 HTTP Version Not Supported</a></h3>
    2160       <p id="rfc.section.7.5.6.p.1">The server does not support, or refuses to support, the protocol version that was used in the request message. The server
    2161          is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described
    2162          in <a href="p1-messaging.html#http.version" title="Protocol Versioning">Section 2.6</a> of <a href="#Part1" id="rfc.xref.Part1.36"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, other than with this error message. The response <em class="bcp14">SHOULD</em> contain a representation describing why that version is not supported and what other protocols are supported by that server.
    2163       </p>
    2164       <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="http.date" href="#http.date">Date/Time Formats</a></h1>
    2165       <p id="rfc.section.8.p.1">HTTP applications have historically allowed three different formats for date/time stamps. However, the preferred format is
    2166          a fixed-length subset of that defined by <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a>:
    2167       </p>
    2168       <div id="rfc.figure.u.9"></div><pre class="text">Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
    2169 </pre><p id="rfc.section.8.p.3">The other formats are described here only for compatibility with obsolete implementations.</p>
    2170       <div id="rfc.figure.u.10"></div><pre class="text">Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
    2171 Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
    2172 </pre><p id="rfc.section.8.p.5">HTTP/1.1 clients and servers that parse a date value <em class="bcp14">MUST</em> accept all three formats (for compatibility with HTTP/1.0), though they <em class="bcp14">MUST</em> only generate the RFC 1123 format for representing HTTP-date values in header fields.
    2173       </p>
    2174       <p id="rfc.section.8.p.6">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated
    2175          Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for
    2176          time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional whitespace beyond that specifically included as SP in the grammar.
    2177       </p>
    2178       <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  <a href="#http.date" class="smpl">HTTP-date</a>    = <a href="#preferred.date.format" class="smpl">rfc1123-date</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a>
    2179 </pre><div id="preferred.date.format">
    2180          <p id="rfc.section.8.p.8">                    Preferred format:</p>
    2181       </div>
    2182       <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span>  <a href="#preferred.date.format" class="smpl">rfc1123-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#notation" class="smpl">SP</a> date1 <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    2183   ; fixed length subset of the format defined in
    2184   ; <a href="http://tools.ietf.org/html/rfc1123#section-5.2.14">Section 5.2.14</a> of <a href="#RFC1123" id="rfc.xref.RFC1123.2"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a>
    2185  
    2186   <a href="#preferred.date.format" class="smpl">day-name</a>     = %x4D.6F.6E ; "Mon", case-sensitive
    2187                / %x54.75.65 ; "Tue", case-sensitive
    2188                / %x57.65.64 ; "Wed", case-sensitive
    2189                / %x54.68.75 ; "Thu", case-sensitive
    2190                / %x46.72.69 ; "Fri", case-sensitive
    2191                / %x53.61.74 ; "Sat", case-sensitive
    2192                / %x53.75.6E ; "Sun", case-sensitive
    2193                
    2194   <a href="#obsolete.date.formats" class="smpl">date1</a>        = <a href="#preferred.date.format" class="smpl">day</a> <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">month</a> <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">year</a>
    2195                ; e.g., 02 Jun 1982
    2196 
    2197   <a href="#preferred.date.format" class="smpl">day</a>          = 2<a href="#notation" class="smpl">DIGIT</a>
    2198   <a href="#preferred.date.format" class="smpl">month</a>        = %x4A.61.6E ; "Jan", case-sensitive
    2199                / %x46.65.62 ; "Feb", case-sensitive
    2200                / %x4D.61.72 ; "Mar", case-sensitive
    2201                / %x41.70.72 ; "Apr", case-sensitive
    2202                / %x4D.61.79 ; "May", case-sensitive
    2203                / %x4A.75.6E ; "Jun", case-sensitive
    2204                / %x4A.75.6C ; "Jul", case-sensitive
    2205                / %x41.75.67 ; "Aug", case-sensitive
    2206                / %x53.65.70 ; "Sep", case-sensitive
    2207                / %x4F.63.74 ; "Oct", case-sensitive
    2208                / %x4E.6F.76 ; "Nov", case-sensitive
    2209                / %x44.65.63 ; "Dec", case-sensitive
    2210   <a href="#preferred.date.format" class="smpl">year</a>         = 4<a href="#notation" class="smpl">DIGIT</a>
    2211 
    2212   <a href="#preferred.date.format" class="smpl">GMT</a>   = %x47.4D.54 ; "GMT", case-sensitive
    2213 
    2214   <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>
    2215                  ; 00:00:00 - 23:59:59
    2216                  
    2217   <a href="#preferred.date.format" class="smpl">hour</a>         = 2<a href="#notation" class="smpl">DIGIT</a>               
    2218   <a href="#preferred.date.format" class="smpl">minute</a>       = 2<a href="#notation" class="smpl">DIGIT</a>               
    2219   <a href="#preferred.date.format" class="smpl">second</a>       = 2<a href="#notation" class="smpl">DIGIT</a>               
    2220 </pre><p id="rfc.section.8.p.10">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 RFC 5322 constructs with the corresponding name (<a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="http://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a>).
    2221       </p>
    2222       <div id="obsolete.date.formats">
    2223          <p id="rfc.section.8.p.11">                Obsolete formats:</p>
    2224       </div>
    2225       <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.19"></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>
    2226 </pre><div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.20"></span>  <a href="#obsolete.date.formats" class="smpl">rfc850-date</a>  = <a href="#obsolete.date.formats" class="smpl">day-name-l</a> "," <a href="#notation" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date2</a> <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    2227   <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="#notation" class="smpl">DIGIT</a>
    2228                  ; day-month-year (e.g., 02-Jun-82)
    2229 
    2230   <a href="#obsolete.date.formats" class="smpl">day-name-l</a>   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
    2231          / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
    2232          / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
    2233          / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
    2234          / %x46.72.69.64.61.79 ; "Friday", case-sensitive
    2235          / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
    2236          / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
    2237 </pre><div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.21"></span>  <a href="#obsolete.date.formats" class="smpl">asctime-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> <a href="#notation" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date3</a> <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#notation" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">year</a>
    2238   <a href="#obsolete.date.formats" class="smpl">date3</a>        = <a href="#preferred.date.format" class="smpl">month</a> <a href="#notation" class="smpl">SP</a> ( 2<a href="#notation" class="smpl">DIGIT</a> / ( <a href="#notation" class="smpl">SP</a> 1<a href="#notation" class="smpl">DIGIT</a> ))
    2239                  ; month day (e.g., Jun  2)
    2240 </pre><div class="note" id="rfc.section.8.p.15">
    2241          <p> <b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that might have been sent by non-HTTP applications,
    2242             as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
    2243          </p>
    2244       </div>
    2245       <div class="note" id="rfc.section.8.p.16">
    2246          <p> <b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers
    2247             are not required to use these formats for user presentation, request logging, etc.
    2248          </p>
    2249       </div>
    2250       <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="product.tokens" href="#product.tokens">Product Tokens</a></h1>
    2251       <p id="rfc.section.9.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
    2252          using product tokens also allow sub-products which form a significant part of the application to be listed, separated by whitespace.
    2253          By convention, the products are listed in order of their significance for identifying the application.
    2254       </p>
    2255       <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.22"></span><span id="rfc.iref.g.23"></span>  <a href="#product.tokens" class="smpl">product</a>         = <a href="#core.rules" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>]
    2256   <a href="#product.tokens" class="smpl">product-version</a> = <a href="#core.rules" class="smpl">token</a>
    2257 </pre><p id="rfc.section.9.p.3">Examples:</p>
    2258       <div id="rfc.figure.u.17"></div><pre class="text">  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
    2259   Server: Apache/0.8.4
    2260 </pre><p id="rfc.section.9.p.5">Product tokens <em class="bcp14">SHOULD</em> be short and to the point. They <em class="bcp14">MUST NOT</em> be used for advertising or other non-essential information. Although any token octet <em class="bcp14">MAY</em> appear in a product-version, this token <em class="bcp14">SHOULD</em> only be used for a version identifier (i.e., successive versions of the same product <em class="bcp14">SHOULD</em> only differ in the product-version portion of the product value).
    2261       </p>
    2262       <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1>
    2263       <p id="rfc.section.10.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to request and response semantics.</p>
    2264       <div id="rfc.iref.a.1"></div>
    2265       <div id="rfc.iref.h.2"></div>
    2266       <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a>&nbsp;<a id="header.allow" href="#header.allow">Allow</a></h2>
    2267       <p id="rfc.section.10.1.p.1">The "Allow" header field lists the set of methods advertised as supported by the target resource. The purpose of this field
    2268          is strictly to inform the recipient of valid request methods associated with the resource.
    2269       </p>
    2270       <div id="rfc.figure.u.18"></div><pre class="inline"><span id="rfc.iref.g.24"></span>  <a href="#header.allow" class="smpl">Allow</a> = #<a href="#method" class="smpl">Method</a>
    2271 </pre><p id="rfc.section.10.1.p.3">Example of use:</p>
    2272       <div id="rfc.figure.u.19"></div><pre class="text">  Allow: GET, HEAD, PUT
    2273 </pre><p id="rfc.section.10.1.p.5">The actual set of allowed methods is defined by the origin server at the time of each request.</p>
    2274       <p id="rfc.section.10.1.p.6">A proxy <em class="bcp14">MUST NOT</em> modify the Allow header field — it does not need to understand all the methods specified in order to handle them according
    2275          to the generic message handling rules.
    2276       </p>
    2277       <div id="rfc.iref.d.2"></div>
    2278       <div id="rfc.iref.h.3"></div>
    2279       <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a>&nbsp;<a id="header.date" href="#header.date">Date</a></h2>
    2280       <p id="rfc.section.10.2.p.1">The "Date" header field represents the date and time at which the message was originated, having the same semantics as the
    2281          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.RFC5322.2"><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;8</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format.
    2282       </p>
    2283       <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.25"></span>  <a href="#header.date" class="smpl">Date</a> = <a href="#http.date" class="smpl">HTTP-date</a>
    2284 </pre><p id="rfc.section.10.2.p.3">An example is</p>
    2285       <div id="rfc.figure.u.21"></div><pre class="text">  Date: Tue, 15 Nov 1994 08:12:31 GMT
    2286 </pre><p id="rfc.section.10.2.p.5">Origin servers <em class="bcp14">MUST</em> include a Date header field in all responses, except in these cases:
    2287       </p>
    2288       <ol>
    2289          <li>If the response status code is 100 (Continue) or 101 (Switching Protocols), the response <em class="bcp14">MAY</em> include a Date header field, at the server's option.
    2290          </li>
    2291          <li>If the response status code conveys a server error, e.g., 500 (Internal Server Error) or 503 (Service Unavailable), and it
    2292             is inconvenient or impossible to generate a valid Date.
    2293          </li>
    2294          <li>If the server does not have a clock that can provide a reasonable approximation of the current time, its responses <em class="bcp14">MUST NOT</em> include a Date header field.
    2295          </li>
    2296       </ol>
    2297       <p id="rfc.section.10.2.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient.
    2298       </p>
    2299       <p id="rfc.section.10.2.p.7">Clients can use the Date header field as well; in order to keep request messages small, they are advised not to include it
    2300          when it doesn't convey any useful information (as is usually the case for requests that do not contain a payload).
    2301       </p>
    2302       <p id="rfc.section.10.2.p.8">The HTTP-date sent in a Date header field <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means
    2303          of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the payload
    2304          is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic
    2305          value.
    2306       </p>
    2307       <div id="rfc.iref.e.1"></div>
    2308       <div id="rfc.iref.h.4"></div>
    2309       <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a>&nbsp;<a id="header.expect" href="#header.expect">Expect</a></h2>
    2310       <p id="rfc.section.10.3.p.1">The "Expect" header field is used to indicate that particular server behaviors are required by the client.</p>
    2311       <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span>  <a href="#header.expect" class="smpl">Expect</a>       = 1#<a href="#header.expect" class="smpl">expectation</a>
    2312  
    2313   <a href="#header.expect" class="smpl">expectation</a>  = <a href="#header.expect" class="smpl">expect-name</a> [ <a href="#core.rules" class="smpl">BWS</a> "=" <a href="#core.rules" class="smpl">BWS</a> <a href="#header.expect" class="smpl">expect-value</a> ]
    2314                              *( <a href="#core.rules" class="smpl">OWS</a> ";" [ <a href="#core.rules" class="smpl">OWS</a> <a href="#header.expect" class="smpl">expect-param</a> ] )
    2315   <a href="#header.expect" class="smpl">expect-param</a> = <a href="#header.expect" class="smpl">expect-name</a> [ <a href="#core.rules" class="smpl">BWS</a> "=" <a href="#core.rules" class="smpl">BWS</a> <a href="#header.expect" class="smpl">expect-value</a> ]
    2316  
    2317   <a href="#header.expect" class="smpl">expect-name</a>  = <a href="#core.rules" class="smpl">token</a>
    2318   <a href="#header.expect" class="smpl">expect-value</a> = <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a>
    2319 </pre><p id="rfc.section.10.3.p.3">If all received Expect header field(s) are syntactically valid but contain an expectation that the recipient does not understand
    2320          or cannot comply with, the recipient <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status code. A recipient of a syntactically invalid Expectation header field <em class="bcp14">MUST</em> respond with a 4xx status code other than 417.
    2321       </p>
    2322       <p id="rfc.section.10.3.p.4">The only expectation defined by this specification is:</p>
    2323       <p id="rfc.section.10.3.p.5"><span id="rfc.iref.89"></span><span id="rfc.iref.e.2"></span> 100-continue
    2324       </p>
    2325       <ul class="empty">
    2326          <li>The "100-continue" expectation is defined <a href="p1-messaging.html#use.of.the.100.status" title="Use of the 100 (Continue) Status">Section 6.2.3</a> of <a href="#Part1" id="rfc.xref.Part1.37"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. It does not support any expect-params.
    2327          </li>
    2328       </ul>
    2329       <p id="rfc.section.10.3.p.6">Comparison is case-insensitive for names (expect-name), and case-sensitive for values (expect-value).</p>
    2330       <p id="rfc.section.10.3.p.7">The Expect mechanism is hop-by-hop: the above requirements apply to any server, including proxies. However, the Expect header
    2331          field itself is end-to-end; it <em class="bcp14">MUST</em> be forwarded if the request is forwarded.
    2332       </p>
    2333       <p id="rfc.section.10.3.p.8">Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect header field.</p>
    2334       <div id="rfc.iref.f.1"></div>
    2335       <div id="rfc.iref.h.5"></div>
    2336       <h2 id="rfc.section.10.4"><a href="#rfc.section.10.4">10.4</a>&nbsp;<a id="header.from" href="#header.from">From</a></h2>
    2337       <p id="rfc.section.10.4.p.1">The "From" header field, if given, <em class="bcp14">SHOULD</em> contain an Internet e-mail address for the human user who controls the requesting user agent. The address <em class="bcp14">SHOULD</em> 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.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>:
    2338       </p>
    2339       <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.31"></span>  <a href="#header.from" class="smpl">From</a>    = <a href="#header.from" class="smpl">mailbox</a>
    2340  
    2341   <a href="#header.from" class="smpl">mailbox</a> = &lt;mailbox, defined in <a href="#RFC5322" id="rfc.xref.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="http://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a>&gt;
    2342 </pre><p id="rfc.section.10.4.p.3">An example is:</p>
    2343       <div id="rfc.figure.u.24"></div><pre class="text">  From: webmaster@example.org
    2344 </pre><p id="rfc.section.10.4.p.5">This header field <em class="bcp14">MAY</em> be used for logging purposes and as a means for identifying the source of invalid or unwanted requests. It <em class="bcp14">SHOULD NOT</em> be used as an insecure form of access protection. The interpretation of this field is that the request is being performed
    2345          on behalf of the person given, who accepts responsibility for the method performed. In particular, robot agents <em class="bcp14">SHOULD</em> include this header field so that the person responsible for running the robot can be contacted if problems occur on the receiving
    2346          end.
    2347       </p>
    2348       <p id="rfc.section.10.4.p.6">The Internet e-mail address in this field <em class="bcp14">MAY</em> be separate from the Internet host which issued the request. For example, when a request is passed through a proxy the original
    2349          issuer's address <em class="bcp14">SHOULD</em> be used.
    2350       </p>
    2351       <p id="rfc.section.10.4.p.7">The client <em class="bcp14">SHOULD NOT</em> send the From header field without the user's approval, as it might conflict with the user's privacy interests or their site's
    2352          security policy. It is strongly recommended that the user be able to disable, enable, and modify the value of this field at
    2353          any time prior to a request.
    2354       </p>
    2355       <div id="rfc.iref.l.1"></div>
    2356       <div id="rfc.iref.h.6"></div>
    2357       <h2 id="rfc.section.10.5"><a href="#rfc.section.10.5">10.5</a>&nbsp;<a id="header.location" href="#header.location">Location</a></h2>
    2358       <p id="rfc.section.10.5.p.1">The "Location" header field <em class="bcp14">MAY</em> be sent in responses to refer to a specific resource in accordance with the semantics of the status code.
    2359       </p>
    2360       <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.32"></span>  <a href="#header.location" class="smpl">Location</a> = <a href="#abnf.dependencies" class="smpl">URI-reference</a>
    2361 </pre><p id="rfc.section.10.5.p.3">For 201 (Created) responses, the Location is the URI of the new resource which was created by the request. For 3xx responses,
    2362          the location <em class="bcp14">SHOULD</em> indicate the server's preferred URI for automatic redirection to the resource.
    2363       </p>
    2364       <p id="rfc.section.10.5.p.4">The field value consists of a single URI-reference. When it has the form of a relative reference (<a href="#RFC3986" id="rfc.xref.RFC3986.1"><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.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-5">Section 5</a>). If the original URI, as navigated to by the user agent, did contain a fragment identifier, and the final value does not,
    2365          then the original URI's fragment identifier is added to the final value.
    2366       </p>
    2367       <div id="rfc.figure.u.26"></div>
    2368       <p>For example, the original URI "http://www.example.org/~tim", combined with a field value given as:</p>  <pre class="text">  Location: /pub/WWW/People.html#tim
    2369 </pre>  <p>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</p>
    2370       <div id="rfc.figure.u.27"></div>
    2371       <p>An original URI "http://www.example.org/index.html#larry", combined with a field value given as:</p>  <pre class="text">  Location: http://www.example.net/index.html
    2372 </pre>  <p>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</p>
    2373       <div class="note" id="rfc.section.10.5.p.7">
    2374          <p> <b>Note:</b> Some recipients attempt to recover from Location fields that are not valid URI references. This specification does not mandate
    2375             or define such processing, but does allow it (see <a href="#intro.conformance.and.error.handling" title="Conformance and Error Handling">Section&nbsp;1.1</a>).
    2376          </p>
    2377       </div>
    2378       <p id="rfc.section.10.5.p.8">There are circumstances in which a fragment identifier in a Location URI would not be appropriate. For instance, when it appears
    2379          in a 201 Created response, where the Location header field specifies the URI for the entire created resource.
    2380       </p>
    2381       <div class="note" id="rfc.section.10.5.p.9">
    2382          <p> <b>Note:</b> The Content-Location header field (<a href="p3-payload.html#header.content-location" title="Content-Location">Section 6.7</a> of <a href="#Part3" id="rfc.xref.Part3.13"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) differs from Location in that the Content-Location identifies the most specific resource corresponding to the enclosed representation.
    2383             It is therefore possible for a response to contain header fields for both Location and Content-Location.
    2384          </p>
    2385       </div>
    2386       <div id="rfc.iref.m.9"></div>
    2387       <div id="rfc.iref.h.7"></div>
    2388       <h2 id="rfc.section.10.6"><a href="#rfc.section.10.6">10.6</a>&nbsp;<a id="header.max-forwards" href="#header.max-forwards">Max-Forwards</a></h2>
    2389       <p id="rfc.section.10.6.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;6.8</a>) and OPTIONS (<a href="#OPTIONS" id="rfc.xref.OPTIONS.2" title="OPTIONS">Section&nbsp;6.2</a>) methods to limit the number of times that the request is forwarded by proxies. This can be useful when the client is attempting
    2390          to trace a request which appears to be failing or looping mid-chain.
    2391       </p>
    2392       <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.33"></span>  <a href="#header.max-forwards" class="smpl">Max-Forwards</a> = 1*<a href="#notation" class="smpl">DIGIT</a>
    2393 </pre><p id="rfc.section.10.6.p.3">The Max-Forwards value is a decimal integer indicating the remaining number of times this request message can be forwarded.</p>
    2394       <p id="rfc.section.10.6.p.4">Each recipient of 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 recipient <em class="bcp14">MUST NOT</em> forward the request; instead, it <em class="bcp14">MUST</em> respond as the final recipient. If the received Max-Forwards value is greater than zero, then the forwarded message <em class="bcp14">MUST</em> contain an updated Max-Forwards field with a value decremented by one (1).
    2395       </p>
    2396       <p id="rfc.section.10.6.p.5">The Max-Forwards header field <em class="bcp14">MAY</em> be ignored for all other request methods.
    2397       </p>
    2398       <div id="rfc.iref.r.1"></div>
    2399       <div id="rfc.iref.h.8"></div>
    2400       <h2 id="rfc.section.10.7"><a href="#rfc.section.10.7">10.7</a>&nbsp;<a id="header.referer" href="#header.referer">Referer</a></h2>
    2401       <p id="rfc.section.10.7.p.1">The "Referer" [sic] header field allows the client to specify the URI of the resource from which the effective request URI
    2402          was obtained (the "referrer", although the header field is misspelled.).
    2403       </p>
    2404       <p id="rfc.section.10.7.p.2">The Referer header field allows servers to generate lists of back-links to resources for interest, logging, optimized caching,
    2405          etc. It also allows obsolete or mistyped links to be traced for maintenance. Some servers use Referer as a means of controlling
    2406          where they allow links from (so-called "deep linking"), but legitimate requests do not always contain a Referer header field.
    2407       </p>
    2408       <p id="rfc.section.10.7.p.3">If the effective request URI was obtained from a source that does not have its own URI (e.g., input from the user keyboard),
    2409          the Referer field <em class="bcp14">MUST</em> either be sent with the value "about:blank", or not be sent at all. Note that this requirement does not apply to sources with
    2410          non-HTTP URIs (e.g., FTP).
    2411       </p>
    2412       <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.34"></span>  <a href="#header.referer" class="smpl">Referer</a> = <a href="#abnf.dependencies" class="smpl">absolute-URI</a> / <a href="#abnf.dependencies" class="smpl">partial-URI</a>
    2413 </pre><p id="rfc.section.10.7.p.5">Example:</p>
    2414       <div id="rfc.figure.u.30"></div><pre class="text">  Referer: http://www.example.org/hypertext/Overview.html
    2415 </pre><p id="rfc.section.10.7.p.7">If the field value is a relative URI, it <em class="bcp14">SHOULD</em> be interpreted relative to the effective request URI. The URI <em class="bcp14">MUST NOT</em> include a fragment. See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URIs">Section&nbsp;12.2</a> for security considerations.
    2416       </p>
    2417       <div id="rfc.iref.r.2"></div>
    2418       <div id="rfc.iref.h.9"></div>
    2419       <h2 id="rfc.section.10.8"><a href="#rfc.section.10.8">10.8</a>&nbsp;<a id="header.retry-after" href="#header.retry-after">Retry-After</a></h2>
    2420       <p id="rfc.section.10.8.p.1">The header "Retry-After" field can be used with a 503 (Service Unavailable) response to indicate how long the service is expected
    2421          to be unavailable to the requesting client. This field <em class="bcp14">MAY</em> also be used with any 3xx (Redirection) response to indicate the minimum time the user-agent is asked to wait before issuing
    2422          the redirected request.
    2423       </p>
    2424       <p id="rfc.section.10.8.p.2">The value of this field can be either an HTTP-date or an integer number of seconds (in decimal) after the time of the response.</p>
    2425       <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.35"></span>  <a href="#header.retry-after" class="smpl">Retry-After</a> = <a href="#http.date" class="smpl">HTTP-date</a> / <a href="#rule.delta-seconds" class="smpl">delta-seconds</a>
    2426 </pre><div id="rule.delta-seconds">
    2427          <p id="rfc.section.10.8.p.4">  Time spans are non-negative decimal integers, representing time in seconds.</p>
    2428       </div>
    2429       <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.36"></span>  <a href="#rule.delta-seconds" class="smpl">delta-seconds</a>  = 1*<a href="#notation" class="smpl">DIGIT</a>
    2430 </pre><p id="rfc.section.10.8.p.6">Two examples of its use are</p>
    2431       <div id="rfc.figure.u.33"></div><pre class="text">  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
    2432   Retry-After: 120
    2433 </pre><p id="rfc.section.10.8.p.8">In the latter example, the delay is 2 minutes.</p>
    2434       <div id="rfc.iref.s.38"></div>
    2435       <div id="rfc.iref.h.10"></div>
    2436       <h2 id="rfc.section.10.9"><a href="#rfc.section.10.9">10.9</a>&nbsp;<a id="header.server" href="#header.server">Server</a></h2>
    2437       <p id="rfc.section.10.9.p.1">The "Server" header field contains information about the software used by the origin server to handle the request.</p>
    2438       <p id="rfc.section.10.9.p.2">The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section&nbsp;9</a>) and comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.38"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) identifying the server and any significant subproducts. The product tokens are listed in order of their significance for
    2439          identifying the application.
    2440       </p>
    2441       <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.37"></span>  <a href="#header.server" class="smpl">Server</a> = <a href="#product.tokens" class="smpl">product</a> *( <a href="#core.rules" class="smpl">RWS</a> ( <a href="#product.tokens" class="smpl">product</a> / <a href="#abnf.dependencies" class="smpl">comment</a> ) )
    2442 </pre><p id="rfc.section.10.9.p.4">Example:</p>
    2443       <div id="rfc.figure.u.35"></div><pre class="text">  Server: CERN/3.0 libwww/2.17
    2444 </pre><p id="rfc.section.10.9.p.6">If the response is being forwarded through a proxy, the proxy application <em class="bcp14">MUST NOT</em> modify the Server header field. Instead, it <em class="bcp14">MUST</em> include a Via field (as described in <a href="p1-messaging.html#header.via" title="Via">Section 8.4</a> of <a href="#Part1" id="rfc.xref.Part1.39"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
    2445       </p>
    2446       <div class="note" id="rfc.section.10.9.p.7">
    2447          <p> <b>Note:</b> Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks
    2448             against software that is known to contain security holes. Server implementors are encouraged to make this field a configurable
    2449             option.
    2450          </p>
    2451       </div>
    2452       <div id="rfc.iref.u.1"></div>
    2453       <div id="rfc.iref.h.11"></div>
    2454       <h2 id="rfc.section.10.10"><a href="#rfc.section.10.10">10.10</a>&nbsp;<a id="header.user-agent" href="#header.user-agent">User-Agent</a></h2>
    2455       <p id="rfc.section.10.10.p.1">The "User-Agent" header field contains information about the user agent originating the request. User agents <em class="bcp14">SHOULD</em> include this field with requests.
    2456       </p>
    2457       <p id="rfc.section.10.10.p.2">Typically, it is used for statistical purposes, the tracing of protocol violations, and tailoring responses to avoid particular
    2458          user agent limitations.
    2459       </p>
    2460       <p id="rfc.section.10.10.p.3">The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section&nbsp;9</a>) and comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.40"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) identifying the agent and its significant subproducts. By convention, the product tokens are listed in order of their significance
    2461          for identifying the application.
    2462       </p>
    2463       <p id="rfc.section.10.10.p.4">Because this field is usually sent on every request a user agent makes, implementations are encouraged not to include needlessly
    2464          fine-grained detail, and to limit (or even prohibit) the addition of subproducts by third parties. Overly long and detailed
    2465          User-Agent field values make requests larger and can also be used to identify ("fingerprint") the user against their wishes.
    2466       </p>
    2467       <p id="rfc.section.10.10.p.5">Likewise, implementations are encouraged not to use the product tokens of other implementations in order to declare compatibility
    2468          with them, as this circumvents the purpose of the field. Finally, they are encouraged not to use comments to identify products;
    2469          doing so makes the field value more difficult to parse.
