source: draft-ietf-httpbis/latest/p3-payload.html @ 1642

Last change on this file since 1642 was 1642, checked in by julian.reschke@…, 8 years ago

Step 4 of p2/p3-merge (see #351)

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456       content: "HTTP/1.1, Part 3"; 
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459       content: "Fielding, et al."; 
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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 Protocol Parameters" href="#rfc.section.2">
486      <link rel="Chapter" title="3 Payload" href="#rfc.section.3">
487      <link rel="Chapter" title="4 Representation" href="#rfc.section.4">
488      <link rel="Chapter" title="5 Content Negotiation" href="#rfc.section.5">
489      <link rel="Chapter" title="6 Header Field Definitions" href="#rfc.section.6">
490      <link rel="Chapter" title="7 IANA Considerations" href="#rfc.section.7">
491      <link rel="Chapter" title="8 Security Considerations" href="#rfc.section.8">
492      <link rel="Chapter" href="#rfc.section.9" title="9 References">
493      <link rel="Appendix" title="A Differences between HTTP and MIME" href="#rfc.section.A">
494      <link rel="Appendix" title="B Additional Features" href="#rfc.section.B">
495      <link rel="Appendix" title="C Changes from RFC 2616" href="#rfc.section.C">
496      <link rel="Appendix" title="D Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.D">
497      <link href="p2-semantics.html" rel="prev">
498      <link href="p4-conditional.html" rel="next">
499      <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      <link rel="schema.dct" href="http://purl.org/dc/terms/">
501      <meta name="dct.creator" content="Fielding, R.">
502      <meta name="dct.creator" content="Lafon, Y.">
503      <meta name="dct.creator" content="Reschke, J. F.">
504      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p3-payload-latest">
505      <meta name="dct.issued" scheme="ISO8601" content="2012-03-30">
506      <meta name="dct.replaces" content="urn:ietf:rfc:2616">
507      <meta name="dct.abstract" content="This part is now obsolete. Please see HTTPbis, Part 2.">
508      <meta name="description" content="This part is now obsolete. Please see HTTPbis, Part 2.">
509   </head>
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511      <table class="header">
512         <tbody>
513            <tr>
514               <td class="left">HTTPbis Working Group</td>
515               <td class="right">R. Fielding, Editor</td>
516            </tr>
517            <tr>
518               <td class="left">Internet-Draft</td>
519               <td class="right">Adobe</td>
520            </tr>
521            <tr>
522               <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
523               </td>
524               <td class="right">Y. Lafon, Editor</td>
525            </tr>
526            <tr>
527               <td class="left">Intended status: Standards Track</td>
528               <td class="right">W3C</td>
529            </tr>
530            <tr>
531               <td class="left">Expires: October 1, 2012</td>
532               <td class="right">J. Reschke, Editor</td>
533            </tr>
534            <tr>
535               <td class="left"></td>
536               <td class="right">greenbytes</td>
537            </tr>
538            <tr>
539               <td class="left"></td>
540               <td class="right">March 30, 2012</td>
541            </tr>
542         </tbody>
543      </table>
544      <p class="title">HTTP/1.1, part 3: Message Payload and Content Negotiation<br><span class="filename">draft-ietf-httpbis-p3-payload-latest</span></p>
545      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> 
546      <p>This part is now obsolete. Please see HTTPbis, Part 2.</p> 
547      <h1><a id="rfc.status" href="#rfc.status">Status of This Memo</a></h1>
548      <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p>
549      <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute
550         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>.
551      </p>
552      <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
553         documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
554         in progress”.
555      </p>
556      <p>This Internet-Draft will expire on October 1, 2012.</p>
557      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
558      <p>Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
559      <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
560         and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License
561         text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified
562         BSD License.
563      </p>
564      <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November
565         10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to
566         allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s)
567         controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative
568         works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate
569         it into languages other than English.
570      </p>
571      <hr class="noprint">
572      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
573      <ul class="toc">
574         <li>1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
575               <li>1.1&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a><ul>
576                     <li>1.1.1&nbsp;&nbsp;&nbsp;<a href="#core.rules">Core Rules</a></li>
577                     <li>1.1.2&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
578                  </ul>
579               </li>
580            </ul>
581         </li>
582         <li>2.&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul>
583               <li>2.1&nbsp;&nbsp;&nbsp;<a href="#character.sets">Character Encodings (charset)</a></li>
584               <li>2.2&nbsp;&nbsp;&nbsp;<a href="#content.codings">Content Codings</a><ul>
585                     <li>2.2.1&nbsp;&nbsp;&nbsp;<a href="#content.coding.registry">Content Coding Registry</a></li>
586                  </ul>
587               </li>
588               <li>2.3&nbsp;&nbsp;&nbsp;<a href="#media.types">Media Types</a><ul>
589                     <li>2.3.1&nbsp;&nbsp;&nbsp;<a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></li>
590                     <li>2.3.2&nbsp;&nbsp;&nbsp;<a href="#multipart.types">Multipart Types</a></li>
591                  </ul>
592               </li>
593               <li>2.4&nbsp;&nbsp;&nbsp;<a href="#language.tags">Language Tags</a></li>
594            </ul>
595         </li>
596         <li>3.&nbsp;&nbsp;&nbsp;<a href="#payload">Payload</a><ul>
597               <li>3.1&nbsp;&nbsp;&nbsp;<a href="#payload.header.fields">Payload Header Fields</a></li>
598               <li>3.2&nbsp;&nbsp;&nbsp;<a href="#payload.body">Payload Body</a></li>
599            </ul>
600         </li>
601         <li>4.&nbsp;&nbsp;&nbsp;<a href="#representation">Representation</a><ul>
602               <li>4.1&nbsp;&nbsp;&nbsp;<a href="#representation.header.fields">Representation Header Fields</a></li>
603               <li>4.2&nbsp;&nbsp;&nbsp;<a href="#representation.data">Representation Data</a></li>
604            </ul>
605         </li>
606         <li>5.&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul>
607               <li>5.1&nbsp;&nbsp;&nbsp;<a href="#server-driven.negotiation">Server-driven Negotiation</a></li>
608               <li>5.2&nbsp;&nbsp;&nbsp;<a href="#agent-driven.negotiation">Agent-driven Negotiation</a></li>
609            </ul>
610         </li>
611         <li>6.&nbsp;&nbsp;&nbsp;<a href="#header.field.definitions">Header Field Definitions</a><ul>
612               <li>6.1&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li>
613               <li>6.2&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li>
614               <li>6.3&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li>
615               <li>6.4&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li>
616               <li>6.5&nbsp;&nbsp;&nbsp;<a href="#header.content-encoding">Content-Encoding</a></li>
617               <li>6.6&nbsp;&nbsp;&nbsp;<a href="#header.content-language">Content-Language</a></li>
618               <li>6.7&nbsp;&nbsp;&nbsp;<a href="#header.content-location">Content-Location</a></li>
619               <li>6.8&nbsp;&nbsp;&nbsp;<a href="#header.content-type">Content-Type</a></li>
620            </ul>
621         </li>
622         <li>7.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
623               <li>7.1&nbsp;&nbsp;&nbsp;<a href="#content.coding.registration">Content Coding Registry</a></li>
624            </ul>
625         </li>
626         <li>8.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
627               <li>8.1&nbsp;&nbsp;&nbsp;<a href="#privacy.issues.connected.to.accept.header.fields">Privacy Issues Connected to Accept Header Fields</a></li>
628            </ul>
629         </li>
630         <li>9.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
631               <li>9.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
632               <li>9.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
633            </ul>
634         </li>
635         <li><a href="#rfc.authors">Authors' Addresses</a></li>
636         <li>A.&nbsp;&nbsp;&nbsp;<a href="#differences.between.http.and.mime">Differences between HTTP and MIME</a><ul>
637               <li>A.1&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li>
638               <li>A.2&nbsp;&nbsp;&nbsp;<a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li>
639               <li>A.3&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
640               <li>A.4&nbsp;&nbsp;&nbsp;<a href="#introduction.of.content-encoding">Introduction of Content-Encoding</a></li>
641               <li>A.5&nbsp;&nbsp;&nbsp;<a href="#no.content-transfer-encoding">No Content-Transfer-Encoding</a></li>
642               <li>A.6&nbsp;&nbsp;&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li>
643               <li>A.7&nbsp;&nbsp;&nbsp;<a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li>
644            </ul>
645         </li>
646         <li>B.&nbsp;&nbsp;&nbsp;<a href="#additional.features">Additional Features</a></li>
647         <li>C.&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
648         <li>D.&nbsp;&nbsp;&nbsp;<a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul>
649               <li>D.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.1">Since RFC 2616</a></li>
650               <li>D.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.2">Since draft-ietf-httpbis-p3-payload-00</a></li>
651               <li>D.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.3">Since draft-ietf-httpbis-p3-payload-01</a></li>
652               <li>D.4&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p3-payload-02</a></li>
653               <li>D.5&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p3-payload-03</a></li>
654               <li>D.6&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p3-payload-04</a></li>
655               <li>D.7&nbsp;&nbsp;&nbsp;<a href="#changes.since.05">Since draft-ietf-httpbis-p3-payload-05</a></li>
656               <li>D.8&nbsp;&nbsp;&nbsp;<a href="#changes.since.06">Since draft-ietf-httpbis-p3-payload-06</a></li>
657               <li>D.9&nbsp;&nbsp;&nbsp;<a href="#changes.since.07">Since draft-ietf-httpbis-p3-payload-07</a></li>
658               <li>D.10&nbsp;&nbsp;&nbsp;<a href="#changes.since.08">Since draft-ietf-httpbis-p3-payload-08</a></li>
659               <li>D.11&nbsp;&nbsp;&nbsp;<a href="#changes.since.09">Since draft-ietf-httpbis-p3-payload-09</a></li>
660               <li>D.12&nbsp;&nbsp;&nbsp;<a href="#changes.since.10">Since draft-ietf-httpbis-p3-payload-10</a></li>
661               <li>D.13&nbsp;&nbsp;&nbsp;<a href="#changes.since.11">Since draft-ietf-httpbis-p3-payload-11</a></li>
662               <li>D.14&nbsp;&nbsp;&nbsp;<a href="#changes.since.12">Since draft-ietf-httpbis-p3-payload-12</a></li>
663               <li>D.15&nbsp;&nbsp;&nbsp;<a href="#changes.since.13">Since draft-ietf-httpbis-p3-payload-13</a></li>
664               <li>D.16&nbsp;&nbsp;&nbsp;<a href="#changes.since.14">Since draft-ietf-httpbis-p3-payload-14</a></li>
665               <li>D.17&nbsp;&nbsp;&nbsp;<a href="#changes.since.15">Since draft-ietf-httpbis-p3-payload-15</a></li>
666               <li>D.18&nbsp;&nbsp;&nbsp;<a href="#changes.since.16">Since draft-ietf-httpbis-p3-payload-16</a></li>
667               <li>D.19&nbsp;&nbsp;&nbsp;<a href="#changes.since.17">Since draft-ietf-httpbis-p3-payload-17</a></li>
668               <li>D.20&nbsp;&nbsp;&nbsp;<a href="#changes.since.18">Since draft-ietf-httpbis-p3-payload-18</a></li>
669               <li>D.21&nbsp;&nbsp;&nbsp;<a href="#changes.since.19">Since draft-ietf-httpbis-p3-payload-19</a></li>
670            </ul>
671         </li>
672         <li><a href="#rfc.index">Index</a></li>
673      </ul>
674      <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
675      <p id="rfc.section.1.p.1">This part is now obsolete. Please see HTTPbis, Part 2.</p>
676      <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a id="notation" href="#notation">Syntax Notation</a></h2>
677      <h3 id="rfc.section.1.1.1"><a href="#rfc.section.1.1.1">1.1.1</a>&nbsp;<a id="core.rules" href="#core.rules">Core Rules</a></h3>
678      <h3 id="rfc.section.1.1.2"><a href="#rfc.section.1.1.2">1.1.2</a>&nbsp;<a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3>
679      <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="protocol.parameters" href="#protocol.parameters">Protocol Parameters</a></h1>
680      <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="character.sets" href="#character.sets">Character Encodings (charset)</a></h2>
681      <p id="rfc.section.2.1.p.1">HTTP uses charset names to indicate the character encoding of a textual representation.</p>
682      <div id="rule.charset">
683         <p id="rfc.section.2.1.p.2">  A character encoding is identified by a case-insensitive token. The complete set of tokens is defined by the IANA Character
684            Set registry (&lt;<a href="http://www.iana.org/assignments/character-sets">http://www.iana.org/assignments/character-sets</a>&gt;).
685         </p>
686      </div>
687      <div id="rfc.figure.u.1"></div><pre class="inline"><span id="rfc.iref.g.1"></span>  <a href="#rule.charset" class="smpl">charset</a> = <a href="#core.rules" class="smpl">token</a>
688</pre><p id="rfc.section.2.1.p.4">Although HTTP allows an arbitrary token to be used as a charset value, any token that has a predefined value within the IANA
689         Character Set registry <em class="bcp14">MUST</em> represent the character encoding defined by that registry. Applications <em class="bcp14">SHOULD</em> limit their use of character encodings to those defined within the IANA registry.
690      </p>
691      <p id="rfc.section.2.1.p.5">HTTP uses charset in two contexts: within an Accept-Charset request header field (in which the charset value is an unquoted
692         token) and as the value of a parameter in a Content-Type header field (within a request or response), in which case the parameter
693         value of the charset parameter can be quoted.
694      </p>
695      <p id="rfc.section.2.1.p.6">Implementors need to be aware of IETF character set requirements <a href="#RFC3629" id="rfc.xref.RFC3629.1"><cite title="UTF-8, a transformation format of ISO 10646">[RFC3629]</cite></a>  <a href="#RFC2277" id="rfc.xref.RFC2277.1"><cite title="IETF Policy on Character Sets and Languages">[RFC2277]</cite></a>.
696      </p>
697      <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="content.codings" href="#content.codings">Content Codings</a></h2>
698      <p id="rfc.section.2.2.p.1">Content coding values indicate an encoding transformation that has been or can be applied to a representation. Content codings
699         are primarily used to allow a representation to be compressed or otherwise usefully transformed without losing the identity
700         of its underlying media type and without loss of information. Frequently, the representation is stored in coded form, transmitted
701         directly, and only decoded by the recipient.
702      </p>
703      <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.2"></span>  <a href="#content.codings" class="smpl">content-coding</a>   = <a href="#core.rules" class="smpl">token</a>
704</pre><p id="rfc.section.2.2.p.3">All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the Accept-Encoding (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.1" title="Accept-Encoding">Section&nbsp;6.3</a>) and Content-Encoding (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section&nbsp;6.5</a>) header fields. Although the value describes the content-coding, what is more important is that it indicates what decoding
705         mechanism will be required to remove the encoding.
706      </p>
707      <p id="rfc.section.2.2.p.4">compress<span id="rfc.iref.c.1"></span><span id="rfc.iref.c.2"></span> 
708      </p>
709      <ul class="empty">
710         <li>See <a href="p1-messaging.html#compress.coding" title="Compress Coding">Section 4.2.1</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
711         </li>
712      </ul>
713      <p id="rfc.section.2.2.p.5">deflate<span id="rfc.iref.d.1"></span><span id="rfc.iref.c.3"></span> 
714      </p>
715      <ul class="empty">
716         <li>See <a href="p1-messaging.html#deflate.coding" title="Deflate Coding">Section 4.2.2</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>.
