source: draft-ietf-httpbis/latest/p3-payload.xml @ 1107

Last change on this file since 1107 was 1107, checked in by fielding@…, 9 years ago

Change the undefined use of "transparent proxy" to a definition
of transforming and non-transforming proxies. Add new definitions
for "intercepts" and the other kind of "transparent proxy".
Should we add informational references to RFC1919 and RFC3040 ?

Addresses #210

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File size: 130.6 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "February">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc rfcedstyle="yes"?>
52<?rfc-ext allow-markup-in-artwork="yes" ?>
53<?rfc-ext include-references-in-index="yes" ?>
54<rfc obsoletes="2616" category="std" x:maturity-level="draft"
55     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
56     xmlns:x='http://purl.org/net/xml2rfc/ext'>
57<front>
58
59  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
60
61  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
62    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
63    <address>
64      <postal>
65        <street>345 Park Ave</street>
66        <city>San Jose</city>
67        <region>CA</region>
68        <code>95110</code>
69        <country>USA</country>
70      </postal>
71      <email>fielding@gbiv.com</email>
72      <uri>http://roy.gbiv.com/</uri>
73    </address>
74  </author>
75
76  <author initials="J." surname="Gettys" fullname="Jim Gettys">
77    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
78    <address>
79      <postal>
80        <street>21 Oak Knoll Road</street>
81        <city>Carlisle</city>
82        <region>MA</region>
83        <code>01741</code>
84        <country>USA</country>
85      </postal>
86      <email>jg@freedesktop.org</email>
87      <uri>http://gettys.wordpress.com/</uri>
88    </address>
89  </author>
90 
91  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
92    <organization abbrev="HP">Hewlett-Packard Company</organization>
93    <address>
94      <postal>
95        <street>HP Labs, Large Scale Systems Group</street>
96        <street>1501 Page Mill Road, MS 1177</street>
97        <city>Palo Alto</city>
98        <region>CA</region>
99        <code>94304</code>
100        <country>USA</country>
101      </postal>
102      <email>JeffMogul@acm.org</email>
103    </address>
104  </author>
105
106  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
107    <organization abbrev="Microsoft">Microsoft Corporation</organization>
108    <address>
109      <postal>
110        <street>1 Microsoft Way</street>
111        <city>Redmond</city>
112        <region>WA</region>
113        <code>98052</code>
114        <country>USA</country>
115      </postal>
116      <email>henrikn@microsoft.com</email>
117    </address>
118  </author>
119
120  <author initials="L." surname="Masinter" fullname="Larry Masinter">
121    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
122    <address>
123      <postal>
124        <street>345 Park Ave</street>
125        <city>San Jose</city>
126        <region>CA</region>
127        <code>95110</code>
128        <country>USA</country>
129      </postal>
130      <email>LMM@acm.org</email>
131      <uri>http://larry.masinter.net/</uri>
132    </address>
133  </author>
134 
135  <author initials="P." surname="Leach" fullname="Paul J. Leach">
136    <organization abbrev="Microsoft">Microsoft Corporation</organization>
137    <address>
138      <postal>
139        <street>1 Microsoft Way</street>
140        <city>Redmond</city>
141        <region>WA</region>
142        <code>98052</code>
143      </postal>
144      <email>paulle@microsoft.com</email>
145    </address>
146  </author>
147   
148  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
149    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
150    <address>
151      <postal>
152        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
153        <street>The Stata Center, Building 32</street>
154        <street>32 Vassar Street</street>
155        <city>Cambridge</city>
156        <region>MA</region>
157        <code>02139</code>
158        <country>USA</country>
159      </postal>
160      <email>timbl@w3.org</email>
161      <uri>http://www.w3.org/People/Berners-Lee/</uri>
162    </address>
163  </author>
164
165  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
166    <organization abbrev="W3C">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>W3C / ERCIM</street>
170        <street>2004, rte des Lucioles</street>
171        <city>Sophia-Antipolis</city>
172        <region>AM</region>
173        <code>06902</code>
174        <country>France</country>
175      </postal>
176      <email>ylafon@w3.org</email>
177      <uri>http://www.raubacapeu.net/people/yves/</uri>
178    </address>
179  </author>
180
181  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
182    <organization abbrev="greenbytes">greenbytes GmbH</organization>
183    <address>
184      <postal>
185        <street>Hafenweg 16</street>
186        <city>Muenster</city><region>NW</region><code>48155</code>
187        <country>Germany</country>
188      </postal>
189      <phone>+49 251 2807760</phone>
190      <facsimile>+49 251 2807761</facsimile>
191      <email>julian.reschke@greenbytes.de</email>
192      <uri>http://greenbytes.de/tech/webdav/</uri>
193    </address>
194  </author>
195
196  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
197  <workgroup>HTTPbis Working Group</workgroup>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 3 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 3 defines HTTP message content,
207   metadata, and content negotiation.
208</t>
209</abstract>
210
211<note title="Editorial Note (To be removed by RFC Editor)">
212  <t>
213    Discussion of this draft should take place on the HTTPBIS working group
214    mailing list (ietf-http-wg@w3.org). The current issues list is
215    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
216    and related documents (including fancy diffs) can be found at
217    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
218  </t>
219  <t>
220    The changes in this draft are summarized in <xref target="changes.since.12"/>.
221  </t>
222</note>
223</front>
224<middle>
225<section title="Introduction" anchor="introduction">
226<t>
227   This document defines HTTP/1.1 message payloads (a.k.a., content), the
228   associated metadata header fields that define how the payload is intended
229   to be interpreted by a recipient, the request header fields that
230   might influence content selection, and the various selection algorithms
231   that are collectively referred to as HTTP content negotiation.
232</t>
233<t>
234   This document is currently disorganized in order to minimize the changes
235   between drafts and enable reviewers to see the smaller errata changes.
236   A future draft will reorganize the sections to better reflect the content.
237   In particular, the sections on entities will be renamed payload and moved
238   to the first half of the document, while the sections on content negotiation
239   and associated request header fields will be moved to the second half.  The
240   current mess reflects how widely dispersed these topics and associated
241   requirements had become in <xref target="RFC2616"/>.
242</t>
243
244<section title="Terminology" anchor="terminology">
245<t>
246   This specification uses a number of terms to refer to the roles
247   played by participants in, and objects of, the HTTP communication.
248</t>
249<t>
250  <iref item="content negotiation"/>
251  <x:dfn>content negotiation</x:dfn>
252  <list>
253    <t>
254      The mechanism for selecting the appropriate representation when
255      servicing a request. The representation in any response
256      can be negotiated (including error responses).
257    </t>
258  </list>
259</t>
260</section>
261
262<section title="Requirements" anchor="intro.requirements">
263<t>
264   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
265   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
266   document are to be interpreted as described in <xref target="RFC2119"/>.
267</t>
268<t>
269   An implementation is not compliant if it fails to satisfy one or more
270   of the "MUST" or "REQUIRED" level requirements for the protocols it
271   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
272   level and all the "SHOULD" level requirements for its protocols is said
273   to be "unconditionally compliant"; one that satisfies all the "MUST"
274   level requirements but not all the "SHOULD" level requirements for its
275   protocols is said to be "conditionally compliant".
276</t>
277</section>
278
279<section title="Syntax Notation" anchor="notation">
280  <x:anchor-alias value="ALPHA"/>
281  <x:anchor-alias value="CR"/>
282  <x:anchor-alias value="DIGIT"/>
283  <x:anchor-alias value="LF"/>
284  <x:anchor-alias value="OCTET"/>
285  <x:anchor-alias value="VCHAR"/>
286  <x:anchor-alias value="WSP"/>
287<t>
288  This specification uses the ABNF syntax defined in &notation; (which
289  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
290  <xref target="collected.abnf"/> shows the collected ABNF, with the list
291  rule expanded.
292</t>
293<t>
294  The following core rules are included by
295  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
296  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
297  DIGIT (decimal 0-9), DQUOTE (double quote),
298  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
299  OCTET (any 8-bit sequence of data), SP (space),
300  VCHAR (any visible USASCII character),
301  and WSP (whitespace).
302</t>
303
304<section title="Core Rules" anchor="core.rules">
305  <x:anchor-alias value="token"/>
306  <x:anchor-alias value="word"/>
307  <x:anchor-alias value="OWS"/>
308<t>
309  The core rules below are defined in &basic-rules;:
310</t>
311<figure><artwork type="abnf2616">
312  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
313  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
314  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
315</artwork></figure>
316</section>
317
318<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
319  <x:anchor-alias value="absolute-URI"/>
320  <x:anchor-alias value="Allow"/>
321  <x:anchor-alias value="Content-Length"/>
322  <x:anchor-alias value="Content-Range"/>
323  <x:anchor-alias value="Expires"/>
324  <x:anchor-alias value="Last-Modified"/>
325  <x:anchor-alias value="partial-URI"/>
326  <x:anchor-alias value="qvalue"/>
327<t>
328  The ABNF rules below are defined in other parts:
329</t>
330<figure><!--Part1--><artwork type="abnf2616">
331  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
332  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
333  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
334  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
335</artwork></figure>
336<figure><!--Part4--><artwork type="abnf2616">
337  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
338</artwork></figure>
339<figure><!--Part5--><artwork type="abnf2616">
340  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
341</artwork></figure>
342<figure><!--Part6--><artwork type="abnf2616">
343  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
344</artwork></figure>
345</section>
346
347</section>
348
349</section>
350
351<section title="Protocol Parameters" anchor="protocol.parameters">
352
353<section title="Character Sets" anchor="character.sets">
354<t>
355   HTTP uses the same definition of the term "character set" as that
356   described for MIME:
357</t>
358<t>
359   The term "character set" is used in this document to refer to a
360   method used with one or more tables to convert a sequence of octets
361   into a sequence of characters. Note that unconditional conversion in
362   the other direction is not required, in that not all characters might
363   be available in a given character set and a character set might provide
364   more than one sequence of octets to represent a particular character.