    2470       </p>
    2471       <div id="rfc.figure.u.36"></div><pre class="inline"><span id="rfc.iref.g.38"></span>  <a href="#header.user-agent" class="smpl">User-Agent</a> = <a href="#product.tokens" class="smpl">product</a> *( <a href="#core.rules" class="smpl">RWS</a> ( <a href="#product.tokens" class="smpl">product</a> / <a href="#abnf.dependencies" class="smpl">comment</a> ) )
    2472 </pre><p id="rfc.section.10.10.p.7">Example:</p>
    2473       <div id="rfc.figure.u.37"></div><pre class="text">  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
    2474 </pre><h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
    2475       <h2 id="rfc.section.11.1"><a href="#rfc.section.11.1">11.1</a>&nbsp;<a id="method.registration" href="#method.registration">Method Registry</a></h2>
    2476       <p id="rfc.section.11.1.p.1">The registration procedure for HTTP request methods is defined by <a href="#method.registry" title="Method Registry">Section&nbsp;2.2</a> of this document.
    2477       </p>
    2478       <p id="rfc.section.11.1.p.2">The HTTP Method Registry shall be created at &lt;<a href="http://www.iana.org/assignments/http-methods">http://www.iana.org/assignments/http-methods</a>&gt; and be populated with the registrations below:
    2479       </p>
    2480       <div id="rfc.table.1">
    2481          <div id="iana.method.registration.table"></div>
    2482          <table class="tt full left" cellpadding="3" cellspacing="0">
    2483             <thead>
    2484                <tr>
    2485                   <th>Method</th>
    2486                   <th>Safe</th>
    2487                   <th>Reference</th>
    2488                </tr>
    2489             </thead>
    2490             <tbody>
    2491                <tr>
    2492                   <td class="left">CONNECT</td>
    2493                   <td class="left">no</td>
    2494                   <td class="left"> <a href="#CONNECT" id="rfc.xref.CONNECT.2" title="CONNECT">Section&nbsp;6.9</a>
    2495                   </td>
    2496                </tr>
    2497                <tr>
    2498                   <td class="left">DELETE</td>
    2499                   <td class="left">no</td>
    2500                   <td class="left"> <a href="#DELETE" id="rfc.xref.DELETE.2" title="DELETE">Section&nbsp;6.7</a>
    2501                   </td>
    2502                </tr>
    2503                <tr>
    2504                   <td class="left">GET</td>
    2505                   <td class="left">yes</td>
    2506                   <td class="left"> <a href="#GET" id="rfc.xref.GET.2" title="GET">Section&nbsp;6.3</a>
    2507                   </td>
    2508                </tr>
    2509                <tr>
    2510                   <td class="left">HEAD</td>
    2511                   <td class="left">yes</td>
    2512                   <td class="left"> <a href="#HEAD" id="rfc.xref.HEAD.2" title="HEAD">Section&nbsp;6.4</a>
    2513                   </td>
    2514                </tr>
    2515                <tr>
    2516                   <td class="left">OPTIONS</td>
    2517                   <td class="left">yes</td>
    2518                   <td class="left"> <a href="#OPTIONS" id="rfc.xref.OPTIONS.3" title="OPTIONS">Section&nbsp;6.2</a>
    2519                   </td>
    2520                </tr>
    2521                <tr>
    2522                   <td class="left">POST</td>
    2523                   <td class="left">no</td>
    2524                   <td class="left"> <a href="#POST" id="rfc.xref.POST.2" title="POST">Section&nbsp;6.5</a>
    2525                   </td>
    2526                </tr>
    2527                <tr>
    2528                   <td class="left">PUT</td>
    2529                   <td class="left">no</td>
    2530                   <td class="left"> <a href="#PUT" id="rfc.xref.PUT.2" title="PUT">Section&nbsp;6.6</a>
    2531                   </td>
    2532                </tr>
    2533                <tr>
    2534                   <td class="left">TRACE</td>
    2535                   <td class="left">yes</td>
    2536                   <td class="left"> <a href="#TRACE" id="rfc.xref.TRACE.3" title="TRACE">Section&nbsp;6.8</a>
    2537                   </td>
    2538                </tr>
    2539             </tbody>
    2540          </table>
    2541       </div>
    2542       <h2 id="rfc.section.11.2"><a href="#rfc.section.11.2">11.2</a>&nbsp;<a id="status.code.registration" href="#status.code.registration">Status Code Registry</a></h2>
    2543       <p id="rfc.section.11.2.p.1">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> — is now defined by <a href="#status.code.registry" title="Status Code Registry">Section&nbsp;4.2</a> of this document.
    2544       </p>
    2545       <p id="rfc.section.11.2.p.2">The HTTP Status Code Registry located at &lt;<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>&gt; shall be updated with the registrations below:
    2546       </p>
    2547       <div id="rfc.table.2">
    2548          <div id="iana.status.code.registration.table"></div>
    2549          <table class="tt full left" cellpadding="3" cellspacing="0">
    2550             <thead>
    2551                <tr>
    2552                   <th>Value</th>
    2553                   <th>Description</th>
    2554                   <th>Reference</th>
    2555                </tr>
    2556             </thead>
    2557             <tbody>
    2558                <tr>
    2559                   <td class="left">100</td>
    2560                   <td class="left">Continue</td>
    2561                   <td class="left"> <a href="#status.100" id="rfc.xref.status.100.2" title="100 Continue">Section&nbsp;7.1.1</a>
    2562                   </td>
    2563                </tr>
    2564                <tr>
    2565                   <td class="left">101</td>
    2566                   <td class="left">Switching Protocols</td>
    2567                   <td class="left"> <a href="#status.101" id="rfc.xref.status.101.2" title="101 Switching Protocols">Section&nbsp;7.1.2</a>
    2568                   </td>
    2569                </tr>
    2570                <tr>
    2571                   <td class="left">200</td>
    2572                   <td class="left">OK</td>
    2573                   <td class="left"> <a href="#status.200" id="rfc.xref.status.200.2" title="200 OK">Section&nbsp;7.2.1</a>
    2574                   </td>
    2575                </tr>
    2576                <tr>
    2577                   <td class="left">201</td>
    2578                   <td class="left">Created</td>
    2579                   <td class="left"> <a href="#status.201" id="rfc.xref.status.201.2" title="201 Created">Section&nbsp;7.2.2</a>
    2580                   </td>
    2581                </tr>
    2582                <tr>
    2583                   <td class="left">202</td>
    2584                   <td class="left">Accepted</td>
    2585                   <td class="left"> <a href="#status.202" id="rfc.xref.status.202.2" title="202 Accepted">Section&nbsp;7.2.3</a>
    2586                   </td>
    2587                </tr>
    2588                <tr>
    2589                   <td class="left">203</td>
    2590                   <td class="left">Non-Authoritative Information</td>
    2591                   <td class="left"> <a href="#status.203" id="rfc.xref.status.203.2" title="203 Non-Authoritative Information">Section&nbsp;7.2.4</a>
    2592                   </td>
    2593                </tr>
    2594                <tr>
    2595                   <td class="left">204</td>
    2596                   <td class="left">No Content</td>
    2597                   <td class="left"> <a href="#status.204" id="rfc.xref.status.204.2" title="204 No Content">Section&nbsp;7.2.5</a>
    2598                   </td>
    2599                </tr>
    2600                <tr>
    2601                   <td class="left">205</td>
    2602                   <td class="left">Reset Content</td>
    2603                   <td class="left"> <a href="#status.205" id="rfc.xref.status.205.2" title="205 Reset Content">Section&nbsp;7.2.6</a>
    2604                   </td>
    2605                </tr>
    2606                <tr>
    2607                   <td class="left">300</td>
    2608                   <td class="left">Multiple Choices</td>
    2609                   <td class="left"> <a href="#status.300" id="rfc.xref.status.300.2" title="300 Multiple Choices">Section&nbsp;7.3.1</a>
    2610                   </td>
    2611                </tr>
    2612                <tr>
    2613                   <td class="left">301</td>
    2614                   <td class="left">Moved Permanently</td>
    2615                   <td class="left"> <a href="#status.301" id="rfc.xref.status.301.2" title="301 Moved Permanently">Section&nbsp;7.3.2</a>
    2616                   </td>
    2617                </tr>
    2618                <tr>
    2619                   <td class="left">302</td>
    2620                   <td class="left">Found</td>
    2621                   <td class="left"> <a href="#status.302" id="rfc.xref.status.302.2" title="302 Found">Section&nbsp;7.3.3</a>
    2622                   </td>
    2623                </tr>
    2624                <tr>
    2625                   <td class="left">303</td>
    2626                   <td class="left">See Other</td>
    2627                   <td class="left"> <a href="#status.303" id="rfc.xref.status.303.2" title="303 See Other">Section&nbsp;7.3.4</a>
    2628                   </td>
    2629                </tr>
    2630                <tr>
    2631                   <td class="left">305</td>
    2632                   <td class="left">Use Proxy</td>
    2633                   <td class="left"> <a href="#status.305" id="rfc.xref.status.305.2" title="305 Use Proxy">Section&nbsp;7.3.5</a>
    2634                   </td>
    2635                </tr>
    2636                <tr>
    2637                   <td class="left">306</td>
    2638                   <td class="left">(Unused)</td>
    2639                   <td class="left"> <a href="#status.306" id="rfc.xref.status.306.1" title="306 (Unused)">Section&nbsp;7.3.6</a>
    2640                   </td>
    2641                </tr>
    2642                <tr>
    2643                   <td class="left">307</td>
    2644                   <td class="left">Temporary Redirect</td>
    2645                   <td class="left"> <a href="#status.307" id="rfc.xref.status.307.2" title="307 Temporary Redirect">Section&nbsp;7.3.7</a>
    2646                   </td>
    2647                </tr>
    2648                <tr>
    2649                   <td class="left">400</td>
    2650                   <td class="left">Bad Request</td>
    2651                   <td class="left"> <a href="#status.400" id="rfc.xref.status.400.2" title="400 Bad Request">Section&nbsp;7.4.1</a>
    2652                   </td>
    2653                </tr>
    2654                <tr>
    2655                   <td class="left">402</td>
    2656                   <td class="left">Payment Required</td>
    2657                   <td class="left"> <a href="#status.402" id="rfc.xref.status.402.2" title="402 Payment Required">Section&nbsp;7.4.2</a>
    2658                   </td>
    2659                </tr>
    2660                <tr>
    2661                   <td class="left">403</td>
    2662                   <td class="left">Forbidden</td>
    2663                   <td class="left"> <a href="#status.403" id="rfc.xref.status.403.2" title="403 Forbidden">Section&nbsp;7.4.3</a>
    2664                   </td>
    2665                </tr>
    2666                <tr>
    2667                   <td class="left">404</td>
    2668                   <td class="left">Not Found</td>
    2669                   <td class="left"> <a href="#status.404" id="rfc.xref.status.404.2" title="404 Not Found">Section&nbsp;7.4.4</a>
    2670                   </td>
    2671                </tr>
    2672                <tr>
    2673                   <td class="left">405</td>
    2674                   <td class="left">Method Not Allowed</td>
    2675                   <td class="left"> <a href="#status.405" id="rfc.xref.status.405.2" title="405 Method Not Allowed">Section&nbsp;7.4.5</a>
    2676                   </td>
    2677                </tr>
    2678                <tr>
    2679                   <td class="left">406</td>
    2680                   <td class="left">Not Acceptable</td>
    2681                   <td class="left"> <a href="#status.406" id="rfc.xref.status.406.2" title="406 Not Acceptable">Section&nbsp;7.4.6</a>
    2682                   </td>
    2683                </tr>
    2684                <tr>
    2685                   <td class="left">408</td>
    2686                   <td class="left">Request Timeout</td>
    2687                   <td class="left"> <a href="#status.408" id="rfc.xref.status.408.2" title="408 Request Timeout">Section&nbsp;7.4.7</a>
    2688                   </td>
    2689                </tr>
    2690                <tr>
    2691                   <td class="left">409</td>
    2692                   <td class="left">Conflict</td>
    2693                   <td class="left"> <a href="#status.409" id="rfc.xref.status.409.2" title="409 Conflict">Section&nbsp;7.4.8</a>
    2694                   </td>
    2695                </tr>
    2696                <tr>
    2697                   <td class="left">410</td>
    2698                   <td class="left">Gone</td>
    2699                   <td class="left"> <a href="#status.410" id="rfc.xref.status.410.2" title="410 Gone">Section&nbsp;7.4.9</a>
    2700                   </td>
    2701                </tr>
    2702                <tr>
    2703                   <td class="left">411</td>
    2704                   <td class="left">Length Required</td>
    2705                   <td class="left"> <a href="#status.411" id="rfc.xref.status.411.2" title="411 Length Required">Section&nbsp;7.4.10</a>
    2706                   </td>
    2707                </tr>
    2708                <tr>
    2709                   <td class="left">413</td>
    2710                   <td class="left">Request Representation Too Large</td>
    2711                   <td class="left"> <a href="#status.413" id="rfc.xref.status.413.2" title="413 Request Representation Too Large">Section&nbsp;7.4.11</a>
    2712                   </td>
    2713                </tr>
    2714                <tr>
    2715                   <td class="left">414</td>
    2716                   <td class="left">URI Too Long</td>
    2717                   <td class="left"> <a href="#status.414" id="rfc.xref.status.414.2" title="414 URI Too Long">Section&nbsp;7.4.12</a>
    2718                   </td>
    2719                </tr>
    2720                <tr>
    2721                   <td class="left">415</td>
    2722                   <td class="left">Unsupported Media Type</td>
    2723                   <td class="left"> <a href="#status.415" id="rfc.xref.status.415.2" title="415 Unsupported Media Type">Section&nbsp;7.4.13</a>
    2724                   </td>
    2725                </tr>
    2726                <tr>
    2727                   <td class="left">417</td>
    2728                   <td class="left">Expectation Failed</td>
    2729                   <td class="left"> <a href="#status.417" id="rfc.xref.status.417.2" title="417 Expectation Failed">Section&nbsp;7.4.14</a>
    2730                   </td>
    2731                </tr>
    2732                <tr>
    2733                   <td class="left">426</td>
    2734                   <td class="left">Upgrade Required</td>
    2735                   <td class="left"> <a href="#status.426" id="rfc.xref.status.426.2" title="426 Upgrade Required">Section&nbsp;7.4.15</a>
    2736                   </td>
    2737                </tr>
    2738                <tr>
    2739                   <td class="left">500</td>
    2740                   <td class="left">Internal Server Error</td>
    2741                   <td class="left"> <a href="#status.500" id="rfc.xref.status.500.2" title="500 Internal Server Error">Section&nbsp;7.5.1</a>
    2742                   </td>
    2743                </tr>
    2744                <tr>
    2745                   <td class="left">501</td>
    2746                   <td class="left">Not Implemented</td>
    2747                   <td class="left"> <a href="#status.501" id="rfc.xref.status.501.2" title="501 Not Implemented">Section&nbsp;7.5.2</a>
    2748                   </td>
    2749                </tr>
    2750                <tr>
    2751                   <td class="left">502</td>
    2752                   <td class="left">Bad Gateway</td>
    2753                   <td class="left"> <a href="#status.502" id="rfc.xref.status.502.2" title="502 Bad Gateway">Section&nbsp;7.5.3</a>
    2754                   </td>
    2755                </tr>
    2756                <tr>
    2757                   <td class="left">503</td>
    2758                   <td class="left">Service Unavailable</td>
    2759                   <td class="left"> <a href="#status.503" id="rfc.xref.status.503.2" title="503 Service Unavailable">Section&nbsp;7.5.4</a>
    2760                   </td>
    2761                </tr>
    2762                <tr>
    2763                   <td class="left">504</td>
    2764                   <td class="left">Gateway Timeout</td>
    2765                   <td class="left"> <a href="#status.504" id="rfc.xref.status.504.2" title="504 Gateway Timeout">Section&nbsp;7.5.5</a>
    2766                   </td>
    2767                </tr>
    2768                <tr>
    2769                   <td class="left">505</td>
    2770                   <td class="left">HTTP Version Not Supported</td>
    2771                   <td class="left"> <a href="#status.505" id="rfc.xref.status.505.2" title="505 HTTP Version Not Supported">Section&nbsp;7.5.6</a>
    2772                   </td>
    2773                </tr>
    2774             </tbody>
    2775          </table>
    2776       </div>
    2777       <h2 id="rfc.section.11.3"><a href="#rfc.section.11.3">11.3</a>&nbsp;<a id="header.field.registration" href="#header.field.registration">Header Field Registration</a></h2>
    2778       <p id="rfc.section.11.3.p.1">The Message Header Field Registry located at &lt;<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>&gt; shall be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.3"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>):
    2779       </p>
    2780       <div id="rfc.table.3">
    2781          <div id="iana.header.registration.table"></div>
    2782          <table class="tt full left" cellpadding="3" cellspacing="0">
    2783             <thead>
    2784                <tr>
    2785                   <th>Header Field Name</th>
    2786                   <th>Protocol</th>
    2787                   <th>Status</th>
    2788                   <th>Reference</th>
    2789                </tr>
    2790             </thead>
    2791             <tbody>
    2792                <tr>
    2793                   <td class="left">Allow</td>
    2794                   <td class="left">http</td>
    2795                   <td class="left">standard</td>
    2796                   <td class="left"> <a href="#header.allow" id="rfc.xref.header.allow.3" title="Allow">Section&nbsp;10.1</a>
    2797                   </td>
    2798                </tr>
    2799                <tr>
    2800                   <td class="left">Date</td>
    2801                   <td class="left">http</td>
    2802                   <td class="left">standard</td>
    2803                   <td class="left"> <a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section&nbsp;10.2</a>
    2804                   </td>
    2805                </tr>
    2806                <tr>
    2807                   <td class="left">Expect</td>
    2808                   <td class="left">http</td>
    2809                   <td class="left">standard</td>
    2810                   <td class="left"> <a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section&nbsp;10.3</a>
    2811                   </td>
    2812                </tr>
    2813                <tr>
    2814                   <td class="left">From</td>
    2815                   <td class="left">http</td>
    2816                   <td class="left">standard</td>
    2817                   <td class="left"> <a href="#header.from" id="rfc.xref.header.from.2" title="From">Section&nbsp;10.4</a>
    2818                   </td>
    2819                </tr>
    2820                <tr>
    2821                   <td class="left">Location</td>
    2822                   <td class="left">http</td>
    2823                   <td class="left">standard</td>
    2824                   <td class="left"> <a href="#header.location" id="rfc.xref.header.location.4" title="Location">Section&nbsp;10.5</a>
    2825                   </td>
    2826                </tr>
    2827                <tr>
    2828                   <td class="left">Max-Forwards</td>
    2829                   <td class="left">http</td>
    2830                   <td class="left">standard</td>
    2831                   <td class="left"> <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.4" title="Max-Forwards">Section&nbsp;10.6</a>
    2832                   </td>
    2833                </tr>
    2834                <tr>
    2835                   <td class="left">Referer</td>
    2836                   <td class="left">http</td>
    2837                   <td class="left">standard</td>
    2838                   <td class="left"> <a href="#header.referer" id="rfc.xref.header.referer.2" title="Referer">Section&nbsp;10.7</a>
    2839                   </td>
    2840                </tr>
    2841                <tr>
    2842                   <td class="left">Retry-After</td>
    2843                   <td class="left">http</td>
    2844                   <td class="left">standard</td>
    2845                   <td class="left"> <a href="#header.retry-after" id="rfc.xref.header.retry-after.3" title="Retry-After">Section&nbsp;10.8</a>
    2846                   </td>
    2847                </tr>
    2848                <tr>
    2849                   <td class="left">Server</td>
    2850                   <td class="left">http</td>
    2851                   <td class="left">standard</td>
    2852                   <td class="left"> <a href="#header.server" id="rfc.xref.header.server.2" title="Server">Section&nbsp;10.9</a>
    2853                   </td>
    2854                </tr>
    2855                <tr>
    2856                   <td class="left">User-Agent</td>
    2857                   <td class="left">http</td>
    2858                   <td class="left">standard</td>
    2859                   <td class="left"> <a href="#header.user-agent" id="rfc.xref.header.user-agent.2" title="User-Agent">Section&nbsp;10.10</a>
    2860                   </td>
    2861                </tr>
    2862             </tbody>
    2863          </table>
    2864       </div>
    2865       <p id="rfc.section.11.3.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
    2866       <h1 id="rfc.section.12"><a href="#rfc.section.12">12.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
    2867       <p id="rfc.section.12.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1
    2868          as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does
    2869          make some suggestions for reducing security risks.
    2870       </p>
    2871       <h2 id="rfc.section.12.1"><a href="#rfc.section.12.1">12.1</a>&nbsp;<a id="security.sensitive" href="#security.sensitive">Transfer of Sensitive Information</a></h2>
    2872       <p id="rfc.section.12.1.p.1">Like any generic data transfer protocol, HTTP cannot regulate the content of the data that is transferred, nor is there any
    2873          a priori method of determining the sensitivity of any particular piece of information within the context of any given request.
    2874          Therefore, applications <em class="bcp14">SHOULD</em> supply as much control over this information as possible to the provider of that information. Four header fields are worth
    2875          special mention in this context: Server, Via, Referer and From.
    2876       </p>
    2877       <p id="rfc.section.12.1.p.2">Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks
    2878          against software that is known to contain security holes. Implementors <em class="bcp14">SHOULD</em> make the Server header field a configurable option.
    2879       </p>
    2880       <p id="rfc.section.12.1.p.3">Proxies which serve as a portal through a network firewall <em class="bcp14">SHOULD</em> take special precautions regarding the transfer of header information that identifies the hosts behind the firewall. In particular,
    2881          they <em class="bcp14">SHOULD</em> remove, or replace with sanitized versions, any Via fields generated behind the firewall.
    2882       </p>
    2883       <p id="rfc.section.12.1.p.4">The Referer header field allows reading patterns to be studied and reverse links drawn. Although it can be very useful, its
    2884          power can be abused if user details are not separated from the information contained in the Referer. Even when the personal
    2885          information has been removed, the Referer header field might indicate a private document's URI whose publication would be
    2886          inappropriate.
    2887       </p>
    2888       <p id="rfc.section.12.1.p.5">The information sent in the From field might conflict with the user's privacy interests or their site's security policy, and
    2889          hence it <em class="bcp14">SHOULD NOT</em> be transmitted without the user being able to disable, enable, and modify the contents of the field. The user <em class="bcp14">MUST</em> be able to set the contents of this field within a user preference or application defaults configuration.
    2890       </p>
    2891       <p id="rfc.section.12.1.p.6">We suggest, though do not require, that a convenient toggle interface be provided for the user to enable or disable the sending
    2892          of From and Referer information.
    2893       </p>
    2894       <p id="rfc.section.12.1.p.7">The User-Agent (<a href="#header.user-agent" id="rfc.xref.header.user-agent.3" title="User-Agent">Section&nbsp;10.10</a>) or Server (<a href="#header.server" id="rfc.xref.header.server.3" title="Server">Section&nbsp;10.9</a>) header fields can sometimes be used to determine that a specific client or server has a particular security hole which might
    2895          be exploited. Unfortunately, this same information is often used for other valuable purposes for which HTTP currently has
    2896          no better mechanism.
    2897       </p>
    2898       <p id="rfc.section.12.1.p.8">Furthermore, the User-Agent header field may contain enough entropy to be used, possibly in conjunction with other material,
    2899          to uniquely identify the user.
    2900       </p>
    2901       <p id="rfc.section.12.1.p.9">Some request methods, like TRACE (<a href="#TRACE" id="rfc.xref.TRACE.4" title="TRACE">Section&nbsp;6.8</a>), expose information that was sent in request header fields within the body of their response. Clients <em class="bcp14">SHOULD</em> be careful with sensitive information, like Cookies, Authorization credentials, and other header fields that might be used
    2902          to collect data from the client.
    2903       </p>
    2904       <h2 id="rfc.section.12.2"><a href="#rfc.section.12.2">12.2</a>&nbsp;<a id="encoding.sensitive.information.in.uris" href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URIs</a></h2>
    2905       <p id="rfc.section.12.2.p.1">Because the source of a link might be private information or might reveal an otherwise private information source, it is strongly
    2906          recommended that the user be able to select whether or not the Referer field is sent. For example, a browser client could
    2907          have a toggle switch for browsing openly/anonymously, which would respectively enable/disable the sending of Referer and From
    2908          information.
    2909       </p>
    2910       <p id="rfc.section.12.2.p.2">Clients <em class="bcp14">SHOULD NOT</em> include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol.
    2911       </p>
    2912       <p id="rfc.section.12.2.p.3">Authors of services <em class="bcp14">SHOULD NOT</em> use GET-based forms for the submission of sensitive data because that data will be placed in the request-target. Many existing
    2913          servers, proxies, and user agents log or display the request-target in places where it might be visible to third parties.
    2914          Such services can use POST-based form submission instead.
    2915       </p>
    2916       <h2 id="rfc.section.12.3"><a href="#rfc.section.12.3">12.3</a>&nbsp;<a id="location.spoofing-leakage" href="#location.spoofing-leakage">Location Header Fields: Spoofing and Information Leakage</a></h2>
    2917       <p id="rfc.section.12.3.p.1">If a single server supports multiple organizations that do not trust one another, then it <em class="bcp14">MUST</em> check the values of Location and Content-Location header fields in responses that are generated under control of said organizations
    2918          to make sure that they do not attempt to invalidate resources over which they have no authority.
    2919       </p>
    2920       <p id="rfc.section.12.3.p.2">Furthermore, appending the fragment identifier from one URI to another one obtained from a Location header field might leak
    2921          confidential information to the target server — although the fragment identifier is not transmitted in the final request,
    2922          it might be visible to the user agent through other means, such as scripting.
    2923       </p>
    2924       <h2 id="rfc.section.12.4"><a href="#rfc.section.12.4">12.4</a>&nbsp;Security Considerations for CONNECT
    2925       </h2>
    2926       <p id="rfc.section.12.4.p.1">Since tunneled data is opaque to the proxy, there are additional risks to tunneling to other well-known or reserved ports.
    2927          A HTTP client CONNECTing to port 25 could relay spam via SMTP, for example. As such, proxies <em class="bcp14">SHOULD</em> restrict CONNECT access to a small number of known ports.
    2928       </p>
    2929       <h1 id="rfc.section.13"><a href="#rfc.section.13">13.</a>&nbsp;<a id="acks" href="#acks">Acknowledgments</a></h1>
    2930       <p id="rfc.section.13.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 11</a> of <a href="#Part1" id="rfc.xref.Part1.41"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
    2931       </p>
    2932       <h1 id="rfc.references"><a id="rfc.section.14" href="#rfc.section.14">14.</a> References
    2933       </h1>
    2934       <h2 id="rfc.references.1"><a href="#rfc.section.14.1" id="rfc.section.14.1">14.1</a> Normative References
    2935       </h2>
    2936       <table>                 
    2937          <tr>
    2938             <td class="reference"><b id="Part1">[Part1]</b></td>
    2939             <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-latest">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p1-messaging-latest (work in progress), March&nbsp;2012.
    2940             </td>
    2941          </tr>
    2942          <tr>
    2943             <td class="reference"><b id="Part3">[Part3]</b></td>
    2944             <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-latest">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p3-payload-latest (work in progress), March&nbsp;2012.
    2945             </td>
    2946          </tr>
    2947          <tr>
    2948             <td class="reference"><b id="Part4">[Part4]</b></td>
    2949             <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-latest">HTTP/1.1, part 4: Conditional Requests</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p4-conditional-latest (work in progress), March&nbsp;2012.
    2950             </td>
    2951          </tr>
    2952          <tr>
    2953             <td class="reference"><b id="Part5">[Part5]</b></td>
    2954             <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-latest">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p5-range-latest (work in progress), March&nbsp;2012.
    2955             </td>
    2956          </tr>
    2957          <tr>
    2958             <td class="reference"><b id="Part6">[Part6]</b></td>
    2959             <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, <a href="mailto:mnot@mnot.net" title="Rackspace">Nottingham, M., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-latest">HTTP/1.1, part 6: Caching</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p6-cache-latest (work in progress), March&nbsp;2012.
    2960             </td>
    2961          </tr>
    2962          <tr>
    2963             <td class="reference"><b id="Part7">[Part7]</b></td>
    2964             <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p7-auth-latest">HTTP/1.1, part 7: Authentication</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p7-auth-latest (work in progress), March&nbsp;2012.
    2965             </td>
    2966          </tr>