717         </li>
718      </ul>
719      <p id="rfc.section.2.2.p.6">gzip<span id="rfc.iref.g.3"></span><span id="rfc.iref.c.4"></span> 
720      </p>
721      <ul class="empty">
722         <li>See <a href="p1-messaging.html#gzip.coding" title="Gzip Coding">Section 4.2.3</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>.
723         </li>
724      </ul>
725      <h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a>&nbsp;<a id="content.coding.registry" href="#content.coding.registry">Content Coding Registry</a></h3>
726      <p id="rfc.section.2.2.1.p.1">The HTTP Content Coding Registry defines the name space for the content coding names.</p>
727      <p id="rfc.section.2.2.1.p.2">Registrations <em class="bcp14">MUST</em> include the following fields:
728      </p>
729      <ul>
730         <li>Name</li>
731         <li>Description</li>
732         <li>Pointer to specification text</li>
733      </ul>
734      <p id="rfc.section.2.2.1.p.3">Names of content codings <em class="bcp14">MUST NOT</em> overlap with names of transfer codings (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 4</a> of <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>), unless the encoding transformation is identical (as is the case for the compression codings defined in <a href="p1-messaging.html#compression.codings" title="Compression Codings">Section 4.2</a> of <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
735      </p>
736      <p id="rfc.section.2.2.1.p.4">Values to be added to this name space require IETF Review (see <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>), and <em class="bcp14">MUST</em> conform to the purpose of content coding defined in this section.
737      </p>
738      <p id="rfc.section.2.2.1.p.5">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.
739      </p>
740      <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="media.types" href="#media.types">Media Types</a></h2>
741      <p id="rfc.section.2.3.p.1">HTTP uses Internet Media Types <a href="#RFC2046" id="rfc.xref.RFC2046.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> in the Content-Type (<a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section&nbsp;6.8</a>) and Accept (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section&nbsp;6.1</a>) header fields in order to provide open and extensible data typing and type negotiation.
742      </p>
743      <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span>  <a href="#media.types" class="smpl">media-type</a> = <a href="#media.types" class="smpl">type</a> "/" <a href="#media.types" class="smpl">subtype</a> *( <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
744  <a href="#media.types" class="smpl">type</a>       = <a href="#core.rules" class="smpl">token</a>
745  <a href="#media.types" class="smpl">subtype</a>    = <a href="#core.rules" class="smpl">token</a>
746</pre><div id="rule.parameter">
747         <p id="rfc.section.2.3.p.3">      The type/subtype <em class="bcp14">MAY</em> be followed by parameters in the form of attribute/value pairs.
748         </p>
749      </div>
750      <div id="rfc.figure.u.4"></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>  <a href="#rule.parameter" class="smpl">parameter</a>      = <a href="#rule.parameter" class="smpl">attribute</a> "=" <a href="#rule.parameter" class="smpl">value</a>
751  <a href="#rule.parameter" class="smpl">attribute</a>      = <a href="#core.rules" class="smpl">token</a>
752  <a href="#rule.parameter" class="smpl">value</a>          = <a href="#core.rules" class="smpl">word</a>
753</pre><p id="rfc.section.2.3.p.5">The type, subtype, and parameter attribute names are case-insensitive. Parameter values might or might not be case-sensitive,
754         depending on the semantics of the parameter name. The presence or absence of a parameter might be significant to the processing
755         of a media-type, depending on its definition within the media type registry.
756      </p>
757      <p id="rfc.section.2.3.p.6">A parameter value that matches the <a href="#core.rules" class="smpl">token</a> production can be transmitted as either a token or within a quoted-string. The quoted and unquoted values are equivalent.
758      </p>
759      <p id="rfc.section.2.3.p.7">Note that some older HTTP applications do not recognize media type parameters. When sending data to older HTTP applications,
760         implementations <em class="bcp14">SHOULD</em> only use media type parameters when they are required by that type/subtype definition.
761      </p>
762      <p id="rfc.section.2.3.p.8">Media-type values are registered with the Internet Assigned Number Authority (IANA). The media type registration process is
763         outlined in <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>. Use of non-registered media types is discouraged.
764      </p>
765      <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a>&nbsp;<a id="canonicalization.and.text.defaults" href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></h3>
766      <p id="rfc.section.2.3.1.p.1">Internet media types are registered with a canonical form. A representation transferred via HTTP messages <em class="bcp14">MUST</em> be in the appropriate canonical form prior to its transmission except for "text" types, as defined in the next paragraph.
767      </p>
768      <p id="rfc.section.2.3.1.p.2">When in canonical form, media subtypes of the "text" type use CRLF as the text line break. HTTP relaxes this requirement and
769         allows the transport of text media with plain CR or LF alone representing a line break when it is done consistently for an
770         entire representation. HTTP applications <em class="bcp14">MUST</em> accept CRLF, bare CR, and bare LF as indicating a line break in text media received via HTTP. In addition, if the text is
771         in a character encoding that does not use octets 13 and 10 for CR and LF respectively, as is the case for some multi-byte
772         character encodings, HTTP allows the use of whatever octet sequences are defined by that character encoding to represent the
773         equivalent of CR and LF for line breaks. This flexibility regarding line breaks applies only to text media in the payload
774         body; a bare CR or LF <em class="bcp14">MUST NOT</em> be substituted for CRLF within any of the HTTP control structures (such as header fields and multipart boundaries).
775      </p>
776      <p id="rfc.section.2.3.1.p.3">If a representation is encoded with a content-coding, the underlying data <em class="bcp14">MUST</em> be in a form defined above prior to being encoded.
777      </p>
778      <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a>&nbsp;<a id="multipart.types" href="#multipart.types">Multipart Types</a></h3>
779      <p id="rfc.section.2.3.2.p.1">MIME provides for a number of "multipart" types — encapsulations of one or more representations within a single message body.
780         All multipart types share a common syntax, as defined in <a href="http://tools.ietf.org/html/rfc2046#section-5.1.1">Section 5.1.1</a> of <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, and <em class="bcp14">MUST</em> include a boundary parameter as part of the media type value. The message body is itself a protocol element and <em class="bcp14">MUST</em> therefore use only CRLF to represent line breaks between body-parts.
781      </p>
782      <p id="rfc.section.2.3.2.p.2">In general, HTTP treats a multipart message body no differently than any other media type: strictly as payload. HTTP does
783         not use the multipart boundary as an indicator of message body length.  In all other respects, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. The MIME header fields within
784         each body-part of a multipart message body do not have any significance to HTTP beyond that defined by their MIME semantics.
785      </p>
786      <p id="rfc.section.2.3.2.p.3">If an application receives an unrecognized multipart subtype, the application <em class="bcp14">MUST</em> treat it as being equivalent to "multipart/mixed".
787      </p>
788      <div class="note" id="rfc.section.2.3.2.p.4"> 
789         <p> <b>Note:</b> The "multipart/form-data" type has been specifically defined for carrying form data suitable for processing via the POST request
790            method, as described in <a href="#RFC2388" id="rfc.xref.RFC2388.1"><cite title="Returning Values from Forms: multipart/form-data">[RFC2388]</cite></a>.
791         </p> 
792      </div>
793      <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a id="language.tags" href="#language.tags">Language Tags</a></h2>
794      <p id="rfc.section.2.4.p.1">A language tag, as defined in <a href="#RFC5646" id="rfc.xref.RFC5646.1"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a>, identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information to
795         other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language and Content-Language
796         fields.
797      </p>
798      <p id="rfc.section.2.4.p.2">In summary, a language tag is composed of one or more parts: A primary language subtag followed by a possibly empty series
799         of subtags:
800      </p>
801      <div id="rfc.figure.u.5"></div><pre class="inline"><span id="rfc.iref.g.10"></span>  <a href="#language.tags" class="smpl">language-tag</a> = &lt;Language-Tag, defined in <a href="#RFC5646" id="rfc.xref.RFC5646.2"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a>, <a href="http://tools.ietf.org/html/rfc5646#section-2.1">Section 2.1</a>&gt;
802</pre><p id="rfc.section.2.4.p.4">White space is not allowed within the tag and all tags are case-insensitive. The name space of language subtags is administered
803         by the IANA (see &lt;<a href="http://www.iana.org/assignments/language-subtag-registry">http://www.iana.org/assignments/language-subtag-registry</a>&gt;).
804      </p>
805      <div id="rfc.figure.u.6"></div> 
806      <p>Example tags include:</p>  <pre class="text">  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
807</pre> <p id="rfc.section.2.4.p.6">See <a href="#RFC5646" id="rfc.xref.RFC5646.3"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a> for further information.
808      </p>
809      <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="payload" href="#payload">Payload</a></h1>
810      <p id="rfc.section.3.p.1">HTTP messages <em class="bcp14">MAY</em> transfer a payload if not otherwise restricted by the request method or response status code. The payload consists of metadata,
811         in the form of header fields, and data, in the form of the sequence of octets in the message body after any transfer-coding
812         has been decoded.
813      </p>
814      <div id="rfc.iref.p.1"></div>
815      <p id="rfc.section.3.p.2">A "<dfn>payload</dfn>" in HTTP is always a partial or complete representation of some resource. We use separate terms for payload and representation
816         because some messages contain only the associated representation's header fields (e.g., responses to HEAD) or only some part(s)
817         of the representation (e.g., the 206 status code).
818      </p>
819      <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="payload.header.fields" href="#payload.header.fields">Payload Header Fields</a></h2>
820      <p id="rfc.section.3.1.p.1">HTTP header fields that specifically define the payload, rather than the associated representation, are referred to as "payload
821         header fields". The following payload header fields are defined by HTTP/1.1:
822      </p>
823      <div id="rfc.table.u.1">
824         <table class="tt full left" cellpadding="3" cellspacing="0">
825            <thead>
826               <tr>
827                  <th>Header Field Name</th>
828                  <th>Defined in...</th>
829               </tr>
830            </thead>
831            <tbody>
832               <tr>
833                  <td class="left">Content-Length</td>
834                  <td class="left"><a href="p1-messaging.html#header.content-length" title="Content-Length">Section 3.3.2</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a></td>
835               </tr>
836               <tr>
837                  <td class="left">Content-Range</td>
838                  <td class="left"><a href="p5-range.html#header.content-range" title="Content-Range">Section 5.2</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>
839               </tr>
840            </tbody>
841         </table>
842      </div>
843      <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="payload.body" href="#payload.body">Payload Body</a></h2>
844      <p id="rfc.section.3.2.p.1">A payload 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.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. The payload body is obtained from the message body by decoding any Transfer-Encoding that might have been applied to ensure
845         safe and proper transfer of the message.
846      </p>
847      <div id="rfc.iref.r.1"></div>
848      <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="representation" href="#representation">Representation</a></h1>
849      <p id="rfc.section.4.p.1">A "<dfn>representation</dfn>" is information in a format that can be readily communicated from one party to another. A resource representation is information
850         that reflects the state of that resource, as observed at some point in the past (e.g., in a response to GET) or to be desired
851         at some point in the future (e.g., in a PUT request).
852      </p>
853      <p id="rfc.section.4.p.2">Most, but not all, representations transferred via HTTP are intended to be a representation of the target resource (the resource
854         identified by the effective request URI). The precise semantics of a representation are determined by the type of message
855         (request or response), the request method, the response status code, and the representation metadata. For example, the above
856         semantic is true for the representation in any 200 (OK) response to GET and for the representation in any PUT request. A 200
857         response to PUT, in contrast, contains either a representation that describes the successful action or a representation of
858         the target resource, with the latter indicated by a Content-Location header field with the same value as the effective request
859         URI. Likewise, response messages with an error status code usually contain a representation that describes the error and what
860         next steps are suggested for resolving it.
861      </p>
862      <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="representation.header.fields" href="#representation.header.fields">Representation Header Fields</a></h2>
863      <p id="rfc.section.4.1.p.1">Representation header fields define metadata about the representation data enclosed in the message body or, if no message
864         body is present, about the representation that would have been transferred in a 200 response to a simultaneous GET request
865         with the same effective request URI.
866      </p>
867      <p id="rfc.section.4.1.p.2">The following header fields are defined as representation metadata:</p>
868      <div id="rfc.table.u.2">
869         <table class="tt full left" cellpadding="3" cellspacing="0">
870            <thead>
871               <tr>
872                  <th>Header Field Name</th>
873                  <th>Defined in...</th>
874               </tr>
875            </thead>
876            <tbody>
877               <tr>
878                  <td class="left">Content-Encoding</td>
879                  <td class="left"><a href="#header.content-encoding" id="rfc.xref.header.content-encoding.2" title="Content-Encoding">Section&nbsp;6.5</a></td>
880               </tr>
881               <tr>
882                  <td class="left">Content-Language</td>
883                  <td class="left"><a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section&nbsp;6.6</a></td>
884               </tr>
885               <tr>
886                  <td class="left">Content-Location</td>
887                  <td class="left"><a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section&nbsp;6.7</a></td>
888               </tr>
889               <tr>
890                  <td class="left">Content-Type</td>
891                  <td class="left"><a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section&nbsp;6.8</a></td>
892               </tr>
893               <tr>
894                  <td class="left">Expires</td>
895                  <td class="left"><a href="p6-cache.html#header.expires" title="Expires">Section 3.3</a> of <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a></td>
896               </tr>
897            </tbody>
898         </table>
899      </div>
900      <p id="rfc.section.4.1.p.3">Additional header fields define metadata about the selected representation, which might differ from the representation included
901         in the message for responses to some state-changing methods. The following header fields are defined as selected representation
902         metadata:
903      </p>
904      <div id="rfc.table.u.3">
905         <table class="tt full left" cellpadding="3" cellspacing="0">
906            <thead>
907               <tr>
908                  <th>Header Field Name</th>
909                  <th>Defined in...</th>
910               </tr>
911            </thead>
912            <tbody>
913               <tr>
914                  <td class="left">ETag</td>
915                  <td class="left"><a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
916               </tr>
917               <tr>
918                  <td class="left">Last-Modified</td>
919                  <td class="left"><a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
920               </tr>
921            </tbody>
922         </table>
923      </div>
924      <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="representation.data" href="#representation.data">Representation Data</a></h2>
925      <p id="rfc.section.4.2.p.1">The representation body associated with an HTTP message is either provided as the payload body of the message or referred
926         to by the message semantics and the effective request URI. The representation data is in a format and encoding defined by
927         the representation metadata header fields.
928      </p>
929      <p id="rfc.section.4.2.p.2">The data type of the representation data is determined via the header fields Content-Type and Content-Encoding. These define
930         a two-layer, ordered encoding model:
931      </p>
932      <div id="rfc.figure.u.7"></div><pre class="text">  representation-data := Content-Encoding( Content-Type( bits ) )
933</pre><p id="rfc.section.4.2.p.4">Content-Type specifies the media type of the underlying data, which defines both the data format and how that data <em class="bcp14">SHOULD</em> be processed by the recipient (within the scope of the request method semantics). Any HTTP/1.1 message containing a payload
934         body <em class="bcp14">SHOULD</em> include a Content-Type header field defining the media type of the associated representation unless that metadata is unknown
935         to the sender. If the Content-Type header field is not present, it indicates that the sender does not know the media type
936         of the representation; recipients <em class="bcp14">MAY</em> either assume that the media type is "application/octet-stream" (<a href="#RFC2046" id="rfc.xref.RFC2046.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, <a href="http://tools.ietf.org/html/rfc2046#section-4.5.1">Section 4.5.1</a>) or examine the content to determine its type.