365   This definition is intended to allow various kinds of character
366   encoding, from simple single-table mappings such as US-ASCII to
367   complex table switching methods such as those that use ISO-2022's
368   techniques. However, the definition associated with a MIME character
369   set name &MUST; fully specify the mapping to be performed from octets
370   to characters. In particular, use of external profiling information
371   to determine the exact mapping is not permitted.
372</t>
373<x:note>
374  <t>
375    <x:h>Note:</x:h> This use of the term "character set" is more commonly
376    referred to as a "character encoding". However, since HTTP and
377    MIME share the same registry, it is important that the terminology
378    also be shared.
379  </t>
380</x:note>
381<t anchor="rule.charset">
382  <x:anchor-alias value="charset"/>
383   HTTP character sets are identified by case-insensitive tokens. The
384   complete set of tokens is defined by the IANA Character Set registry
385   (<eref target="http://www.iana.org/assignments/character-sets"/>).
386</t>
387<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
388  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
389</artwork></figure>
390<t>
391   Although HTTP allows an arbitrary token to be used as a charset
392   value, any token that has a predefined value within the IANA
393   Character Set registry &MUST; represent the character set defined
394   by that registry. Applications &SHOULD; limit their use of character
395   sets to those defined by the IANA registry.
396</t>
397<t>
398   HTTP uses charset in two contexts: within an Accept-Charset request
399   header field (in which the charset value is an unquoted token) and as the
400   value of a parameter in a Content-Type header field (within a request or
401   response), in which case the parameter value of the charset parameter
402   can be quoted.
403</t>
404<t>
405   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
406   <xref target="RFC2277"/>.
407</t>
408
409<section title="Missing Charset" anchor="missing.charset">
410<t>
411   Some HTTP/1.0 software has interpreted a Content-Type header field without
412   charset parameter incorrectly to mean "recipient should guess".
413   Senders wishing to defeat this behavior &MAY; include a charset
414   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
415   it is known that it will not confuse the recipient.
416</t>
417<t>
418   Unfortunately, some older HTTP/1.0 clients did not deal properly with
419   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
420   charset label provided by the sender; and those user agents that have
421   a provision to "guess" a charset &MUST; use the charset from the
422   content-type field if they support that charset, rather than the
423   recipient's preference, when initially displaying a document. See
424   <xref target="canonicalization.and.text.defaults"/>.
425</t>
426</section>
427</section>
428
429<section title="Content Codings" anchor="content.codings">
430  <x:anchor-alias value="content-coding"/>
431<t>
432   Content coding values indicate an encoding transformation that has
433   been or can be applied to a representation. Content codings are primarily
434   used to allow a representation to be compressed or otherwise usefully
435   transformed without losing the identity of its underlying media type
436   and without loss of information. Frequently, the representation is stored in
437   coded form, transmitted directly, and only decoded by the recipient.
438</t>
439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
440  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
441</artwork></figure>
442<t>
443   All content-coding values are case-insensitive. HTTP/1.1 uses
444   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
445   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
446   describes the content-coding, what is more important is that it
447   indicates what decoding mechanism will be required to remove the
448   encoding.
449</t>
450<t>
451   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
452  <list>
453    <t>
454      See &compress-coding;.
455    </t>
456  </list>
457</t>
458<t>
459   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
460  <list>
461    <t>
462      See &deflate-coding;.
463    </t>
464  </list>
465</t>
466<t>
467   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
468  <list>
469    <t>
470      See &gzip-coding;.
471    </t>
472  </list>
473</t>
474<t>
475   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
476  <list><t>
477        The default (identity) encoding; the use of no transformation
478        whatsoever. This content-coding is used only in the Accept-Encoding
479        header field, and &SHOULD-NOT;  be used in the Content-Encoding
480        header field.
481  </t></list>
482</t>
483
484<section title="Content Coding Registry" anchor="content.coding.registry">
485<t>
486   The HTTP Content Coding Registry defines the name space for the content
487   coding names.
488</t>
489<t>
490   Registrations &MUST; include the following fields:
491   <list style="symbols">
492     <t>Name</t>
493     <t>Description</t>
494     <t>Pointer to specification text</t>
495   </list>
496</t>
497<t>
498   Names of content codings &MUST-NOT; overlap with names of transfer codings
499   (&transfer-codings;), unless the encoding transformation is identical (as it
500   is the case for the compression codings defined in
501   &compression-codings;).
502</t>
503<t>
504   Values to be added to this name space require a specification
505   (see "Specification Required" in
506   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
507   conform to the purpose of content coding defined in this section.
508</t>
509<t>
510   The registry itself is maintained at
511   <eref target="http://www.iana.org/assignments/http-parameters"/>.
512</t>
513</section>
514
515</section>
516
517<section title="Media Types" anchor="media.types">
518  <x:anchor-alias value="media-type"/>
519  <x:anchor-alias value="type"/>
520  <x:anchor-alias value="subtype"/>
521<t>
522   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
523   and Accept (<xref target="header.accept"/>) header fields in order to provide
524   open and extensible data typing and type negotiation.
525</t>
526<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/>
527  <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
528  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
529  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
530</artwork></figure>
531<t anchor="rule.parameter">
532  <x:anchor-alias value="attribute"/>
533  <x:anchor-alias value="parameter"/>
534  <x:anchor-alias value="value"/>
535   Parameters &MAY; follow the type/subtype in the form of attribute/value
536   pairs.
537</t>
538<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
539  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
540  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
541  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
542</artwork></figure>
543<t>
544   The type, subtype, and parameter attribute names are case-insensitive.
545   Parameter values might or might not be case-sensitive, depending on the
546   semantics of the parameter name.  The presence or absence of a parameter might
547   be significant to the processing of a media-type, depending on its
548   definition within the media type registry.
549</t>
550<t>
551   A parameter value that matches the <x:ref>token</x:ref> production can be
552   transmitted as either a token or within a quoted-string. The quoted and
553   unquoted values are equivalent.
554</t>
555<t>
556   Note that some older HTTP applications do not recognize media type
557   parameters. When sending data to older HTTP applications,
558   implementations &SHOULD; only use media type parameters when they are
559   required by that type/subtype definition.
560</t>
561<t>
562   Media-type values are registered with the Internet Assigned Number
563   Authority (IANA). The media type registration process is
564   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
565   discouraged.
566</t>
567
568<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
569<t>
570   Internet media types are registered with a canonical form. A
571   representation transferred via HTTP messages &MUST; be in the
572   appropriate canonical form prior to its transmission except for
573   "text" types, as defined in the next paragraph.
574</t>
575<t>
576   When in canonical form, media subtypes of the "text" type use CRLF as
577   the text line break. HTTP relaxes this requirement and allows the
578   transport of text media with plain CR or LF alone representing a line
579   break when it is done consistently for an entire representation. HTTP
580   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
581   a line break in text media received via HTTP. In
582   addition, if the text is in a character encoding that does not
583   use octets 13 and 10 for CR and LF respectively, as is the case for
584   some multi-byte character encodings, HTTP allows the use of whatever octet
585   sequences are defined by that character encoding to represent the
586   equivalent of CR and LF for line breaks. This flexibility regarding
587   line breaks applies only to text media in the payload body; a bare CR
588   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
589   structures (such as header fields and multipart boundaries).
590</t>
591<t>
592   If a representation is encoded with a content-coding, the underlying
593   data &MUST; be in a form defined above prior to being encoded.
594</t>
595<t>
596   The "charset" parameter is used with some media types to define the
597   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
598   parameter is provided by the sender, media subtypes of the "text"
599   type are defined to have a default charset value of "ISO-8859-1" when
600   received via HTTP. Data in character encodings other than "ISO-8859-1" or
601   its subsets &MUST; be labeled with an appropriate charset value. See
602   <xref target="missing.charset"/> for compatibility problems.
603</t>
604</section>
605
606<section title="Multipart Types" anchor="multipart.types">
607<t>
608   MIME provides for a number of "multipart" types &mdash; encapsulations of
609   one or more representations within a single message-body. All multipart
610   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
611   and &MUST; include a boundary parameter as part of the media type
612   value. The message body is itself a protocol element and &MUST;
613   therefore use only CRLF to represent line breaks between body-parts.
614</t>
615<t>
616   In general, HTTP treats a multipart message-body no differently than
617   any other media type: strictly as payload.  HTTP does not use the
618   multipart boundary as an indicator of message-body length.
619   <!-- jre: re-insert removed text pointing to caching? -->
620   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
621   behavior as a MIME user agent would upon receipt of a multipart type.
622   The MIME header fields within each body-part of a multipart message-body
623   do not have any significance to HTTP beyond that defined by
624   their MIME semantics.
625</t>
626<t>
627   If an application receives an unrecognized multipart subtype, the
628   application &MUST; treat it as being equivalent to "multipart/mixed".
629</t>
630<x:note>
631  <t>
632    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
633    for carrying form data suitable for processing via the POST
634    request method, as described in <xref target="RFC2388"/>.
635  </t>
636</x:note>
637</section>
638</section>
639
640<section title="Language Tags" anchor="language.tags">
641  <x:anchor-alias value="language-tag"/>
642<t>
643   A language tag, as defined in <xref target="RFC5646"/>, identifies a
644   natural language spoken, written, or otherwise conveyed by human beings for
645   communication of information to other human beings. Computer languages are
646   explicitly excluded. HTTP uses language tags within the Accept-Language and
647   Content-Language fields.
648</t>
649<t>
650   In summary, a language tag is composed of one or more parts: A primary
651   language subtag followed by a possibly empty series of subtags:
652</t>
653<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
654  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
655</artwork></figure>
656<t>
657   White space is not allowed within the tag and all tags are case-insensitive.
658   The name space of language subtags is administered by the IANA (see
659   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
660</t>
661<figure>
662  <preamble>Example tags include:</preamble>
663<artwork type="example">
664  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
665</artwork>
666</figure>
667<t>
668   See <xref target="RFC5646"/> for further information.
669</t>
670</section>
671</section>
672
673<section title="Payload" anchor="payload">
674<t>
675   HTTP messages &MAY; transfer a payload if not otherwise restricted by
676   the request method or response status code.  The payload consists of
677   metadata, in the form of header fields, and data, in the form of the
678   sequence of octets in the message-body after any transfer-coding has
679   been decoded.