    2967          <tr>
    2968             <td class="reference"><b id="RFC2119">[RFC2119]</b></td>
    2969             <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997.
    2970             </td>
    2971          </tr>
    2972          <tr>
    2973             <td class="reference"><b id="RFC3986">[RFC3986]</b></td>
    2974             <td class="top"><a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R.</a>, and <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">L. Masinter</a>, “<a href="http://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>”, STD&nbsp;66, RFC&nbsp;3986, January&nbsp;2005.
    2975             </td>
    2976          </tr>
    2977          <tr>
    2978             <td class="reference"><b id="RFC5234">[RFC5234]</b></td>
    2979             <td class="top"><a href="mailto:dcrocker@bbiw.net" title="Brandenburg InternetWorking">Crocker, D., Ed.</a> and <a href="mailto:paul.overell@thus.net" title="THUS plc.">P. Overell</a>, “<a href="http://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>”, STD&nbsp;68, RFC&nbsp;5234, January&nbsp;2008.
    2980             </td>
    2981          </tr>
    2982       </table>
    2983       <h2 id="rfc.references.2"><a href="#rfc.section.14.2" id="rfc.section.14.2">14.2</a> Informative References
    2984       </h2>
    2985       <table>                   
    2986          <tr>
    2987             <td class="reference"><b id="RFC1123">[RFC1123]</b></td>
    2988             <td class="top"><a href="mailto:Braden@ISI.EDU" title="University of Southern California (USC), Information Sciences Institute">Braden, R.</a>, “<a href="http://tools.ietf.org/html/rfc1123">Requirements for Internet Hosts - Application and Support</a>”, STD&nbsp;3, RFC&nbsp;1123, October&nbsp;1989.
    2989             </td>
    2990          </tr>
    2991          <tr>
    2992             <td class="reference"><b id="RFC1945">[RFC1945]</b></td>
    2993             <td class="top"><a href="mailto:timbl@w3.org" title="MIT, Laboratory for Computer Science">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium, MIT Laboratory for Computer Science">H. Nielsen</a>, “<a href="http://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>”, RFC&nbsp;1945, May&nbsp;1996.
    2994             </td>
    2995          </tr>
    2996          <tr>
    2997             <td class="reference"><b id="RFC2068">[RFC2068]</b></td>
    2998             <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Digital Equipment Corporation, Western Research Laboratory">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Nielsen, H.</a>, and <a href="mailto:timbl@w3.org" title="MIT Laboratory for Computer Science">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2068, January&nbsp;1997.
    2999             </td>
    3000          </tr>
    3001          <tr>
    3002             <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
    3003             <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2616, June&nbsp;1999.
    3004             </td>
    3005          </tr>
    3006          <tr>
    3007             <td class="reference"><b id="RFC2817">[RFC2817]</b></td>
    3008             <td class="top"><a href="mailto:rohit@4K-associates.com" title="4K Associates / UC Irvine">Khare, R.</a> and <a href="mailto:lawrence@agranat.com" title="Agranat Systems, Inc.">S. Lawrence</a>, “<a href="http://tools.ietf.org/html/rfc2817">Upgrading to TLS Within HTTP/1.1</a>”, RFC&nbsp;2817, May&nbsp;2000.
    3009             </td>
    3010          </tr>
    3011          <tr>
    3012             <td class="reference"><b id="RFC3864">[RFC3864]</b></td>
    3013             <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="http://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP&nbsp;90, RFC&nbsp;3864, September&nbsp;2004.
    3014             </td>
    3015          </tr>
    3016          <tr>
    3017             <td class="reference"><b id="RFC5226">[RFC5226]</b></td>
    3018             <td class="top"><a href="mailto:narten@us.ibm.com" title="IBM">Narten, T.</a> and <a href="mailto:Harald@Alvestrand.no" title="Google">H. Alvestrand</a>, “<a href="http://tools.ietf.org/html/rfc5226">Guidelines for Writing an IANA Considerations Section in RFCs</a>”, BCP&nbsp;26, RFC&nbsp;5226, May&nbsp;2008.
    3019             </td>
    3020          </tr>
    3021          <tr>
    3022             <td class="reference"><b id="RFC5322">[RFC5322]</b></td>
    3023             <td class="top">Resnick, P., “<a href="http://tools.ietf.org/html/rfc5322">Internet Message Format</a>”, RFC&nbsp;5322, October&nbsp;2008.
    3024             </td>
    3025          </tr>
    3026          <tr>
    3027             <td class="reference"><b id="RFC5789">[RFC5789]</b></td>
    3028             <td class="top">Dusseault, L. and J. Snell, “<a href="http://tools.ietf.org/html/rfc5789">PATCH Method for HTTP</a>”, RFC&nbsp;5789, March&nbsp;2010.
    3029             </td>
    3030          </tr>
    3031          <tr>
    3032             <td class="reference"><b id="RFC5987">[RFC5987]</b></td>
    3033             <td class="top"><a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">Reschke, J.</a>, “<a href="http://tools.ietf.org/html/rfc5987">Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</a>”, RFC&nbsp;5987, August&nbsp;2010.
    3034             </td>
    3035          </tr>
    3036       </table>
    3037       <div class="avoidbreak">
    3038          <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1>
    3039          <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span>
    3040                (editor)
    3041                <span class="n hidden"><span class="family-name">Fielding</span><span class="given-name">Roy T.</span></span></span><span class="org vcardline">Adobe Systems Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:fielding@gbiv.com"><span class="email">fielding@gbiv.com</span></a></span><span class="vcardline">URI: <a href="http://roy.gbiv.com/" class="url">http://roy.gbiv.com/</a></span></address>
    3042          <address class="vcard"><span class="vcardline"><span class="fn">Jim Gettys</span><span class="n hidden"><span class="family-name">Gettys</span><span class="given-name">Jim</span></span></span><span class="org vcardline">Alcatel-Lucent Bell Labs</span><span class="adr"><span class="street-address vcardline">21 Oak Knoll Road</span><span class="vcardline"><span class="locality">Carlisle</span>, <span class="region">MA</span>&nbsp;<span class="postal-code">01741</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:jg@freedesktop.org"><span class="email">jg@freedesktop.org</span></a></span><span class="vcardline">URI: <a href="http://gettys.wordpress.com/" class="url">http://gettys.wordpress.com/</a></span></address>
    3043          <address class="vcard"><span class="vcardline"><span class="fn">Jeffrey C. Mogul</span><span class="n hidden"><span class="family-name">Mogul</span><span class="given-name">Jeffrey C.</span></span></span><span class="org vcardline">Hewlett-Packard Company</span><span class="adr"><span class="street-address vcardline">HP Labs, Large Scale Systems Group</span><span class="street-address vcardline">1501 Page Mill Road, MS 1177</span><span class="vcardline"><span class="locality">Palo Alto</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">94304</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:JeffMogul@acm.org"><span class="email">JeffMogul@acm.org</span></a></span></address>
    3044          <address class="vcard"><span class="vcardline"><span class="fn">Henrik Frystyk Nielsen</span><span class="n hidden"><span class="family-name">Frystyk</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span>&nbsp;<span class="postal-code">98052</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:henrikn@microsoft.com"><span class="email">henrikn@microsoft.com</span></a></span></address>
    3045          <address class="vcard"><span class="vcardline"><span class="fn">Larry Masinter</span><span class="n hidden"><span class="family-name">Masinter</span><span class="given-name">Larry</span></span></span><span class="org vcardline">Adobe Systems Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:LMM@acm.org"><span class="email">LMM@acm.org</span></a></span><span class="vcardline">URI: <a href="http://larry.masinter.net/" class="url">http://larry.masinter.net/</a></span></address>
    3046          <address class="vcard"><span class="vcardline"><span class="fn">Paul J. Leach</span><span class="n hidden"><span class="family-name">Leach</span><span class="given-name">Paul J.</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span>&nbsp;<span class="postal-code">98052</span></span></span><span class="vcardline">Email: <a href="mailto:paulle@microsoft.com"><span class="email">paulle@microsoft.com</span></a></span></address>
    3047          <address class="vcard"><span class="vcardline"><span class="fn">Tim Berners-Lee</span><span class="n hidden"><span class="family-name">Berners-Lee</span><span class="given-name">Tim</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">MIT Computer Science and Artificial Intelligence Laboratory</span><span class="street-address vcardline">The Stata Center, Building 32</span><span class="street-address vcardline">32 Vassar Street</span><span class="vcardline"><span class="locality">Cambridge</span>, <span class="region">MA</span>&nbsp;<span class="postal-code">02139</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:timbl@w3.org"><span class="email">timbl@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.w3.org/People/Berners-Lee/" class="url">http://www.w3.org/People/Berners-Lee/</a></span></address>
    3048          <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span>
    3049                (editor)
    3050                <span class="n hidden"><span class="family-name">Lafon</span><span class="given-name">Yves</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">W3C / ERCIM</span><span class="street-address vcardline">2004, rte des Lucioles</span><span class="vcardline"><span class="locality">Sophia-Antipolis</span>, <span class="region">AM</span>&nbsp;<span class="postal-code">06902</span></span><span class="country-name vcardline">France</span></span><span class="vcardline">Email: <a href="mailto:ylafon@w3.org"><span class="email">ylafon@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.raubacapeu.net/people/yves/" class="url">http://www.raubacapeu.net/people/yves/</a></span></address>
    3051          <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span>
    3052                (editor)
    3053                <span class="n hidden"><span class="family-name">Reschke</span><span class="given-name">Julian F.</span></span></span><span class="org vcardline">greenbytes GmbH</span><span class="adr"><span class="street-address vcardline">Hafenweg 16</span><span class="vcardline"><span class="locality">Muenster</span>, <span class="region">NW</span>&nbsp;<span class="postal-code">48155</span></span><span class="country-name vcardline">Germany</span></span><span class="vcardline tel">Phone: <a href="tel:+492512807760"><span class="value">+49 251 2807760</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+492512807761"><span class="value">+49 251 2807761</span></a></span><span class="vcardline">Email: <a href="mailto:julian.reschke@greenbytes.de"><span class="email">julian.reschke@greenbytes.de</span></a></span><span class="vcardline">URI: <a href="http://greenbytes.de/tech/webdav/" class="url">http://greenbytes.de/tech/webdav/</a></span></address>
    3054       </div>
    3055       <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1>
    3056       <p id="rfc.section.A.p.1">This document takes over the Status Code Registry, 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.RFC2817.2"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. (<a href="#status.code.registry" title="Status Code Registry">Section&nbsp;4.2</a>)
    3057       </p>
    3058       <p id="rfc.section.A.p.2">Clarify definition of POST. (<a href="#POST" id="rfc.xref.POST.3" title="POST">Section&nbsp;6.5</a>)
    3059       </p>
    3060       <p id="rfc.section.A.p.3">Remove requirement to handle all Content-* header fields; ban use of Content-Range with PUT. (<a href="#PUT" id="rfc.xref.PUT.3" title="PUT">Section&nbsp;6.6</a>)
    3061       </p>
    3062       <p id="rfc.section.A.p.4">Take over definition of CONNECT method from <a href="#RFC2817" id="rfc.xref.RFC2817.3"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. (<a href="#CONNECT" id="rfc.xref.CONNECT.3" title="CONNECT">Section&nbsp;6.9</a>)
    3063       </p>
    3064       <p id="rfc.section.A.p.5">Broadened the definition of 203 (Non-Authoritative Information) to include cases of payload transformations as well. (<a href="#status.203" id="rfc.xref.status.203.3" title="203 Non-Authoritative Information">Section&nbsp;7.2.4</a>)
    3065       </p>
    3066       <p id="rfc.section.A.p.6">Status codes 301, 302, and 307: removed the normative requirements on both response payloads and user interaction. (<a href="#status.3xx" title="Redirection 3xx">Section&nbsp;7.3</a>)
    3067       </p>
    3068       <p id="rfc.section.A.p.7">Failed to consider that there are many other request methods that are safe to automatically redirect, and further that the
    3069          user agent is able to make that determination based on the request method semantics. Furthermore, allow user agents to rewrite
    3070          the method from POST to GET for status codes 301 and 302. (Sections <a href="#status.301" id="rfc.xref.status.301.3" title="301 Moved Permanently">7.3.2</a>, <a href="#status.302" id="rfc.xref.status.302.3" title="302 Found">7.3.3</a> and <a href="#status.307" id="rfc.xref.status.307.3" title="307 Temporary Redirect">7.3.7</a>)
    3071       </p>
    3072       <p id="rfc.section.A.p.8">Deprecate 305 Use Proxy status code, because user agents did not implement it. It used to indicate that the target resource
    3073          must be accessed through the proxy given by the Location field. The Location field gave the URI of the proxy. The recipient
    3074          was expected to repeat this single request via the proxy. (<a href="#status.305" id="rfc.xref.status.305.3" title="305 Use Proxy">Section&nbsp;7.3.5</a>)
    3075       </p>
    3076       <p id="rfc.section.A.p.9">Define status 426 (Upgrade Required) (this was incorporated from <a href="#RFC2817" id="rfc.xref.RFC2817.4"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>). (<a href="#status.426" id="rfc.xref.status.426.3" title="426 Upgrade Required">Section&nbsp;7.4.15</a>)
    3077       </p>
    3078       <p id="rfc.section.A.p.10">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section&nbsp;10</a>)
    3079       </p>
    3080       <p id="rfc.section.A.p.11">Reclassify "Allow" as response header field, removing the option to specify it in a PUT request. Relax the server requirement
    3081          on the contents of the Allow header field and remove requirement on clients to always trust the header field value. (<a href="#header.allow" id="rfc.xref.header.allow.4" title="Allow">Section&nbsp;10.1</a>)
    3082       </p>
    3083       <p id="rfc.section.A.p.12">The ABNF for the Expect header field has been both fixed (allowing parameters for value-less expectations as well) and simplified
    3084          (allowing trailing semicolons after "100-continue" when they were invalid before). (<a href="#header.expect" id="rfc.xref.header.expect.4" title="Expect">Section&nbsp;10.3</a>)
    3085       </p>
    3086       <p id="rfc.section.A.p.13">Correct syntax of Location header field to allow URI references (including relative references and fragments), as referred
    3087          symbol "absoluteURI" wasn't what was expected, and add some clarifications as to when use of fragments would not be appropriate.
    3088          (<a href="#header.location" id="rfc.xref.header.location.5" title="Location">Section&nbsp;10.5</a>)
    3089       </p>
    3090       <p id="rfc.section.A.p.14">Restrict Max-Forwards header field to OPTIONS and TRACE (previously, extension methods could have used it as well). (<a href="#header.max-forwards" id="rfc.xref.header.max-forwards.5" title="Max-Forwards">Section&nbsp;10.6</a>)
    3091       </p>
    3092       <p id="rfc.section.A.p.15">Allow Referer field value of "about:blank" as alternative to not specifying it. (<a href="#header.referer" id="rfc.xref.header.referer.3" title="Referer">Section&nbsp;10.7</a>)
    3093       </p>
    3094       <p id="rfc.section.A.p.16">In the description of the Server header field, the Via field was described as a SHOULD. The requirement was and is stated
    3095          correctly in the description of the Via header field in <a href="p1-messaging.html#header.via" title="Via">Section 8.4</a> of <a href="#Part1" id="rfc.xref.Part1.42"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. (<a href="#header.server" id="rfc.xref.header.server.4" title="Server">Section&nbsp;10.9</a>)
    3096       </p>
    3097       <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1>
    3098       <div id="rfc.figure.u.38"></div> <pre class="inline"><a href="#header.allow" class="smpl">Allow</a> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
    3099 
    3100 <a href="#core.rules" class="smpl">BWS</a> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
    3101 
    3102 <a href="#header.date" class="smpl">Date</a> = HTTP-date
    3103 
    3104 <a href="#header.expect" class="smpl">Expect</a> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
    3105 
    3106 <a href="#header.from" class="smpl">From</a> = mailbox
    3107 
    3108 <a href="#preferred.date.format" class="smpl">GMT</a> = %x47.4D.54 ; GMT
    3109 
    3110 <a href="#http.date" class="smpl">HTTP-date</a> = rfc1123-date / obs-date
    3111 
    3112 <a href="#header.location" class="smpl">Location</a> = URI-reference
    3113 
    3114 <a href="#header.max-forwards" class="smpl">Max-Forwards</a> = 1*DIGIT
    3115 <a href="#method" class="smpl">Method</a> = token
    3116 
    3117 <a href="#core.rules" class="smpl">OWS</a> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
    3118 
    3119 <a href="#core.rules" class="smpl">RWS</a> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
    3120 <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> = *( HTAB / SP / VCHAR / obs-text )
    3121 <a href="#header.referer" class="smpl">Referer</a> = absolute-URI / partial-URI
    3122 <a href="#header.retry-after" class="smpl">Retry-After</a> = HTTP-date / delta-seconds
    3123 
    3124 <a href="#header.server" class="smpl">Server</a> = product *( RWS ( product / comment ) )
    3125 <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> = 3DIGIT
    3126 
    3127 <a href="#abnf.dependencies" class="smpl">URI-reference</a> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
    3128 <a href="#header.user-agent" class="smpl">User-Agent</a> = product *( RWS ( product / comment ) )
    3129 
    3130 <a href="#abnf.dependencies" class="smpl">absolute-URI</a> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
    3131 <a href="#obsolete.date.formats" class="smpl">asctime-date</a> = day-name SP date3 SP time-of-day SP year
    3132 
    3133 <a href="#abnf.dependencies" class="smpl">comment</a> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
    3134 
    3135 <a href="#obsolete.date.formats" class="smpl">date1</a> = day SP month SP year
    3136 <a href="#obsolete.date.formats" class="smpl">date2</a> = day "-" month "-" 2DIGIT
    3137 <a href="#obsolete.date.formats" class="smpl">date3</a> = month SP ( 2DIGIT / ( SP DIGIT ) )
    3138 <a href="#preferred.date.format" class="smpl">day</a> = 2DIGIT
    3139 <a href="#preferred.date.format" class="smpl">day-name</a> = %x4D.6F.6E ; Mon
    3140  / %x54.75.65 ; Tue
    3141  / %x57.65.64 ; Wed
    3142  / %x54.68.75 ; Thu
    3143  / %x46.72.69 ; Fri
    3144  / %x53.61.74 ; Sat
    3145  / %x53.75.6E ; Sun
    3146 <a href="#obsolete.date.formats" class="smpl">day-name-l</a> = %x4D.6F.6E.64.61.79 ; Monday
    3147  / %x54.75.65.73.64.61.79 ; Tuesday
    3148  / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
    3149  / %x54.68.75.72.73.64.61.79 ; Thursday
    3150  / %x46.72.69.64.61.79 ; Friday
    3151  / %x53.61.74.75.72.64.61.79 ; Saturday
    3152  / %x53.75.6E.64.61.79 ; Sunday
    3153 <a href="#rule.delta-seconds" class="smpl">delta-seconds</a> = 1*DIGIT
    3154 
    3155 <a href="#header.expect" class="smpl">expect-name</a> = token
    3156 <a href="#header.expect" class="smpl">expect-param</a> = expect-name [ BWS "=" BWS expect-value ]
    3157 <a href="#header.expect" class="smpl">expect-value</a> = token / quoted-string
    3158 <a href="#header.expect" class="smpl">expectation</a> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
    3159  OWS expect-param ] )
    3160 
    3161 <a href="#preferred.date.format" class="smpl">hour</a> = 2DIGIT
    3162 
    3163 <a href="#header.from" class="smpl">mailbox</a> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
    3164 <a href="#preferred.date.format" class="smpl">minute</a> = 2DIGIT
    3165 <a href="#preferred.date.format" class="smpl">month</a> = %x4A.61.6E ; Jan
    3166  / %x46.65.62 ; Feb
    3167  / %x4D.61.72 ; Mar
    3168  / %x41.70.72 ; Apr
    3169  / %x4D.61.79 ; May
    3170  / %x4A.75.6E ; Jun
    3171  / %x4A.75.6C ; Jul
    3172  / %x41.75.67 ; Aug
    3173  / %x53.65.70 ; Sep
    3174  / %x4F.63.74 ; Oct
    3175  / %x4E.6F.76 ; Nov
    3176  / %x44.65.63 ; Dec
    3177 
    3178 <a href="#obsolete.date.formats" class="smpl">obs-date</a> = rfc850-date / asctime-date
    3179 <a href="#core.rules" class="smpl">obs-text</a> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
    3180 
    3181 <a href="#abnf.dependencies" class="smpl">partial-URI</a> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
    3182 <a href="#product.tokens" class="smpl">product</a> = token [ "/" product-version ]
    3183 <a href="#product.tokens" class="smpl">product-version</a> = token
    3184 
    3185 <a href="#core.rules" class="smpl">quoted-string</a> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
    3186 
    3187 <a href="#preferred.date.format" class="smpl">rfc1123-date</a> = day-name "," SP date1 SP time-of-day SP GMT
    3188 <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> = day-name-l "," SP date2 SP time-of-day SP GMT
    3189 
    3190 <a href="#preferred.date.format" class="smpl">second</a> = 2DIGIT
    3191 
    3192 <a href="#preferred.date.format" class="smpl">time-of-day</a> = hour ":" minute ":" second
    3193 <a href="#core.rules" class="smpl">token</a> = &lt;token, defined in [Part1], Section 3.2.4&gt;
    3194 
    3195 <a href="#preferred.date.format" class="smpl">year</a> = 4DIGIT
    3196 </pre> <div id="rfc.figure.u.39"></div>
    3197       <p>ABNF diagnostics:</p><pre class="inline">; Allow defined but not used
    3198 ; Date defined but not used
    3199 ; Expect defined but not used
    3200 ; From defined but not used
    3201 ; Location defined but not used
    3202 ; Max-Forwards defined but not used
    3203 ; Reason-Phrase defined but not used
    3204 ; Referer defined but not used
    3205 ; Retry-After defined but not used
    3206 ; Server defined but not used
    3207 ; Status-Code defined but not used
    3208 ; User-Agent defined but not used
    3209 </pre><h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a>&nbsp;<a id="change.log" href="#change.log">Change Log (to be removed by RFC Editor before publication)</a></h1>
    3210       <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a>&nbsp;Since RFC 2616
    3211       </h2>
    3212       <p id="rfc.section.C.1.p.1">Extracted relevant partitions from <a href="#RFC2616" id="rfc.xref.RFC2616.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
    3213       </p>
    3214       <h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a>&nbsp;Since draft-ietf-httpbis-p2-semantics-00
    3215       </h2>
    3216       <p id="rfc.section.C.2.p.1">Closed issues: </p>
    3217       <ul>
    3218          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/5">http://tools.ietf.org/wg/httpbis/trac/ticket/5</a>&gt;: "Via is a MUST" (&lt;<a href="http://purl.org/NET/http-errata#via-must">http://purl.org/NET/http-errata#via-must</a>&gt;)
    3219          </li>
    3220          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/6">http://tools.ietf.org/wg/httpbis/trac/ticket/6</a>&gt;: "Fragments allowed in Location" (&lt;<a href="http://purl.org/NET/http-errata#location-fragments">http://purl.org/NET/http-errata#location-fragments</a>&gt;)
    3221          </li>
    3222          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/10">http://tools.ietf.org/wg/httpbis/trac/ticket/10</a>&gt;: "Safe Methods vs Redirection" (&lt;<a href="http://purl.org/NET/http-errata#saferedirect">http://purl.org/NET/http-errata#saferedirect</a>&gt;)
    3223          </li>
    3224          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/17">http://tools.ietf.org/wg/httpbis/trac/ticket/17</a>&gt;: "Revise description of the POST method" (&lt;<a href="http://purl.org/NET/http-errata#post">http://purl.org/NET/http-errata#post</a>&gt;)
    3225          </li>
    3226          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/35">http://tools.ietf.org/wg/httpbis/trac/ticket/35</a>&gt;: "Normative and Informative references"
    3227          </li>
    3228          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/42">http://tools.ietf.org/wg/httpbis/trac/ticket/42</a>&gt;: "RFC2606 Compliance"
    3229          </li>
    3230          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/65">http://tools.ietf.org/wg/httpbis/trac/ticket/65</a>&gt;: "Informative references"
    3231          </li>
    3232          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/84">http://tools.ietf.org/wg/httpbis/trac/ticket/84</a>&gt;: "Redundant cross-references"
    3233          </li>
    3234       </ul>
    3235       <p id="rfc.section.C.2.p.2">Other changes: </p>
    3236       <ul>
    3237          <li>Move definitions of 304 and 412 condition codes to <a href="#Part4" id="rfc.xref.Part4.11"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>
    3238          </li>
    3239       </ul>
    3240       <h2 id="rfc.section.C.3"><a href="#rfc.section.C.3">C.3</a>&nbsp;Since draft-ietf-httpbis-p2-semantics-01
    3241       </h2>
    3242       <p id="rfc.section.C.3.p.1">Closed issues: </p>
    3243       <ul>
    3244          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/21">http://tools.ietf.org/wg/httpbis/trac/ticket/21</a>&gt;: "PUT side effects"
    3245          </li>
    3246          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/91">http://tools.ietf.org/wg/httpbis/trac/ticket/91</a>&gt;: "Duplicate Host header requirements"
    3247          </li>
    3248       </ul>
    3249       <p id="rfc.section.C.3.p.2">Ongoing work on ABNF conversion (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>&gt;):
    3250       </p>
    3251       <ul>
    3252          <li>Move "Product Tokens" section (back) into Part 1, as "token" is used in the definition of the Upgrade header field.</li>
    3253          <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li>
    3254          <li>Copy definition of delta-seconds from Part6 instead of referencing it.</li>
    3255       </ul>
    3256       <h2 id="rfc.section.C.4"><a href="#rfc.section.C.4">C.4</a>&nbsp;<a id="changes.since.02" href="#changes.since.02">Since draft-ietf-httpbis-p2-semantics-02</a></h2>
    3257       <p id="rfc.section.C.4.p.1">Closed issues: </p>
    3258       <ul>
    3259          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/24">http://tools.ietf.org/wg/httpbis/trac/ticket/24</a>&gt;: "Requiring Allow in 405 responses"
    3260          </li>
    3261          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/59">http://tools.ietf.org/wg/httpbis/trac/ticket/59</a>&gt;: "Status Code Registry"
    3262          </li>
    3263          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/61">http://tools.ietf.org/wg/httpbis/trac/ticket/61</a>&gt;: "Redirection vs. Location"
    3264          </li>
    3265          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/70">http://tools.ietf.org/wg/httpbis/trac/ticket/70</a>&gt;: "Cacheability of 303 response"
    3266          </li>
    3267          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/76">http://tools.ietf.org/wg/httpbis/trac/ticket/76</a>&gt;: "305 Use Proxy"
    3268          </li>
    3269          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/105">http://tools.ietf.org/wg/httpbis/trac/ticket/105</a>&gt;: "Classification for Allow header"
    3270          </li>
    3271          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/112">http://tools.ietf.org/wg/httpbis/trac/ticket/112</a>&gt;: "PUT - 'store under' vs 'store at'"
    3272          </li>
    3273       </ul>
    3274       <p id="rfc.section.C.4.p.2">Ongoing work on IANA Message Header Field Registration (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/40">http://tools.ietf.org/wg/httpbis/trac/ticket/40</a>&gt;):
    3275       </p>
    3276       <ul>
    3277          <li>Reference RFC 3984, and update header field registrations for headers defined in this document.</li>
    3278       </ul>
    3279       <p id="rfc.section.C.4.p.3">Ongoing work on ABNF conversion (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>&gt;):
    3280       </p>
    3281       <ul>
    3282          <li>Replace string literals when the string really is case-sensitive (method).</li>
    3283       </ul>
    3284       <h2 id="rfc.section.C.5"><a href="#rfc.section.C.5">C.5</a>&nbsp;<a id="changes.since.03" href="#changes.since.03">Since draft-ietf-httpbis-p2-semantics-03</a></h2>
    3285       <p id="rfc.section.C.5.p.1">Closed issues: </p>
    3286       <ul>
    3287          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/98">http://tools.ietf.org/wg/httpbis/trac/ticket/98</a>&gt;: "OPTIONS request bodies"
    3288          </li>
    3289          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/119">http://tools.ietf.org/wg/httpbis/trac/ticket/119</a>&gt;: "Description of CONNECT should refer to RFC2817"
    3290          </li>
    3291          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/125">http://tools.ietf.org/wg/httpbis/trac/ticket/125</a>&gt;: "Location Content-Location reference request/response mixup"
    3292          </li>
    3293       </ul>
    3294       <p id="rfc.section.C.5.p.2">Ongoing work on Method Registry (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/72">http://tools.ietf.org/wg/httpbis/trac/ticket/72</a>&gt;):
    3295       </p>
    3296       <ul>
    3297          <li>Added initial proposal for registration process, plus initial content (non-HTTP/1.1 methods to be added by a separate specification).</li>
    3298       </ul>
    3299       <h2 id="rfc.section.C.6"><a href="#rfc.section.C.6">C.6</a>&nbsp;<a id="changes.since.04" href="#changes.since.04">Since draft-ietf-httpbis-p2-semantics-04</a></h2>
    3300       <p id="rfc.section.C.6.p.1">Closed issues: </p>
    3301       <ul>
    3302          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/103">http://tools.ietf.org/wg/httpbis/trac/ticket/103</a>&gt;: "Content-*"
    3303          </li>
    3304          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/132">http://tools.ietf.org/wg/httpbis/trac/ticket/132</a>&gt;: "RFC 2822 is updated by RFC 5322"
    3305          </li>
    3306       </ul>
    3307       <p id="rfc.section.C.6.p.2">Ongoing work on ABNF conversion (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>&gt;):
    3308       </p>
    3309       <ul>
    3310          <li>Use "/" instead of "|" for alternatives.</li>
    3311          <li>Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS").</li>
    3312          <li>Rewrite ABNFs to spell out whitespace rules, factor out header field value format definitions.</li>
    3313       </ul>
    3314       <h2 id="rfc.section.C.7"><a href="#rfc.section.C.7">C.7</a>&nbsp;<a id="changes.since.05" href="#changes.since.05">Since draft-ietf-httpbis-p2-semantics-05</a></h2>
    3315       <p id="rfc.section.C.7.p.1">Closed issues: </p>
    3316       <ul>
    3317          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/94">http://tools.ietf.org/wg/httpbis/trac/ticket/94</a>&gt;: "Reason-Phrase BNF"
    3318          </li>
    3319       </ul>
    3320       <p id="rfc.section.C.7.p.2">Final work on ABNF conversion (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>&gt;):
    3321       </p>
    3322       <ul>
    3323          <li>Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.</li>
    3324       </ul>
    3325       <h2 id="rfc.section.C.8"><a href="#rfc.section.C.8">C.8</a>&nbsp;<a id="changes.since.06" href="#changes.since.06">Since draft-ietf-httpbis-p2-semantics-06</a></h2>
    3326       <p id="rfc.section.C.8.p.1">Closed issues: </p>
    3327       <ul>
    3328          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/144">http://tools.ietf.org/wg/httpbis/trac/ticket/144</a>&gt;: "Clarify when Referer is sent"
    3329          </li>
    3330          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/164">http://tools.ietf.org/wg/httpbis/trac/ticket/164</a>&gt;: "status codes vs methods"