937      </p>
938      <p id="rfc.section.4.2.p.5">In practice, resource owners do not always properly configure their origin server to provide the correct Content-Type for
939         a given representation, with the result that some clients will examine a response body's content and override the specified
940         type. Clients that do so risk drawing incorrect conclusions, which might expose additional security risks (e.g., "privilege
941         escalation"). Furthermore, it is impossible to determine the sender's intent by examining the data format: many data formats
942         match multiple media types that differ only in processing semantics. Implementers are encouraged to provide a means of disabling
943         such "content sniffing" when it is used.
944      </p>
945      <p id="rfc.section.4.2.p.6">Content-Encoding is used to indicate any additional content codings applied to the data, usually for the purpose of data compression,
946         that are a property of the representation. If Content-Encoding is not present, then there is no additional encoding beyond
947         that defined by the Content-Type.
948      </p>
949      <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="content.negotiation" href="#content.negotiation">Content Negotiation</a></h1>
950      <p id="rfc.section.5.p.1">HTTP responses include a representation which contains information for interpretation, whether by a human user or for further
951         processing. Often, the server has different ways of representing the same information; for example, in different formats,
952         languages, or using different character encodings.
953      </p>
954      <p id="rfc.section.5.p.2">HTTP clients and their users might have different or variable capabilities, characteristics or preferences which would influence
955         which representation, among those available from the server, would be best for the server to deliver. For this reason, HTTP
956         provides mechanisms for "content negotiation" — a process of allowing selection of a representation of a given resource, when
957         more than one is available.
958      </p>
959      <p id="rfc.section.5.p.3">This specification defines two patterns of content negotiation; "server-driven", where the server selects the representation
960         based upon the client's stated preferences, and "agent-driven" negotiation, where the server provides a list of representations
961         for the client to choose from, based upon their metadata. In addition, there are other patterns: some applications use an
962         "active content" pattern, where the server returns active content which runs on the client and, based on client available
963         parameters, selects additional resources to invoke. "Transparent Content Negotiation" (<a href="#RFC2295" id="rfc.xref.RFC2295.1"><cite title="Transparent Content Negotiation in HTTP">[RFC2295]</cite></a>) has also been proposed.
964      </p>
965      <p id="rfc.section.5.p.4">These patterns are all widely used, and have trade-offs in applicability and practicality. In particular, when the number
966         of preferences or capabilities to be expressed by a client are large (such as when many different formats are supported by
967         a user-agent), server-driven negotiation becomes unwieldy, and might not be appropriate. Conversely, when the number of representations
968         to choose from is very large, agent-driven negotiation might not be appropriate.
969      </p>
970      <p id="rfc.section.5.p.5">Note that in all cases, the supplier of representations has the responsibility for determining which representations might
971         be considered to be the "same information".
972      </p>
973      <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="server-driven.negotiation" href="#server-driven.negotiation">Server-driven Negotiation</a></h2>
974      <p id="rfc.section.5.1.p.1">If the selection of the best representation for a response is made by an algorithm located at the server, it is called server-driven
975         negotiation. Selection is based on the available representations of the response (the dimensions over which it can vary; e.g.,
976         language, content-coding, etc.) and the contents of particular header fields in the request message or on other information
977         pertaining to the request (such as the network address of the client).
978      </p>
979      <p id="rfc.section.5.1.p.2">Server-driven negotiation is advantageous when the algorithm for selecting from among the available representations is difficult
980         to describe to the user agent, or when the server desires to send its "best guess" to the client along with the first response
981         (hoping to avoid the round-trip delay of a subsequent request if the "best guess" is good enough for the user). In order to
982         improve the server's guess, the user agent <em class="bcp14">MAY</em> include request header fields (Accept, Accept-Language, Accept-Encoding, etc.) which describe its preferences for such a response.
983      </p>
984      <p id="rfc.section.5.1.p.3">Server-driven negotiation has disadvantages: </p>
985      <ol>
986         <li>It is impossible for the server to accurately determine what might be "best" for any given user, since that would require
987            complete knowledge of both the capabilities of the user agent and the intended use for the response (e.g., does the user want
988            to view it on screen or print it on paper?).
989         </li>
990         <li>Having the user agent describe its capabilities in every request can be both very inefficient (given that only a small percentage
991            of responses have multiple representations) and a potential violation of the user's privacy.
992         </li>
993         <li>It complicates the implementation of an origin server and the algorithms for generating responses to a request.</li>
994         <li>It might limit a public cache's ability to use the same response for multiple user's requests.</li>
995      </ol>
996      <p id="rfc.section.5.1.p.4">Server-driven negotiation allows the user agent to specify its preferences, but it cannot expect responses to always honor
997         them. For example, the origin server might not implement server-driven negotiation, or it might decide that sending a response
998         that doesn't conform to them is better than sending a 406 (Not Acceptable) response.
999      </p>
1000      <p id="rfc.section.5.1.p.5">Many of the mechanisms for expressing preferences use quality values to declare relative preference. See <a href="p1-messaging.html#quality.values" title="Quality Values">Section 4.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for more information.
1001      </p>
1002      <p id="rfc.section.5.1.p.6">HTTP/1.1 includes the following header fields for enabling server-driven negotiation through description of user agent capabilities
1003         and user preferences: Accept (<a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section&nbsp;6.1</a>), Accept-Charset (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.1" title="Accept-Charset">Section&nbsp;6.2</a>), Accept-Encoding (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.2" title="Accept-Encoding">Section&nbsp;6.3</a>), Accept-Language (<a href="#header.accept-language" id="rfc.xref.header.accept-language.1" title="Accept-Language">Section&nbsp;6.4</a>), and User-Agent (<a href="p2-semantics.html#header.user-agent" title="User-Agent">Section 7.10</a> of <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). However, an origin server is not limited to these dimensions and <em class="bcp14">MAY</em> vary the response based on any aspect of the request, including aspects of the connection (e.g., IP address) or information
1004         within extension header fields not defined by this specification.
1005      </p>
1006      <div class="note" id="rfc.section.5.1.p.7"> 
1007         <p> <b>Note:</b> In practice, User-Agent based negotiation is fragile, because new clients might not be recognized.
1008         </p> 
1009      </div>
1010      <p id="rfc.section.5.1.p.8">The Vary header field (<a href="p6-cache.html#header.vary" title="Vary">Section 3.5</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can be used to express the parameters the server uses to select a representation that is subject to server-driven negotiation.
1011      </p>
1012      <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a id="agent-driven.negotiation" href="#agent-driven.negotiation">Agent-driven Negotiation</a></h2>
1013      <p id="rfc.section.5.2.p.1">With agent-driven negotiation, selection of the best representation for a response is performed by the user agent after receiving
1014         an initial response from the origin server. Selection is based on a list of the available representations of the response
1015         included within the header fields or body of the initial response, with each representation identified by its own URI. Selection
1016         from among the representations can be performed automatically (if the user agent is capable of doing so) or manually by the
1017         user selecting from a generated (possibly hypertext) menu.
1018      </p>
1019      <p id="rfc.section.5.2.p.2">Agent-driven negotiation is advantageous when the response would vary over commonly-used dimensions (such as type, language,
1020         or encoding), when the origin server is unable to determine a user agent's capabilities from examining the request, and generally
1021         when public caches are used to distribute server load and reduce network usage.
1022      </p>
1023      <p id="rfc.section.5.2.p.3">Agent-driven negotiation suffers from the disadvantage of needing a second request to obtain the best alternate representation.
1024         This second request is only efficient when caching is used. In addition, this specification does not define any mechanism
1025         for supporting automatic selection, though it also does not prevent any such mechanism from being developed as an extension
1026         and used within HTTP/1.1.
1027      </p>
1028      <p id="rfc.section.5.2.p.4">This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable) status codes for enabling agent-driven negotiation
1029         when the server is unwilling or unable to provide a varying response using server-driven negotiation.
1030      </p>
1031      <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1>
1032      <p id="rfc.section.6.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to the payload of messages.</p>
1033      <div id="rfc.iref.a.1"></div>
1034      <div id="rfc.iref.h.1"></div>
1035      <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="header.accept" href="#header.accept">Accept</a></h2>
1036      <p id="rfc.section.6.1.p.1">The "Accept" header field can be used by user agents to specify response media types that are acceptable. Accept header fields
1037         can be used to indicate that the request is specifically limited to a small set of desired types, as in the case of a request
1038         for an in-line image.
1039      </p>
1040      <div id="rfc.figure.u.8"></div><pre class="inline"><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>  <a href="#header.accept" class="smpl">Accept</a> = #( <a href="#header.accept" class="smpl">media-range</a> [ <a href="#header.accept" class="smpl">accept-params</a> ] )
1041 
1042  <a href="#header.accept" class="smpl">media-range</a>    = ( "*/*"
1043                   / ( <a href="#media.types" class="smpl">type</a> "/" "*" )
1044                   / ( <a href="#media.types" class="smpl">type</a> "/" <a href="#media.types" class="smpl">subtype</a> )
1045                   ) *( <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
1046  <a href="#header.accept" class="smpl">accept-params</a>  = <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> *( <a href="#header.accept" class="smpl">accept-ext</a> )
1047  <a href="#header.accept" class="smpl">accept-ext</a>     = <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> <a href="#core.rules" class="smpl">token</a> [ "=" <a href="#core.rules" class="smpl">word</a> ]
1048</pre><p id="rfc.section.6.1.p.3">The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating
1049         all subtypes of that type. The media-range <em class="bcp14">MAY</em> include media type parameters that are applicable to that range.
1050      </p>
1051      <p id="rfc.section.6.1.p.4">Each media-range <em class="bcp14">MAY</em> be followed by one or more accept-params, beginning with the "q" parameter for indicating a relative quality factor. The first
1052         "q" parameter (if any) separates the media-range parameter(s) from the accept-params. Quality factors allow the user or user
1053         agent to indicate the relative degree of preference for that media-range, using the qvalue scale from 0 to 1 (<a href="p1-messaging.html#quality.values" title="Quality Values">Section 4.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.9"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). The default value is q=1.
1054      </p>
1055      <div class="note" id="rfc.section.6.1.p.5"> 
1056         <p> <b>Note:</b> Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to historical practice.
1057            Although this prevents any media type parameter named "q" from being used with a media range, such an event is believed to
1058            be unlikely given the lack of any "q" parameters in the IANA media type registry and the rare usage of any media type parameters
1059            in Accept. Future media types are discouraged from registering any parameter named "q".
1060         </p> 
1061      </div>
1062      <p id="rfc.section.6.1.p.6">The example</p>
1063      <div id="rfc.figure.u.9"></div><pre class="text">  Accept: audio/*; q=0.2, audio/basic
1064</pre><p id="rfc.section.6.1.p.8"> <em class="bcp14">SHOULD</em> be interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80% mark-down in
1065         quality".
1066      </p>
1067      <p id="rfc.section.6.1.p.9">A request without any Accept header field implies that the user agent will accept any media type in response. If an Accept
1068         header field is present in a request and none of the available representations for the response have a media type that is
1069         listed as acceptable, the origin server <em class="bcp14">MAY</em> either honor the Accept header field by sending a 406 (Not Acceptable) response or disregard the Accept header field by treating
1070         the response as if it is not subject to content negotiation.
1071      </p>
1072      <p id="rfc.section.6.1.p.10">A more elaborate example is</p>
1073      <div id="rfc.figure.u.10"></div><pre class="text">  Accept: text/plain; q=0.5, text/html,
1074          text/x-dvi; q=0.8, text/x-c
1075</pre><p id="rfc.section.6.1.p.12">Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but if they do not exist, then
1076         send the text/x-dvi representation, and if that does not exist, send the text/plain representation".
1077      </p>
1078      <p id="rfc.section.6.1.p.13">Media ranges can be overridden by more specific media ranges or specific media types. If more than one media range applies
1079         to a given type, the most specific reference has precedence. For example,
1080      </p>
1081      <div id="rfc.figure.u.11"></div><pre class="text">  Accept: text/*, text/plain, text/plain;format=flowed, */*
1082</pre><p id="rfc.section.6.1.p.15">have the following precedence: </p>
1083      <ol>
1084         <li>text/plain;format=flowed</li>
1085         <li>text/plain</li>
1086         <li>text/*</li>
1087         <li>*/*</li>
1088      </ol>
1089      <p id="rfc.section.6.1.p.16">The media type quality factor associated with a given type is determined by finding the media range with the highest precedence
1090         which matches that type. For example,
1091      </p>
1092      <div id="rfc.figure.u.12"></div><pre class="text">  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1093          text/html;level=2;q=0.4, */*;q=0.5
1094</pre><p id="rfc.section.6.1.p.18">would cause the following values to be associated:</p>
1095      <div id="rfc.table.u.4">
1096         <table class="tt full left" cellpadding="3" cellspacing="0">
1097            <thead>
1098               <tr>
1099                  <th>Media Type</th>
1100                  <th>Quality Value</th>
1101               </tr>
1102            </thead>
1103            <tbody>
1104               <tr>
1105                  <td class="left">text/html;level=1</td>
1106                  <td class="left">1</td>
1107               </tr>
1108               <tr>
1109                  <td class="left">text/html</td>
1110                  <td class="left">0.7</td>
1111               </tr>
1112               <tr>
1113                  <td class="left">text/plain</td>
1114                  <td class="left">0.3</td>
1115               </tr>
1116               <tr>
1117                  <td class="left">image/jpeg</td>
1118                  <td class="left">0.5</td>
1119               </tr>
1120               <tr>
1121                  <td class="left">text/html;level=2</td>
1122                  <td class="left">0.4</td>
1123               </tr>
1124               <tr>
1125                  <td class="left">text/html;level=3</td>
1126                  <td class="left">0.7</td>
1127               </tr>
1128            </tbody>
1129         </table>
1130      </div>
1131      <p id="rfc.section.6.1.p.19"> <b>Note:</b> A user agent might be provided with a default set of quality values for certain media ranges. However, unless the user agent
1132         is a closed system which cannot interact with other rendering agents, this default set ought to be configurable by the user.
1133      </p>
1134      <div id="rfc.iref.a.2"></div>
1135      <div id="rfc.iref.h.2"></div>
1136      <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a id="header.accept-charset" href="#header.accept-charset">Accept-Charset</a></h2>
1137      <p id="rfc.section.6.2.p.1">The "Accept-Charset" header field can be used by user agents to indicate what character encodings are acceptable in a response
1138         payload. This field allows clients capable of understanding more comprehensive or special-purpose character encodings to signal
1139         that capability to a server which is capable of representing documents in those character encodings.