680</t>
681<iref item="payload"/>
682<t>   
683   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
684   representation of some resource.  We use separate terms for payload
685   and representation because some messages contain only the associated
686   representation's header fields (e.g., responses to HEAD) or only some
687   part(s) of the representation (e.g., the 206 status code).
688</t>
689<section title="Payload Header Fields" anchor="payload.header.fields">
690  <x:anchor-alias value="payload-header"/>
691<t>
692   HTTP header fields that specifically define the payload, rather than the
693   associated representation, are referred to as "payload header fields".
694   The following payload header fields are defined by HTTP/1.1:
695</t>
696<figure><artwork type="inline">
697   <x:ref>Content-Length</x:ref>           ; &header-content-length;
698   <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
699   <x:ref>Content-Range</x:ref>            ; &header-content-range;
700</artwork></figure>
701</section>
702
703<section title="Payload Body" anchor="payload.body">
704  <x:anchor-alias value="payload-body"/>
705<t>
706   A payload body is only present in a message when a message-body is
707   present, as described in &message-body;. The payload body is obtained
708   from the message-body by decoding any Transfer-Encoding that might
709   have been applied to ensure safe and proper transfer of the message.
710</t>
711</section>
712</section>
713
714<section title="Representation" anchor="representation">
715<iref item="representation"/>
716<t>
717   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
718   communicated from one party to another.  A resource representation
719   is information that reflects the state of that resource, as observed
720   at some point in the past (e.g., in a response to GET) or to be
721   desired at some point in the future (e.g., in a PUT request).
722</t>
723<t>
724   Most, but not all, representations transferred via HTTP are intended
725   to be a representation of the target resource (the resource identified
726   by the effective request URI).  The precise semantics of a representation
727   are determined by the type of message (request or response), the request
728   method, the response status code, and the representation metadata.
729   For example, the above semantic is true for the representation in any
730   200 (OK) response to GET and for the representation in any PUT request.
731   A 200 response to PUT, in contrast, contains either a representation
732   that describes the successful action or a representation of the target
733   resource, with the latter indicated by a Content-Location header field
734   with the same value as the effective request URI.  Likewise, response
735   messages with an error status code usually contain a representation that
736   describes the error and what next steps are suggested for resolving it.
737</t>
738
739<section title="Representation Header Fields" anchor="representation.header.fields">
740  <x:anchor-alias value="representation-header"/>
741<t>
742   Representation header fields define metadata about the representation data
743   enclosed in the message-body or, if no message-body is present, about
744   the representation that would have been transferred in a 200 response
745   to a simultaneous GET request with the same effective request URI.
746</t>
747<t>
748   The following header fields are defined as representation metadata:
749</t>
750<figure><artwork type="inline">
751   <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
752   <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
753   <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
754   <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
755   <x:ref>Expires</x:ref>                  ; &header-expires;
756   <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
757</artwork></figure>
758</section>
759
760<section title="Representation Data" anchor="representation.data">
761  <x:anchor-alias value="representation-data"/>
762<t>
763   The representation body associated with an HTTP message is
764   either provided as the payload body of the message or
765   referred to by the message semantics and the effective request
766   URI.  The representation data is in a format and encoding defined by
767   the representation metadata header fields.
768</t>
769<t>
770   The data type of the representation data
771   is determined via the header fields Content-Type and Content-Encoding.
772   These define a two-layer, ordered encoding model:
773</t>
774<figure><artwork type="example">
775  representation-data := Content-Encoding( Content-Type( bits ) )
776</artwork></figure>
777<t>
778   Content-Type specifies the media type of the underlying data, which
779   defines both the data format and how that data &SHOULD; be processed
780   by the recipient (within the scope of the request method semantics).
781   Any HTTP/1.1 message containing a payload body &SHOULD; include a
782   Content-Type header field defining the media type of the associated
783   representation unless that metadata is unknown to the sender.
784   If the Content-Type header field is not present, it indicates that
785   the sender does not know the media type of the representation;
786   recipients &MAY; either assume that the media type is
787   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
788   or examine the content to determine its type.
789</t>
790<t>
791   In practice, resource owners do not always properly configure their origin
792   server to provide the correct Content-Type for a given representation,
793   with the result that some clients will examine a response body's content
794   and override the specified type.
795   Clients that do so risk drawing incorrect conclusions, which might expose
796   additional security risks (e.g., "privilege escalation").  Furthermore,
797   it is impossible to determine the sender's intent by examining the data
798   format: many data formats match multiple media types that differ only in
799   processing semantics.  Implementers are encouraged to provide a means of
800   disabling such "content sniffing" when it is used.
801</t>
802<t>
803   Content-Encoding is used to indicate any additional content
804   codings applied to the data, usually for the purpose of data
805   compression, that are a property of the representation.  If
806   Content-Encoding is not present, then there is no additional
807   encoding beyond that defined by the Content-Type.
808</t>
809</section>
810</section>
811
812<section title="Content Negotiation" anchor="content.negotiation">
813<t>
814   HTTP responses include a representation which contains information for
815   interpretation, whether by a human user or for further processing.
816   Often, the server has different ways of representing the
817   same information; for example, in different formats, languages,
818   or using different character encodings.
819</t>
820<t>
821   HTTP clients and their users might have different or variable
822   capabilities, characteristics or preferences which would influence
823   which representation, among those available from the server,
824   would be best for the server to deliver. For this reason, HTTP
825   provides mechanisms for "content negotiation" &mdash; a process of
826   allowing selection of a representation of a given resource,
827   when more than one is available.
828</t>
829<t>
830   This specification defines two patterns of content negotiation;
831   "server-driven", where the server selects the representation based
832   upon the client's stated preferences, and "agent-driven" negotiation,
833   where the server provides a list of representations for the client to
834   choose from, based upon their metadata. In addition,  there are
835   other patterns: some applications use an "active content" pattern,
836   where the server returns active content which runs on the client
837   and, based on client available parameters, selects additional
838   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
839   has also been proposed.
840</t>
841<t>
842   These patterns are all widely used, and have trade-offs in applicability
843   and practicality. In particular, when the number of preferences or
844   capabilities to be expressed by a client are large (such as when many
845   different formats are supported by a user-agent), server-driven
846   negotiation becomes unwieldy, and might not be appropriate. Conversely,
847   when the number of representations to choose from is very large,
848   agent-driven negotiation might not be appropriate.
849</t>
850<t>
851   Note that in all cases, the supplier of representations has the
852   responsibility for determining which representations might be
853   considered to be the "same information".
854</t>
855
856<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
857<t>
858   If the selection of the best representation for a response is made by
859   an algorithm located at the server, it is called server-driven
860   negotiation. Selection is based on the available representations of
861   the response (the dimensions over which it can vary; e.g., language,
862   content-coding, etc.) and the contents of particular header fields in
863   the request message or on other information pertaining to the request
864   (such as the network address of the client).
865</t>
866<t>
867   Server-driven negotiation is advantageous when the algorithm for
868   selecting from among the available representations is difficult to
869   describe to the user agent, or when the server desires to send its
870   "best guess" to the client along with the first response (hoping to
871   avoid the round-trip delay of a subsequent request if the "best
872   guess" is good enough for the user). In order to improve the server's
873   guess, the user agent &MAY; include request header fields (Accept,
874   Accept-Language, Accept-Encoding, etc.) which describe its
875   preferences for such a response.
876</t>
877<t>
878   Server-driven negotiation has disadvantages:
879  <list style="numbers">
880    <t>
881         It is impossible for the server to accurately determine what
882         might be "best" for any given user, since that would require
883         complete knowledge of both the capabilities of the user agent
884         and the intended use for the response (e.g., does the user want
885         to view it on screen or print it on paper?).
886    </t>
887    <t>
888         Having the user agent describe its capabilities in every
889         request can be both very inefficient (given that only a small
890         percentage of responses have multiple representations) and a
891         potential violation of the user's privacy.
892    </t>
893    <t>
894         It complicates the implementation of an origin server and the
895         algorithms for generating responses to a request.
896    </t>
897    <t>
898         It might limit a public cache's ability to use the same response
899         for multiple user's requests.
900    </t>
901  </list>
902</t>
903<t>
904   HTTP/1.1 includes the following request-header fields for enabling
905   server-driven negotiation through description of user agent
906   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
907   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
908   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
909   However, an origin server is not limited to these dimensions and &MAY; vary
910   the response based on any aspect of the request, including information
911   outside the request-header fields or within extension header fields
912   not defined by this specification.
913</t>
914<x:note>
915  <t>
916    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
917    because new clients might not be recognized.
918  </t>
919</x:note>
920<t>
921   The Vary header field (&header-vary;) can be used to express the parameters the
922   server uses to select a representation that is subject to server-driven
923   negotiation.
924</t>
925</section>
926
927<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
928<t>
929   With agent-driven negotiation, selection of the best representation
930   for a response is performed by the user agent after receiving an
931   initial response from the origin server. Selection is based on a list
932   of the available representations of the response included within the
933   header fields or body of the initial response, with each
934   representation identified by its own URI. Selection from among the
935   representations can be performed automatically (if the user agent is
936   capable of doing so) or manually by the user selecting from a
937   generated (possibly hypertext) menu.
938</t>
939<t>
940   Agent-driven negotiation is advantageous when the response would vary
941   over commonly-used dimensions (such as type, language, or encoding),
942   when the origin server is unable to determine a user agent's
943   capabilities from examining the request, and generally when public
944   caches are used to distribute server load and reduce network usage.
945</t>
946<t>
947   Agent-driven negotiation suffers from the disadvantage of needing a
948   second request to obtain the best alternate representation. This
949   second request is only efficient when caching is used. In addition,
950   this specification does not define any mechanism for supporting
951   automatic selection, though it also does not prevent any such
952   mechanism from being developed as an extension and used within
953   HTTP/1.1.
954</t>
955<t>
956   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
957   status codes for enabling agent-driven negotiation when the server is
958   unwilling or unable to provide a varying response using server-driven
959   negotiation.