    3331          </li>
    3332          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/170">http://tools.ietf.org/wg/httpbis/trac/ticket/170</a>&gt;: "Do not require "updates" relation for specs that register status codes or method names"
    3333          </li>
    3334       </ul>
    3335       <h2 id="rfc.section.C.9"><a href="#rfc.section.C.9">C.9</a>&nbsp;<a id="changes.since.07" href="#changes.since.07">Since draft-ietf-httpbis-p2-semantics-07</a></h2>
    3336       <p id="rfc.section.C.9.p.1">Closed issues: </p>
    3337       <ul>
    3338          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/27">http://tools.ietf.org/wg/httpbis/trac/ticket/27</a>&gt;: "Idempotency"
    3339          </li>
    3340          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/33">http://tools.ietf.org/wg/httpbis/trac/ticket/33</a>&gt;: "TRACE security considerations"
    3341          </li>
    3342          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/110">http://tools.ietf.org/wg/httpbis/trac/ticket/110</a>&gt;: "Clarify rules for determining what entities a response carries"
    3343          </li>
    3344          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/140">http://tools.ietf.org/wg/httpbis/trac/ticket/140</a>&gt;: "update note citing RFC 1945 and 2068"
    3345          </li>
    3346          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/182">http://tools.ietf.org/wg/httpbis/trac/ticket/182</a>&gt;: "update note about redirect limit"
    3347          </li>
    3348          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/191">http://tools.ietf.org/wg/httpbis/trac/ticket/191</a>&gt;: "Location header ABNF should use 'URI'"
    3349          </li>
    3350          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/192">http://tools.ietf.org/wg/httpbis/trac/ticket/192</a>&gt;: "fragments in Location vs status 303"
    3351          </li>
    3352          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/198">http://tools.ietf.org/wg/httpbis/trac/ticket/198</a>&gt;: "move IANA registrations for optional status codes"
    3353          </li>
    3354       </ul>
    3355       <p id="rfc.section.C.9.p.2">Partly resolved issues: </p>
    3356       <ul>
    3357          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/171">http://tools.ietf.org/wg/httpbis/trac/ticket/171</a>&gt;: "Are OPTIONS and TRACE safe?"
    3358          </li>
    3359       </ul>
    3360       <h2 id="rfc.section.C.10"><a href="#rfc.section.C.10">C.10</a>&nbsp;<a id="changes.since.08" href="#changes.since.08">Since draft-ietf-httpbis-p2-semantics-08</a></h2>
    3361       <p id="rfc.section.C.10.p.1">Closed issues: </p>
    3362       <ul>
    3363          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/10">http://tools.ietf.org/wg/httpbis/trac/ticket/10</a>&gt;: "Safe Methods vs Redirection" (we missed the introduction to the 3xx status codes when fixing this previously)
    3364          </li>
    3365       </ul>
    3366       <h2 id="rfc.section.C.11"><a href="#rfc.section.C.11">C.11</a>&nbsp;<a id="changes.since.09" href="#changes.since.09">Since draft-ietf-httpbis-p2-semantics-09</a></h2>
    3367       <p id="rfc.section.C.11.p.1">Closed issues: </p>
    3368       <ul>
    3369          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/43">http://tools.ietf.org/wg/httpbis/trac/ticket/43</a>&gt;: "Fragment combination / precedence during redirects"
    3370          </li>
    3371       </ul>
    3372       <p id="rfc.section.C.11.p.2">Partly resolved issues: </p>
    3373       <ul>
    3374          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/185">http://tools.ietf.org/wg/httpbis/trac/ticket/185</a>&gt;: "Location header payload handling"
    3375          </li>
    3376          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/196">http://tools.ietf.org/wg/httpbis/trac/ticket/196</a>&gt;: "Term for the requested resource's URI"
    3377          </li>
    3378       </ul>
    3379       <h2 id="rfc.section.C.12"><a href="#rfc.section.C.12">C.12</a>&nbsp;<a id="changes.since.10" href="#changes.since.10">Since draft-ietf-httpbis-p2-semantics-10</a></h2>
    3380       <p id="rfc.section.C.12.p.1">Closed issues: </p>
    3381       <ul>
    3382          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/69">http://tools.ietf.org/wg/httpbis/trac/ticket/69</a>&gt;: "Clarify 'Requested Variant'"
    3383          </li>
    3384          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/109">http://tools.ietf.org/wg/httpbis/trac/ticket/109</a>&gt;: "Clarify entity / representation / variant terminology"
    3385          </li>
    3386          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/139">http://tools.ietf.org/wg/httpbis/trac/ticket/139</a>&gt;: "Methods and Caching"
    3387          </li>
    3388          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/190">http://tools.ietf.org/wg/httpbis/trac/ticket/190</a>&gt;: "OPTIONS vs Max-Forwards"
    3389          </li>
    3390          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/199">http://tools.ietf.org/wg/httpbis/trac/ticket/199</a>&gt;: "Status codes and caching"
    3391          </li>
    3392          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/220">http://tools.ietf.org/wg/httpbis/trac/ticket/220</a>&gt;: "consider removing the 'changes from 2068' sections"
    3393          </li>
    3394       </ul>
    3395       <h2 id="rfc.section.C.13"><a href="#rfc.section.C.13">C.13</a>&nbsp;<a id="changes.since.11" href="#changes.since.11">Since draft-ietf-httpbis-p2-semantics-11</a></h2>
    3396       <p id="rfc.section.C.13.p.1">Closed issues: </p>
    3397       <ul>
    3398          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/229">http://tools.ietf.org/wg/httpbis/trac/ticket/229</a>&gt;: "Considerations for new status codes"
    3399          </li>
    3400          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/230">http://tools.ietf.org/wg/httpbis/trac/ticket/230</a>&gt;: "Considerations for new methods"
    3401          </li>
    3402          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/232">http://tools.ietf.org/wg/httpbis/trac/ticket/232</a>&gt;: "User-Agent guidelines" (relating to the 'User-Agent' header field)
    3403          </li>
    3404       </ul>
    3405       <h2 id="rfc.section.C.14"><a href="#rfc.section.C.14">C.14</a>&nbsp;<a id="changes.since.12" href="#changes.since.12">Since draft-ietf-httpbis-p2-semantics-12</a></h2>
    3406       <p id="rfc.section.C.14.p.1">Closed issues: </p>
    3407       <ul>
    3408          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/43">http://tools.ietf.org/wg/httpbis/trac/ticket/43</a>&gt;: "Fragment combination / precedence during redirects" (added warning about having a fragid on the redirect may cause inconvenience
    3409             in some cases)
    3410          </li>
    3411          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/79">http://tools.ietf.org/wg/httpbis/trac/ticket/79</a>&gt;: "Content-* vs. PUT"
    3412          </li>
    3413          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/88">http://tools.ietf.org/wg/httpbis/trac/ticket/88</a>&gt;: "205 Bodies"
    3414          </li>
    3415          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/102">http://tools.ietf.org/wg/httpbis/trac/ticket/102</a>&gt;: "Understanding Content-* on non-PUT requests"
    3416          </li>
    3417          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/103">http://tools.ietf.org/wg/httpbis/trac/ticket/103</a>&gt;: "Content-*"
    3418          </li>
    3419          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/104">http://tools.ietf.org/wg/httpbis/trac/ticket/104</a>&gt;: "Header type defaulting"
    3420          </li>
    3421          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/112">http://tools.ietf.org/wg/httpbis/trac/ticket/112</a>&gt;: "PUT - 'store under' vs 'store at'"
    3422          </li>
    3423          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/137">http://tools.ietf.org/wg/httpbis/trac/ticket/137</a>&gt;: "duplicate ABNF for Reason-Phrase"
    3424          </li>
    3425          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/180">http://tools.ietf.org/wg/httpbis/trac/ticket/180</a>&gt;: "Note special status of Content-* prefix in header registration procedures"
    3426          </li>
    3427          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/203">http://tools.ietf.org/wg/httpbis/trac/ticket/203</a>&gt;: "Max-Forwards vs extension methods"
    3428          </li>
    3429          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/213">http://tools.ietf.org/wg/httpbis/trac/ticket/213</a>&gt;: "What is the value space of HTTP status codes?" (actually fixed in draft-ietf-httpbis-p2-semantics-11)
    3430          </li>
    3431          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/224">http://tools.ietf.org/wg/httpbis/trac/ticket/224</a>&gt;: "Header Classification"
    3432          </li>
    3433          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/225">http://tools.ietf.org/wg/httpbis/trac/ticket/225</a>&gt;: "PUT side effect: invalidation or just stale?"
    3434          </li>
    3435          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/226">http://tools.ietf.org/wg/httpbis/trac/ticket/226</a>&gt;: "proxies not supporting certain methods"
    3436          </li>
    3437          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/239">http://tools.ietf.org/wg/httpbis/trac/ticket/239</a>&gt;: "Migrate CONNECT from RFC2817 to p2"
    3438          </li>
    3439          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/240">http://tools.ietf.org/wg/httpbis/trac/ticket/240</a>&gt;: "Migrate Upgrade details from RFC2817"
    3440          </li>
    3441          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/267">http://tools.ietf.org/wg/httpbis/trac/ticket/267</a>&gt;: "clarify PUT semantics'"
    3442          </li>
    3443          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/275">http://tools.ietf.org/wg/httpbis/trac/ticket/275</a>&gt;: "duplicate ABNF for 'Method'"
    3444          </li>
    3445          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/276">http://tools.ietf.org/wg/httpbis/trac/ticket/276</a>&gt;: "untangle ABNFs for header fields"
    3446          </li>
    3447       </ul>
    3448       <h2 id="rfc.section.C.15"><a href="#rfc.section.C.15">C.15</a>&nbsp;<a id="changes.since.13" href="#changes.since.13">Since draft-ietf-httpbis-p2-semantics-13</a></h2>
    3449       <p id="rfc.section.C.15.p.1">Closed issues: </p>
    3450       <ul>
    3451          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/276">http://tools.ietf.org/wg/httpbis/trac/ticket/276</a>&gt;: "untangle ABNFs for header fields"
    3452          </li>
    3453          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/251">http://tools.ietf.org/wg/httpbis/trac/ticket/251</a>&gt;: "message body in CONNECT request"
    3454          </li>
    3455       </ul>
    3456       <h2 id="rfc.section.C.16"><a href="#rfc.section.C.16">C.16</a>&nbsp;<a id="changes.since.14" href="#changes.since.14">Since draft-ietf-httpbis-p2-semantics-14</a></h2>
    3457       <p id="rfc.section.C.16.p.1">Closed issues: </p>
    3458       <ul>
    3459          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/255">http://tools.ietf.org/wg/httpbis/trac/ticket/255</a>&gt;: "Clarify status code for rate limiting"
    3460          </li>
    3461          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/294">http://tools.ietf.org/wg/httpbis/trac/ticket/294</a>&gt;: "clarify 403 forbidden"
    3462          </li>
    3463          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/296">http://tools.ietf.org/wg/httpbis/trac/ticket/296</a>&gt;: "Clarify 203 Non-Authoritative Information"
    3464          </li>
    3465          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/298">http://tools.ietf.org/wg/httpbis/trac/ticket/298</a>&gt;: "update default reason phrase for 413"
    3466          </li>
    3467       </ul>
    3468       <h2 id="rfc.section.C.17"><a href="#rfc.section.C.17">C.17</a>&nbsp;<a id="changes.since.15" href="#changes.since.15">Since draft-ietf-httpbis-p2-semantics-15</a></h2>
    3469       <p id="rfc.section.C.17.p.1">Closed issues: </p>
    3470       <ul>
    3471          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/285">http://tools.ietf.org/wg/httpbis/trac/ticket/285</a>&gt;: "Strength of requirements on Accept re: 406"
    3472          </li>
    3473          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/303">http://tools.ietf.org/wg/httpbis/trac/ticket/303</a>&gt;: "400 response isn't generic"
    3474          </li>
    3475       </ul>
    3476       <h2 id="rfc.section.C.18"><a href="#rfc.section.C.18">C.18</a>&nbsp;<a id="changes.since.16" href="#changes.since.16">Since draft-ietf-httpbis-p2-semantics-16</a></h2>
    3477       <p id="rfc.section.C.18.p.1">Closed issues: </p>
    3478       <ul>
    3479          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/160">http://tools.ietf.org/wg/httpbis/trac/ticket/160</a>&gt;: "Redirects and non-GET methods"
    3480          </li>
    3481          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/186">http://tools.ietf.org/wg/httpbis/trac/ticket/186</a>&gt;: "Document HTTP's error-handling philosophy"
    3482          </li>
    3483          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/231">http://tools.ietf.org/wg/httpbis/trac/ticket/231</a>&gt;: "Considerations for new headers"
    3484          </li>
    3485          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/310">http://tools.ietf.org/wg/httpbis/trac/ticket/310</a>&gt;: "clarify 303 redirect on HEAD"
    3486          </li>
    3487       </ul>
    3488       <h2 id="rfc.section.C.19"><a href="#rfc.section.C.19">C.19</a>&nbsp;<a id="changes.since.17" href="#changes.since.17">Since draft-ietf-httpbis-p2-semantics-17</a></h2>
    3489       <p id="rfc.section.C.19.p.1">Closed issues: </p>
    3490       <ul>
    3491          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/185">http://tools.ietf.org/wg/httpbis/trac/ticket/185</a>&gt;: "Location header payload handling"
    3492          </li>
    3493          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/255">http://tools.ietf.org/wg/httpbis/trac/ticket/255</a>&gt;: "Clarify status code for rate limiting" (change backed out because a new status code is being defined for this purpose)
    3494          </li>
    3495          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/312">http://tools.ietf.org/wg/httpbis/trac/ticket/312</a>&gt;: "should there be a permanent variant of 307"
    3496          </li>
    3497          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/325">http://tools.ietf.org/wg/httpbis/trac/ticket/325</a>&gt;: "When are Location's semantics triggered?"
    3498          </li>
    3499          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/327">http://tools.ietf.org/wg/httpbis/trac/ticket/327</a>&gt;: "'expect' grammar missing OWS"
    3500          </li>
    3501          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/329">http://tools.ietf.org/wg/httpbis/trac/ticket/329</a>&gt;: "header field considerations: quoted-string vs use of double quotes"
    3502          </li>
    3503       </ul>
    3504       <h2 id="rfc.section.C.20"><a href="#rfc.section.C.20">C.20</a>&nbsp;<a id="changes.since.18" href="#changes.since.18">Since draft-ietf-httpbis-p2-semantics-18</a></h2>
    3505       <p id="rfc.section.C.20.p.1">Closed issues: </p>
    3506       <ul>
    3507          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/238">http://tools.ietf.org/wg/httpbis/trac/ticket/238</a>&gt;: "Requirements for user intervention during redirects"
    3508          </li>
    3509          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/295">http://tools.ietf.org/wg/httpbis/trac/ticket/295</a>&gt;: "Applying original fragment to 'plain' redirected URI"
    3510          </li>
    3511          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/302">http://tools.ietf.org/wg/httpbis/trac/ticket/302</a>&gt;: "Misplaced text on connection handling in p2"
    3512          </li>
    3513          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/332">http://tools.ietf.org/wg/httpbis/trac/ticket/332</a>&gt;: "relax requirements on hypertext in 3/4/5xx error responses"
    3514          </li>
    3515          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/333">http://tools.ietf.org/wg/httpbis/trac/ticket/333</a>&gt;: "example for 426 response should have a payload"
    3516          </li>
    3517          <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/336">http://tools.ietf.org/wg/httpbis/trac/ticket/336</a>&gt;: "drop indirection entries for status codes"
    3518          </li>
    3519       </ul>
    3520       <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1>
    3521       <p class="noprint"><a href="#rfc.index.1">1</a> <a href="#rfc.index.2">2</a> <a href="#rfc.index.3">3</a> <a href="#rfc.index.4">4</a> <a href="#rfc.index.5">5</a> <a href="#rfc.index.A">A</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.D">D</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.F">F</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.I">I</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.O">O</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.T">T</a> <a href="#rfc.index.U">U</a>
    3522       </p>
    3523       <div class="print2col">
    3524          <ul class="ind">
    3525             <li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul>
    3526                   <li>100 Continue (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.100.1">4.1</a>, <a href="#rfc.iref.22"><b>7.1.1</b></a>, <a href="#rfc.xref.status.100.2">11.2</a></li>
    3527                   <li>100-continue (expect value)&nbsp;&nbsp;<a href="#rfc.iref.89"><b>10.3</b></a></li>
    3528                   <li>101 Switching Protocols (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.101.1">4.1</a>, <a href="#rfc.iref.23"><b>7.1.2</b></a>, <a href="#rfc.xref.status.101.2">11.2</a></li>
    3529                </ul>
    3530             </li>
    3531             <li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul>
    3532                   <li>200 OK (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.200.1">4.1</a>, <a href="#rfc.iref.24"><b>7.2.1</b></a>, <a href="#rfc.xref.status.200.2">11.2</a></li>
    3533                   <li>201 Created (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.201.1">4.1</a>, <a href="#rfc.iref.25"><b>7.2.2</b></a>, <a href="#rfc.xref.status.201.2">11.2</a></li>
    3534                   <li>202 Accepted (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.202.1">4.1</a>, <a href="#rfc.iref.26"><b>7.2.3</b></a>, <a href="#rfc.xref.status.202.2">11.2</a></li>
    3535                   <li>203 Non-Authoritative Information (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.203.1">4.1</a>, <a href="#rfc.iref.27"><b>7.2.4</b></a>, <a href="#rfc.xref.status.203.2">11.2</a>, <a href="#rfc.xref.status.203.3">A</a></li>
    3536                   <li>204 No Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.204.1">4.1</a>, <a href="#rfc.iref.28"><b>7.2.5</b></a>, <a href="#rfc.xref.status.204.2">11.2</a></li>
    3537                   <li>205 Reset Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.205.1">4.1</a>, <a href="#rfc.iref.29"><b>7.2.6</b></a>, <a href="#rfc.xref.status.205.2">11.2</a></li>
    3538                </ul>
    3539             </li>
    3540             <li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul>
    3541                   <li>300 Multiple Choices (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.300.1">4.1</a>, <a href="#rfc.iref.30"><b>7.3.1</b></a>, <a href="#rfc.xref.status.300.2">11.2</a></li>
    3542                   <li>301 Moved Permanently (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.301.1">4.1</a>, <a href="#rfc.iref.31"><b>7.3.2</b></a>, <a href="#rfc.xref.status.301.2">11.2</a>, <a href="#rfc.xref.status.301.3">A</a></li>
    3543                   <li>302 Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.302.1">4.1</a>, <a href="#rfc.iref.32"><b>7.3.3</b></a>, <a href="#rfc.xref.status.302.2">11.2</a>, <a href="#rfc.xref.status.302.3">A</a></li>
    3544                   <li>303 See Other (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.303.1">4.1</a>, <a href="#rfc.iref.33"><b>7.3.4</b></a>, <a href="#rfc.xref.status.303.2">11.2</a></li>
    3545                   <li>305 Use Proxy (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.305.1">4.1</a>, <a href="#rfc.iref.34"><b>7.3.5</b></a>, <a href="#rfc.xref.status.305.2">11.2</a>, <a href="#rfc.xref.status.305.3">A</a></li>
    3546                   <li>306 (Unused) (status code)&nbsp;&nbsp;<a href="#rfc.iref.35"><b>7.3.6</b></a>, <a href="#rfc.xref.status.306.1">11.2</a></li>
    3547                   <li>307 Temporary Redirect (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.307.1">4.1</a>, <a href="#rfc.iref.36"><b>7.3.7</b></a>, <a href="#rfc.xref.status.307.2">11.2</a>, <a href="#rfc.xref.status.307.3">A</a></li>
    3548                </ul>
    3549             </li>
    3550             <li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul>
    3551                   <li>400 Bad Request (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.400.1">4.1</a>, <a href="#rfc.iref.37"><b>7.4.1</b></a>, <a href="#rfc.xref.status.400.2">11.2</a></li>
    3552                   <li>402 Payment Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.402.1">4.1</a>, <a href="#rfc.iref.38"><b>7.4.2</b></a>, <a href="#rfc.xref.status.402.2">11.2</a></li>
    3553                   <li>403 Forbidden (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.403.1">4.1</a>, <a href="#rfc.iref.39"><b>7.4.3</b></a>, <a href="#rfc.xref.status.403.2">11.2</a></li>
    3554                   <li>404 Not Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.404.1">4.1</a>, <a href="#rfc.iref.40"><b>7.4.4</b></a>, <a href="#rfc.xref.status.404.2">11.2</a></li>
    3555                   <li>405 Method Not Allowed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.405.1">4.1</a>, <a href="#rfc.iref.41"><b>7.4.5</b></a>, <a href="#rfc.xref.status.405.2">11.2</a></li>
    3556                   <li>406 Not Acceptable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.406.1">4.1</a>, <a href="#rfc.iref.42"><b>7.4.6</b></a>, <a href="#rfc.xref.status.406.2">11.2</a></li>
    3557                   <li>408 Request Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.408.1">4.1</a>, <a href="#rfc.iref.43"><b>7.4.7</b></a>, <a href="#rfc.xref.status.408.2">11.2</a></li>
    3558                   <li>409 Conflict (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.409.1">4.1</a>, <a href="#rfc.iref.44"><b>7.4.8</b></a>, <a href="#rfc.xref.status.409.2">11.2</a></li>
    3559                   <li>410 Gone (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.410.1">4.1</a>, <a href="#rfc.iref.45"><b>7.4.9</b></a>, <a href="#rfc.xref.status.410.2">11.2</a></li>
    3560                   <li>411 Length Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.411.1">4.1</a>, <a href="#rfc.iref.46"><b>7.4.10</b></a>, <a href="#rfc.xref.status.411.2">11.2</a></li>
    3561                   <li>413 Request Representation Too Large (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.413.1">4.1</a>, <a href="#rfc.iref.47"><b>7.4.11</b></a>, <a href="#rfc.xref.status.413.2">11.2</a></li>
    3562                   <li>414 URI Too Long (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.414.1">4.1</a>, <a href="#rfc.iref.48"><b>7.4.12</b></a>, <a href="#rfc.xref.status.414.2">11.2</a></li>
    3563                   <li>415 Unsupported Media Type (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.415.1">4.1</a>, <a href="#rfc.iref.49"><b>7.4.13</b></a>, <a href="#rfc.xref.status.415.2">11.2</a></li>
    3564                   <li>417 Expectation Failed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.417.1">4.1</a>, <a href="#rfc.iref.50"><b>7.4.14</b></a>, <a href="#rfc.xref.status.417.2">11.2</a></li>
    3565                   <li>426 Upgrade Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.426.1">4.1</a>, <a href="#rfc.iref.51"><b>7.4.15</b></a>, <a href="#rfc.xref.status.426.2">11.2</a>, <a href="#rfc.xref.status.426.3">A</a></li>
    3566                </ul>
    3567             </li>
    3568             <li><a id="rfc.index.5" href="#rfc.index.5"><b>5</b></a><ul>
    3569                   <li>500 Internal Server Error (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.500.1">4.1</a>, <a href="#rfc.iref.52"><b>7.5.1</b></a>, <a href="#rfc.xref.status.500.2">11.2</a></li>
    3570                   <li>501 Not Implemented (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.501.1">4.1</a>, <a href="#rfc.iref.53"><b>7.5.2</b></a>, <a href="#rfc.xref.status.501.2">11.2</a></li>
    3571                   <li>502 Bad Gateway (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.502.1">4.1</a>, <a href="#rfc.iref.54"><b>7.5.3</b></a>, <a href="#rfc.xref.status.502.2">11.2</a></li>
    3572                   <li>503 Service Unavailable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.503.1">4.1</a>, <a href="#rfc.iref.55"><b>7.5.4</b></a>, <a href="#rfc.xref.status.503.2">11.2</a></li>
    3573                   <li>504 Gateway Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.504.1">4.1</a>, <a href="#rfc.iref.56"><b>7.5.5</b></a>, <a href="#rfc.xref.status.504.2">11.2</a></li>
    3574                   <li>505 HTTP Version Not Supported (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.505.1">4.1</a>, <a href="#rfc.iref.57"><b>7.5.6</b></a>, <a href="#rfc.xref.status.505.2">11.2</a></li>
    3575                </ul>
    3576             </li>
    3577             <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul>
    3578                   <li>Allow header field&nbsp;&nbsp;<a href="#rfc.xref.header.allow.1">2</a>, <a href="#rfc.xref.header.allow.2">3.3</a>, <a href="#rfc.iref.a.1"><b>10.1</b></a>, <a href="#rfc.xref.header.allow.3">11.3</a>, <a href="#rfc.xref.header.allow.4">A</a></li>
    3579                </ul>
    3580             </li>
    3581             <li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul>
    3582                   <li>CONNECT method&nbsp;&nbsp;<a href="#rfc.xref.CONNECT.1">2.1</a>, <a href="#rfc.iref.c.1"><b>6.9</b></a>, <a href="#rfc.xref.CONNECT.2">11.1</a>, <a href="#rfc.xref.CONNECT.3">A</a></li>
    3583                </ul>
    3584             </li>
    3585             <li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul>
    3586                   <li>Date header field&nbsp;&nbsp;<a href="#rfc.xref.header.date.1">3.3</a>, <a href="#rfc.iref.d.2"><b>10.2</b></a>, <a href="#rfc.xref.header.date.2">11.3</a></li>
    3587                   <li>DELETE method&nbsp;&nbsp;<a href="#rfc.xref.DELETE.1">2.1</a>, <a href="#rfc.iref.d.1"><b>6.7</b></a>, <a href="#rfc.xref.DELETE.2">11.1</a></li>
    3588                </ul>
    3589             </li>
    3590             <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul>
    3591                   <li>Expect header field&nbsp;&nbsp;<a href="#rfc.xref.header.expect.1">3.2</a>, <a href="#rfc.xref.header.expect.2">7.4.14</a>, <a href="#rfc.iref.e.1"><b>10.3</b></a>, <a href="#rfc.xref.header.expect.3">11.3</a>, <a href="#rfc.xref.header.expect.4">A</a></li>
    3592                   <li>Expect Values&nbsp;&nbsp;
    3593                      <ul>
    3594                         <li>100-continue&nbsp;&nbsp;<a href="#rfc.iref.e.2"><b>10.3</b></a></li>
    3595                      </ul>
    3596                   </li>
    3597                </ul>
    3598             </li>
    3599             <li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul>
    3600                   <li>From header field&nbsp;&nbsp;<a href="#rfc.xref.header.from.1">3.2</a>, <a href="#rfc.iref.f.1"><b>10.4</b></a>, <a href="#rfc.xref.header.from.2">11.3</a></li>
    3601                </ul>
    3602             </li>
    3603             <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul>
    3604                   <li>GET method&nbsp;&nbsp;<a href="#rfc.xref.GET.1">2.1</a>, <a href="#rfc.iref.g.5"><b>6.3</b></a>, <a href="#rfc.xref.GET.2">11.1</a></li>
    3605                   <li><tt>Grammar</tt>&nbsp;&nbsp;
    3606                      <ul>
    3607                         <li><tt>Allow</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.24"><b>10.1</b></a></li>
    3608                         <li><tt>asctime-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.21"><b>8</b></a></li>
    3609                         <li><tt>Date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.25"><b>10.2</b></a></li>
    3610                         <li><tt>date1</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>8</b></a></li>
    3611                         <li><tt>day</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>8</b></a></li>
    3612                         <li><tt>day-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.13"><b>8</b></a></li>
    3613                         <li><tt>day-name-l</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>8</b></a></li>
    3614                         <li><tt>delta-seconds</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.36"><b>10.8</b></a></li>
    3615                         <li><tt>Expect</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.26"><b>10.3</b></a></li>
    3616                         <li><tt>expect-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.30"><b>10.3</b></a></li>
    3617                         <li><tt>expect-param</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.28"><b>10.3</b></a></li>
    3618                         <li><tt>expect-value</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.29"><b>10.3</b></a></li>
    3619                         <li><tt>expectation</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.27"><b>10.3</b></a></li>
    3620                         <li><tt>extension-code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>4</b></a></li>
    3621                         <li><tt>From</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.31"><b>10.4</b></a></li>
    3622                         <li><tt>GMT</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.18"><b>8</b></a></li>
    3623                         <li><tt>hour</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>8</b></a></li>
    3624                         <li><tt>HTTP-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>8</b></a></li>
    3625                         <li><tt>Location</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.32"><b>10.5</b></a></li>
    3626                         <li><tt>Max-Forwards</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.33"><b>10.6</b></a></li>
    3627                         <li><tt>Method</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2</b></a></li>
    3628                         <li><tt>minute</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>8</b></a></li>
    3629                         <li><tt>month</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.16"><b>8</b></a></li>
    3630                         <li><tt>obs-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.19"><b>8</b></a></li>
    3631                         <li><tt>product</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.22"><b>9</b></a></li>
    3632                         <li><tt>product-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.23"><b>9</b></a></li>
    3633                         <li><tt>Reason-Phrase</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>4</b></a></li>
    3634                         <li><tt>Referer</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.34"><b>10.7</b></a></li>
    3635                         <li><tt>Retry-After</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.35"><b>10.8</b></a></li>
    3636                         <li><tt>rfc1123-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>8</b></a></li>
    3637                         <li><tt>rfc850-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.20"><b>8</b></a></li>
    3638                         <li><tt>second</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>8</b></a></li>
    3639                         <li><tt>Server</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.37"><b>10.9</b></a></li>
    3640                         <li><tt>Status-Code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>4</b></a></li>
    3641                         <li><tt>time-of-day</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>8</b></a></li>
    3642                         <li><tt>User-Agent</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.38"><b>10.10</b></a></li>
    3643                         <li><tt>year</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.17"><b>8</b></a></li>
    3644                      </ul>
    3645                   </li>
    3646                </ul>
    3647             </li>
    3648             <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul>