1140      </p>
1141      <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.15"></span>  <a href="#header.accept-charset" class="smpl">Accept-Charset</a> = 1#( ( <a href="#rule.charset" class="smpl">charset</a> / "*" )
1142                         [ <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> ] )
1143</pre><p id="rfc.section.6.2.p.3">Character encoding values (a.k.a., charsets) are described in <a href="#character.sets" title="Character Encodings (charset)">Section&nbsp;2.1</a>. Each charset <em class="bcp14">MAY</em> be given an associated quality value which represents the user's preference for that charset. The default value is q=1. An
1144         example is
1145      </p>
1146      <div id="rfc.figure.u.14"></div><pre class="text">  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1147</pre><p id="rfc.section.6.2.p.5">The special value "*", if present in the Accept-Charset field, matches every character encoding which is not mentioned elsewhere
1148         in the Accept-Charset field. If no "*" is present in an Accept-Charset field, then all character encodings not explicitly
1149         mentioned get a quality value of 0.
1150      </p>
1151      <p id="rfc.section.6.2.p.6">A request without any Accept-Charset header field implies that the user agent will accept any character encoding in response.
1152         If an Accept-Charset header field is present in a request and none of the available representations for the response have
1153         a character encoding that is listed as acceptable, the origin server <em class="bcp14">MAY</em> either honor the Accept-Charset header field by sending a 406 (Not Acceptable) response or disregard the Accept-Charset header
1154         field by treating the response as if it is not subject to content negotiation.
1155      </p>
1156      <div id="rfc.iref.a.3"></div>
1157      <div id="rfc.iref.h.3"></div>
1158      <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a id="header.accept-encoding" href="#header.accept-encoding">Accept-Encoding</a></h2>
1159      <p id="rfc.section.6.3.p.1">The "Accept-Encoding" header field can be used by user agents to indicate what response content-codings (<a href="#content.codings" title="Content Codings">Section&nbsp;2.2</a>) are acceptable in the response. An "identity" token is used as a synonym for "no encoding" in order to communicate when
1160         no encoding is preferred.
1161      </p>
1162      <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span>  <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a>  = #( <a href="#header.accept-encoding" class="smpl">codings</a> [ <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> ] )
1163  <a href="#header.accept-encoding" class="smpl">codings</a>          = <a href="#content.codings" class="smpl">content-coding</a> / "identity" / "*"
1164</pre><p id="rfc.section.6.3.p.3">Each codings value <em class="bcp14">MAY</em> be given an associated quality value which represents the preference for that encoding. The default value is q=1.
1165      </p>
1166      <p id="rfc.section.6.3.p.4">For example,</p>
1167      <div id="rfc.figure.u.16"></div><pre class="text">  Accept-Encoding: compress, gzip
1168  Accept-Encoding:
1169  Accept-Encoding: *
1170  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1171  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1172</pre><p id="rfc.section.6.3.p.6">A server tests whether a content-coding for a given representation is acceptable, according to an Accept-Encoding field, using
1173         these rules:
1174      </p>
1175      <ol>
1176         <li>The special "*" symbol in an Accept-Encoding field matches any available content-coding not explicitly listed in the header
1177            field.
1178         </li>
1179         <li>If the representation has no content-coding, then it is acceptable by default unless specifically excluded by the Accept-Encoding
1180            field stating either "identity;q=0" or "*;q=0" without a more specific entry for "identity".
1181         </li>
1182         <li>If the representation's content-coding is one of the content-codings listed in the Accept-Encoding field, then it is acceptable
1183            unless it is accompanied by a qvalue of 0. (As defined in <a href="p1-messaging.html#quality.values" title="Quality Values">Section 4.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.10"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, a qvalue of 0 means "not acceptable".)
1184         </li>
1185         <li>If multiple content-codings are acceptable, then the acceptable content-coding with the highest non-zero qvalue is preferred.</li>
1186      </ol>
1187      <p id="rfc.section.6.3.p.7">An Accept-Encoding header field with a combined field-value that is empty implies that the user agent does not want any content-coding
1188         in response. If an Accept-Encoding header field is present in a request and none of the available representations for the
1189         response have a content-coding that is listed as acceptable, the origin server <em class="bcp14">SHOULD</em> send a response without any content-coding.
1190      </p>
1191      <p id="rfc.section.6.3.p.8">A request without an Accept-Encoding header field implies that the user agent will accept any content-coding in response,
1192         but a representation without content-coding is preferred for compatibility with the widest variety of user agents.
1193      </p>
1194      <div class="note" id="rfc.section.6.3.p.9"> 
1195         <p> <b>Note:</b> Most HTTP/1.0 applications do not recognize or obey qvalues associated with content-codings. This means that qvalues will
1196            not work and are not permitted with x-gzip or x-compress.
1197         </p> 
1198      </div>
1199      <div id="rfc.iref.a.4"></div>
1200      <div id="rfc.iref.h.4"></div>
1201      <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a id="header.accept-language" href="#header.accept-language">Accept-Language</a></h2>
1202      <p id="rfc.section.6.4.p.1">The "Accept-Language" header field can be used by user agents to indicate the set of natural languages that are preferred
1203         in the response. Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;2.4</a>.
1204      </p>
1205      <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span>  <a href="#header.accept-language" class="smpl">Accept-Language</a> =
1206                    1#( <a href="#header.accept-language" class="smpl">language-range</a> [ <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> ] )
1207  <a href="#header.accept-language" class="smpl">language-range</a>  =
1208            &lt;language-range, defined in <a href="#RFC4647" id="rfc.xref.RFC4647.1"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-2.1">Section 2.1</a>&gt;
1209</pre><p id="rfc.section.6.4.p.3">Each language-range can be given an associated quality value which represents an estimate of the user's preference for the
1210         languages specified by that range. The quality value defaults to "q=1". For example,
1211      </p>
1212      <div id="rfc.figure.u.18"></div><pre class="text">  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1213</pre><p id="rfc.section.6.4.p.5">would mean: "I prefer Danish, but will accept British English and other types of English". (see also <a href="http://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>)
1214      </p>
1215      <p id="rfc.section.6.4.p.6">For matching, <a href="http://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements.
1216      </p>
1217      <div class="note" id="rfc.section.6.4.p.7"> 
1218         <p> <b>Note:</b> The "Basic Filtering" scheme (<a href="#RFC4647" id="rfc.xref.RFC4647.4"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-3.3.1">Section 3.3.1</a>) is identical to the matching scheme that was previously defined in <a href="http://tools.ietf.org/html/rfc2616#section-14.4">Section 14.4</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
1219         </p> 
1220      </div>
1221      <p id="rfc.section.6.4.p.8">It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic
1222         preferences of the user in every request. For a discussion of this issue, see <a href="#privacy.issues.connected.to.accept.header.fields" title="Privacy Issues Connected to Accept Header Fields">Section&nbsp;8.1</a>.
1223      </p>
1224      <p id="rfc.section.6.4.p.9">As intelligibility is highly dependent on the individual user, it is recommended that client applications make the choice
1225         of linguistic preference available to the user. If the choice is not made available, then the Accept-Language header field <em class="bcp14">MUST NOT</em> be given in the request.
1226      </p>
1227      <div class="note" id="rfc.section.6.4.p.10"> 
1228         <p> <b>Note:</b> When making the choice of linguistic preference available to the user, we remind implementors of the fact that users are not
1229            familiar with the details of language matching as described above, and ought to be provided appropriate guidance. As an example,
1230            users might assume that on selecting "en-gb", they will be served any kind of English document if British English is not available.
1231            A user agent might suggest in such a case to add "en" to get the best matching behavior.
1232         </p> 
1233      </div>
1234      <div id="rfc.iref.c.5"></div>
1235      <div id="rfc.iref.h.5"></div>
1236      <h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a>&nbsp;<a id="header.content-encoding" href="#header.content-encoding">Content-Encoding</a></h2>
1237      <p id="rfc.section.6.5.p.1">The "Content-Encoding" header field indicates what content-codings have been applied to the representation beyond those inherent
1238         in the media type, and thus what decoding mechanisms have to be applied in order to obtain the media-type referenced by the
1239         Content-Type header field. Content-Encoding is primarily used to allow a representation to be compressed without losing the
1240         identity of its underlying media type.
1241      </p>
1242      <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.20"></span>  <a href="#header.content-encoding" class="smpl">Content-Encoding</a> = 1#<a href="#content.codings" class="smpl">content-coding</a>
1243</pre><p id="rfc.section.6.5.p.3">Content codings are defined in <a href="#content.codings" title="Content Codings">Section&nbsp;2.2</a>. An example of its use is
1244      </p>
1245      <div id="rfc.figure.u.20"></div><pre class="text">  Content-Encoding: gzip
1246</pre><p id="rfc.section.6.5.p.5">The content-coding is a characteristic of the representation. Typically, the representation body is stored with this encoding
1247         and is only decoded before rendering or analogous usage. However, a transforming proxy <em class="bcp14">MAY</em> modify the content-coding if the new coding is known to be acceptable to the recipient, unless the "no-transform" cache-control
1248         directive is present in the message.
1249      </p>
1250      <p id="rfc.section.6.5.p.6">If the media type includes an inherent encoding, such as a data format that is always compressed, then that encoding would
1251         not be restated as a Content-Encoding even if it happens to be the same algorithm as one of the content-codings. Such a content-coding
1252         would only be listed if, for some bizarre reason, it is applied a second time to form the representation. Likewise, an origin
1253         server might choose to publish the same payload data as multiple representations that differ only in whether the coding is
1254         defined as part of Content-Type or Content-Encoding, since some user agents will behave differently in their handling of each
1255         response (e.g., open a "Save as ..." dialog instead of automatic decompression and rendering of content).
1256      </p>
1257      <p id="rfc.section.6.5.p.7">A representation that has a content-coding applied to it <em class="bcp14">MUST</em> include a Content-Encoding header field (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.3" title="Content-Encoding">Section&nbsp;6.5</a>) that lists the content-coding(s) applied.
1258      </p>
1259      <p id="rfc.section.6.5.p.8">If multiple encodings have been applied to a representation, the content codings <em class="bcp14">MUST</em> be listed in the order in which they were applied. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other header fields not defined by this specification.
1260      </p>
1261      <p id="rfc.section.6.5.p.9">If the content-coding of a representation in a request message is not acceptable to the origin server, the server <em class="bcp14">SHOULD</em> respond with a status code of 415 (Unsupported Media Type).
1262      </p>
1263      <div id="rfc.iref.c.6"></div>
1264      <div id="rfc.iref.h.6"></div>
1265      <h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a>&nbsp;<a id="header.content-language" href="#header.content-language">Content-Language</a></h2>
1266      <p id="rfc.section.6.6.p.1">The "Content-Language" header field describes the natural language(s) of the intended audience for the representation. Note
1267         that this might not be equivalent to all the languages used within the representation.
1268      </p>
1269      <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.21"></span>  <a href="#header.content-language" class="smpl">Content-Language</a> = 1#<a href="#language.tags" class="smpl">language-tag</a>
1270</pre><p id="rfc.section.6.6.p.3">Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;2.4</a>. The primary purpose of Content-Language is to allow a user to identify and differentiate representations according to the
1271         user's own preferred language. Thus, if the body content is intended only for a Danish-literate audience, the appropriate
1272         field is
1273      </p>
1274      <div id="rfc.figure.u.22"></div><pre class="text">  Content-Language: da
1275</pre><p id="rfc.section.6.6.p.5">If no Content-Language is specified, the default is that the content is intended for all language audiences. This might mean
1276         that the sender does not consider it to be specific to any natural language, or that the sender does not know for which language
1277         it is intended.
1278      </p>
1279      <p id="rfc.section.6.6.p.6">Multiple languages <em class="bcp14">MAY</em> be listed for content that is intended for multiple audiences. For example, a rendition of the "Treaty of Waitangi", presented
1280         simultaneously in the original Maori and English versions, would call for
1281      </p>
1282      <div id="rfc.figure.u.23"></div><pre class="text">  Content-Language: mi, en
1283</pre><p id="rfc.section.6.6.p.8">However, just because multiple languages are present within a representation does not mean that it is intended for multiple
1284         linguistic audiences. An example would be a beginner's language primer, such as "A First Lesson in Latin", which is clearly
1285         intended to be used by an English-literate audience. In this case, the Content-Language would properly only include "en".
1286      </p>
1287      <p id="rfc.section.6.6.p.9">Content-Language <em class="bcp14">MAY</em> be applied to any media type — it is not limited to textual documents.
1288      </p>
1289      <div id="rfc.iref.c.7"></div>
1290      <div id="rfc.iref.h.7"></div>
1291      <h2 id="rfc.section.6.7"><a href="#rfc.section.6.7">6.7</a>&nbsp;<a id="header.content-location" href="#header.content-location">Content-Location</a></h2>
1292      <p id="rfc.section.6.7.p.1">The "Content-Location" header field supplies a URI that can be used as a specific identifier for the representation in this
1293         message. In other words, if one were to perform a GET on this URI at the time of this message's generation, then a 200 response
1294         would contain the same representation that is enclosed as payload in this message.
1295      </p>
1296      <div id="rfc.figure.u.24"></div><pre class="inline"><span id="rfc.iref.g.22"></span>  <a href="#header.content-location" class="smpl">Content-Location</a> = <a href="#abnf.dependencies" class="smpl">absolute-URI</a> / <a href="#abnf.dependencies" class="smpl">partial-URI</a>
1297</pre><p id="rfc.section.6.7.p.3">The Content-Location value is not a replacement for the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). It is representation metadata. It has the same syntax and semantics as the header field of the same name defined for MIME
1298         body parts in <a href="http://tools.ietf.org/html/rfc2557#section-4">Section 4</a> of <a href="#RFC2557" id="rfc.xref.RFC2557.1"><cite title="MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)">[RFC2557]</cite></a>. However, its appearance in an HTTP message has some special implications for HTTP recipients.
1299      </p>
1300      <p id="rfc.section.6.7.p.4">If Content-Location is included in a response message and its value is the same as the effective request URI, then the response
1301         payload <em class="bcp14">SHOULD</em> be considered a current representation of that resource. For a GET or HEAD request, this is the same as the default semantics
1302         when no Content-Location is provided by the server. For a state-changing request like PUT or POST, it implies that the server's
1303         response contains the new representation of that resource, thereby distinguishing it from representations that might only
1304         report about the action (e.g., "It worked!"). This allows authoring applications to update their local copies without the
1305         need for a subsequent GET request.
1306      </p>
1307      <p id="rfc.section.6.7.p.5">If Content-Location is included in a response message and its value differs from the effective request URI, then the origin
1308         server is informing recipients that this representation has its own, presumably more specific, identifier. For a GET or HEAD
1309         request, this is an indication that the effective request URI identifies a resource that is subject to content negotiation
1310         and the selected representation for this response can also be found at the identified URI. For other methods, such a Content-Location
1311         indicates that this representation contains a report on the action's status and the same report is available (for future access
1312         with GET) at the given URI. For example, a purchase transaction made via a POST request might include a receipt document as
1313         the payload of the 200 response; the Content-Location value provides an identifier for retrieving a copy of that same receipt
1314         in the future.
1315      </p>
1316      <p id="rfc.section.6.7.p.6">If Content-Location is included in a request message, then it <em class="bcp14">MAY</em> be interpreted by the origin server as an indication of where the user agent originally obtained the content of the enclosed
1317         representation (prior to any subsequent modification of the content by that user agent). In other words, the user agent is
1318         providing the same representation metadata that it received with the original representation. However, such interpretation <em class="bcp14">MUST NOT</em> be used to alter the semantics of the method requested by the client. For example, if a client makes a PUT request on a negotiated
1319         resource and the origin server accepts that PUT (without redirection), then the new set of values for that resource is expected
1320         to be consistent with the one representation supplied in that PUT; the Content-Location cannot be used as a form of reverse
1321         content selection that identifies only one of the negotiated representations to be updated. If the user agent had wanted the
1322         latter semantics, it would have applied the PUT directly to the Content-Location URI.