960</t>
961</section>
962</section>
963
964<section title="Header Field Definitions" anchor="header.fields">
965<t>
966   This section defines the syntax and semantics of HTTP/1.1 header fields
967   related to the payload of messages.
968</t>
969
970<section title="Accept" anchor="header.accept">
971  <iref primary="true" item="Accept header" x:for-anchor=""/>
972  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
973  <x:anchor-alias value="Accept"/>
974  <x:anchor-alias value="Accept-v"/>
975  <x:anchor-alias value="accept-ext"/>
976  <x:anchor-alias value="accept-params"/>
977  <x:anchor-alias value="media-range"/>
978<t>
979   The "Accept" request-header field can be used by user agents to specify
980   response media types that are acceptable. Accept header fields can be used to
981   indicate that the request is specifically limited to a small set of desired
982   types, as in the case of a request for an in-line image.
983</t>
984<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
985  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
986  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
987 
988  <x:ref>media-range</x:ref>    = ( "*/*"
989                   / ( <x:ref>type</x:ref> "/" "*" )
990                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
991                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
992  <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
993  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
994</artwork></figure>
995<t>
996   The asterisk "*" character is used to group media types into ranges,
997   with "*/*" indicating all media types and "type/*" indicating all
998   subtypes of that type. The media-range &MAY; include media type
999   parameters that are applicable to that range.
1000</t>
1001<t>
1002   Each media-range &MAY; be followed by one or more accept-params,
1003   beginning with the "q" parameter for indicating a relative quality
1004   factor. The first "q" parameter (if any) separates the media-range
1005   parameter(s) from the accept-params. Quality factors allow the user
1006   or user agent to indicate the relative degree of preference for that
1007   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1008   default value is q=1.
1009</t>
1010<x:note>
1011  <t>
1012    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1013    parameters from Accept extension parameters is due to historical
1014    practice. Although this prevents any media type parameter named
1015    "q" from being used with a media range, such an event is believed
1016    to be unlikely given the lack of any "q" parameters in the IANA
1017    media type registry and the rare usage of any media type
1018    parameters in Accept. Future media types are discouraged from
1019    registering any parameter named "q".
1020  </t>
1021</x:note>
1022<t>
1023   The example
1024</t>
1025<figure><artwork type="example">
1026  Accept: audio/*; q=0.2, audio/basic
1027</artwork></figure>
1028<t>
1029   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1030   type if it is the best available after an 80% mark-down in quality".
1031</t>
1032<t>
1033   If no Accept header field is present, then it is assumed that the
1034   client accepts all media types. If an Accept header field is present,
1035   and if the server cannot send a response which is acceptable
1036   according to the combined Accept field value, then the server &SHOULD;
1037   send a 406 (Not Acceptable) response.
1038</t>
1039<t>
1040   A more elaborate example is
1041</t>
1042<figure><artwork type="example">
1043  Accept: text/plain; q=0.5, text/html,
1044          text/x-dvi; q=0.8, text/x-c
1045</artwork></figure>
1046<t>
1047   Verbally, this would be interpreted as "text/html and text/x-c are
1048   the preferred media types, but if they do not exist, then send the
1049   text/x-dvi representation, and if that does not exist, send the text/plain
1050   representation".
1051</t>
1052<t>
1053   Media ranges can be overridden by more specific media ranges or
1054   specific media types. If more than one media range applies to a given
1055   type, the most specific reference has precedence. For example,
1056</t>
1057<figure><artwork type="example">
1058  Accept: text/*, text/html, text/html;level=1, */*
1059</artwork></figure>
1060<t>
1061   have the following precedence:
1062   <list style="numbers">
1063    <t>text/html;level=1</t>
1064    <t>text/html</t>
1065    <t>text/*</t>
1066    <t>*/*</t>
1067   </list>
1068</t>
1069<t>
1070   The media type quality factor associated with a given type is
1071   determined by finding the media range with the highest precedence
1072   which matches that type. For example,
1073</t>
1074<figure><artwork type="example">
1075  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1076          text/html;level=2;q=0.4, */*;q=0.5
1077</artwork></figure>
1078<t>
1079   would cause the following values to be associated:
1080</t>
1081<texttable align="left">
1082  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1083  <c>text/html;level=1</c>    <c>1</c>
1084  <c>text/html</c>            <c>0.7</c>
1085  <c>text/plain</c>           <c>0.3</c>
1086  <c>image/jpeg</c>           <c>0.5</c>
1087  <c>text/html;level=2</c>    <c>0.4</c>
1088  <c>text/html;level=3</c>    <c>0.7</c>
1089</texttable>
1090<t>
1091      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1092      values for certain media ranges. However, unless the user agent is
1093      a closed system which cannot interact with other rendering agents,
1094      this default set ought to be configurable by the user.
1095</t>
1096</section>
1097
1098<section title="Accept-Charset" anchor="header.accept-charset">
1099  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1100  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1101  <x:anchor-alias value="Accept-Charset"/>
1102  <x:anchor-alias value="Accept-Charset-v"/>
1103<t>
1104   The "Accept-Charset" request-header field can be used by user agents to
1105   indicate what response character sets are acceptable. This field allows
1106   clients capable of understanding more comprehensive or special-purpose
1107   character sets to signal that capability to a server which is capable of
1108   representing documents in those character sets.
1109</t>
1110<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1111  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1112          <x:ref>Accept-Charset-v</x:ref>
1113  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1114                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1115</artwork></figure>
1116<t>
1117   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1118   be given an associated quality value which represents the user's
1119   preference for that charset. The default value is q=1. An example is
1120</t>
1121<figure><artwork type="example">
1122  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1123</artwork></figure>
1124<t>
1125   The special value "*", if present in the Accept-Charset field,
1126   matches every character set (including ISO-8859-1) which is not
1127   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1128   in an Accept-Charset field, then all character sets not explicitly
1129   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1130   a quality value of 1 if not explicitly mentioned.
1131</t>
1132<t>
1133   If no Accept-Charset header field is present, the default is that any
1134   character set is acceptable. If an Accept-Charset header field is present,
1135   and if the server cannot send a response which is acceptable
1136   according to the Accept-Charset header field, then the server &SHOULD; send
1137   an error response with the 406 (Not Acceptable) status code, though
1138   the sending of an unacceptable response is also allowed.
1139</t>
1140</section>
1141
1142<section title="Accept-Encoding" anchor="header.accept-encoding">
1143  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1144  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1145  <x:anchor-alias value="Accept-Encoding"/>
1146  <x:anchor-alias value="Accept-Encoding-v"/>
1147  <x:anchor-alias value="codings"/>
1148<t>
1149   The "Accept-Encoding" request-header field can be used by user agents to
1150   indicate what response content-codings (<xref target="content.codings"/>)
1151   are acceptable in the response.
1152</t>
1153<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1154  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1155                     <x:ref>Accept-Encoding-v</x:ref>
1156  <x:ref>Accept-Encoding-v</x:ref>  =
1157                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1158  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1159</artwork></figure>
1160<t>
1161   Each codings value &MAY; be given an associated quality value which
1162   represents the preference for that encoding. The default value is q=1.
1163</t>
1164<t>
1165   Examples of its use are:
1166</t>
1167<figure><artwork type="example">
1168  Accept-Encoding: compress, gzip
1169  Accept-Encoding:
1170  Accept-Encoding: *
1171  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1172  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1173</artwork></figure>
1174<t>
1175   A server tests whether a content-coding is acceptable, according to
1176   an Accept-Encoding field, using these rules:
1177  <list style="numbers">
1178      <t>If the content-coding is one of the content-codings listed in
1179         the Accept-Encoding field, then it is acceptable, unless it is
1180         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1181         qvalue of 0 means "not acceptable".)</t>
1182
1183      <t>The special "*" symbol in an Accept-Encoding field matches any
1184         available content-coding not explicitly listed in the header
1185         field.</t>
1186
1187      <t>If multiple content-codings are acceptable, then the acceptable
1188         content-coding with the highest non-zero qvalue is preferred.</t>
1189
1190      <t>The "identity" content-coding is always acceptable, unless
1191         specifically refused because the Accept-Encoding field includes
1192         "identity;q=0", or because the field includes "*;q=0" and does
1193         not explicitly include the "identity" content-coding. If the
1194         Accept-Encoding field-value is empty, then only the "identity"
1195         encoding is acceptable.</t>
1196  </list>
1197</t>
1198<t>
1199   If an Accept-Encoding field is present in a request, and if the
1200   server cannot send a response which is acceptable according to the
1201   Accept-Encoding header field, then the server &SHOULD; send an error response
1202   with the 406 (Not Acceptable) status code.
1203</t>
1204<t>
1205   If no Accept-Encoding field is present in a request, the server &MAY;
1206   assume that the client will accept any content coding. In this case,
1207   if "identity" is one of the available content-codings, then the
1208   server &SHOULD; use the "identity" content-coding, unless it has
1209   additional information that a different content-coding is meaningful
1210   to the client.
1211</t>
1212<x:note>
1213  <t>
1214    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1215    and if the "identity" content-coding is unavailable, then
1216    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1217    "gzip" and "compress") are preferred; some older clients
1218    improperly display messages sent with other content-codings.  The
1219    server might also make this decision based on information about
1220    the particular user-agent or client.
1221  </t>
1222</x:note>
1223<x:note>
1224  <t>
1225    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1226    associated with content-codings. This means that qvalues will not
1227    work and are not permitted with x-gzip or x-compress.
1228  </t>
1229</x:note>
1230</section>
1231
1232<section title="Accept-Language" anchor="header.accept-language">
1233  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1234  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1235  <x:anchor-alias value="Accept-Language"/>
1236  <x:anchor-alias value="Accept-Language-v"/>
1237  <x:anchor-alias value="language-range"/>
1238<t>
1239   The "Accept-Language" request-header field can be used by user agents to
1240   indicate the set of natural languages that are preferred in the response.