    3649                   <li>HEAD method&nbsp;&nbsp;<a href="#rfc.xref.HEAD.1">2.1</a>, <a href="#rfc.iref.h.1"><b>6.4</b></a>, <a href="#rfc.xref.HEAD.2">11.1</a></li>
    3650                   <li>Header Fields&nbsp;&nbsp;
    3651                      <ul>
    3652                         <li>Allow&nbsp;&nbsp;<a href="#rfc.xref.header.allow.1">2</a>, <a href="#rfc.xref.header.allow.2">3.3</a>, <a href="#rfc.iref.h.2"><b>10.1</b></a>, <a href="#rfc.xref.header.allow.3">11.3</a>, <a href="#rfc.xref.header.allow.4">A</a></li>
    3653                         <li>Date&nbsp;&nbsp;<a href="#rfc.xref.header.date.1">3.3</a>, <a href="#rfc.iref.h.3"><b>10.2</b></a>, <a href="#rfc.xref.header.date.2">11.3</a></li>
    3654                         <li>Expect&nbsp;&nbsp;<a href="#rfc.xref.header.expect.1">3.2</a>, <a href="#rfc.xref.header.expect.2">7.4.14</a>, <a href="#rfc.iref.h.4"><b>10.3</b></a>, <a href="#rfc.xref.header.expect.3">11.3</a>, <a href="#rfc.xref.header.expect.4">A</a></li>
    3655                         <li>From&nbsp;&nbsp;<a href="#rfc.xref.header.from.1">3.2</a>, <a href="#rfc.iref.h.5"><b>10.4</b></a>, <a href="#rfc.xref.header.from.2">11.3</a></li>
    3656                         <li>Location&nbsp;&nbsp;<a href="#rfc.xref.header.location.1">3.3</a>, <a href="#rfc.xref.header.location.2">6.5</a>, <a href="#rfc.xref.header.location.3">7.3</a>, <a href="#rfc.iref.h.6"><b>10.5</b></a>, <a href="#rfc.xref.header.location.4">11.3</a>, <a href="#rfc.xref.header.location.5">A</a></li>
    3657                         <li>Max-Forwards&nbsp;&nbsp;<a href="#rfc.xref.header.max-forwards.1">3.2</a>, <a href="#rfc.xref.header.max-forwards.2">6.2</a>, <a href="#rfc.xref.header.max-forwards.3">6.8</a>, <a href="#rfc.iref.h.7"><b>10.6</b></a>, <a href="#rfc.xref.header.max-forwards.4">11.3</a>, <a href="#rfc.xref.header.max-forwards.5">A</a></li>
    3658                         <li>Referer&nbsp;&nbsp;<a href="#rfc.xref.header.referer.1">3.2</a>, <a href="#rfc.iref.h.8"><b>10.7</b></a>, <a href="#rfc.xref.header.referer.2">11.3</a>, <a href="#rfc.xref.header.referer.3">A</a></li>
    3659                         <li>Retry-After&nbsp;&nbsp;<a href="#rfc.xref.header.retry-after.1">3.3</a>, <a href="#rfc.xref.header.retry-after.2">7.5.4</a>, <a href="#rfc.iref.h.9"><b>10.8</b></a>, <a href="#rfc.xref.header.retry-after.3">11.3</a></li>
    3660                         <li>Server&nbsp;&nbsp;<a href="#rfc.xref.header.server.1">3.3</a>, <a href="#rfc.iref.h.10"><b>10.9</b></a>, <a href="#rfc.xref.header.server.2">11.3</a>, <a href="#rfc.xref.header.server.3">12.1</a>, <a href="#rfc.xref.header.server.4">A</a></li>
    3661                         <li>User-Agent&nbsp;&nbsp;<a href="#rfc.xref.header.user-agent.1">3.2</a>, <a href="#rfc.iref.h.11"><b>10.10</b></a>, <a href="#rfc.xref.header.user-agent.2">11.3</a>, <a href="#rfc.xref.header.user-agent.3">12.1</a></li>
    3662                      </ul>
    3663                   </li>
    3664                </ul>
    3665             </li>
    3666             <li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul>
    3667                   <li>Idempotent Methods&nbsp;&nbsp;<a href="#rfc.iref.i.1"><b>6.1.2</b></a></li>
    3668                </ul>
    3669             </li>
    3670             <li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul>
    3671                   <li>Location header field&nbsp;&nbsp;<a href="#rfc.xref.header.location.1">3.3</a>, <a href="#rfc.xref.header.location.2">6.5</a>, <a href="#rfc.xref.header.location.3">7.3</a>, <a href="#rfc.iref.l.1"><b>10.5</b></a>, <a href="#rfc.xref.header.location.4">11.3</a>, <a href="#rfc.xref.header.location.5">A</a></li>
    3672                </ul>
    3673             </li>
    3674             <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul>
    3675                   <li>Max-Forwards header field&nbsp;&nbsp;<a href="#rfc.xref.header.max-forwards.1">3.2</a>, <a href="#rfc.xref.header.max-forwards.2">6.2</a>, <a href="#rfc.xref.header.max-forwards.3">6.8</a>, <a href="#rfc.iref.m.9"><b>10.6</b></a>, <a href="#rfc.xref.header.max-forwards.4">11.3</a>, <a href="#rfc.xref.header.max-forwards.5">A</a></li>
    3676                   <li>Methods&nbsp;&nbsp;
    3677                      <ul>
    3678                         <li>CONNECT&nbsp;&nbsp;<a href="#rfc.xref.CONNECT.1">2.1</a>, <a href="#rfc.iref.m.8"><b>6.9</b></a>, <a href="#rfc.xref.CONNECT.2">11.1</a>, <a href="#rfc.xref.CONNECT.3">A</a></li>
    3679                         <li>DELETE&nbsp;&nbsp;<a href="#rfc.xref.DELETE.1">2.1</a>, <a href="#rfc.iref.m.6"><b>6.7</b></a>, <a href="#rfc.xref.DELETE.2">11.1</a></li>
    3680                         <li>GET&nbsp;&nbsp;<a href="#rfc.xref.GET.1">2.1</a>, <a href="#rfc.iref.m.2"><b>6.3</b></a>, <a href="#rfc.xref.GET.2">11.1</a></li>
    3681                         <li>HEAD&nbsp;&nbsp;<a href="#rfc.xref.HEAD.1">2.1</a>, <a href="#rfc.iref.m.3"><b>6.4</b></a>, <a href="#rfc.xref.HEAD.2">11.1</a></li>
    3682                         <li>OPTIONS&nbsp;&nbsp;<a href="#rfc.xref.OPTIONS.1">2.1</a>, <a href="#rfc.iref.m.1"><b>6.2</b></a>, <a href="#rfc.xref.OPTIONS.2">10.6</a>, <a href="#rfc.xref.OPTIONS.3">11.1</a></li>
    3683                         <li>POST&nbsp;&nbsp;<a href="#rfc.xref.POST.1">2.1</a>, <a href="#rfc.iref.m.4"><b>6.5</b></a>, <a href="#rfc.xref.POST.2">11.1</a>, <a href="#rfc.xref.POST.3">A</a></li>
    3684                         <li>PUT&nbsp;&nbsp;<a href="#rfc.xref.PUT.1">2.1</a>, <a href="#rfc.iref.m.5"><b>6.6</b></a>, <a href="#rfc.xref.PUT.2">11.1</a>, <a href="#rfc.xref.PUT.3">A</a></li>
    3685                         <li>TRACE&nbsp;&nbsp;<a href="#rfc.xref.TRACE.1">2.1</a>, <a href="#rfc.iref.m.7"><b>6.8</b></a>, <a href="#rfc.xref.TRACE.2">10.6</a>, <a href="#rfc.xref.TRACE.3">11.1</a>, <a href="#rfc.xref.TRACE.4">12.1</a></li>
    3686                      </ul>
    3687                   </li>
    3688                </ul>
    3689             </li>
    3690             <li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul>
    3691                   <li>OPTIONS method&nbsp;&nbsp;<a href="#rfc.xref.OPTIONS.1">2.1</a>, <a href="#rfc.iref.o.1"><b>6.2</b></a>, <a href="#rfc.xref.OPTIONS.2">10.6</a>, <a href="#rfc.xref.OPTIONS.3">11.1</a></li>
    3692                </ul>
    3693             </li>
    3694             <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
    3695                   <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1</a>, <a href="#rfc.xref.Part1.2">1.1</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">1.2.1</a>, <a href="#rfc.xref.Part1.5">1.2.1</a>, <a href="#rfc.xref.Part1.6">1.2.1</a>, <a href="#rfc.xref.Part1.7">1.2.1</a>, <a href="#rfc.xref.Part1.8">1.2.1</a>, <a href="#rfc.xref.Part1.9">1.2.1</a>, <a href="#rfc.xref.Part1.10">1.2.1</a>, <a href="#rfc.xref.Part1.11">1.2.2</a>, <a href="#rfc.xref.Part1.12">1.2.2</a>, <a href="#rfc.xref.Part1.13">1.2.2</a>, <a href="#rfc.xref.Part1.14">1.2.2</a>, <a href="#rfc.xref.Part1.15">2</a>, <a href="#rfc.xref.Part1.16">2.2.1</a>, <a href="#rfc.xref.Part1.17">3</a>, <a href="#rfc.xref.Part1.18">3.1</a>, <a href="#rfc.xref.Part1.19">3.1</a>, <a href="#rfc.xref.Part1.20">3.1</a>, <a href="#rfc.xref.Part1.21">3.1</a>, <a href="#rfc.xref.Part1.22">3.1</a>, <a href="#rfc.xref.Part1.23">3.2</a>, <a href="#rfc.xref.Part1.24">3.2</a>, <a href="#rfc.xref.Part1.25">3.3</a>, <a href="#rfc.xref.Part1.26">5</a>, <a href="#rfc.xref.Part1.27">5.1</a>, <a href="#rfc.xref.Part1.28">6.8</a>, <a href="#rfc.xref.Part1.29">6.8</a>, <a href="#rfc.xref.Part1.30">6.9</a>, <a href="#rfc.xref.Part1.31">7.1.1</a>, <a href="#rfc.xref.Part1.32">7.1.2</a>, <a href="#rfc.xref.Part1.33">7.2.4</a>, <a href="#rfc.xref.Part1.34">7.2.6</a>, <a href="#rfc.xref.Part1.35">7.4.15</a>, <a href="#rfc.xref.Part1.36">7.5.6</a>, <a href="#rfc.xref.Part1.37">10.3</a>, <a href="#rfc.xref.Part1.38">10.9</a>, <a href="#rfc.xref.Part1.39">10.9</a>, <a href="#rfc.xref.Part1.40">10.10</a>, <a href="#rfc.xref.Part1.41">13</a>, <a href="#Part1"><b>14.1</b></a>, <a href="#rfc.xref.Part1.42">A</a><ul>
    3696                         <li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.3">1.2</a></li>
    3697                         <li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">1.1</a></li>
    3698                         <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.33">7.2.4</a></li>
    3699                         <li><em>Section 2.6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.36">7.5.6</a></li>
    3700                         <li><em>Section 2.7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.11">1.2.2</a>, <a href="#rfc.xref.Part1.13">1.2.2</a>, <a href="#rfc.xref.Part1.14">1.2.2</a></li>
    3701                         <li><em>Section 3.1.1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.30">6.9</a></li>
    3702                         <li><em>Section 3.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">1.2.1</a>, <a href="#rfc.xref.Part1.6">1.2.1</a>, <a href="#rfc.xref.Part1.7">1.2.1</a></li>
    3703                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.17">3</a>, <a href="#rfc.xref.Part1.20">3.1</a>, <a href="#rfc.xref.Part1.38">10.9</a>, <a href="#rfc.xref.Part1.40">10.10</a></li>
    3704                         <li><em>Section 3.2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.8">1.2.1</a>, <a href="#rfc.xref.Part1.9">1.2.1</a>, <a href="#rfc.xref.Part1.10">1.2.1</a>, <a href="#rfc.xref.Part1.12">1.2.2</a>, <a href="#rfc.xref.Part1.19">3.1</a></li>
    3705                         <li><em>Section 3.2.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.18">3.1</a></li>
    3706                         <li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.16">2.2.1</a>, <a href="#rfc.xref.Part1.26">5</a>, <a href="#rfc.xref.Part1.34">7.2.6</a></li>
    3707                         <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.15">2</a>, <a href="#rfc.xref.Part1.25">3.3</a>, <a href="#rfc.xref.Part1.27">5.1</a></li>
    3708                         <li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.22">3.1</a></li>
    3709                         <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.24">3.2</a></li>
    3710                         <li><em>Section 6.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.31">7.1.1</a>, <a href="#rfc.xref.Part1.37">10.3</a></li>
    3711                         <li><em>Section 8.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.21">3.1</a></li>
    3712                         <li><em>Section 8.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.23">3.2</a></li>
    3713                         <li><em>Section 8.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.32">7.1.2</a>, <a href="#rfc.xref.Part1.35">7.4.15</a></li>
    3714                         <li><em>Section 8.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.28">6.8</a>, <a href="#rfc.xref.Part1.39">10.9</a>, <a href="#rfc.xref.Part1.42">A</a></li>
    3715                         <li><em>Section 9.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.29">6.8</a></li>
    3716                         <li><em>Section 11</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.41">13</a></li>
    3717                      </ul>
    3718                   </li>
    3719                   <li><em>Part3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">3.1</a>, <a href="#rfc.xref.Part3.2">3.1</a>, <a href="#rfc.xref.Part3.3">3.2</a>, <a href="#rfc.xref.Part3.4">3.2</a>, <a href="#rfc.xref.Part3.5">3.2</a>, <a href="#rfc.xref.Part3.6">3.2</a>, <a href="#rfc.xref.Part3.7">5</a>, <a href="#rfc.xref.Part3.8">6.5</a>, <a href="#rfc.xref.Part3.9">7</a>, <a href="#rfc.xref.Part3.10">7.3</a>, <a href="#rfc.xref.Part3.11">7.3.1</a>, <a href="#rfc.xref.Part3.12">7.4.6</a>, <a href="#rfc.xref.Part3.13">10.5</a>, <a href="#Part3"><b>14.1</b></a><ul>
    3720                         <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.2">3.1</a></li>
    3721                         <li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.11">7.3.1</a></li>
    3722                         <li><em>Section 5.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.10">7.3</a></li>
    3723                         <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.3">3.2</a></li>
    3724                         <li><em>Section 6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.12">7.4.6</a></li>
    3725                         <li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.4">3.2</a></li>
    3726                         <li><em>Section 6.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.5">3.2</a></li>
    3727                         <li><em>Section 6.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.6">3.2</a></li>
    3728                         <li><em>Section 6.7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.8">6.5</a>, <a href="#rfc.xref.Part3.13">10.5</a></li>
    3729                         <li><em>Section 6.8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">3.1</a>, <a href="#rfc.xref.Part3.9">7</a></li>
    3730                      </ul>
    3731                   </li>
    3732                   <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">3.2</a>, <a href="#rfc.xref.Part4.2">3.2</a>, <a href="#rfc.xref.Part4.3">3.2</a>, <a href="#rfc.xref.Part4.4">3.2</a>, <a href="#rfc.xref.Part4.5">3.3</a>, <a href="#rfc.xref.Part4.6">4.1</a>, <a href="#rfc.xref.Part4.7">4.1</a>, <a href="#rfc.xref.Part4.8">4.1</a>, <a href="#rfc.xref.Part4.9">7.2.2</a>, <a href="#rfc.xref.Part4.10">7.3</a>, <a href="#Part4"><b>14.1</b></a>, <a href="#rfc.xref.Part4.11">C.2</a><ul>
    3733                         <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.5">3.3</a>, <a href="#rfc.xref.Part4.9">7.2.2</a></li>
    3734                         <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">3.2</a></li>
    3735                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">3.2</a></li>
    3736                         <li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.2">3.2</a></li>
    3737                         <li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.4">3.2</a></li>
    3738                         <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.6">4.1</a></li>
    3739                         <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.7">4.1</a>, <a href="#rfc.xref.Part4.10">7.3</a></li>
    3740                         <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.8">4.1</a></li>
    3741                      </ul>
    3742                   </li>
    3743                   <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">3.2</a>, <a href="#rfc.xref.Part5.2">3.2</a>, <a href="#rfc.xref.Part5.3">3.3</a>, <a href="#rfc.xref.Part5.4">4.1</a>, <a href="#rfc.xref.Part5.5">4.1</a>, <a href="#rfc.xref.Part5.6">4.1</a>, <a href="#rfc.xref.Part5.7">6.3</a>, <a href="#Part5"><b>14.1</b></a><ul>
    3744                         <li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.4">4.1</a></li>
    3745                         <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.5">4.1</a></li>
    3746                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.6">4.1</a></li>
    3747                         <li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.3">3.3</a></li>
    3748                         <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">3.2</a></li>
    3749                         <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.2">3.2</a>, <a href="#rfc.xref.Part5.7">6.3</a></li>
    3750                      </ul>
    3751                   </li>
    3752                   <li><em>Part6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">2.2.1</a>, <a href="#rfc.xref.Part6.2">3.1</a>, <a href="#rfc.xref.Part6.3">3.3</a>, <a href="#rfc.xref.Part6.4">3.3</a>, <a href="#rfc.xref.Part6.5">4.2.1</a>, <a href="#rfc.xref.Part6.6">6.3</a>, <a href="#rfc.xref.Part6.7">6.4</a>, <a href="#rfc.xref.Part6.8">6.5</a>, <a href="#rfc.xref.Part6.9">6.6</a>, <a href="#rfc.xref.Part6.10">6.7</a>, <a href="#rfc.xref.Part6.11">7.2.1</a>, <a href="#rfc.xref.Part6.12">7.2.4</a>, <a href="#rfc.xref.Part6.13">7.2.4</a>, <a href="#rfc.xref.Part6.14">7.2.4</a>, <a href="#rfc.xref.Part6.15">7.3.1</a>, <a href="#rfc.xref.Part6.16">7.3.2</a>, <a href="#rfc.xref.Part6.17">7.4.9</a>, <a href="#Part6"><b>14.1</b></a><ul>
    3753                         <li><em>Section 2.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.8">6.5</a></li>
    3754                         <li><em>Section 2.3.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.11">7.2.1</a>, <a href="#rfc.xref.Part6.14">7.2.4</a>, <a href="#rfc.xref.Part6.15">7.3.1</a>, <a href="#rfc.xref.Part6.16">7.3.2</a>, <a href="#rfc.xref.Part6.17">7.4.9</a></li>
    3755                         <li><em>Section 2.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.9">6.6</a>, <a href="#rfc.xref.Part6.10">6.7</a></li>
    3756                         <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.3">3.3</a></li>
    3757                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.12">7.2.4</a></li>
    3758                         <li><em>Section 3.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.4">3.3</a></li>
    3759                         <li><em>Section 3.6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.13">7.2.4</a></li>
    3760                      </ul>
    3761                   </li>
    3762                   <li><em>Part7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">3.2</a>, <a href="#rfc.xref.Part7.2">3.2</a>, <a href="#rfc.xref.Part7.3">3.3</a>, <a href="#rfc.xref.Part7.4">3.3</a>, <a href="#rfc.xref.Part7.5">4.1</a>, <a href="#rfc.xref.Part7.6">4.1</a>, <a href="#rfc.xref.Part7.7">4.1</a>, <a href="#Part7"><b>14.1</b></a><ul>
    3763                         <li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.5">4.1</a></li>
    3764                         <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.6">4.1</a></li>
    3765                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.7">4.1</a></li>
    3766                         <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">3.2</a></li>
    3767                         <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.3">3.3</a></li>
    3768                         <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.2">3.2</a></li>
    3769                         <li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.4">3.3</a></li>
    3770                      </ul>
    3771                   </li>
    3772                   <li>POST method&nbsp;&nbsp;<a href="#rfc.xref.POST.1">2.1</a>, <a href="#rfc.iref.p.1"><b>6.5</b></a>, <a href="#rfc.xref.POST.2">11.1</a>, <a href="#rfc.xref.POST.3">A</a></li>
    3773                   <li>PUT method&nbsp;&nbsp;<a href="#rfc.xref.PUT.1">2.1</a>, <a href="#rfc.iref.p.2"><b>6.6</b></a>, <a href="#rfc.xref.PUT.2">11.1</a>, <a href="#rfc.xref.PUT.3">A</a></li>
    3774                </ul>
    3775             </li>
    3776             <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul>
    3777                   <li>Referer header field&nbsp;&nbsp;<a href="#rfc.xref.header.referer.1">3.2</a>, <a href="#rfc.iref.r.1"><b>10.7</b></a>, <a href="#rfc.xref.header.referer.2">11.3</a>, <a href="#rfc.xref.header.referer.3">A</a></li>
    3778                   <li>Retry-After header field&nbsp;&nbsp;<a href="#rfc.xref.header.retry-after.1">3.3</a>, <a href="#rfc.xref.header.retry-after.2">7.5.4</a>, <a href="#rfc.iref.r.2"><b>10.8</b></a>, <a href="#rfc.xref.header.retry-after.3">11.3</a></li>
    3779                   <li><em>RFC1123</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1123.1">8</a>, <a href="#rfc.xref.RFC1123.2">8</a>, <a href="#RFC1123"><b>14.2</b></a><ul>
    3780                         <li><em>Section 5.2.14</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1123.2">8</a></li>
    3781                      </ul>
    3782                   </li>
    3783                   <li><em>RFC1945</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">7.3</a>, <a href="#RFC1945"><b>14.2</b></a><ul>
    3784                         <li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">7.3</a></li>
    3785                      </ul>
    3786                   </li>
    3787                   <li><em>RFC2068</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.1">7.3</a>, <a href="#rfc.xref.RFC2068.2">7.3</a>, <a href="#RFC2068"><b>14.2</b></a><ul>
    3788                         <li><em>Section 10.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.2">7.3</a></li>
    3789                         <li><em>Section 10.3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.1">7.3</a></li>
    3790                      </ul>
    3791                   </li>
    3792                   <li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>14.1</b></a></li>
    3793                   <li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">1</a>, <a href="#rfc.xref.RFC2616.2">7.3</a>, <a href="#RFC2616"><b>14.2</b></a>, <a href="#rfc.xref.RFC2616.3">C.1</a><ul>
    3794                         <li><em>Section 10.3.8</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.2">7.3</a></li>
    3795                      </ul>
    3796                   </li>
    3797                   <li><em>RFC2817</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">11.2</a>, <a href="#RFC2817"><b>14.2</b></a>, <a href="#rfc.xref.RFC2817.2">A</a>, <a href="#rfc.xref.RFC2817.3">A</a>, <a href="#rfc.xref.RFC2817.4">A</a><ul>
    3798                         <li><em>Section 7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">11.2</a>, <a href="#rfc.xref.RFC2817.2">A</a></li>
    3799                      </ul>
    3800                   </li>
    3801                   <li><em>RFC3864</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3864.1">3.1</a>, <a href="#rfc.xref.RFC3864.2">3.1</a>, <a href="#rfc.xref.RFC3864.3">11.3</a>, <a href="#RFC3864"><b>14.2</b></a><ul>
    3802                         <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3864.2">3.1</a></li>
    3803                      </ul>
    3804                   </li>
    3805                   <li><em>RFC3986</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.1">10.5</a>, <a href="#rfc.xref.RFC3986.2">10.5</a>, <a href="#RFC3986"><b>14.1</b></a><ul>
    3806                         <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.1">10.5</a></li>
    3807                         <li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.2">10.5</a></li>
    3808                      </ul>
    3809                   </li>
    3810                   <li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">2.2</a>, <a href="#rfc.xref.RFC5226.2">4.2</a>, <a href="#RFC5226"><b>14.2</b></a><ul>
    3811                         <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">2.2</a>, <a href="#rfc.xref.RFC5226.2">4.2</a></li>
    3812                      </ul>
    3813                   </li>
    3814                   <li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">1.2</a>, <a href="#rfc.xref.RFC5234.3">3.1</a>, <a href="#RFC5234"><b>14.1</b></a><ul>
    3815                         <li><em>Appendix B.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.2">1.2</a></li>
    3816                      </ul>
    3817                   </li>
    3818                   <li><em>RFC5322</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">8</a>, <a href="#rfc.xref.RFC5322.2">10.2</a>, <a href="#rfc.xref.RFC5322.3">10.4</a>, <a href="#rfc.xref.RFC5322.4">10.4</a>, <a href="#RFC5322"><b>14.2</b></a><ul>
    3819                         <li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">8</a></li>
    3820                         <li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.3">10.4</a>, <a href="#rfc.xref.RFC5322.4">10.4</a></li>
    3821                         <li><em>Section 3.6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.2">10.2</a></li>
    3822                      </ul>
    3823                   </li>
    3824                   <li><em>RFC5789</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5789.1">6.6</a>, <a href="#RFC5789"><b>14.2</b></a></li>
    3825                   <li><em>RFC5987</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5987.1">3.1</a>, <a href="#RFC5987"><b>14.2</b></a></li>
    3826                </ul>
    3827             </li>
    3828             <li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul>
    3829                   <li>Safe Methods&nbsp;&nbsp;<a href="#rfc.iref.s.1"><b>6.1.1</b></a></li>
    3830                   <li>Server header field&nbsp;&nbsp;<a href="#rfc.xref.header.server.1">3.3</a>, <a href="#rfc.iref.s.38"><b>10.9</b></a>, <a href="#rfc.xref.header.server.2">11.3</a>, <a href="#rfc.xref.header.server.3">12.1</a>, <a href="#rfc.xref.header.server.4">A</a></li>
    3831                   <li>Status Codes&nbsp;&nbsp;
    3832                      <ul>
    3833                         <li>100 Continue&nbsp;&nbsp;<a href="#rfc.xref.status.100.1">4.1</a>, <a href="#rfc.iref.s.2"><b>7.1.1</b></a>, <a href="#rfc.xref.status.100.2">11.2</a></li>
    3834                         <li>101 Switching Protocols&nbsp;&nbsp;<a href="#rfc.xref.status.101.1">4.1</a>, <a href="#rfc.iref.s.3"><b>7.1.2</b></a>, <a href="#rfc.xref.status.101.2">11.2</a></li>
    3835                         <li>200 OK&nbsp;&nbsp;<a href="#rfc.xref.status.200.1">4.1</a>, <a href="#rfc.iref.s.4"><b>7.2.1</b></a>, <a href="#rfc.xref.status.200.2">11.2</a></li>
    3836                         <li>201 Created&nbsp;&nbsp;<a href="#rfc.xref.status.201.1">4.1</a>, <a href="#rfc.iref.s.5"><b>7.2.2</b></a>, <a href="#rfc.xref.status.201.2">11.2</a></li>
    3837                         <li>202 Accepted&nbsp;&nbsp;<a href="#rfc.xref.status.202.1">4.1</a>, <a href="#rfc.iref.s.6"><b>7.2.3</b></a>, <a href="#rfc.xref.status.202.2">11.2</a></li>
    3838                         <li>203 Non-Authoritative Information&nbsp;&nbsp;<a href="#rfc.xref.status.203.1">4.1</a>, <a href="#rfc.iref.s.7"><b>7.2.4</b></a>, <a href="#rfc.xref.status.203.2">11.2</a>, <a href="#rfc.xref.status.203.3">A</a></li>
    3839                         <li>204 No Content&nbsp;&nbsp;<a href="#rfc.xref.status.204.1">4.1</a>, <a href="#rfc.iref.s.8"><b>7.2.5</b></a>, <a href="#rfc.xref.status.204.2">11.2</a></li>
    3840                         <li>205 Reset Content&nbsp;&nbsp;<a href="#rfc.xref.status.205.1">4.1</a>, <a href="#rfc.iref.s.9"><b>7.2.6</b></a>, <a href="#rfc.xref.status.205.2">11.2</a></li>
    3841                         <li>300 Multiple Choices&nbsp;&nbsp;<a href="#rfc.xref.status.300.1">4.1</a>, <a href="#rfc.iref.s.10"><b>7.3.1</b></a>, <a href="#rfc.xref.status.300.2">11.2</a></li>
    3842                         <li>301 Moved Permanently&nbsp;&nbsp;<a href="#rfc.xref.status.301.1">4.1</a>, <a href="#rfc.iref.s.11"><b>7.3.2</b></a>, <a href="#rfc.xref.status.301.2">11.2</a>, <a href="#rfc.xref.status.301.3">A</a></li>
    3843                         <li>302 Found&nbsp;&nbsp;<a href="#rfc.xref.status.302.1">4.1</a>, <a href="#rfc.iref.s.12"><b>7.3.3</b></a>, <a href="#rfc.xref.status.302.2">11.2</a>, <a href="#rfc.xref.status.302.3">A</a></li>
    3844                         <li>303 See Other&nbsp;&nbsp;<a href="#rfc.xref.status.303.1">4.1</a>, <a href="#rfc.iref.s.13"><b>7.3.4</b></a>, <a href="#rfc.xref.status.303.2">11.2</a></li>
    3845                         <li>305 Use Proxy&nbsp;&nbsp;<a href="#rfc.xref.status.305.1">4.1</a>, <a href="#rfc.iref.s.14"><b>7.3.5</b></a>, <a href="#rfc.xref.status.305.2">11.2</a>, <a href="#rfc.xref.status.305.3">A</a></li>
    3846                         <li>306 (Unused)&nbsp;&nbsp;<a href="#rfc.iref.s.15"><b>7.3.6</b></a>, <a href="#rfc.xref.status.306.1">11.2</a></li>
    3847                         <li>307 Temporary Redirect&nbsp;&nbsp;<a href="#rfc.xref.status.307.1">4.1</a>, <a href="#rfc.iref.s.16"><b>7.3.7</b></a>, <a href="#rfc.xref.status.307.2">11.2</a>, <a href="#rfc.xref.status.307.3">A</a></li>
    3848                         <li>400 Bad Request&nbsp;&nbsp;<a href="#rfc.xref.status.400.1">4.1</a>, <a href="#rfc.iref.s.17"><b>7.4.1</b></a>, <a href="#rfc.xref.status.400.2">11.2</a></li>
    3849                         <li>402 Payment Required&nbsp;&nbsp;<a href="#rfc.xref.status.402.1">4.1</a>, <a href="#rfc.iref.s.18"><b>7.4.2</b></a>, <a href="#rfc.xref.status.402.2">11.2</a></li>
    3850                         <li>403 Forbidden&nbsp;&nbsp;<a href="#rfc.xref.status.403.1">4.1</a>, <a href="#rfc.iref.s.19"><b>7.4.3</b></a>, <a href="#rfc.xref.status.403.2">11.2</a></li>
    3851                         <li>404 Not Found&nbsp;&nbsp;<a href="#rfc.xref.status.404.1">4.1</a>, <a href="#rfc.iref.s.20"><b>7.4.4</b></a>, <a href="#rfc.xref.status.404.2">11.2</a></li>
    3852                         <li>405 Method Not Allowed&nbsp;&nbsp;<a href="#rfc.xref.status.405.1">4.1</a>, <a href="#rfc.iref.s.21"><b>7.4.5</b></a>, <a href="#rfc.xref.status.405.2">11.2</a></li>
    3853                         <li>406 Not Acceptable&nbsp;&nbsp;<a href="#rfc.xref.status.406.1">4.1</a>, <a href="#rfc.iref.s.22"><b>7.4.6</b></a>, <a href="#rfc.xref.status.406.2">11.2</a></li>
    3854                         <li>408 Request Timeout&nbsp;&nbsp;<a href="#rfc.xref.status.408.1">4.1</a>, <a href="#rfc.iref.s.23"><b>7.4.7</b></a>, <a href="#rfc.xref.status.408.2">11.2</a></li>
    3855                         <li>409 Conflict&nbsp;&nbsp;<a href="#rfc.xref.status.409.1">4.1</a>, <a href="#rfc.iref.s.24"><b>7.4.8</b></a>, <a href="#rfc.xref.status.409.2">11.2</a></li>
    3856                         <li>410 Gone&nbsp;&nbsp;<a href="#rfc.xref.status.410.1">4.1</a>, <a href="#rfc.iref.s.25"><b>7.4.9</b></a>, <a href="#rfc.xref.status.410.2">11.2</a></li>
    3857                         <li>411 Length Required&nbsp;&nbsp;<a href="#rfc.xref.status.411.1">4.1</a>, <a href="#rfc.iref.s.26"><b>7.4.10</b></a>, <a href="#rfc.xref.status.411.2">11.2</a></li>
    3858                         <li>413 Request Representation Too Large&nbsp;&nbsp;<a href="#rfc.xref.status.413.1">4.1</a>, <a href="#rfc.iref.s.27"><b>7.4.11</b></a>, <a href="#rfc.xref.status.413.2">11.2</a></li>
    3859                         <li>414 URI Too Long&nbsp;&nbsp;<a href="#rfc.xref.status.414.1">4.1</a>, <a href="#rfc.iref.s.28"><b>7.4.12</b></a>, <a href="#rfc.xref.status.414.2">11.2</a></li>
    3860                         <li>415 Unsupported Media Type&nbsp;&nbsp;<a href="#rfc.xref.status.415.1">4.1</a>, <a href="#rfc.iref.s.29"><b>7.4.13</b></a>, <a href="#rfc.xref.status.415.2">11.2</a></li>
    3861                         <li>417 Expectation Failed&nbsp;&nbsp;<a href="#rfc.xref.status.417.1">4.1</a>, <a href="#rfc.iref.s.30"><b>7.4.14</b></a>, <a href="#rfc.xref.status.417.2">11.2</a></li>
    3862                         <li>426 Upgrade Required&nbsp;&nbsp;<a href="#rfc.xref.status.426.1">4.1</a>, <a href="#rfc.iref.s.31"><b>7.4.15</b></a>, <a href="#rfc.xref.status.426.2">11.2</a>, <a href="#rfc.xref.status.426.3">A</a></li>
    3863                         <li>500 Internal Server Error&nbsp;&nbsp;<a href="#rfc.xref.status.500.1">4.1</a>, <a href="#rfc.iref.s.32"><b>7.5.1</b></a>, <a href="#rfc.xref.status.500.2">11.2</a></li>
    3864                         <li>501 Not Implemented&nbsp;&nbsp;<a href="#rfc.xref.status.501.1">4.1</a>, <a href="#rfc.iref.s.33"><b>7.5.2</b></a>, <a href="#rfc.xref.status.501.2">11.2</a></li>
    3865                         <li>502 Bad Gateway&nbsp;&nbsp;<a href="#rfc.xref.status.502.1">4.1</a>, <a href="#rfc.iref.s.34"><b>7.5.3</b></a>, <a href="#rfc.xref.status.502.2">11.2</a></li>
    3866                         <li>503 Service Unavailable&nbsp;&nbsp;<a href="#rfc.xref.status.503.1">4.1</a>, <a href="#rfc.iref.s.35"><b>7.5.4</b></a>, <a href="#rfc.xref.status.503.2">11.2</a></li>
    3867                         <li>504 Gateway Timeout&nbsp;&nbsp;<a href="#rfc.xref.status.504.1">4.1</a>, <a href="#rfc.iref.s.36"><b>7.5.5</b></a>, <a href="#rfc.xref.status.504.2">11.2</a></li>
    3868                         <li>505 HTTP Version Not Supported&nbsp;&nbsp;<a href="#rfc.xref.status.505.1">4.1</a>, <a href="#rfc.iref.s.37"><b>7.5.6</b></a>, <a href="#rfc.xref.status.505.2">11.2</a></li>
    3869                      </ul>
    3870                   </li>
    3871                </ul>
    3872             </li>
    3873             <li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul>
    3874                   <li>TRACE method&nbsp;&nbsp;<a href="#rfc.xref.TRACE.1">2.1</a>, <a href="#rfc.iref.t.1"><b>6.8</b></a>, <a href="#rfc.xref.TRACE.2">10.6</a>, <a href="#rfc.xref.TRACE.3">11.1</a>, <a href="#rfc.xref.TRACE.4">12.1</a></li>
    3875                </ul>
    3876             </li>
    3877             <li><a id="rfc.index.U" href="#rfc.index.U"><b>U</b></a><ul>
    3878                   <li>User-Agent header field&nbsp;&nbsp;<a href="#rfc.xref.header.user-agent.1">3.2</a>, <a href="#rfc.iref.u.1"><b>10.10</b></a>, <a href="#rfc.xref.header.user-agent.2">11.3</a>, <a href="#rfc.xref.header.user-agent.3">12.1</a></li>
    3879                </ul>
    3880             </li>
    3881          </ul>
    3882       </div>
    3883    </body>
    3884 </html>
  • draft-ietf-httpbis/latest/p2-semantics.xml