1323      </p>
1324      <p id="rfc.section.6.7.p.7">A Content-Location field received in a request message is transitory information that <em class="bcp14">SHOULD NOT</em> be saved with other representation metadata for use in later responses. The Content-Location's value might be saved for use
1325         in other contexts, such as within source links or other metadata.
1326      </p>
1327      <p id="rfc.section.6.7.p.8">A cache cannot assume that a representation with a Content-Location different from the URI used to retrieve it can be used
1328         to respond to later requests on that Content-Location URI.
1329      </p>
1330      <p id="rfc.section.6.7.p.9">If the Content-Location value is a partial URI, the partial URI is interpreted relative to the effective request URI.</p>
1331      <div id="rfc.iref.c.8"></div>
1332      <div id="rfc.iref.h.8"></div>
1333      <h2 id="rfc.section.6.8"><a href="#rfc.section.6.8">6.8</a>&nbsp;<a id="header.content-type" href="#header.content-type">Content-Type</a></h2>
1334      <p id="rfc.section.6.8.p.1">The "Content-Type" header field indicates the media type of the representation. In the case of responses to the HEAD method,
1335         the media type is that which would have been sent had the request been a GET.
1336      </p>
1337      <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.23"></span>  <a href="#header.content-type" class="smpl">Content-Type</a> = <a href="#media.types" class="smpl">media-type</a>
1338</pre><p id="rfc.section.6.8.p.3">Media types are defined in <a href="#media.types" title="Media Types">Section&nbsp;2.3</a>. An example of the field is
1339      </p>
1340      <div id="rfc.figure.u.26"></div><pre class="text">  Content-Type: text/html; charset=ISO-8859-4
1341</pre><p id="rfc.section.6.8.p.5">Further discussion of Content-Type is provided in <a href="#representation.data" title="Representation Data">Section&nbsp;4.2</a>.
1342      </p>
1343      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
1344      <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="content.coding.registration" href="#content.coding.registration">Content Coding Registry</a></h2>
1345      <p id="rfc.section.7.1.p.1">The registration procedure for HTTP Content Codings is now defined by <a href="#content.coding.registry" title="Content Coding Registry">Section&nbsp;2.2.1</a> of this document.
1346      </p>
1347      <p id="rfc.section.7.1.p.2">The HTTP Content Codings Registry located at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt; shall be updated with the registration below:
1348      </p>
1349      <div id="rfc.table.1">
1350         <div id="iana.content.coding.registration.table"></div>
1351         <table class="tt full left" cellpadding="3" cellspacing="0">
1352            <thead>
1353               <tr>
1354                  <th>Name</th>
1355                  <th>Description</th>
1356                  <th>Reference</th>
1357               </tr>
1358            </thead>
1359            <tbody>
1360               <tr>
1361                  <td class="left">compress</td>
1362                  <td class="left">UNIX "compress" program method</td>
1363                  <td class="left"> <a href="p1-messaging.html#compress.coding" title="Compress Coding">Section 4.2.1</a> of <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> 
1364                  </td>
1365               </tr>
1366               <tr>
1367                  <td class="left">deflate</td>
1368                  <td class="left">"deflate" compression mechanism (<a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>) used inside the "zlib" data format (<a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a>)
1369                  </td>
1370                  <td class="left"> <a href="p1-messaging.html#deflate.coding" title="Deflate Coding">Section 4.2.2</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> 
1371                  </td>
1372               </tr>
1373               <tr>
1374                  <td class="left">gzip</td>
1375                  <td class="left">Same as GNU zip <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a></td>
1376                  <td class="left"> <a href="p1-messaging.html#gzip.coding" title="Gzip Coding">Section 4.2.3</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> 
1377                  </td>
1378               </tr>
1379               <tr>
1380                  <td class="left">identity</td>
1381                  <td class="left">reserved (synonym for "no encoding" in Accept-Encoding header field)</td>
1382                  <td class="left"> <a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.3" title="Accept-Encoding">Section&nbsp;6.3</a> 
1383                  </td>
1384               </tr>
1385            </tbody>
1386         </table>
1387      </div>
1388      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
1389      <p id="rfc.section.8.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1
1390         as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does
1391         make some suggestions for reducing security risks.
1392      </p>
1393      <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a id="privacy.issues.connected.to.accept.header.fields" href="#privacy.issues.connected.to.accept.header.fields">Privacy Issues Connected to Accept Header Fields</a></h2>
1394      <p id="rfc.section.8.1.p.1">Accept header fields can reveal information about the user to all servers which are accessed. The Accept-Language header field
1395         in particular can reveal information the user would consider to be of a private nature, because the understanding of particular
1396         languages is often strongly correlated to the membership of a particular ethnic group. User agents which offer the option
1397         to configure the contents of an Accept-Language header field to be sent in every request are strongly encouraged to let the
1398         configuration process include a message which makes the user aware of the loss of privacy involved.
1399      </p>
1400      <p id="rfc.section.8.1.p.2">An approach that limits the loss of privacy would be for a user agent to omit the sending of Accept-Language header fields
1401         by default, and to ask the user whether or not to start sending Accept-Language header fields to a server if it detects, by
1402         looking for any Vary header fields generated by the server, that such sending could improve the quality of service.
1403      </p>
1404      <p id="rfc.section.8.1.p.3">Elaborate user-customized accept header fields sent in every request, in particular if these include quality values, can be
1405         used by servers as relatively reliable and long-lived user identifiers. Such user identifiers would allow content providers
1406         to do click-trail tracking, and would allow collaborating content providers to match cross-server click-trails or form submissions
1407         of individual users. Note that for many users not behind a proxy, the network address of the host running the user agent will
1408         also serve as a long-lived user identifier. In environments where proxies are used to enhance privacy, user agents ought to
1409         be conservative in offering accept header configuration options to end users. As an extreme privacy measure, proxies could
1410         filter the accept header fields in relayed requests. General purpose user agents which provide a high degree of header configurability <em class="bcp14">SHOULD</em> warn users about the loss of privacy which can be involved.
1411      </p>
1412      <h1 id="rfc.references"><a id="rfc.section.9" href="#rfc.section.9">9.</a> References
1413      </h1>
1414      <h2 id="rfc.references.1"><a href="#rfc.section.9.1" id="rfc.section.9.1">9.1</a> Normative References
1415      </h2>
1416      <table>                       
1417         <tr>
1418            <td class="reference"><b id="Part1">[Part1]</b></td>
1419            <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</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.
1420            </td>
1421         </tr>
1422         <tr>
1423            <td class="reference"><b id="Part2">[Part2]</b></td>
1424            <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</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-p2-semantics-latest">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p2-semantics-latest (work in progress), March&nbsp;2012.
1425            </td>
1426         </tr>
1427         <tr>
1428            <td class="reference"><b id="Part4">[Part4]</b></td>
1429            <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</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.
1430            </td>
1431         </tr>
1432         <tr>
1433            <td class="reference"><b id="Part5">[Part5]</b></td>
1434            <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</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.
1435            </td>
1436         </tr>
1437         <tr>
1438            <td class="reference"><b id="Part6">[Part6]</b></td>
1439            <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</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.
1440            </td>
1441         </tr>
1442         <tr>
1443            <td class="reference"><b id="RFC1950">[RFC1950]</b></td>
1444            <td class="top"><a href="mailto:ghost@aladdin.com" title="Aladdin Enterprises">Deutsch, L.</a> and J-L. Gailly, “<a href="http://tools.ietf.org/html/rfc1950">ZLIB Compressed Data Format Specification version 3.3</a>”, RFC&nbsp;1950, May&nbsp;1996.
1445            </td>
1446         </tr>
1447         <tr>
1448            <td class="reference"><b id="RFC1951">[RFC1951]</b></td>
1449            <td class="top"><a href="mailto:ghost@aladdin.com" title="Aladdin Enterprises">Deutsch, P.</a>, “<a href="http://tools.ietf.org/html/rfc1951">DEFLATE Compressed Data Format Specification version 1.3</a>”, RFC&nbsp;1951, May&nbsp;1996.
1450            </td>
1451         </tr>
1452         <tr>
1453            <td class="reference"><b id="RFC1952">[RFC1952]</b></td>
1454            <td class="top"><a href="mailto:ghost@aladdin.com" title="Aladdin Enterprises">Deutsch, P.</a>, <a href="mailto:gzip@prep.ai.mit.edu">Gailly, J-L.</a>, <a href="mailto:madler@alumni.caltech.edu">Adler, M.</a>, <a href="mailto:ghost@aladdin.com">Deutsch, L.</a>, and <a href="mailto:randeg@alumni.rpi.edu">G. Randers-Pehrson</a>, “<a href="http://tools.ietf.org/html/rfc1952">GZIP file format specification version 4.3</a>”, RFC&nbsp;1952, May&nbsp;1996.
1455            </td>
1456         </tr>
1457         <tr>
1458            <td class="reference"><b id="RFC2045">[RFC2045]</b></td>
1459            <td class="top"><a href="mailto:ned@innosoft.com" title="Innosoft International, Inc.">Freed, N.</a> and <a href="mailto:nsb@nsb.fv.com" title="First Virtual Holdings">N. Borenstein</a>, “<a href="http://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>”, RFC&nbsp;2045, November&nbsp;1996.
1460            </td>
1461         </tr>
1462         <tr>
1463            <td class="reference"><b id="RFC2046">[RFC2046]</b></td>
1464            <td class="top"><a href="mailto:ned@innosoft.com" title="Innosoft International, Inc.">Freed, N.</a> and <a href="mailto:nsb@nsb.fv.com" title="First Virtual Holdings">N. Borenstein</a>, “<a href="http://tools.ietf.org/html/rfc2046">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</a>”, RFC&nbsp;2046, November&nbsp;1996.
1465            </td>
1466         </tr>
1467         <tr>
1468            <td class="reference"><b id="RFC4647">[RFC4647]</b></td>
1469            <td class="top"><a href="mailto:addison@inter-locale.com" title="Yahoo! Inc.">Phillips, A., Ed.</a> and <a href="mailto:mark.davis@macchiato.com" title="Google">M. Davis, Ed.</a>, “<a href="http://tools.ietf.org/html/rfc4647">Matching of Language Tags</a>”, BCP&nbsp;47, RFC&nbsp;4647, September&nbsp;2006.
1470            </td>
1471         </tr>
1472         <tr>
1473            <td class="reference"><b id="RFC5646">[RFC5646]</b></td>
1474            <td class="top"><a href="mailto:addison@inter-locale.com" title="Lab126">Phillips, A., Ed.</a> and <a href="mailto:mark.davis@google.com" title="Google">M. Davis, Ed.</a>, “<a href="http://tools.ietf.org/html/rfc5646">Tags for Identifying Languages</a>”, BCP&nbsp;47, RFC&nbsp;5646, September&nbsp;2009.
1475            </td>
1476         </tr>
1477      </table>
1478      <h2 id="rfc.references.2"><a href="#rfc.section.9.2" id="rfc.section.9.2">9.2</a> Informative References
1479      </h2>
1480      <table>                               
1481         <tr>
1482            <td class="reference"><b id="RFC1945">[RFC1945]</b></td>
1483            <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.
1484            </td>
1485         </tr>
1486         <tr>
1487            <td class="reference"><b id="RFC2049">[RFC2049]</b></td>
1488            <td class="top"><a href="mailto:ned@innosoft.com" title="Innosoft International, Inc.">Freed, N.</a> and <a href="mailto:nsb@nsb.fv.com" title="First Virtual Holdings">N. Borenstein</a>, “<a href="http://tools.ietf.org/html/rfc2049">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</a>”, RFC&nbsp;2049, November&nbsp;1996.
1489            </td>
1490         </tr>
1491         <tr>
1492            <td class="reference"><b id="RFC2068">[RFC2068]</b></td>
1493            <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.
1494            </td>
1495         </tr>
1496         <tr>
1497            <td class="reference"><b id="RFC2076">[RFC2076]</b></td>
1498            <td class="top"><a href="mailto:jpalme@dsv.su.se" title="Stockholm University/KTH">Palme, J.</a>, “<a href="http://tools.ietf.org/html/rfc2076">Common Internet Message Headers</a>”, RFC&nbsp;2076, February&nbsp;1997.
1499            </td>
1500         </tr>
1501         <tr>
1502            <td class="reference"><b id="RFC2277">[RFC2277]</b></td>
1503            <td class="top"><a href="mailto:Harald.T.Alvestrand@uninett.no" title="UNINETT">Alvestrand, H.</a>, “<a href="http://tools.ietf.org/html/rfc2277">IETF Policy on Character Sets and Languages</a>”, BCP&nbsp;18, RFC&nbsp;2277, January&nbsp;1998.
1504            </td>
1505         </tr>
1506         <tr>
1507            <td class="reference"><b id="RFC2295">[RFC2295]</b></td>
1508            <td class="top"><a href="mailto:koen@win.tue.nl" title="Technische Universiteit Eindhoven">Holtman, K.</a> and <a href="mailto:mutz@hpl.hp.com" title="Hewlett-Packard Company">A. Mutz</a>, “<a href="http://tools.ietf.org/html/rfc2295">Transparent Content Negotiation in HTTP</a>”, RFC&nbsp;2295, March&nbsp;1998.
1509            </td>
1510         </tr>
1511         <tr>
1512            <td class="reference"><b id="RFC2388">[RFC2388]</b></td>
1513            <td class="top"><a href="mailto:masinter@parc.xerox.com" title="Xerox Palo Alto Research Center">Masinter, L.</a>, “<a href="http://tools.ietf.org/html/rfc2388">Returning Values from Forms: multipart/form-data</a>”, RFC&nbsp;2388, August&nbsp;1998.
1514            </td>
1515         </tr>
1516         <tr>
1517            <td class="reference"><b id="RFC2557">[RFC2557]</b></td>
1518            <td class="top"><a href="mailto:jpalme@dsv.su.se" title="Stockholm University and KTH">Palme, F.</a>, <a href="mailto:alexhop@microsoft.com" title="Microsoft Corporation">Hopmann, A.</a>, <a href="mailto:Shelness@lotus.com" title="Lotus Development Corporation">Shelness, N.</a>, and <a href="mailto:stef@nma.com">E. Stefferud</a>, “<a href="http://tools.ietf.org/html/rfc2557">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</a>”, RFC&nbsp;2557, March&nbsp;1999.
1519            </td>
1520         </tr>
1521         <tr>
1522            <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
1523            <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.
1524            </td>
1525         </tr>
1526         <tr>
1527            <td class="reference"><b id="RFC3629">[RFC3629]</b></td>
1528            <td class="top"><a href="mailto:fyergeau@alis.com" title="Alis Technologies">Yergeau, F.</a>, “<a href="http://tools.ietf.org/html/rfc3629">UTF-8, a transformation format of ISO 10646</a>”, STD&nbsp;63, RFC&nbsp;3629, November&nbsp;2003.