1241   Language tags are defined in <xref target="language.tags"/>.
1242</t>
1243<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1244  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1245                    <x:ref>Accept-Language-v</x:ref>
1246  <x:ref>Accept-Language-v</x:ref> =
1247                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1248  <x:ref>language-range</x:ref>    =
1249            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1250</artwork></figure>
1251<t>
1252   Each language-range can be given an associated quality value which
1253   represents an estimate of the user's preference for the languages
1254   specified by that range. The quality value defaults to "q=1". For
1255   example,
1256</t>
1257<figure><artwork type="example">
1258  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1259</artwork></figure>
1260<t>
1261   would mean: "I prefer Danish, but will accept British English and
1262   other types of English".
1263   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1264</t>
1265<t>
1266   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1267   several matching schemes. Implementations can offer the most appropriate
1268   matching scheme for their requirements.
1269</t>
1270<x:note>
1271  <t>
1272    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1273    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1274    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1275  </t>
1276</x:note>
1277<t>
1278   It might be contrary to the privacy expectations of the user to send
1279   an Accept-Language header field with the complete linguistic preferences of
1280   the user in every request. For a discussion of this issue, see
1281   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1282</t>
1283<t>
1284   As intelligibility is highly dependent on the individual user, it is
1285   recommended that client applications make the choice of linguistic
1286   preference available to the user. If the choice is not made
1287   available, then the Accept-Language header field &MUST-NOT; be given in
1288   the request.
1289</t>
1290<x:note>
1291  <t>
1292    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1293    the user, we remind implementors of  the fact that users are not
1294    familiar with the details of language matching as described above,
1295    and ought to be provided appropriate guidance. As an example, users
1296    might assume that on selecting "en-gb", they will be served any
1297    kind of English document if British English is not available. A
1298    user agent might suggest in such a case to add "en" to get the
1299    best matching behavior.
1300  </t>
1301</x:note>
1302</section>
1303
1304<section title="Content-Encoding" anchor="header.content-encoding">
1305  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1306  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1307  <x:anchor-alias value="Content-Encoding"/>
1308  <x:anchor-alias value="Content-Encoding-v"/>
1309<t>
1310   The "Content-Encoding" header field indicates what content-codings
1311   have been applied to the representation, and thus what decoding mechanisms
1312   must be applied in order to obtain the media-type referenced by the
1313   Content-Type header field. Content-Encoding is primarily used to allow a
1314   representation to be compressed without losing the identity of its underlying
1315   media type.
1316</t>
1317<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1318  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1319  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1320</artwork></figure>
1321<t>
1322   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1323</t>
1324<figure><artwork type="example">
1325  Content-Encoding: gzip
1326</artwork></figure>
1327<t>
1328   The content-coding is a characteristic of the representation.
1329   Typically, the representation body is stored with this
1330   encoding and is only decoded before rendering or analogous usage.
1331   However, a transforming proxy &MAY; modify the content-coding if the
1332   new coding is known to be acceptable to the recipient, unless the
1333   "no-transform" cache-control directive is present in the message.
1334</t>
1335<t>
1336   If the content-coding of a representation is not "identity", then the
1337   representation metadata &MUST; include a Content-Encoding header
1338   field (<xref target="header.content-encoding"/>)
1339   that lists the non-identity content-coding(s) used.
1340</t>
1341<t>
1342   If the content-coding of a representation in a request message is not
1343   acceptable to the origin server, the server &SHOULD; respond with a
1344   status code of 415 (Unsupported Media Type).
1345</t>
1346<t>
1347   If multiple encodings have been applied to a representation, the content
1348   codings &MUST; be listed in the order in which they were applied.
1349   Additional information about the encoding parameters &MAY; be provided
1350   by other header fields not defined by this specification.
1351</t>
1352</section>
1353
1354<section title="Content-Language" anchor="header.content-language">
1355  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1356  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1357  <x:anchor-alias value="Content-Language"/>
1358  <x:anchor-alias value="Content-Language-v"/>
1359<t>
1360   The "Content-Language" header field describes the natural
1361   language(s) of the intended audience for the representation. Note that this might
1362   not be equivalent to all the languages used within the representation.
1363</t>
1364<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1365  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1366  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1367</artwork></figure>
1368<t>
1369   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1370   Content-Language is to allow a user to identify and differentiate
1371   representations according to the user's own preferred language. Thus, if the
1372   body content is intended only for a Danish-literate audience, the
1373   appropriate field is
1374</t>
1375<figure><artwork type="example">
1376  Content-Language: da
1377</artwork></figure>
1378<t>
1379   If no Content-Language is specified, the default is that the content
1380   is intended for all language audiences. This might mean that the
1381   sender does not consider it to be specific to any natural language,
1382   or that the sender does not know for which language it is intended.
1383</t>
1384<t>
1385   Multiple languages &MAY; be listed for content that is intended for
1386   multiple audiences. For example, a rendition of the "Treaty of
1387   Waitangi", presented simultaneously in the original Maori and English
1388   versions, would call for
1389</t>
1390<figure><artwork type="example">
1391  Content-Language: mi, en
1392</artwork></figure>
1393<t>
1394   However, just because multiple languages are present within a representation
1395   does not mean that it is intended for multiple linguistic audiences.
1396   An example would be a beginner's language primer, such as "A First
1397   Lesson in Latin", which is clearly intended to be used by an
1398   English-literate audience. In this case, the Content-Language would
1399   properly only include "en".
1400</t>
1401<t>
1402   Content-Language &MAY; be applied to any media type &mdash; it is not
1403   limited to textual documents.
1404</t>
1405</section>
1406
1407<section title="Content-Location" anchor="header.content-location">
1408  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1409  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1410  <x:anchor-alias value="Content-Location"/>
1411  <x:anchor-alias value="Content-Location-v"/>
1412<t>
1413   The "Content-Location" header field supplies a URI that can be used
1414   as a specific identifier for the representation in this message.
1415   In other words, if one were to perform a GET on this URI at the time
1416   of this message's generation, then a 200 response would contain the
1417   same representation that is enclosed as payload in this message.
1418</t>
1419<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1420  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1421                    <x:ref>Content-Location-v</x:ref>
1422  <x:ref>Content-Location-v</x:ref> =
1423                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1424</artwork></figure>
1425<t>
1426   The Content-Location value is not a replacement for the effective
1427   Request URI (&effective-request-uri;).  It is representation metadata.
1428   It has the same syntax and semantics as the header field of the same name
1429   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1430   However, its appearance in an HTTP message has some special implications
1431   for HTTP recipients.
1432</t>
1433<t>
1434   If Content-Location is included in a response message and its value
1435   is the same as the effective request URI, then the response payload
1436   &SHOULD; be considered the current representation of that resource.
1437   For a GET or HEAD request, this is the same as the default semantics
1438   when no Content-Location is provided by the server.  For a state-changing
1439   method like PUT or POST, it implies that the server's response contains
1440   the new representation of that resource, thereby distinguishing it from
1441   representations that might only report about the action (e.g., "It worked!").
1442   This allows authoring applications to update their local copies without
1443   the need for a subsequent GET request.
1444</t>
1445<t>
1446   If Content-Location is included in a response message and its value
1447   differs from the effective request URI, then the origin server is
1448   informing recipients that this representation has its own, presumably
1449   more specific, identifier.  For a GET or HEAD request, this is an
1450   indication that the effective request URI identifies a resource that
1451   is subject to content negotiation and the representation selected for
1452   this response can also be found at the identified URI.  For other
1453   methods, such a Content-Location indicates that this representation
1454   contains a report on the action's status and the same report is
1455   available (for future access with GET) at the given URI.  For
1456   example, a purchase transaction made via the POST method might
1457   include a receipt document as the payload of the 200 response;
1458   the Content-Location value provides an identifier for retrieving
1459   a copy of that same receipt in the future.
1460</t>
1461<t>
1462   If Content-Location is included in a request message, then it &MAY;
1463   be interpreted by the origin server as an indication of where the
1464   user agent originally obtained the content of the enclosed
1465   representation (prior to any subsequent modification of the content
1466   by that user agent).  In other words, the user agent is providing
1467   the same representation metadata that it received with the original
1468   representation.  However, such interpretation &MUST-NOT; be used to
1469   alter the semantics of the method requested by the client.  For
1470   example, if a client makes a PUT request on a negotiated resource
1471   and the origin server accepts that PUT (without redirection), then the
1472   new set of values for that resource is expected to be consistent with
1473   the one representation supplied in that PUT; the Content-Location
1474   cannot be used as a form of reverse content selection that
1475   identifies only one of the negotiated representations to be updated.
1476   If the user agent had wanted the latter semantics, it would have applied
1477   the PUT directly to the Content-Location URI.
1478</t>
1479<t>
1480   A Content-Location field received in a request message is transitory
1481   information that &SHOULD-NOT; be saved with other representation
1482   metadata for use in later responses.  The Content-Location's value
1483   might be saved for use in other contexts, such as within source links
1484   or other metadata.
1485</t>
1486<t>
1487   A cache cannot assume that a representation with a Content-Location
1488   different from the URI used to retrieve it can be used to respond to
1489   later requests on that Content-Location URI.
1490</t>
1491<t>
1492   If the Content-Location value is a partial URI, the partial URI is
1493   interpreted relative to the effective request URI.
1494</t>
1495</section>
1496
1497<section title="Content-MD5" anchor="header.content-md5">
1498  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1499  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1500  <x:anchor-alias value="Content-MD5"/>
1501  <x:anchor-alias value="Content-MD5-v"/>
1502<t>
1503   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
1504   an MD5 digest of the payload body that provides an end-to-end message
1505   integrity check (MIC) of the payload body (the message-body after any
1506   transfer-coding is decoded). Note that a MIC is good for
1507   detecting accidental modification of the payload body in transit, but is not
1508   proof against malicious attacks.