    r1552 r1554  
    8686  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8787  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     88  <!ENTITY p6-head                 "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8889]>
    8990<?rfc toc="yes" ?>
     
    10361037<t>
    10371038   The response to a HEAD request is cacheable and &MAY; be used to satisfy
    1038    a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
    1039    representation from that resource; if the new field values
    1040    indicate that the cached representation differs from the current representation (as
    1041    would be indicated by a change in Content-Length, ETag
    1042    or Last-Modified), then the cache &MUST; treat the cache entry as
    1043    stale.
     1039   a subsequent HEAD request. It also has potential side effects on
     1040   previously stored responses to GET; see &p6-head;.
    10441041</t>
    10451042<t>
  • draft-ietf-httpbis/latest/p6-cache.html

    r1552 r1554  
    463463  }
    464464  @bottom-center {
    465        content: "Expires September 2012";
     465       content: "Expires September 4, 2012";
    466466  }
    467467  @bottom-right {
     
    498498      <link href="p5-range.html" rel="prev">
    499499      <link href="p7-auth.html" rel="next">
    500       <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.570, 2012-02-13 19:17:35, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">
     500      <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.570, 2012-02-13 19:17:35, XSLT vendor: SAXON 9.1.0.8 from Saxonica http://www.saxonica.com/">
    501501      <link rel="schema.dct" href="http://purl.org/dc/terms/">
    502502      <meta name="dct.creator" content="Fielding, R.">
     