1529            </td>
1530         </tr>
1531         <tr>
1532            <td class="reference"><b id="RFC4288">[RFC4288]</b></td>
1533            <td class="top"><a href="mailto:ned.freed@mrochek.com" title="Sun Microsystems">Freed, N.</a> and <a href="mailto:klensin+ietf@jck.com">J. Klensin</a>, “<a href="http://tools.ietf.org/html/rfc4288">Media Type Specifications and Registration Procedures</a>”, BCP&nbsp;13, RFC&nbsp;4288, December&nbsp;2005.
1534            </td>
1535         </tr>
1536         <tr>
1537            <td class="reference"><b id="RFC5226">[RFC5226]</b></td>
1538            <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.
1539            </td>
1540         </tr>
1541         <tr>
1542            <td class="reference"><b id="RFC5322">[RFC5322]</b></td>
1543            <td class="top">Resnick, P., “<a href="http://tools.ietf.org/html/rfc5322">Internet Message Format</a>”, RFC&nbsp;5322, October&nbsp;2008.
1544            </td>
1545         </tr>
1546         <tr>
1547            <td class="reference"><b id="RFC6151">[RFC6151]</b></td>
1548            <td class="top">Turner, S. and L. Chen, “<a href="http://tools.ietf.org/html/rfc6151">Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</a>”, RFC&nbsp;6151, March&nbsp;2011.
1549            </td>
1550         </tr>
1551         <tr>
1552            <td class="reference"><b id="RFC6266">[RFC6266]</b></td>
1553            <td class="top"><a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">Reschke, J.</a>, “<a href="http://tools.ietf.org/html/rfc6266">Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)</a>”, RFC&nbsp;6266, June&nbsp;2011.
1554            </td>
1555         </tr>
1556      </table>
1557      <div class="avoidbreak">
1558         <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1>
1559         <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span>
1560               (editor)
1561               <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>
1562         <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span>
1563               (editor)
1564               <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>
1565         <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span>
1566               (editor)
1567               <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>
1568      </div>
1569      <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a id="differences.between.http.and.mime" href="#differences.between.http.and.mime">Differences between HTTP and MIME</a></h1>
1570      <p id="rfc.section.A.p.1">HTTP/1.1 uses many of the constructs defined for Internet Mail (<a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a>) and the Multipurpose Internet Mail Extensions (MIME <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>) to allow a message body to be transmitted in an open variety of representations and with extensible mechanisms. However,
1571         RFC 2045 discusses mail, and HTTP has a few features that are different from those described in MIME. These differences were
1572         carefully chosen to optimize performance over binary connections, to allow greater freedom in the use of new media types,
1573         to make date comparisons easier, and to acknowledge the practice of some early HTTP servers and clients.
1574      </p>
1575      <p id="rfc.section.A.p.2">This appendix describes specific areas where HTTP differs from MIME. Proxies and gateways to strict MIME environments <em class="bcp14">SHOULD</em> be aware of these differences and provide the appropriate conversions where necessary. Proxies and gateways from MIME environments
1576         to HTTP also need to be aware of the differences because some conversions might be required.
1577      </p>
1578      <div id="rfc.iref.m.1"></div>
1579      <div id="rfc.iref.h.9"></div>
1580      <h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a>&nbsp;<a id="mime-version" href="#mime-version">MIME-Version</a></h2>
1581      <p id="rfc.section.A.1.p.1">HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages <em class="bcp14">MAY</em> include a single MIME-Version header field to indicate what version of the MIME protocol was used to construct the message.
1582         Use of the MIME-Version header field indicates that the message is in full conformance with the MIME protocol (as defined
1583         in <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>). Proxies/gateways are responsible for ensuring full conformance (where possible) when exporting HTTP messages to strict
1584         MIME environments.
1585      </p>
1586      <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.24"></span>  <a href="#mime-version" class="smpl">MIME-Version</a> = 1*<a href="#notation" class="smpl">DIGIT</a> "." 1*<a href="#notation" class="smpl">DIGIT</a>
1587</pre><p id="rfc.section.A.1.p.3">MIME version "1.0" is the default for use in HTTP/1.1. However, HTTP/1.1 message parsing and semantics are defined by this
1588         document and not the MIME specification.
1589      </p>
1590      <h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a>&nbsp;<a id="conversion.to.canonical.form" href="#conversion.to.canonical.form">Conversion to Canonical Form</a></h2>
1591      <p id="rfc.section.A.2.p.1">MIME requires that an Internet mail body-part be converted to canonical form prior to being transferred, as described in <a href="http://tools.ietf.org/html/rfc2049#section-4">Section 4</a> of <a href="#RFC2049" id="rfc.xref.RFC2049.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples">[RFC2049]</cite></a>. <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;2.3.1</a> of this document describes the forms allowed for subtypes of the "text" media type when transmitted over HTTP. <a href="#RFC2046" id="rfc.xref.RFC2046.4"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> requires that content with a type of "text" represent line breaks as CRLF and forbids the use of CR or LF outside of line
1592         break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a line break within text content when a message is transmitted
1593         over HTTP.
1594      </p>
1595      <p id="rfc.section.A.2.p.2">Where it is possible, a proxy or gateway from HTTP to a strict MIME environment <em class="bcp14">SHOULD</em> translate all line breaks within the text media types described in <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;2.3.1</a> of this document to the RFC 2049 canonical form of CRLF. Note, however, that this might be complicated by the presence of
1596         a Content-Encoding and by the fact that HTTP allows the use of some character encodings which do not use octets 13 and 10
1597         to represent CR and LF, respectively, as is the case for some multi-byte character encodings.
1598      </p>
1599      <p id="rfc.section.A.2.p.3">Conversion will break any cryptographic checksums applied to the original content unless the original content is already in
1600         canonical form. Therefore, the canonical form is recommended for any content that uses such checksums in HTTP.
1601      </p>
1602      <h2 id="rfc.section.A.3"><a href="#rfc.section.A.3">A.3</a>&nbsp;<a id="conversion.of.date.formats" href="#conversion.of.date.formats">Conversion of Date Formats</a></h2>
1603      <p id="rfc.section.A.3.p.1">HTTP/1.1 uses a restricted set of date formats (<a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 6.1</a> of <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) to simplify the process of date comparison. Proxies and gateways from other protocols <em class="bcp14">SHOULD</em> ensure that any Date header field present in a message conforms to one of the HTTP/1.1 formats and rewrite the date if necessary.
1604      </p>
1605      <h2 id="rfc.section.A.4"><a href="#rfc.section.A.4">A.4</a>&nbsp;<a id="introduction.of.content-encoding" href="#introduction.of.content-encoding">Introduction of Content-Encoding</a></h2>
1606      <p id="rfc.section.A.4.p.1">MIME does not include any concept equivalent to HTTP/1.1's Content-Encoding header field. Since this acts as a modifier on
1607         the media type, proxies and gateways from HTTP to MIME-compliant protocols <em class="bcp14">MUST</em> either change the value of the Content-Type header field or decode the representation before forwarding the message. (Some
1608         experimental applications of Content-Type for Internet mail have used a media-type parameter of ";conversions=&lt;content-coding&gt;"
1609         to perform a function equivalent to Content-Encoding. However, this parameter is not part of the MIME standards).
1610      </p>
1611      <div id="rfc.iref.c.9"></div>
1612      <div id="rfc.iref.h.10"></div>
1613      <h2 id="rfc.section.A.5"><a href="#rfc.section.A.5">A.5</a>&nbsp;<a id="no.content-transfer-encoding" href="#no.content-transfer-encoding">No Content-Transfer-Encoding</a></h2>
1614      <p id="rfc.section.A.5.p.1">HTTP does not use the Content-Transfer-Encoding field of MIME. Proxies and gateways from MIME-compliant protocols to HTTP <em class="bcp14">MUST</em> remove any Content-Transfer-Encoding prior to delivering the response message to an HTTP client.
1615      </p>
1616      <p id="rfc.section.A.5.p.2">Proxies and gateways from HTTP to MIME-compliant protocols are responsible for ensuring that the message is in the correct
1617         format and encoding for safe transport on that protocol, where "safe transport" is defined by the limitations of the protocol
1618         being used. Such a proxy or gateway <em class="bcp14">SHOULD</em> label the data with an appropriate Content-Transfer-Encoding if doing so will improve the likelihood of safe transport over
1619         the destination protocol.
1620      </p>
1621      <h2 id="rfc.section.A.6"><a href="#rfc.section.A.6">A.6</a>&nbsp;<a id="introduction.of.transfer-encoding" href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></h2>
1622      <p id="rfc.section.A.6.p.1">HTTP/1.1 introduces the Transfer-Encoding header field (<a href="p1-messaging.html#header.transfer-encoding" title="Transfer-Encoding">Section 3.3.1</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>). Proxies/gateways <em class="bcp14">MUST</em> remove any transfer-coding prior to forwarding a message via a MIME-compliant protocol.
1623      </p>
1624      <h2 id="rfc.section.A.7"><a href="#rfc.section.A.7">A.7</a>&nbsp;<a id="mhtml.line.length" href="#mhtml.line.length">MHTML and Line Length Limitations</a></h2>
1625      <p id="rfc.section.A.7.p.1">HTTP implementations which share code with MHTML <a href="#RFC2557" id="rfc.xref.RFC2557.2"><cite title="MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)">[RFC2557]</cite></a> implementations need to be aware of MIME line length limitations. Since HTTP does not have this limitation, HTTP does not
1626         fold long lines. MHTML messages being transported by HTTP follow all conventions of MHTML, including line length limitations
1627         and folding, canonicalization, etc., since HTTP transports all message-bodies as payload (see <a href="#multipart.types" title="Multipart Types">Section&nbsp;2.3.2</a>) and does not interpret the content or any MIME header lines that might be contained therein.
1628      </p>
1629      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="additional.features" href="#additional.features">Additional Features</a></h1>
1630      <p id="rfc.section.B.p.1"> <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a> and <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> document protocol elements used by some existing HTTP implementations, but not consistently and correctly across most HTTP/1.1
1631         applications. Implementors are advised to be aware of these features, but cannot rely upon their presence in, or interoperability
1632         with, other HTTP/1.1 applications. Some of these describe proposed experimental features, and some describe features that
1633         experimental deployment found lacking that are now addressed in the base HTTP/1.1 specification.
1634      </p>
1635      <p id="rfc.section.B.p.2">A number of other header fields, such as Content-Disposition and Title, from SMTP and MIME are also often implemented (see <a href="#RFC6266" id="rfc.xref.RFC6266.1"><cite title="Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)">[RFC6266]</cite></a> and <a href="#RFC2076" id="rfc.xref.RFC2076.1"><cite title="Common Internet Message Headers">[RFC2076]</cite></a>).
1636      </p>
1637      <h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1>
1638      <p id="rfc.section.C.p.1">Clarify contexts that charset is used in. (<a href="#character.sets" title="Character Encodings (charset)">Section&nbsp;2.1</a>)
1639      </p>
1640      <p id="rfc.section.C.p.2">Registration of Content Codings now requires IETF Review (<a href="#content.coding.registry" title="Content Coding Registry">Section&nbsp;2.2.1</a>)
1641      </p>
1642      <p id="rfc.section.C.p.3">Remove the default character encoding for text media types; the default now is whatever the media type definition says. (<a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;2.3.1</a>)
1643      </p>
1644      <p id="rfc.section.C.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;6</a>)
1645      </p>
1646      <p id="rfc.section.C.p.5">Remove definition of Content-MD5 header field because it was inconsistently implemented with respect to partial responses,
1647         and also because of known deficiencies in the hash algorithm itself (see <a href="#RFC6151" id="rfc.xref.RFC6151.1"><cite title="Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms">[RFC6151]</cite></a> for details). (<a href="#header.field.definitions" title="Header Field Definitions">Section&nbsp;6</a>)
1648      </p>
1649      <p id="rfc.section.C.p.6">Remove ISO-8859-1 special-casing in Accept-Charset. (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.2" title="Accept-Charset">Section&nbsp;6.2</a>)
1650      </p>
1651      <p id="rfc.section.C.p.7">Remove base URI setting semantics for Content-Location due to poor implementation support, which was caused by too many broken
1652         servers emitting bogus Content-Location header fields, and also the potentially undesirable effect of potentially breaking
1653         relative links in content-negotiated resources. (<a href="#header.content-location" id="rfc.xref.header.content-location.2" title="Content-Location">Section&nbsp;6.7</a>)
1654      </p>
1655      <p id="rfc.section.C.p.8">Remove reference to non-existant identity transfer-coding value tokens. (<a href="#no.content-transfer-encoding" id="rfc.xref.no.content-transfer-encoding.1" title="No Content-Transfer-Encoding">Appendix&nbsp;A.5</a>)
1656      </p>
1657      <p id="rfc.section.C.p.9">Remove discussion of Content-Disposition header field, it is now defined by <a href="#RFC6266" id="rfc.xref.RFC6266.2"><cite title="Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)">[RFC6266]</cite></a>. (<a href="#additional.features" title="Additional Features">Appendix&nbsp;B</a>)
1658      </p>
1659      <h1 id="rfc.section.D"><a href="#rfc.section.D">D.</a>&nbsp;<a id="change.log" href="#change.log">Change Log (to be removed by RFC Editor before publication)</a></h1>
1660      <h2 id="rfc.section.D.1"><a href="#rfc.section.D.1">D.1</a>&nbsp;Since RFC 2616
1661      </h2>
1662      <p id="rfc.section.D.1.p.1">Extracted relevant partitions from <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
1663      </p>
1664      <h2 id="rfc.section.D.2"><a href="#rfc.section.D.2">D.2</a>&nbsp;Since draft-ietf-httpbis-p3-payload-00
1665      </h2>
1666      <p id="rfc.section.D.2.p.1">Closed issues: </p>
1667      <ul>
1668         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/8">http://tools.ietf.org/wg/httpbis/trac/ticket/8</a>&gt;: "Media Type Registrations" (&lt;<a href="http://purl.org/NET/http-errata#media-reg">http://purl.org/NET/http-errata#media-reg</a>&gt;)
1669         </li>
1670         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/14">http://tools.ietf.org/wg/httpbis/trac/ticket/14</a>&gt;: "Clarification regarding quoting of charset values" (&lt;<a href="http://purl.org/NET/http-errata#charactersets">http://purl.org/NET/http-errata#charactersets</a>&gt;)
1671         </li>
1672         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/16">http://tools.ietf.org/wg/httpbis/trac/ticket/16</a>&gt;: "Remove 'identity' token references" (&lt;<a href="http://purl.org/NET/http-errata#identity">http://purl.org/NET/http-errata#identity</a>&gt;)
1673         </li>
1674         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/25">http://tools.ietf.org/wg/httpbis/trac/ticket/25</a>&gt;: "Accept-Encoding BNF"
1675         </li>
1676         <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"
1677         </li>
1678         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/46">http://tools.ietf.org/wg/httpbis/trac/ticket/46</a>&gt;: "RFC1700 references"
1679         </li>
1680         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/55">http://tools.ietf.org/wg/httpbis/trac/ticket/55</a>&gt;: "Updating to RFC4288"
1681         </li>
1682         <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"
1683         </li>
1684         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/66">http://tools.ietf.org/wg/httpbis/trac/ticket/66</a>&gt;: "ISO-8859-1 Reference"
1685         </li>
1686         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/68">http://tools.ietf.org/wg/httpbis/trac/ticket/68</a>&gt;: "Encoding References Normative"
1687         </li>
1688         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/86">http://tools.ietf.org/wg/httpbis/trac/ticket/86</a>&gt;: "Normative up-to-date references"
1689         </li>
1690      </ul>
1691      <h2 id="rfc.section.D.3"><a href="#rfc.section.D.3">D.3</a>&nbsp;Since draft-ietf-httpbis-p3-payload-01
1692      </h2>
1693      <p id="rfc.section.D.3.p.1">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;):
1694      </p>
1695      <ul>
1696         <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li>
1697      </ul>
1698      <h2 id="rfc.section.D.4"><a href="#rfc.section.D.4">D.4</a>&nbsp;<a id="changes.since.02" href="#changes.since.02">Since draft-ietf-httpbis-p3-payload-02</a></h2>
1699      <p id="rfc.section.D.4.p.1">Closed issues: </p>
1700      <ul>
1701         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/67">http://tools.ietf.org/wg/httpbis/trac/ticket/67</a>&gt;: "Quoting Charsets"
1702         </li>
1703         <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"
1704         </li>
1705         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/115">http://tools.ietf.org/wg/httpbis/trac/ticket/115</a>&gt;: "missing default for qvalue in description of Accept-Encoding"
1706         </li>
1707      </ul>
1708      <p id="rfc.section.D.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;):
1709      </p>
1710      <ul>
1711         <li>Reference RFC 3984, and update header field registrations for headers defined in this document.</li>
1712      </ul>
1713      <h2 id="rfc.section.D.5"><a href="#rfc.section.D.5">D.5</a>&nbsp;<a id="changes.since.03" href="#changes.since.03">Since draft-ietf-httpbis-p3-payload-03</a></h2>
1714      <p id="rfc.section.D.5.p.1">Closed issues: </p>
1715      <ul>
1716         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/67">http://tools.ietf.org/wg/httpbis/trac/ticket/67</a>&gt;: "Quoting Charsets"
1717         </li>
1718         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/113">http://tools.ietf.org/wg/httpbis/trac/ticket/113</a>&gt;: "language tag matching (Accept-Language) vs RFC4647"
1719         </li>
1720         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/121">http://tools.ietf.org/wg/httpbis/trac/ticket/121</a>&gt;: "RFC 1806 has been replaced by RFC2183"
1721         </li>
1722      </ul>
1723      <p id="rfc.section.D.5.p.2">Other changes: </p>
1724      <ul>
1725         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/68">http://tools.ietf.org/wg/httpbis/trac/ticket/68</a>&gt;: "Encoding References Normative" — rephrase the annotation and reference BCP97.