1509</t>
1510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1511  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1512  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1513</artwork></figure>
1514<t>
1515   The Content-MD5 header field &MAY; be generated by an origin server or
1516   client to function as an integrity check of the payload body. Only
1517   origin servers or user agents &MAY; generate the Content-MD5 header field;
1518   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1519   value as an end-to-end integrity check. Any recipient &MAY; check that
1520   the digest value in this header field matches a corresponding digest
1521   calculated on payload body as received.
1522</t>
1523<t>
1524   The MD5 digest is computed based on the content of the payload body,
1525   including any content-coding, but not including any transfer-coding
1526   applied to the message-body because such transfer-codings might be
1527   applied or removed anywhere along the request/response chain.
1528   If the message is received with a transfer-coding, that encoding &MUST;
1529   be decoded prior to checking the Content-MD5 value against the received
1530   payload.
1531</t>
1532<t>
1533   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1534   composite media-types (e.g., multipart/* and message/rfc822), but
1535   this does not change how the digest is computed as defined in the
1536   preceding paragraph.
1537</t>
1538<t>
1539   There are several consequences of this. The payload for composite
1540   types &MAY; contain many body-parts, each with its own MIME and HTTP
1541   header fields (including Content-MD5, Content-Transfer-Encoding, and
1542   Content-Encoding header fields). If a body-part has a Content-Transfer-Encoding
1543   or Content-Encoding header field, it is assumed that the content
1544   of the body-part has had the encoding applied, and the body-part is
1545   included in the Content-MD5 digest as is &mdash; i.e., after the
1546   application. The Transfer-Encoding header field is not allowed within
1547   body-parts.
1548</t>
1549<t>
1550   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1551   computing or checking the digest: the line break convention used in
1552   the text actually transmitted &MUST; be left unaltered when computing
1553   the digest.
1554</t>
1555<x:note>
1556  <t>
1557    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1558    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1559    in which the application of Content-MD5 to HTTP entity-bodies
1560    differs from its application to MIME entity-bodies. One is that
1561    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1562    does use Transfer-Encoding and Content-Encoding. Another is that
1563    HTTP more frequently uses binary content types than MIME, so it is
1564    worth noting that, in such cases, the byte order used to compute
1565    the digest is the transmission byte order defined for the type.
1566    Lastly, HTTP allows transmission of text types with any of several
1567    line break conventions and not just the canonical form using CRLF.
1568  </t>
1569</x:note>
1570</section>
1571
1572<section title="Content-Type" anchor="header.content-type">
1573  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1574  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1575  <x:anchor-alias value="Content-Type"/>
1576  <x:anchor-alias value="Content-Type-v"/>
1577<t>
1578   The "Content-Type" header field indicates the media type of the
1579   representation. In the case of responses to the HEAD method, the media type is
1580   that which would have been sent had the request been a GET.
1581</t>
1582<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1583  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1584  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1585</artwork></figure>
1586<t>
1587   Media types are defined in <xref target="media.types"/>. An example of the field is
1588</t>
1589<figure><artwork type="example">
1590  Content-Type: text/html; charset=ISO-8859-4
1591</artwork></figure>
1592<t>
1593   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1594</t>
1595</section>
1596
1597</section>
1598
1599<section title="IANA Considerations" anchor="IANA.considerations">
1600<section title="Header Field Registration" anchor="header.field.registration">
1601<t>
1602   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1603   with the permanent registrations below (see <xref target="RFC3864"/>):
1604</t>
1605<?BEGININC p3-payload.iana-headers ?>
1606<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1607<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1608   <ttcol>Header Field Name</ttcol>
1609   <ttcol>Protocol</ttcol>
1610   <ttcol>Status</ttcol>
1611   <ttcol>Reference</ttcol>
1612
1613   <c>Accept</c>
1614   <c>http</c>
1615   <c>standard</c>
1616   <c>
1617      <xref target="header.accept"/>
1618   </c>
1619   <c>Accept-Charset</c>
1620   <c>http</c>
1621   <c>standard</c>
1622   <c>
1623      <xref target="header.accept-charset"/>
1624   </c>
1625   <c>Accept-Encoding</c>
1626   <c>http</c>
1627   <c>standard</c>
1628   <c>
1629      <xref target="header.accept-encoding"/>
1630   </c>
1631   <c>Accept-Language</c>
1632   <c>http</c>
1633   <c>standard</c>
1634   <c>
1635      <xref target="header.accept-language"/>
1636   </c>
1637   <c>Content-Encoding</c>
1638   <c>http</c>
1639   <c>standard</c>
1640   <c>
1641      <xref target="header.content-encoding"/>
1642   </c>
1643   <c>Content-Language</c>
1644   <c>http</c>
1645   <c>standard</c>
1646   <c>
1647      <xref target="header.content-language"/>
1648   </c>
1649   <c>Content-Location</c>
1650   <c>http</c>
1651   <c>standard</c>
1652   <c>
1653      <xref target="header.content-location"/>
1654   </c>
1655   <c>Content-MD5</c>
1656   <c>http</c>
1657   <c>standard</c>
1658   <c>
1659      <xref target="header.content-md5"/>
1660   </c>
1661   <c>Content-Type</c>
1662   <c>http</c>
1663   <c>standard</c>
1664   <c>
1665      <xref target="header.content-type"/>
1666   </c>
1667   <c>MIME-Version</c>
1668   <c>http</c>
1669   <c>standard</c>
1670   <c>
1671      <xref target="mime-version"/>
1672   </c>
1673</texttable>
1674<!--(END)-->
1675<?ENDINC p3-payload.iana-headers ?>
1676<t>
1677   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1678</t>
1679</section>
1680
1681<section title="Content Coding Registry" anchor="content.coding.registration">
1682<t>
1683   The registration procedure for HTTP Content Codings is now defined
1684   by <xref target="content.coding.registry"/> of this document.
1685</t>
1686<t>
1687   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1688   shall be updated with the registration below:
1689</t>
1690<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1691   <ttcol>Name</ttcol>
1692   <ttcol>Description</ttcol>
1693   <ttcol>Reference</ttcol>
1694   <c>compress</c>
1695   <c>UNIX "compress" program method</c>
1696   <c>
1697      &compress-coding;
1698   </c>
1699   <c>deflate</c>
1700   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1701   the "zlib" data format (<xref target="RFC1950"/>)
1702   </c>
1703   <c>
1704      &deflate-coding;
1705   </c>
1706   <c>gzip</c>
1707   <c>Same as GNU zip <xref target="RFC1952"/></c>
1708   <c>
1709      &gzip-coding;
1710   </c>
1711   <c>identity</c>
1712   <c>No transformation</c>
1713   <c>
1714      <xref target="content.codings"/>
1715   </c>
1716</texttable>
1717</section>
1718
1719</section>
1720
1721<section title="Security Considerations" anchor="security.considerations">
1722<t>
1723   This section is meant to inform application developers, information
1724   providers, and users of the security limitations in HTTP/1.1 as
1725   described by this document. The discussion does not include
1726   definitive solutions to the problems revealed, though it does make
1727   some suggestions for reducing security risks.
1728</t>
1729
1730<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1731<t>
1732   Accept request-headers fields can reveal information about the user to all
1733   servers which are accessed. The Accept-Language header field in particular
1734   can reveal information the user would consider to be of a private
1735   nature, because the understanding of particular languages is often
1736   strongly correlated to the membership of a particular ethnic group.
1737   User agents which offer the option to configure the contents of an
1738   Accept-Language header field to be sent in every request are strongly
1739   encouraged to let the configuration process include a message which
1740   makes the user aware of the loss of privacy involved.
1741</t>
1742<t>
1743   An approach that limits the loss of privacy would be for a user agent
1744   to omit the sending of Accept-Language header fields by default, and to ask
1745   the user whether or not to start sending Accept-Language header fields to a
1746   server if it detects, by looking for any Vary response-header fields
1747   generated by the server, that such sending could improve the quality
1748   of service.
1749</t>
1750<t>
1751   Elaborate user-customized accept header fields sent in every request,
1752   in particular if these include quality values, can be used by servers
1753   as relatively reliable and long-lived user identifiers. Such user
1754   identifiers would allow content providers to do click-trail tracking,
1755   and would allow collaborating content providers to match cross-server
1756   click-trails or form submissions of individual users. Note that for
1757   many users not behind a proxy, the network address of the host
1758   running the user agent will also serve as a long-lived user
1759   identifier. In environments where proxies are used to enhance
1760   privacy, user agents ought to be conservative in offering accept
1761   header configuration options to end users. As an extreme privacy
1762   measure, proxies could filter the accept header fields in relayed requests.
1763   General purpose user agents which provide a high degree of header
1764   configurability &SHOULD; warn users about the loss of privacy which can
1765   be involved.