    511511      <meta name="dct.creator" content="Reschke, J. F.">
    512512      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p6-cache-latest">
    513       <meta name="dct.issued" scheme="ISO8601" content="2012-03">
     513      <meta name="dct.issued" scheme="ISO8601" content="2012-03-03">
    514514      <meta name="dct.replaces" content="urn:ietf:rfc:2616">
    515515      <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 6 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 6 defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages.">
     
    537537            </tr>
    538538            <tr>
    539                <td class="left">Expires: September 2012</td>
     539               <td class="left">Expires: September 4, 2012</td>
    540540               <td class="right">J. Mogul</td>
    541541            </tr>
     
    602602            <tr>
    603603               <td class="left"></td>
    604                <td class="right">March 2012</td>
     604               <td class="right">March 3, 2012</td>
    605605            </tr>
    606606         </tbody>
     
    632632         in progress”.
    633633      </p>
    634       <p>This Internet-Draft will expire in September 2012.</p>
     634      <p>This Internet-Draft will expire on September 4, 2012.</p>
    635635      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    636636      <p>Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
     
    675675               </li>
    676676               <li>2.4&nbsp;&nbsp;&nbsp;<a href="#validation.model">Validation Model</a><ul>
    677                      <li>2.4.1&nbsp;&nbsp;&nbsp;<a href="#freshening.responses">Freshening Responses</a></li>
     677                     <li>2.4.1&nbsp;&nbsp;&nbsp;<a href="#freshening.responses">Freshening Responses with 304 Not Modified</a></li>
    678678                  </ul>
    679679               </li>
    680                <li>2.5&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></li>
    681                <li>2.6&nbsp;&nbsp;&nbsp;<a href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></li>
    682                <li>2.7&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
    683                <li>2.8&nbsp;&nbsp;&nbsp;<a href="#combining.responses">Combining Partial Content</a></li>
     680               <li>2.5&nbsp;&nbsp;&nbsp;<a href="#head.effects">Updating Caches with HEAD Responses</a></li>
     681               <li>2.6&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></li>
     682               <li>2.7&nbsp;&nbsp;&nbsp;<a href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></li>
     683               <li>2.8&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
     684               <li>2.9&nbsp;&nbsp;&nbsp;<a href="#combining.responses">Combining Partial Content</a></li>
    684685            </ul>
    685686         </li>
     
    904905      </p>
    905906      <p id="rfc.section.2.p.4">If a request target is subject to content negotiation, its cache entry might consist of multiple stored responses, each differentiated
    906          by a secondary key for the values of the original request's selecting header fields (<a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</a>).
     907         by a secondary key for the values of the original request's selecting header fields (<a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>).
    907908      </p>
    908909      <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="response.cacheability" href="#response.cacheability">Response Cacheability</a></h2>
     
    916917         <li>the "private" cache response directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>) does not appear in the response, if the cache is shared, and
    917918         </li>
    918          <li>the "Authorization" header field (see <a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.1"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>) does not appear in the request, if the cache is shared, unless the response explicitly allows it (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section&nbsp;2.6</a>), and
     919         <li>the "Authorization" header field (see <a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.1"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>) does not appear in the request, if the cache is shared, unless the response explicitly allows it (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section&nbsp;2.7</a>), and
    919920         </li>
    920921         <li>the response either:
     
    945946         not understand the range units used in those fields.
    946947      </p>
    947       <p id="rfc.section.2.1.p.6">A cache <em class="bcp14">MAY</em> complete a stored incomplete response by making a subsequent range request (<a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) and combining the successful response with the stored entry, as defined in <a href="#combining.responses" title="Combining Partial Content">Section&nbsp;2.8</a>. A cache <em class="bcp14">MUST NOT</em> use an incomplete response to answer requests unless the response has been made complete or the request is partial and specifies
     948      <p id="rfc.section.2.1.p.6">A cache <em class="bcp14">MAY</em> complete a stored incomplete response by making a subsequent range request (<a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) and combining the successful response with the stored entry, as defined in <a href="#combining.responses" title="Combining Partial Content">Section&nbsp;2.9</a>. A cache <em class="bcp14">MUST NOT</em> use an incomplete response to answer requests unless the response has been made complete or the request is partial and specifies
    948949         a range that is wholly within the incomplete response. A cache <em class="bcp14">MUST NOT</em> send a partial response to a client without explicitly marking it as such using the 206 (Partial Content) status code.
    949950      </p>
     
    955956         </li>
    956957         <li>the request method associated with the stored response allows it to be used for the presented request, and</li>
    957          <li>selecting header fields nominated by the stored response (if any) match those presented (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</a>), and
     958         <li>selecting header fields nominated by the stored response (if any) match those presented (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>), and
    958959         </li>
    959960         <li>the presented request does not contain the no-cache pragma (<a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section&nbsp;3.4</a>), nor the no-cache cache directive (<a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;3.2.1</a>), unless the stored response is successfully validated (<a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>), and
     