1726         </li>
1727      </ul>
1728      <h2 id="rfc.section.D.6"><a href="#rfc.section.D.6">D.6</a>&nbsp;<a id="changes.since.04" href="#changes.since.04">Since draft-ietf-httpbis-p3-payload-04</a></h2>
1729      <p id="rfc.section.D.6.p.1">Closed issues: </p>
1730      <ul>
1731         <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"
1732         </li>
1733      </ul>
1734      <p id="rfc.section.D.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;):
1735      </p>
1736      <ul>
1737         <li>Use "/" instead of "|" for alternatives.</li>
1738         <li>Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS").</li>
1739         <li>Rewrite ABNFs to spell out whitespace rules, factor out header field value format definitions.</li>
1740      </ul>
1741      <h2 id="rfc.section.D.7"><a href="#rfc.section.D.7">D.7</a>&nbsp;<a id="changes.since.05" href="#changes.since.05">Since draft-ietf-httpbis-p3-payload-05</a></h2>
1742      <p id="rfc.section.D.7.p.1">Closed issues: </p>
1743      <ul>
1744         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/118">http://tools.ietf.org/wg/httpbis/trac/ticket/118</a>&gt;: "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
1745         </li>
1746      </ul>
1747      <p id="rfc.section.D.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;):
1748      </p>
1749      <ul>
1750         <li>Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.</li>
1751      </ul>
1752      <p id="rfc.section.D.7.p.3">Other changes: </p>
1753      <ul>
1754         <li>Move definition of quality values into Part 1.</li>
1755      </ul>
1756      <h2 id="rfc.section.D.8"><a href="#rfc.section.D.8">D.8</a>&nbsp;<a id="changes.since.06" href="#changes.since.06">Since draft-ietf-httpbis-p3-payload-06</a></h2>
1757      <p id="rfc.section.D.8.p.1">Closed issues: </p>
1758      <ul>
1759         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/80">http://tools.ietf.org/wg/httpbis/trac/ticket/80</a>&gt;: "Content-Location isn't special"
1760         </li>
1761         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/155">http://tools.ietf.org/wg/httpbis/trac/ticket/155</a>&gt;: "Content Sniffing"
1762         </li>
1763      </ul>
1764      <h2 id="rfc.section.D.9"><a href="#rfc.section.D.9">D.9</a>&nbsp;<a id="changes.since.07" href="#changes.since.07">Since draft-ietf-httpbis-p3-payload-07</a></h2>
1765      <p id="rfc.section.D.9.p.1">Closed issues: </p>
1766      <ul>
1767         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/13">http://tools.ietf.org/wg/httpbis/trac/ticket/13</a>&gt;: "Updated reference for language tags"
1768         </li>
1769         <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"
1770         </li>
1771         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/154">http://tools.ietf.org/wg/httpbis/trac/ticket/154</a>&gt;: "Content-Location base-setting problems"
1772         </li>
1773         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/155">http://tools.ietf.org/wg/httpbis/trac/ticket/155</a>&gt;: "Content Sniffing"
1774         </li>
1775         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/188">http://tools.ietf.org/wg/httpbis/trac/ticket/188</a>&gt;: "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
1776         </li>
1777         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/189">http://tools.ietf.org/wg/httpbis/trac/ticket/189</a>&gt;: "move definitions of gzip/deflate/compress to part 1"
1778         </li>
1779      </ul>
1780      <p id="rfc.section.D.9.p.2">Partly resolved issues: </p>
1781      <ul>
1782         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/148">http://tools.ietf.org/wg/httpbis/trac/ticket/148</a>&gt;: "update IANA requirements wrt Transfer-Coding values" (add the IANA Considerations subsection)
1783         </li>
1784         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/149">http://tools.ietf.org/wg/httpbis/trac/ticket/149</a>&gt;: "update IANA requirements wrt Content-Coding values" (add the IANA Considerations subsection)
1785         </li>
1786      </ul>
1787      <h2 id="rfc.section.D.10"><a href="#rfc.section.D.10">D.10</a>&nbsp;<a id="changes.since.08" href="#changes.since.08">Since draft-ietf-httpbis-p3-payload-08</a></h2>
1788      <p id="rfc.section.D.10.p.1">Closed issues: </p>
1789      <ul>
1790         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/81">http://tools.ietf.org/wg/httpbis/trac/ticket/81</a>&gt;: "Content Negotiation for media types"
1791         </li>
1792         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/181">http://tools.ietf.org/wg/httpbis/trac/ticket/181</a>&gt;: "Accept-Language: which RFC4647 filtering?"
1793         </li>
1794      </ul>
1795      <h2 id="rfc.section.D.11"><a href="#rfc.section.D.11">D.11</a>&nbsp;<a id="changes.since.09" href="#changes.since.09">Since draft-ietf-httpbis-p3-payload-09</a></h2>
1796      <p id="rfc.section.D.11.p.1">Closed issues: </p>
1797      <ul>
1798         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/122">http://tools.ietf.org/wg/httpbis/trac/ticket/122</a>&gt;: "MIME-Version not listed in P1, general header fields"
1799         </li>
1800         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/143">http://tools.ietf.org/wg/httpbis/trac/ticket/143</a>&gt;: "IANA registry for content/transfer encodings"
1801         </li>
1802         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/155">http://tools.ietf.org/wg/httpbis/trac/ticket/155</a>&gt;: "Content Sniffing"
1803         </li>
1804         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/200">http://tools.ietf.org/wg/httpbis/trac/ticket/200</a>&gt;: "use of term "word" when talking about header structure"
1805         </li>
1806      </ul>
1807      <p id="rfc.section.D.11.p.2">Partly resolved issues: </p>
1808      <ul>
1809         <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"
1810         </li>
1811      </ul>
1812      <h2 id="rfc.section.D.12"><a href="#rfc.section.D.12">D.12</a>&nbsp;<a id="changes.since.10" href="#changes.since.10">Since draft-ietf-httpbis-p3-payload-10</a></h2>
1813      <p id="rfc.section.D.12.p.1">Closed issues: </p>
1814      <ul>
1815         <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'"
1816         </li>
1817         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/80">http://tools.ietf.org/wg/httpbis/trac/ticket/80</a>&gt;: "Content-Location isn't special"
1818         </li>
1819         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/90">http://tools.ietf.org/wg/httpbis/trac/ticket/90</a>&gt;: "Delimiting messages with multipart/byteranges"
1820         </li>
1821         <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"
1822         </li>
1823         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/136">http://tools.ietf.org/wg/httpbis/trac/ticket/136</a>&gt;: "confusing req. language for Content-Location"
1824         </li>
1825         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/167">http://tools.ietf.org/wg/httpbis/trac/ticket/167</a>&gt;: "Content-Location on 304 responses"
1826         </li>
1827         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/183">http://tools.ietf.org/wg/httpbis/trac/ticket/183</a>&gt;: "'requested resource' in content-encoding definition"
1828         </li>
1829         <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"
1830         </li>
1831      </ul>
1832      <p id="rfc.section.D.12.p.2">Partly resolved issues: </p>
1833      <ul>
1834         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/178">http://tools.ietf.org/wg/httpbis/trac/ticket/178</a>&gt;: "Content-MD5 and partial responses"
1835         </li>
1836      </ul>
1837      <h2 id="rfc.section.D.13"><a href="#rfc.section.D.13">D.13</a>&nbsp;<a id="changes.since.11" href="#changes.since.11">Since draft-ietf-httpbis-p3-payload-11</a></h2>
1838      <p id="rfc.section.D.13.p.1">Closed issues: </p>
1839      <ul>
1840         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/123">http://tools.ietf.org/wg/httpbis/trac/ticket/123</a>&gt;: "Factor out Content-Disposition"
1841         </li>
1842      </ul>
1843      <h2 id="rfc.section.D.14"><a href="#rfc.section.D.14">D.14</a>&nbsp;<a id="changes.since.12" href="#changes.since.12">Since draft-ietf-httpbis-p3-payload-12</a></h2>
1844      <p id="rfc.section.D.14.p.1">Closed issues: </p>
1845      <ul>
1846         <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"
1847         </li>
1848         <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"
1849         </li>
1850         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/277">http://tools.ietf.org/wg/httpbis/trac/ticket/277</a>&gt;: "potentially misleading MAY in media-type def"
1851         </li>
1852      </ul>
1853      <h2 id="rfc.section.D.15"><a href="#rfc.section.D.15">D.15</a>&nbsp;<a id="changes.since.13" href="#changes.since.13">Since draft-ietf-httpbis-p3-payload-13</a></h2>
1854      <p id="rfc.section.D.15.p.1">Closed issues: </p>
1855      <ul>
1856         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/20">http://tools.ietf.org/wg/httpbis/trac/ticket/20</a>&gt;: "Default charsets for text media types"
1857         </li>
1858         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/178">http://tools.ietf.org/wg/httpbis/trac/ticket/178</a>&gt;: "Content-MD5 and partial responses"
1859         </li>
1860         <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"
1861         </li>
1862         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/281">http://tools.ietf.org/wg/httpbis/trac/ticket/281</a>&gt;: "confusing undefined parameter in media range example"
1863         </li>
1864      </ul>
1865      <h2 id="rfc.section.D.16"><a href="#rfc.section.D.16">D.16</a>&nbsp;<a id="changes.since.14" href="#changes.since.14">Since draft-ietf-httpbis-p3-payload-14</a></h2>
1866      <p id="rfc.section.D.16.p.1">None.</p>
1867      <h2 id="rfc.section.D.17"><a href="#rfc.section.D.17">D.17</a>&nbsp;<a id="changes.since.15" href="#changes.since.15">Since draft-ietf-httpbis-p3-payload-15</a></h2>
1868      <p id="rfc.section.D.17.p.1">Closed issues: </p>
1869      <ul>
1870         <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"
1871         </li>
1872      </ul>
1873      <h2 id="rfc.section.D.18"><a href="#rfc.section.D.18">D.18</a>&nbsp;<a id="changes.since.16" href="#changes.since.16">Since draft-ietf-httpbis-p3-payload-16</a></h2>
1874      <p id="rfc.section.D.18.p.1">Closed issues: </p>
1875      <ul>
1876         <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"
1877         </li>
1878      </ul>
1879      <h2 id="rfc.section.D.19"><a href="#rfc.section.D.19">D.19</a>&nbsp;<a id="changes.since.17" href="#changes.since.17">Since draft-ietf-httpbis-p3-payload-17</a></h2>
1880      <p id="rfc.section.D.19.p.1">Closed issues: </p>
1881      <ul>
1882         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/323">http://tools.ietf.org/wg/httpbis/trac/ticket/323</a>&gt;: "intended maturity level vs normative references"
1883         </li>
1884      </ul>
1885      <h2 id="rfc.section.D.20"><a href="#rfc.section.D.20">D.20</a>&nbsp;<a id="changes.since.18" href="#changes.since.18">Since draft-ietf-httpbis-p3-payload-18</a></h2>
1886      <p id="rfc.section.D.20.p.1">Closed issues: </p>
1887      <ul>
1888         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/330">http://tools.ietf.org/wg/httpbis/trac/ticket/330</a>&gt;: "is ETag a representation header field?"