1766</t>
1767</section>
1768
1769</section>
1770
1771<section title="Acknowledgments" anchor="ack">
1772</section>
1773</middle>
1774<back>
1775
1776<references title="Normative References">
1777
1778<reference anchor="ISO-8859-1">
1779  <front>
1780    <title>
1781     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1782    </title>
1783    <author>
1784      <organization>International Organization for Standardization</organization>
1785    </author>
1786    <date year="1998"/>
1787  </front>
1788  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1789</reference>
1790
1791<reference anchor="Part1">
1792  <front>
1793    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1794    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1795      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1796      <address><email>fielding@gbiv.com</email></address>
1797    </author>
1798    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1799      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1800      <address><email>jg@freedesktop.org</email></address>
1801    </author>
1802    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1803      <organization abbrev="HP">Hewlett-Packard Company</organization>
1804      <address><email>JeffMogul@acm.org</email></address>
1805    </author>
1806    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1807      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1808      <address><email>henrikn@microsoft.com</email></address>
1809    </author>
1810    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1811      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1812      <address><email>LMM@acm.org</email></address>
1813    </author>
1814    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1815      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1816      <address><email>paulle@microsoft.com</email></address>
1817    </author>
1818    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1819      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1820      <address><email>timbl@w3.org</email></address>
1821    </author>
1822    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1823      <organization abbrev="W3C">World Wide Web Consortium</organization>
1824      <address><email>ylafon@w3.org</email></address>
1825    </author>
1826    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1827      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1828      <address><email>julian.reschke@greenbytes.de</email></address>
1829    </author>
1830    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1831  </front>
1832  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1833  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1834</reference>
1835
1836<reference anchor="Part2">
1837  <front>
1838    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1839    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1840      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1841      <address><email>fielding@gbiv.com</email></address>
1842    </author>
1843    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1844      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1845      <address><email>jg@freedesktop.org</email></address>
1846    </author>
1847    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1848      <organization abbrev="HP">Hewlett-Packard Company</organization>
1849      <address><email>JeffMogul@acm.org</email></address>
1850    </author>
1851    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1852      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1853      <address><email>henrikn@microsoft.com</email></address>
1854    </author>
1855    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1856      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1857      <address><email>LMM@acm.org</email></address>
1858    </author>
1859    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1860      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1861      <address><email>paulle@microsoft.com</email></address>
1862    </author>
1863    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1864      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1865      <address><email>timbl@w3.org</email></address>
1866    </author>
1867    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1868      <organization abbrev="W3C">World Wide Web Consortium</organization>
1869      <address><email>ylafon@w3.org</email></address>
1870    </author>
1871    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1872      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1873      <address><email>julian.reschke@greenbytes.de</email></address>
1874    </author>
1875    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1876  </front>
1877  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1878  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1879</reference>
1880
1881<reference anchor="Part4">
1882  <front>
1883    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1884    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1885      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1886      <address><email>fielding@gbiv.com</email></address>
1887    </author>
1888    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1889      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1890      <address><email>jg@freedesktop.org</email></address>
1891    </author>
1892    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1893      <organization abbrev="HP">Hewlett-Packard Company</organization>
1894      <address><email>JeffMogul@acm.org</email></address>
1895    </author>
1896    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1897      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1898      <address><email>henrikn@microsoft.com</email></address>
1899    </author>
1900    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1901      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1902      <address><email>LMM@acm.org</email></address>
1903    </author>
1904    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1905      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1906      <address><email>paulle@microsoft.com</email></address>
1907    </author>
1908    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1909      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1910      <address><email>timbl@w3.org</email></address>
1911    </author>
1912    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1913      <organization abbrev="W3C">World Wide Web Consortium</organization>
1914      <address><email>ylafon@w3.org</email></address>
1915    </author>
1916    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1917      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1918      <address><email>julian.reschke@greenbytes.de</email></address>
1919    </author>
1920    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1921  </front>
1922  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1923  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1924</reference>
1925
1926<reference anchor="Part5">
1927  <front>
1928    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1929    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1930      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1931      <address><email>fielding@gbiv.com</email></address>
1932    </author>
1933    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1934      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1935      <address><email>jg@freedesktop.org</email></address>
1936    </author>
1937    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1938      <organization abbrev="HP">Hewlett-Packard Company</organization>
1939      <address><email>JeffMogul@acm.org</email></address>
1940    </author>
1941    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1942      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1943      <address><email>henrikn@microsoft.com</email></address>
1944    </author>
1945    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1946      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1947      <address><email>LMM@acm.org</email></address>
1948    </author>
1949    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1950      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1951      <address><email>paulle@microsoft.com</email></address>
1952    </author>
1953    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1954      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1955      <address><email>timbl@w3.org</email></address>
1956    </author>
1957    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1958      <organization abbrev="W3C">World Wide Web Consortium</organization>
1959      <address><email>ylafon@w3.org</email></address>
1960    </author>
1961    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1962      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1963      <address><email>julian.reschke@greenbytes.de</email></address>
1964    </author>
1965    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1966  </front>
1967  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1968  <x:source href="p5-range.xml" basename="p5-range"/>
1969</reference>
1970
1971<reference anchor="Part6">
1972  <front>
1973    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1974    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1975      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1976      <address><email>fielding@gbiv.com</email></address>
1977    </author>
1978    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1979      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1980      <address><email>jg@freedesktop.org</email></address>
1981    </author>
1982    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1983      <organization abbrev="HP">Hewlett-Packard Company</organization>
1984      <address><email>JeffMogul@acm.org</email></address>
1985    </author>
1986    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1987      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1988      <address><email>henrikn@microsoft.com</email></address>
1989    </author>
1990    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1991      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1992      <address><email>LMM@acm.org</email></address>
1993    </author>
1994    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1995      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1996      <address><email>paulle@microsoft.com</email></address>
1997    </author>
1998    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1999      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2000      <address><email>timbl@w3.org</email></address>
2001    </author>
2002    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2003      <organization abbrev="W3C">World Wide Web Consortium</organization>
2004      <address><email>ylafon@w3.org</email></address>
2005    </author>
2006    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2007      <address><email>mnot@mnot.net</email></address>
2008    </author>
2009    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2010      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2011      <address><email>julian.reschke@greenbytes.de</email></address>
2012    </author>
2013    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2014  </front>
2015  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2016  <x:source href="p6-cache.xml" basename="p6-cache"/>
2017</reference>
2018
2019<reference anchor="RFC1864">
2020  <front>
2021    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2022    <author initials="J." surname="Myers" fullname="John G. Myers">
2023      <organization>Carnegie Mellon University</organization>
2024      <address><email>jgm+@cmu.edu</email></address>
2025    </author>
2026    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2027      <organization>Dover Beach Consulting, Inc.</organization>
2028      <address><email>mrose@dbc.mtview.ca.us</email></address>
2029    </author>
2030    <date month="October" year="1995"/>
2031  </front>
2032  <seriesInfo name="RFC" value="1864"/>
2033</reference>
2034
2035<reference anchor="RFC1950">
2036  <front>
2037    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2038    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2039      <organization>Aladdin Enterprises</organization>
2040      <address><email>ghost@aladdin.com</email></address>
2041    </author>
2042    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2043    <date month="May" year="1996"/>
2044  </front>
2045  <seriesInfo name="RFC" value="1950"/>
2046  <annotation>
2047    RFC 1950 is an Informational RFC, thus it might be less stable than
2048    this specification. On the other hand, this downward reference was
2049    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2050    therefore it is unlikely to cause problems in practice. See also
2051    <xref target="BCP97"/>.
2052  </annotation>
2053</reference>
2054
2055<reference anchor="RFC1951">
2056  <front>
2057    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2058    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2059      <organization>Aladdin Enterprises</organization>
2060      <address><email>ghost@aladdin.com</email></address>
2061    </author>
2062    <date month="May" year="1996"/>
2063  </front>
2064  <seriesInfo name="RFC" value="1951"/>
2065  <annotation>
2066    RFC 1951 is an Informational RFC, thus it might be less stable than
2067    this specification. On the other hand, this downward reference was
2068    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2069    therefore it is unlikely to cause problems in practice. See also
2070    <xref target="BCP97"/>.
2071  </annotation>
2072</reference>
2073
2074<reference anchor="RFC1952">
2075  <front>
2076    <title>GZIP file format specification version 4.3</title>
2077    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2078      <organization>Aladdin Enterprises</organization>
2079      <address><email>ghost@aladdin.com</email></address>
2080    </author>
2081    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2082      <address><email>gzip@prep.ai.mit.edu</email></address>
2083    </author>
2084    <author initials="M." surname="Adler" fullname="Mark Adler">
2085      <address><email>madler@alumni.caltech.edu</email></address>
2086    </author>
2087    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2088      <address><email>ghost@aladdin.com</email></address>
2089    </author>
2090    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2091      <address><email>randeg@alumni.rpi.edu</email></address>
2092    </author>
2093    <date month="May" year="1996"/>
2094  </front>
2095  <seriesInfo name="RFC" value="1952"/>
2096  <annotation>
2097    RFC 1952 is an Informational RFC, thus it might be less stable than
2098    this specification. On the other hand, this downward reference was
2099    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2100    therefore it is unlikely to cause problems in practice. See also
2101    <xref target="BCP97"/>.