    979980         having received a corresponding response.
    980981      </p>
    981       <p id="rfc.section.2.2.p.5">Also, note that unsafe requests might invalidate already stored responses; see <a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;2.5</a>.
     982      <p id="rfc.section.2.2.p.5">Also, note that unsafe requests might invalidate already stored responses; see <a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;2.6</a>.
    982983      </p>
    983984      <p id="rfc.section.2.2.p.6">When more than one suitable response is stored, a cache <em class="bcp14">MUST</em> use the most recent response (as determined by the Date header field). It can also forward a request with "Cache-Control:
     
    11361137      <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a id="validation.model" href="#validation.model">Validation Model</a></h2>
    11371138      <p id="rfc.section.2.4.p.1">When a cache has one or more stored responses for a requested URI, but cannot serve any of them (e.g., because they are not
    1138          fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a> in the forwarded request to give the origin server an opportunity to both select a valid stored response to be used, and to
     1139         fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a> in the forwarded request to give the origin server an opportunity to both select a valid stored response to be used, and to
    11391140         update it. This process is known as "validating" or "revalidating" the stored response.
    11401141      </p>
    11411142      <p id="rfc.section.2.4.p.2">When sending such a conditional request, a cache adds an If-Modified-Since header field whose value is that of the Last-Modified
    1142          header field from the selected (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</a>) stored response, if available.
     1143         header field from the selected (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>) stored response, if available.
    11431144      </p>
    11441145      <p id="rfc.section.2.4.p.3">Additionally, a cache can add an If-None-Match header field whose value is that of the ETag header field(s) from all responses
     
    11501151      <p id="rfc.section.2.4.p.5"> </p>
    11511152      <ul>
    1152          <li>A 304 (Not Modified) response status code indicates that the stored response can be updated and reused; see <a href="#freshening.responses" title="Freshening Responses">Section&nbsp;2.4.1</a>.
     1153         <li>A 304 (Not Modified) response status code indicates that the stored response can be updated and reused; see <a href="#freshening.responses" title="Freshening Responses with 304 Not Modified">Section&nbsp;2.4.1</a>.
    11531154         </li>
    11541155         <li>A full response (i.e., one with a response body) indicates that none of the stored responses nominated in the conditional
     
    11601161         </li>
    11611162      </ul>
    1162       <h3 id="rfc.section.2.4.1"><a href="#rfc.section.2.4.1">2.4.1</a>&nbsp;<a id="freshening.responses" href="#freshening.responses">Freshening Responses</a></h3>
     1163      <h3 id="rfc.section.2.4.1"><a href="#rfc.section.2.4.1">2.4.1</a>&nbsp;<a id="freshening.responses" href="#freshening.responses">Freshening Responses with 304 Not Modified</a></h3>
    11631164      <p id="rfc.section.2.4.1.p.1">When a cache receives a 304 (Not Modified) response and already has one or more stored 200 (OK) responses for the same cache
    11641165         key, the cache needs to identify which of the stored responses are updated by this new response and then update the stored
     
    11871188         </li>
    11881189      </ul>
    1189       <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></h2>
    1190       <p id="rfc.section.2.5.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 6.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them
     1190      <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="head.effects" href="#head.effects">Updating Caches with HEAD Responses</a></h2>
     1191      <p id="rfc.section.2.5.p.1">A response to the HEAD method is identical to what an equivalent request made with a GET would have been, except it lacks
     1192         a body. This property of HEAD responses is used to both invalidate and update cached GET responses.
     1193      </p>
     1194      <p id="rfc.section.2.5.p.2">If one or more stored GET responses can be selected (as per <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>) for a HEAD request, and the Content-Length, ETag or Last-Modified value of a HEAD response differs from that in a selected
     1195         GET response, the cache <em class="bcp14">MUST</em> consider that selected response to be stale.
     1196      </p>
     1197      <p id="rfc.section.2.5.p.3">If the Content-Length, ETag and Last-Modified values of a HEAD response (when present) are the same as that in a selected
     1198         GET response (as per <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>), the cache SHOULD update the remaining headers in the stored response using the following rules:
     1199      </p>
     1200      <ul>
     1201         <li>delete any Warning header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section&nbsp;3.6</a>);
     1202         </li>
     1203         <li>retain any Warning header fields in the stored response with warn-code 2xx; and,</li>
     1204         <li>use other header fields provided in the response to replace all instances of the corresponding header fields in the stored
     1205            response.
     1206         </li>
     1207      </ul>
     1208      <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a>&nbsp;<a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></h2>
     1209      <p id="rfc.section.2.6.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 6.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them
    11911210         to keep their contents up-to-date.
    11921211      </p>
    1193       <p id="rfc.section.2.5.p.2">A cache <em class="bcp14">MUST</em> invalidate the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) as well as the URI(s) in the Location and Content-Location response header fields (if present) when a non-error response
     1212      <p id="rfc.section.2.6.p.2">A cache <em class="bcp14">MUST</em> invalidate the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) as well as the URI(s) in the Location and Content-Location response header fields (if present) when a non-error response
    11941213         to a request with an unsafe method is received.
    11951214      </p>
    1196       <p id="rfc.section.2.5.p.3">However, a cache <em class="bcp14">MUST NOT</em> invalidate a URI from a Location or Content-Location response header field if the host part of that URI differs from the host
     1215      <p id="rfc.section.2.6.p.3">However, a cache <em class="bcp14">MUST NOT</em> invalidate a URI from a Location or Content-Location response header field if the host part of that URI differs from the host
    11971216         part in the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.14"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). This helps prevent denial of service attacks.
    11981217      </p>
    1199       <p id="rfc.section.2.5.p.4">A cache <em class="bcp14">MUST</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.15"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) when it receives a non-error response to a request with a method whose safety is unknown.
    1200       </p>
    1201       <p id="rfc.section.2.5.p.5">Here, a "non-error response" is one with a 2xx or 3xx status code. "Invalidate" means that the cache will either remove all
     1218      <p id="rfc.section.2.6.p.4">A cache <em class="bcp14">MUST</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.15"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) when it receives a non-error response to a request with a method whose safety is unknown.
     1219      </p>
     1220      <p id="rfc.section.2.6.p.5">Here, a "non-error response" is one with a 2xx or 3xx status code. "Invalidate" means that the cache will either remove all
    12021221         stored responses related to the effective request URI, or will mark these as "invalid" and in need of a mandatory validation
    12031222         before they can be returned in response to a subsequent request.
    12041223      </p>
    1205       <p id="rfc.section.2.5.p.6">Note that this does not guarantee that all appropriate responses are invalidated. For example, the request that caused the
     1224      <p id="rfc.section.2.6.p.6">Note that this does not guarantee that all appropriate responses are invalidated. For example, the request that caused the
    12061225         change at the origin server might not have gone through the cache where a response is stored.
    12071226      </p>
    1208       <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a>&nbsp;<a id="caching.authenticated.responses" href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></h2>
    1209       <p id="rfc.section.2.6.p.1">A shared cache <em class="bcp14">MUST NOT</em> use a cached response to a request with an Authorization header field (<a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.2"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>) to satisfy any subsequent request unless a cache directive that allows such responses to be stored is present in the response.
    1210       </p>
    1211       <p id="rfc.section.2.6.p.2">In this specification, the following Cache-Control response directives (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>) have such an effect: must-revalidate, public, s-maxage.
    1212       </p>
    1213       <p id="rfc.section.2.6.p.3">Note that cached responses that contain the "must-revalidate" and/or "s-maxage" response directives are not allowed to be
     1227      <h2 id="rfc.section.2.7"><a href="#rfc.section.2.7">2.7</a>&nbsp;<a id="caching.authenticated.responses" href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></h2>
     1228      <p id="rfc.section.2.7.p.1">A shared cache <em class="bcp14">MUST NOT</em> use a cached response to a request with an Authorization header field (<a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.2"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>) to satisfy any subsequent request unless a cache directive that allows such responses to be stored is present in the response.
     1229      </p>
     1230      <p id="rfc.section.2.7.p.2">In this specification, the following Cache-Control response directives (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>) have such an effect: must-revalidate, public, s-maxage.
     1231      </p>
     1232      <p id="rfc.section.2.7.p.3">Note that cached responses that contain the "must-revalidate" and/or "s-maxage" response directives are not allowed to be
    12141233         served stale (<a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;2.3.3</a>) by shared caches. In particular, a response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be used to satisfy
    12151234         a subsequent request without revalidating it on the origin server.
    12161235      </p>
    1217       <h2 id="rfc.section.2.7"><a href="#rfc.section.2.7">2.7</a>&nbsp;<a id="caching.negotiated.responses" href="#caching.negotiated.responses">Caching Negotiated Responses</a></h2>
    1218       <p id="rfc.section.2.7.p.1">When a cache receives a request that can be satisfied by a stored response that has a Vary header field (<a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section&nbsp;3.5</a>), it <em class="bcp14">MUST NOT</em> use that response unless all of the selecting header fields nominated by the Vary header field match in both the original
     1236      <h2 id="rfc.section.2.8"><a href="#rfc.section.2.8">2.8</a>&nbsp;<a id="caching.negotiated.responses" href="#caching.negotiated.responses">Caching Negotiated Responses</a></h2>
     1237      <p id="rfc.section.2.8.p.1">When a cache receives a request that can be satisfied by a stored response that has a Vary header field (<a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section&nbsp;3.5</a>), it <em class="bcp14">MUST NOT</em> use that response unless all of the selecting header fields nominated by the Vary header field match in both the original
    12191238         request (i.e., that associated with the stored response), and the presented request.
    12201239      </p>
    1221       <p id="rfc.section.2.7.p.2">The selecting header fields from two requests are defined to match if and only if those in the first request can be transformed
     1240      <p id="rfc.section.2.8.p.2">The selecting header fields from two requests are defined to match if and only if those in the first request can be transformed
    12221241         to those in the second request by applying any of the following:
    12231242      </p>
     
    12301249         </li>
    12311250      </ul>
    1232       <p id="rfc.section.2.7.p.3">If (after any normalization that might take place) a header field is absent from a request, it can only match another request
     1251      <p id="rfc.section.2.8.p.3">If (after any normalization that might take place) a header field is absent from a request, it can only match another request
    12331252         if it is also absent there.
    12341253      </p>
    1235       <p id="rfc.section.2.7.p.4">A Vary header field-value of "*" always fails to match, and subsequent requests to that resource can only be properly interpreted
     1254      <p id="rfc.section.2.8.p.4">A Vary header field-value of "*" always fails to match, and subsequent requests to that resource can only be properly interpreted
    12361255         by the origin server.
    12371256      </p>
    1238       <p id="rfc.section.2.7.p.5">The stored response with matching selecting header fields is known as the selected response.</p>
    1239       <p id="rfc.section.2.7.p.6">If multiple selected responses are available, the most recent response (as determined by the Date header field) is used; see <a href="#constructing.responses.from.caches" title="Constructing Responses from Caches">Section&nbsp;2.2</a>.
    1240       </p>
    1241       <p id="rfc.section.2.7.p.7">If no selected response is available, the cache can forward the presented request to the origin server in a conditional request;
     1257      <p id="rfc.section.2.8.p.5">The stored response with matching selecting header fields is known as the selected response.</p>
     1258      <p id="rfc.section.2.8.p.6">If multiple selected responses are available, the most recent response (as determined by the Date header field) is used; see <a href="#constructing.responses.from.caches" title="Constructing Responses from Caches">Section&nbsp;2.2</a>.
     1259      </p>
     1260      <p id="rfc.section.2.8.p.7">If no selected response is available, the cache can forward the presented request to the origin server in a conditional request;
    12421261         see <a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>.
    12431262      </p>
    1244       <h2 id="rfc.section.2.8"><a href="#rfc.section.2.8">2.8</a>&nbsp;<a id="combining.responses" href="#combining.responses">Combining Partial Content</a></h2>
    1245       <p id="rfc.section.2.8.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or
     1263      <h2 id="rfc.section.2.9"><a href="#rfc.section.2.9">2.9</a>&nbsp;<a id="combining.responses" href="#combining.responses">Combining Partial Content</a></h2>
     1264      <p id="rfc.section.2.9.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or
    12461265         more Range specifiers (<a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>). After several such transfers, a cache might have received several ranges of the same representation. A cache <em class="bcp14">MAY</em> combine these ranges into a single stored response, and reuse that response to satisfy later requests, if they all share the
    12471266         same strong validator and the cache complies with the client requirements in <a href="p5-range.html#combining.byte.ranges" title="Combining Ranges">Section 4.2</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>.
    12481267      </p>
    1249       <p id="rfc.section.2.8.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>:
    1250       </p>
    1251       <ul>
    1252          <li>delete any Warning header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section&nbsp;3.6</a>);
     1268      <p id="rfc.section.2.9.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>:
     1269      </p>
     1270      <ul>
     1271         <li>delete any Warning header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;3.6</a>);
    12531272         </li>
    12541273         <li>retain any Warning header fields in the stored response with warn-code 2xx; and,</li>
     
    13771396      </p>
    13781397      <ul class="empty">
    1379          <li>The public response directive indicates that a response whose associated request contains an 'Authentication' header <em class="bcp14">MAY</em> be stored (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section&nbsp;2.6</a>).
     1398         <li>The public response directive indicates that a response whose associated request contains an 'Authentication' header <em class="bcp14">MAY</em> be stored (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section&nbsp;2.7</a>).
    13801399         </li>
    13811400      </ul>
     
    15581577      <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="header.vary" href="#header.vary">Vary</a></h2>
    15591578      <p id="rfc.section.3.5.p.1">The "Vary" header field conveys the set of header fields that were used to select the representation.</p>
    1560       <p id="rfc.section.3.5.p.2">Caches use this information, in part, to determine whether a stored response can be used to satisfy a given request; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</a>. determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request
    1561          without validation; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</a>.
     1579      <p id="rfc.section.3.5.p.2">Caches use this information, in part, to determine whether a stored response can be used to satisfy a given request; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>. determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request
     1580         without validation; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>.
    15621581      </p>
    15631582      <p id="rfc.section.3.5.p.3">In uncacheable or stale responses, the Vary field value advises the user agent about the criteria that were used to select
     
    18951914                  <td class="left">http</td>
    18961915                  <td class="left">standard</td>
    1897                   <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;3.6</a>
     1916                  <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section&nbsp;3.6</a>
    18981917                  </td>
    18991918               </tr>
     
    20082027         use. (<a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>)
    20092028      </p>
    2010       <p id="rfc.section.A.p.3">Clarify denial of service attack avoidance requirement. (<a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;2.5</a>)
     2029      <p id="rfc.section.A.p.3">Clarify denial of service attack avoidance requirement. (<a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;2.6</a>)
    20112030      </p>
    20122031      <p id="rfc.section.A.p.4">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section&nbsp;3</a>)
    20132032      </p>
    20142033      <p id="rfc.section.A.p.5">Do not mention RFC 2047 encoding and multiple languages in Warning header fields anymore, as these aspects never were implemented.
    2015          (<a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section&nbsp;3.6</a>)
     2034         (<a href="#header.warning" id="rfc.xref.header.warning.6" title="Warning">Section&nbsp;3.6</a>)
    20162035      </p>
    20172036      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1>
     
    23862405                        <li>Expires&nbsp;&nbsp;<a href="#rfc.xref.header.expires.1">2.1</a>, <a href="#rfc.xref.header.expires.2">2.3</a>, <a href="#rfc.xref.header.expires.3">2.3.1</a>, <a href="#rfc.iref.h.4"><b>3.3</b></a>, <a href="#rfc.xref.header.expires.4">5.3</a></li>
    23872406                        <li>Pragma&nbsp;&nbsp;<a href="#rfc.xref.header.pragma.1">2.2</a>, <a href="#rfc.xref.header.pragma.2">3.2</a>, <a href="#rfc.iref.h.5"><b>3.4</b></a>, <a href="#rfc.xref.header.pragma.3">5.3</a></li>
    2388                         <li>Vary&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.7</a>, <a href="#rfc.iref.h.6"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.3</a></li>
    2389                         <li>Warning&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.8</a>, <a href="#rfc.iref.h.7"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.4">5.3</a>, <a href="#rfc.xref.header.warning.5">A</a></li>
     2407                        <li>Vary&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.8</a>, <a href="#rfc.iref.h.6"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.3</a></li>
     2408                        <li>Warning&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.5</a>, <a href="#rfc.xref.header.warning.4">2.9</a>, <a href="#rfc.iref.h.7"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.5">5.3</a>, <a href="#rfc.xref.header.warning.6">A</a></li>
    23902409                     </ul>
    23912410                  </li>
     
    24432462            </li>
    24442463            <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
    2445                   <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.3</a>, <a href="#rfc.xref.Part1.2">1.4</a>, <a href="#rfc.xref.Part1.3">1.4.1</a>, <a href="#rfc.xref.Part1.4">1.4.1</a>, <a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a>, <a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.9">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a>, <a href="#rfc.xref.Part1.11">2.1</a>, <a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.5</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a>, <a href="#rfc.xref.Part1.16">2.7</a>, <a href="#rfc.xref.Part1.17">7</a>, <a href="#Part1"><b>8.1</b></a><ul>
     2464                  <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.3</a>, <a href="#rfc.xref.Part1.2">1.4</a>, <a href="#rfc.xref.Part1.3">1.4.1</a>, <a href="#rfc.xref.Part1.4">1.4.1</a>, <a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a>, <a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.9">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a>, <a href="#rfc.xref.Part1.11">2.1</a>, <a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.6</a>, <a href="#rfc.xref.Part1.14">2.6</a>, <a href="#rfc.xref.Part1.15">2.6</a>, <a href="#rfc.xref.Part1.16">2.8</a>, <a href="#rfc.xref.Part1.17">7</a>, <a href="#Part1"><b>8.1</b></a><ul>
    24462465                        <li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">1.4</a></li>
    24472466                        <li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.3</a></li>
    24482467                        <li><em>Section 2.7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a></li>
    24492468                        <li><em>Section 3.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.4">1.4.1</a></li>
    2450                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.16">2.7</a></li>
     2469                        <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.16">2.8</a></li>
    24512470                        <li><em>Section 3.2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a></li>
    2452                         <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.5</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a></li>
     2471                        <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.6</a>, <a href="#rfc.xref.Part1.14">2.6</a>, <a href="#rfc.xref.Part1.15">2.6</a></li>
    24532472                        <li><em>Section 8.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.9">1.4.2</a></li>
    24542473                        <li><em>Section 11</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.17">7</a></li>
    24552474                     </ul>
    24562475                  </li>
    2457                   <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.2">2</a>, <a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.4">2.3.1.1</a>, <a href="#rfc.xref.Part2.5">2.3.2</a>, <a href="#rfc.xref.Part2.6">2.5</a>, <a href="#rfc.xref.Part2.7">3.3</a>, <a href="#Part2"><b>8.1</b></a><ul>
    2458                         <li><em>Section 6.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.6">2.5</a></li>
     2476                  <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.2">2</a>, <a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.4">2.3.1.1</a>, <a href="#rfc.xref.Part2.5">2.3.2</a>, <a href="#rfc.xref.Part2.6">2.6</a>, <a href="#rfc.xref.Part2.7">3.3</a>, <a href="#Part2"><b>8.1</b></a><ul>
     2477                        <li><em>Section 6.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.6">2.6</a></li>
    24592478                        <li><em>Section 7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.4">2.3.1.1</a></li>
    24602479                        <li><em>Section 8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.7">3.3</a></li>
     
    24692488                     </ul>
    24702489                  </li>
    2471                   <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.1</a>, <a href="#rfc.xref.Part5.2">2.8</a>, <a href="#rfc.xref.Part5.3">2.8</a>, <a href="#Part5"><b>8.1</b></a><ul>
    2472                         <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.3">2.8</a></li>
     2490                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.1</a>, <a href="#rfc.xref.Part5.2">2.9</a>, <a href="#rfc.xref.Part5.3">2.9</a>, <a href="#Part5"><b>8.1</b></a><ul>
     2491                        <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.3">2.9</a></li>
    24732492                     </ul>
    24742493                  </li>
    2475                   <li><em>Part7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.6</a>, <a href="#Part7"><b>8.1</b></a><ul>
    2476                         <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.6</a></li>
     2494                  <li><em>Part7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.7</a>, <a href="#Part7"><b>8.1</b></a><ul>
     2495                        <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.7</a></li>
    24772496                     </ul>
    24782497                  </li>
     
    25352554                     </ul>
    25362555                  </li>
    2537                   <li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.7</a>, <a href="#rfc.iref.v.3"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.3</a></li>
     2556                  <li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.8</a>, <a href="#rfc.iref.v.3"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.3</a></li>
    25382557               </ul>
    25392558            </li>
     
    25502569                     </ul>
    25512570                  </li>
    2552                   <li>Warning header field&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.8</a>, <a href="#rfc.iref.w.1"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.4">5.3</a>, <a href="#rfc.xref.header.warning.5">A</a></li>
     2571                  <li>Warning header field&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.5</a>, <a href="#rfc.xref.header.warning.4">2.9</a>, <a href="#rfc.iref.w.1"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.5">5.3</a>, <a href="#rfc.xref.header.warning.6">A</a></li>
    25532572               </ul>
    25542573            </li>
  • draft-ietf-httpbis/latest/p6-cache.xml

    r1552 r1554  
    10141014</t>
    10151015
    1016 <section anchor="freshening.responses" title="Freshening Responses">
     1016<section anchor="freshening.responses" title="Freshening Responses with 304 Not Modified">
    10171017<t>
    10181018   When a cache receives a 304 (Not Modified) response and already has one
     
    10551055</t>
    10561056</section>
     1057
     1058</section>
     1059
     1060<section anchor="head.effects" title="Updating Caches with HEAD Responses">
     1061<t>
     1062   A response to the HEAD method is identical to what an equivalent request
     1063   made with a GET would have been, except it lacks a body. This property
     1064   of HEAD responses is used to both invalidate and update cached GET
     1065   responses.
     1066</t>
     1067<t>
     1068   If one or more stored GET responses can be selected (as per <xref
     1069   target="caching.negotiated.responses"/>) for a HEAD request, and the
     1070   Content-Length, ETag or Last-Modified value of a HEAD response differs from
     1071   that in a selected GET response, the cache &MUST; consider that selected
     1072   response to be stale.
     1073</t>
     1074<t>
     1075   If the Content-Length, ETag and Last-Modified values of a HEAD response
     1076   (when present) are the same as that in a selected GET response (as per
     1077   <xref target="caching.negotiated.responses"/>), the cache SHOULD update the
     1078   remaining headers in the stored response using the following rules:
     1079   <list style="symbols">
     1080      <t>delete any Warning header fields in the stored response with
     1081         warn-code 1xx (see <xref target="header.warning" />);</t>
     1082      <t>retain any Warning header fields in the stored response with
     1083         warn-code 2xx; and,</t>
     1084      <t>use other header fields provided in the response to replace
     1085         all instances of the corresponding header fields in the stored
     1086         response.</t>
     1087   </list>
     1088</t>
    10571089
    105810