1889         </li>
1890         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/338">http://tools.ietf.org/wg/httpbis/trac/ticket/338</a>&gt;: "Content-Location doesn't constrain the cardinality of representations"
1891         </li>
1892         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/346">http://tools.ietf.org/wg/httpbis/trac/ticket/346</a>&gt;: "make IANA policy definitions consistent"
1893         </li>
1894      </ul>
1895      <h2 id="rfc.section.D.21"><a href="#rfc.section.D.21">D.21</a>&nbsp;<a id="changes.since.19" href="#changes.since.19">Since draft-ietf-httpbis-p3-payload-19</a></h2>
1896      <p id="rfc.section.D.21.p.1">None yet.</p>
1897      <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1>
1898      <p class="noprint"><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.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> 
1899      </p>
1900      <div class="print2col">
1901         <ul class="ind">
1902            <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul>
1903                  <li>Accept header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept.1">2.3</a>, <a href="#rfc.xref.header.accept.2">5.1</a>, <a href="#rfc.iref.a.1"><b>6.1</b></a></li>
1904                  <li>Accept-Charset header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-charset.1">5.1</a>, <a href="#rfc.iref.a.2"><b>6.2</b></a>, <a href="#rfc.xref.header.accept-charset.2">C</a></li>
1905                  <li>Accept-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-encoding.1">2.2</a>, <a href="#rfc.xref.header.accept-encoding.2">5.1</a>, <a href="#rfc.iref.a.3"><b>6.3</b></a>, <a href="#rfc.xref.header.accept-encoding.3">7.1</a></li>
1906                  <li>Accept-Language header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-language.1">5.1</a>, <a href="#rfc.iref.a.4"><b>6.4</b></a></li>
1907               </ul>
1908            </li>
1909            <li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul>
1910                  <li>Coding Format&nbsp;&nbsp;
1911                     <ul>
1912                        <li>compress&nbsp;&nbsp;<a href="#rfc.iref.c.2">2.2</a></li>
1913                        <li>deflate&nbsp;&nbsp;<a href="#rfc.iref.c.3">2.2</a></li>
1914                        <li>gzip&nbsp;&nbsp;<a href="#rfc.iref.c.4">2.2</a></li>
1915                     </ul>
1916                  </li>
1917                  <li>compress (Coding Format)&nbsp;&nbsp;<a href="#rfc.iref.c.1">2.2</a></li>
1918                  <li>Content-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-encoding.1">2.2</a>, <a href="#rfc.xref.header.content-encoding.2">4.1</a>, <a href="#rfc.iref.c.5"><b>6.5</b></a>, <a href="#rfc.xref.header.content-encoding.3">6.5</a></li>
1919                  <li>Content-Language header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-language.1">4.1</a>, <a href="#rfc.iref.c.6"><b>6.6</b></a></li>
1920                  <li>Content-Location header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-location.1">4.1</a>, <a href="#rfc.iref.c.7"><b>6.7</b></a>, <a href="#rfc.xref.header.content-location.2">C</a></li>
1921                  <li>Content-Transfer-Encoding header field&nbsp;&nbsp;<a href="#rfc.iref.c.9">A.5</a>, <a href="#rfc.xref.no.content-transfer-encoding.1">C</a></li>
1922                  <li>Content-Type header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-type.1">2.3</a>, <a href="#rfc.xref.header.content-type.2">4.1</a>, <a href="#rfc.iref.c.8"><b>6.8</b></a></li>
1923               </ul>
1924            </li>
1925            <li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul>
1926                  <li>deflate (Coding Format)&nbsp;&nbsp;<a href="#rfc.iref.d.1">2.2</a></li>
1927               </ul>
1928            </li>
1929            <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul>
1930                  <li><tt>Grammar</tt>&nbsp;&nbsp;
1931                     <ul>
1932                        <li><tt>Accept</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>6.1</b></a></li>
1933                        <li><tt>Accept-Charset</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>6.2</b></a></li>
1934                        <li><tt>Accept-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.16"><b>6.3</b></a></li>
1935                        <li><tt>accept-ext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>6.1</b></a></li>
1936                        <li><tt>Accept-Language</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.18"><b>6.4</b></a></li>
1937                        <li><tt>accept-params</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.13"><b>6.1</b></a></li>
1938                        <li><tt>attribute</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>2.3</b></a></li>
1939                        <li><tt>charset</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2.1</b></a></li>
1940                        <li><tt>codings</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.17"><b>6.3</b></a></li>
1941                        <li><tt>content-coding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2.2</b></a></li>
1942                        <li><tt>Content-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.20"><b>6.5</b></a></li>
1943                        <li><tt>Content-Language</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.21"><b>6.6</b></a></li>
1944                        <li><tt>Content-Location</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.22"><b>6.7</b></a></li>
1945                        <li><tt>Content-Type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.23"><b>6.8</b></a></li>
1946                        <li><tt>language-range</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.19"><b>6.4</b></a></li>
1947                        <li><tt>language-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>2.4</b></a></li>
1948                        <li><tt>media-range</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>6.1</b></a></li>
1949                        <li><tt>media-type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>2.3</b></a></li>
1950                        <li><tt>MIME-Version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.24"><b>A.1</b></a></li>
1951                        <li><tt>parameter</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>2.3</b></a></li>
1952                        <li><tt>subtype</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>2.3</b></a></li>
1953                        <li><tt>type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>2.3</b></a></li>
1954                        <li><tt>value</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>2.3</b></a></li>
1955                     </ul>
1956                  </li>
1957                  <li>gzip (Coding Format)&nbsp;&nbsp;<a href="#rfc.iref.g.3">2.2</a></li>
1958               </ul>
1959            </li>
1960            <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul>
1961                  <li>Header Fields&nbsp;&nbsp;
1962                     <ul>
1963                        <li>Accept&nbsp;&nbsp;<a href="#rfc.xref.header.accept.1">2.3</a>, <a href="#rfc.xref.header.accept.2">5.1</a>, <a href="#rfc.iref.h.1"><b>6.1</b></a></li>
1964                        <li>Accept-Charset&nbsp;&nbsp;<a href="#rfc.xref.header.accept-charset.1">5.1</a>, <a href="#rfc.iref.h.2"><b>6.2</b></a>, <a href="#rfc.xref.header.accept-charset.2">C</a></li>
1965                        <li>Accept-Encoding&nbsp;&nbsp;<a href="#rfc.xref.header.accept-encoding.1">2.2</a>, <a href="#rfc.xref.header.accept-encoding.2">5.1</a>, <a href="#rfc.iref.h.3"><b>6.3</b></a>, <a href="#rfc.xref.header.accept-encoding.3">7.1</a></li>
1966                        <li>Accept-Language&nbsp;&nbsp;<a href="#rfc.xref.header.accept-language.1">5.1</a>, <a href="#rfc.iref.h.4"><b>6.4</b></a></li>
1967                        <li>Content-Encoding&nbsp;&nbsp;<a href="#rfc.xref.header.content-encoding.1">2.2</a>, <a href="#rfc.xref.header.content-encoding.2">4.1</a>, <a href="#rfc.iref.h.5"><b>6.5</b></a>, <a href="#rfc.xref.header.content-encoding.3">6.5</a></li>
1968                        <li>Content-Language&nbsp;&nbsp;<a href="#rfc.xref.header.content-language.1">4.1</a>, <a href="#rfc.iref.h.6"><b>6.6</b></a></li>
1969                        <li>Content-Location&nbsp;&nbsp;<a href="#rfc.xref.header.content-location.1">4.1</a>, <a href="#rfc.iref.h.7"><b>6.7</b></a>, <a href="#rfc.xref.header.content-location.2">C</a></li>
1970                        <li>Content-Transfer-Encoding&nbsp;&nbsp;<a href="#rfc.iref.h.10">A.5</a>, <a href="#rfc.xref.no.content-transfer-encoding.1">C</a></li>
1971                        <li>Content-Type&nbsp;&nbsp;<a href="#rfc.xref.header.content-type.1">2.3</a>, <a href="#rfc.xref.header.content-type.2">4.1</a>, <a href="#rfc.iref.h.8"><b>6.8</b></a></li>
1972                        <li>MIME-Version&nbsp;&nbsp;<a href="#rfc.iref.h.9"><b>A.1</b></a></li>
1973                     </ul>
1974                  </li>
1975               </ul>
1976            </li>
1977            <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul>
1978                  <li>MIME-Version header field&nbsp;&nbsp;<a href="#rfc.iref.m.1"><b>A.1</b></a></li>
1979               </ul>
1980            </li>
1981            <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
1982                  <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">2.2</a>, <a href="#rfc.xref.Part1.2">2.2</a>, <a href="#rfc.xref.Part1.3">2.2</a>, <a href="#rfc.xref.Part1.4">2.2.1</a>, <a href="#rfc.xref.Part1.5">2.2.1</a>, <a href="#rfc.xref.Part1.6">3.1</a>, <a href="#rfc.xref.Part1.7">3.2</a>, <a href="#rfc.xref.Part1.8">5.1</a>, <a href="#rfc.xref.Part1.9">6.1</a>, <a href="#rfc.xref.Part1.10">6.3</a>, <a href="#rfc.xref.Part1.11">6.7</a>, <a href="#rfc.xref.Part1.12">7.1</a>, <a href="#rfc.xref.Part1.13">7.1</a>, <a href="#rfc.xref.Part1.14">7.1</a>, <a href="#Part1"><b>9.1</b></a>, <a href="#rfc.xref.Part1.15">A.6</a><ul>
1983                        <li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">3.2</a></li>
1984                        <li><em>Section 3.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.15">A.6</a></li>
1985                        <li><em>Section 3.3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.6">3.1</a></li>
1986                        <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.4">2.2.1</a></li>
1987                        <li><em>Section 4.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">2.2</a>, <a href="#rfc.xref.Part1.12">7.1</a></li>
1988                        <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">2.2.1</a></li>
1989                        <li><em>Section 4.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">2.2</a>, <a href="#rfc.xref.Part1.13">7.1</a></li>
1990                        <li><em>Section 4.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.3">2.2</a>, <a href="#rfc.xref.Part1.14">7.1</a></li>
1991                        <li><em>Section 4.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.8">5.1</a>, <a href="#rfc.xref.Part1.9">6.1</a>, <a href="#rfc.xref.Part1.10">6.3</a></li>
1992                        <li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.11">6.7</a></li>
1993                     </ul>
1994                  </li>
1995                  <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">5.1</a>, <a href="#Part2"><b>9.1</b></a>, <a href="#rfc.xref.Part2.2">A.3</a><ul>
1996                        <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.2">A.3</a></li>
1997                        <li><em>Section 7.10</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">5.1</a></li>
1998                     </ul>
1999                  </li>
2000                  <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">4.1</a>, <a href="#rfc.xref.Part4.2">4.1</a>, <a href="#Part4"><b>9.1</b></a><ul>
2001                        <li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.2">4.1</a></li>
2002                        <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">4.1</a></li>
2003                     </ul>
2004                  </li>
2005                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">3.1</a>, <a href="#Part5"><b>9.1</b></a><ul>
2006                        <li><em>Section 5.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">3.1</a></li>
2007                     </ul>
2008                  </li>
2009                  <li><em>Part6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">4.1</a>, <a href="#rfc.xref.Part6.2">5.1</a>, <a href="#Part6"><b>9.1</b></a><ul>
2010                        <li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">4.1</a></li>
2011                        <li><em>Section 3.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.2">5.1</a></li>
2012                     </ul>
2013                  </li>
2014                  <li>payload&nbsp;&nbsp;<a href="#rfc.iref.p.1">3</a></li>
2015               </ul>
2016            </li>
2017            <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul>
2018                  <li>representation&nbsp;&nbsp;<a href="#rfc.iref.r.1">4</a></li>
2019                  <li><em>RFC1945</em>&nbsp;&nbsp;<a href="#RFC1945"><b>9.2</b></a>, <a href="#rfc.xref.RFC1945.1">B</a></li>
2020                  <li><em>RFC1950</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1950.1">7.1</a>, <a href="#RFC1950"><b>9.1</b></a></li>
2021                  <li><em>RFC1951</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1951.1">7.1</a>, <a href="#RFC1951"><b>9.1</b></a></li>
2022                  <li><em>RFC1952</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1952.1">7.1</a>, <a href="#RFC1952"><b>9.1</b></a></li>
2023                  <li><em>RFC2045</em>&nbsp;&nbsp;<a href="#RFC2045"><b>9.1</b></a>, <a href="#rfc.xref.RFC2045.1">A</a>, <a href="#rfc.xref.RFC2045.2">A.1</a></li>
2024                  <li><em>RFC2046</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.1">2.3</a>, <a href="#rfc.xref.RFC2046.2">2.3.2</a>, <a href="#rfc.xref.RFC2046.3">4.2</a>, <a href="#RFC2046"><b>9.1</b></a>, <a href="#rfc.xref.RFC2046.4">A.2</a><ul>
2025                        <li><em>Section 4.5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.3">4.2</a></li>
2026                        <li><em>Section 5.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.2">2.3.2</a></li>
2027                     </ul>
2028                  </li>
2029                  <li><em>RFC2049</em>&nbsp;&nbsp;<a href="#RFC2049"><b>9.2</b></a>, <a href="#rfc.xref.RFC2049.1">A.2</a><ul>
2030                        <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2049.1">A.2</a></li>
2031                     </ul>
2032                  </li>
2033                  <li><em>RFC2068</em>&nbsp;&nbsp;<a href="#RFC2068"><b>9.2</b></a>, <a href="#rfc.xref.RFC2068.1">B</a></li>
2034                  <li><em>RFC2076</em>&nbsp;&nbsp;<a href="#RFC2076"><b>9.2</b></a>, <a href="#rfc.xref.RFC2076.1">B</a></li>
2035                  <li><em>RFC2277</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2277.1">2.1</a>, <a href="#RFC2277"><b>9.2</b></a></li>
2036                  <li><em>RFC2295</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2295.1">5</a>, <a href="#RFC2295"><b>9.2</b></a></li>
2037                  <li><em>RFC2388</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2388.1">2.3.2</a>, <a href="#RFC2388"><b>9.2</b></a></li>
2038                  <li><em>RFC2557</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2557.1">6.7</a>, <a href="#RFC2557"><b>9.2</b></a>, <a href="#rfc.xref.RFC2557.2">A.7</a><ul>
2039                        <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2557.1">6.7</a></li>
2040                     </ul>
2041                  </li>
2042                  <li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">6.4</a>, <a href="#RFC2616"><b>9.2</b></a>, <a href="#rfc.xref.RFC2616.2">D.1</a><ul>
2043                        <li><em>Section 14.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">6.4</a></li>
2044                     </ul>
2045                  </li>
2046                  <li><em>RFC3629</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3629.1">2.1</a>, <a href="#RFC3629"><b>9.2</b></a></li>
2047                  <li><em>RFC4288</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4288.1">2.3</a>, <a href="#RFC4288"><b>9.2</b></a></li>
2048                  <li><em>RFC4647</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.1">6.4</a>, <a href="#rfc.xref.RFC4647.2">6.4</a>, <a href="#rfc.xref.RFC4647.3">6.4</a>, <a href="#rfc.xref.RFC4647.4">6.4</a>, <a href="#RFC4647"><b>9.1</b></a><ul>
2049                        <li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.1">6.4</a></li>
2050                        <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.2">6.4</a></li>
2051                        <li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.3">6.4</a></li>
2052                        <li><em>Section 3.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.4">6.4</a></li>
2053                     </ul>
2054                  </li>
2055                  <li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">2.2.1</a>, <a href="#RFC5226"><b>9.2</b></a><ul>
2056                        <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">2.2.1</a></li>
2057                     </ul>
2058                  </li>
2059                  <li><em>RFC5322</em>&nbsp;&nbsp;<a href="#RFC5322"><b>9.2</b></a>, <a href="#rfc.xref.RFC5322.1">A</a></li>
2060                  <li><em>RFC5646</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5646.1">2.4</a>, <a href="#rfc.xref.RFC5646.2">2.4</a>, <a href="#rfc.xref.RFC5646.3">2.4</a>, <a href="#RFC5646"><b>9.1</b></a><ul>
2061                        <li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5646.2">2.4</a></li>
2062                     </ul>
2063                  </li>
2064                  <li><em>RFC6151</em>&nbsp;&nbsp;<a href="#RFC6151"><b>9.2</b></a>, <a href="#rfc.xref.RFC6151.1">C</a></li>
2065                  <li><em>RFC6266</em>&nbsp;&nbsp;<a href="#RFC6266"><b>9.2</b></a>, <a href="#rfc.xref.RFC6266.1">B</a>, <a href="#rfc.xref.RFC6266.2">C</a></li>
2066               </ul>
2067            </li>
2068         </ul>
2069      </div>
2070   </body>
2071</html>
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