2102  </annotation>
2103</reference>
2104
2105<reference anchor="RFC2045">
2106  <front>
2107    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2108    <author initials="N." surname="Freed" fullname="Ned Freed">
2109      <organization>Innosoft International, Inc.</organization>
2110      <address><email>ned@innosoft.com</email></address>
2111    </author>
2112    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2113      <organization>First Virtual Holdings</organization>
2114      <address><email>nsb@nsb.fv.com</email></address>
2115    </author>
2116    <date month="November" year="1996"/>
2117  </front>
2118  <seriesInfo name="RFC" value="2045"/>
2119</reference>
2120
2121<reference anchor="RFC2046">
2122  <front>
2123    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2124    <author initials="N." surname="Freed" fullname="Ned Freed">
2125      <organization>Innosoft International, Inc.</organization>
2126      <address><email>ned@innosoft.com</email></address>
2127    </author>
2128    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2129      <organization>First Virtual Holdings</organization>
2130      <address><email>nsb@nsb.fv.com</email></address>
2131    </author>
2132    <date month="November" year="1996"/>
2133  </front>
2134  <seriesInfo name="RFC" value="2046"/>
2135</reference>
2136
2137<reference anchor="RFC2119">
2138  <front>
2139    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2140    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2141      <organization>Harvard University</organization>
2142      <address><email>sob@harvard.edu</email></address>
2143    </author>
2144    <date month="March" year="1997"/>
2145  </front>
2146  <seriesInfo name="BCP" value="14"/>
2147  <seriesInfo name="RFC" value="2119"/>
2148</reference>
2149
2150<reference anchor='RFC4647'>
2151  <front>
2152    <title>Matching of Language Tags</title>
2153    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2154      <organization>Yahoo! Inc.</organization>
2155      <address><email>addison@inter-locale.com</email></address>
2156    </author>
2157    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2158      <organization>Google</organization>
2159      <address><email>mark.davis@macchiato.com</email></address>
2160    </author>
2161    <date year='2006' month='September' />
2162  </front>
2163  <seriesInfo name='BCP' value='47' />
2164  <seriesInfo name='RFC' value='4647' />
2165</reference>
2166
2167<reference anchor="RFC5234">
2168  <front>
2169    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2170    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2171      <organization>Brandenburg InternetWorking</organization>
2172      <address>
2173        <email>dcrocker@bbiw.net</email>
2174      </address> 
2175    </author>
2176    <author initials="P." surname="Overell" fullname="Paul Overell">
2177      <organization>THUS plc.</organization>
2178      <address>
2179        <email>paul.overell@thus.net</email>
2180      </address>
2181    </author>
2182    <date month="January" year="2008"/>
2183  </front>
2184  <seriesInfo name="STD" value="68"/>
2185  <seriesInfo name="RFC" value="5234"/>
2186</reference>
2187
2188<reference anchor='RFC5646'>
2189  <front>
2190    <title>Tags for Identifying Languages</title>
2191    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2192      <organization>Lab126</organization>
2193      <address><email>addison@inter-locale.com</email></address>
2194    </author>
2195    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2196      <organization>Google</organization>
2197      <address><email>mark.davis@google.com</email></address>
2198    </author>
2199    <date month='September' year='2009' />
2200  </front>
2201  <seriesInfo name='BCP' value='47' />
2202  <seriesInfo name='RFC' value='5646' />
2203</reference>
2204
2205</references>
2206
2207<references title="Informative References">
2208
2209<reference anchor="RFC1945">
2210  <front>
2211    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2212    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2213      <organization>MIT, Laboratory for Computer Science</organization>
2214      <address><email>timbl@w3.org</email></address>
2215    </author>
2216    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2217      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2218      <address><email>fielding@ics.uci.edu</email></address>
2219    </author>
2220    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2221      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2222      <address><email>frystyk@w3.org</email></address>
2223    </author>
2224    <date month="May" year="1996"/>
2225  </front>
2226  <seriesInfo name="RFC" value="1945"/>
2227</reference>
2228
2229<reference anchor="RFC2049">
2230  <front>
2231    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2232    <author initials="N." surname="Freed" fullname="Ned Freed">
2233      <organization>Innosoft International, Inc.</organization>
2234      <address><email>ned@innosoft.com</email></address>
2235    </author>
2236    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2237      <organization>First Virtual Holdings</organization>
2238      <address><email>nsb@nsb.fv.com</email></address>
2239    </author>
2240    <date month="November" year="1996"/>
2241  </front>
2242  <seriesInfo name="RFC" value="2049"/>
2243</reference>
2244
2245<reference anchor="RFC2068">
2246  <front>
2247    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2248    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2249      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2250      <address><email>fielding@ics.uci.edu</email></address>
2251    </author>
2252    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2253      <organization>MIT Laboratory for Computer Science</organization>
2254      <address><email>jg@w3.org</email></address>
2255    </author>
2256    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2257      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2258      <address><email>mogul@wrl.dec.com</email></address>
2259    </author>
2260    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2261      <organization>MIT Laboratory for Computer Science</organization>
2262      <address><email>frystyk@w3.org</email></address>
2263    </author>
2264    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2265      <organization>MIT Laboratory for Computer Science</organization>
2266      <address><email>timbl@w3.org</email></address>
2267    </author>
2268    <date month="January" year="1997"/>
2269  </front>
2270  <seriesInfo name="RFC" value="2068"/>
2271</reference>
2272
2273<reference anchor="RFC2076">
2274  <front>
2275    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2276    <author initials="J." surname="Palme" fullname="Jacob Palme">
2277      <organization>Stockholm University/KTH</organization>
2278      <address><email>jpalme@dsv.su.se</email></address>
2279    </author>
2280    <date month="February" year="1997"/>
2281  </front>
2282  <seriesInfo name="RFC" value="2076"/>
2283</reference>
2284
2285<reference anchor="RFC2277">
2286  <front>
2287    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2288    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2289      <organization>UNINETT</organization>
2290      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2291    </author>
2292    <date month="January" year="1998"/>
2293  </front>
2294  <seriesInfo name="BCP" value="18"/>
2295  <seriesInfo name="RFC" value="2277"/>
2296</reference>
2297
2298<reference anchor='RFC2295'>
2299  <front>
2300    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2301    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2302      <organization>Technische Universiteit Eindhoven</organization>
2303      <address>
2304        <email>koen@win.tue.nl</email>
2305      </address>
2306    </author>
2307    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2308      <organization>Hewlett-Packard Company</organization>
2309      <address>
2310        <email>mutz@hpl.hp.com</email>
2311      </address>
2312    </author>
2313    <date year='1998' month='March'/>
2314  </front>
2315  <seriesInfo name='RFC' value='2295'/>
2316</reference>
2317
2318<reference anchor="RFC2388">
2319  <front>
2320    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2321    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2322      <organization>Xerox Palo Alto Research Center</organization>
2323      <address><email>masinter@parc.xerox.com</email></address>
2324    </author>
2325    <date year="1998" month="August"/>
2326  </front>
2327  <seriesInfo name="RFC" value="2388"/>
2328</reference>
2329
2330<reference anchor="RFC2557">
2331  <front>
2332    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2333    <author initials="F." surname="Palme" fullname="Jacob Palme">
2334      <organization>Stockholm University and KTH</organization>
2335      <address><email>jpalme@dsv.su.se</email></address>
2336    </author>
2337    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2338      <organization>Microsoft Corporation</organization>
2339      <address><email>alexhop@microsoft.com</email></address>
2340    </author>
2341    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2342      <organization>Lotus Development Corporation</organization>
2343      <address><email>Shelness@lotus.com</email></address>
2344    </author>
2345    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2346      <address><email>stef@nma.com</email></address>
2347    </author>
2348    <date year="1999" month="March"/>
2349  </front>
2350  <seriesInfo name="RFC" value="2557"/>
2351</reference>
2352
2353<reference anchor="RFC2616">
2354  <front>
2355    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2356    <author initials="R." surname="Fielding" fullname="R. Fielding">
2357      <organization>University of California, Irvine</organization>
2358      <address><email>fielding@ics.uci.edu</email></address>
2359    </author>
2360    <author initials="J." surname="Gettys" fullname="J. Gettys">
2361      <organization>W3C</organization>
2362      <address><email>jg@w3.org</email></address>
2363    </author>
2364    <author initials="J." surname="Mogul" fullname="J. Mogul">
2365      <organization>Compaq Computer Corporation</organization>
2366      <address><email>mogul@wrl.dec.com</email></address>
2367    </author>
2368    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2369      <organization>MIT Laboratory for Computer Science</organization>
2370      <address><email>frystyk@w3.org</email></address>
2371    </author>
2372    <author initials="L." surname="Masinter" fullname="L. Masinter">
2373      <organization>Xerox Corporation</organization>
2374      <address><email>masinter@parc.xerox.com</email></address>
2375    </author>
2376    <author initials="P." surname="Leach" fullname="P. Leach">
2377      <organization>Microsoft Corporation</organization>
2378      <address><email>paulle@microsoft.com</email></address>
2379    </author>
2380    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2381      <organization>W3C</organization>
2382      <address><email>timbl@w3.org</email></address>
2383    </author>
2384    <date month="June" year="1999"/>
2385  </front>
2386  <seriesInfo name="RFC" value="2616"/>
2387</reference>
2388
2389<reference anchor="RFC3629">
2390  <front>
2391    <title>UTF-8, a transformation format of ISO 10646</title>
2392    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2393      <organization>Alis Technologies</organization>
2394      <address><email>fyergeau@alis.com</email></address>
2395    </author>
2396    <date month="November" year="2003"/>
2397  </front>
2398  <seriesInfo name="STD" value="63"/>
2399  <seriesInfo name="RFC" value="3629"/>
2400</reference>
2401
2402<reference anchor='RFC3864'>
2403  <front>
2404    <title>Registration Procedures for Message Header Fields</title>
2405    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2406      <organization>Nine by Nine</organization>
2407      <address><email>GK-IETF@ninebynine.org</email></address>
2408    </author>
2409    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2410      <organization>BEA Systems</organization>
2411      <address><email>mnot@pobox.com</email></address>
2412    </author>
2413    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2414      <organization>HP Labs</organization>
2415      <address><email>JeffMogul@acm.org</email></address>
2416    </author>
2417    <date year='2004' month='September' />
2418  </front>
2419  <seriesInfo name='BCP' value='90' />
2420  <seriesInfo name='RFC' value='3864' />
2421</reference>
2422
2423<reference anchor="RFC4288">
2424  <front>
2425    <title>Media Type Specifications and Registration Procedures</title>
2426    <author initials="N." surname="Freed" fullname="N. Freed">
2427      <organization>Sun Microsystems</organization>
2428      <address>
2429        <email>ned.freed@mrochek.com</email>
2430      </address>
2431    </author>
2432    <author initials="J." surname="Klensin" fullname="J. Klensin">
2433      <address>
2434        <email>klensin+ietf@jck.com</email>
2435      </address>
2436    </author>
2437    <date year="2005" month="December"/>
2438  </front>
2439  <seriesInfo name="BCP" value="13"/>
2440  <seriesInfo name="RFC" value="4288"/>
2441</reference>
2442
2443<reference anchor='RFC5226'>
2444  <front>
2445    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2446    <author initials='T.' surname='Narten' fullname='T. Narten'>
2447      <organization>IBM</organization>
2448      <address><email>narten@us.ibm.com</email></address>
2449    </author>
2450    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2451      <organization>Google</organization>
2452      <address><email>Harald@Alvestrand.no</email></address>
2453    </author>
2454    <date year='2008' month='May' />
2455  </front>
2456  <seriesInfo name='BCP' value='26' />
2457  <seriesInfo name='RFC' value='5226' />
2458</reference>
2459
2460<reference anchor="RFC5322">
2461  <front>
2462    <title>Internet Message Format</title>
2463    <author initials="P." surname="Resnick" fullname="P. Resnick">
2464      <organization>Qualcomm Incorporated</organization>
2465    </author>
2466    <date year="2008" month="October"/>
2467  </front> 
2468  <seriesInfo name="RFC" value="5322"/>
2469</reference>
2470
2471<reference anchor='BCP97'>
2472  <front>
2473    <title>Handling Normative References to Standards-Track Documents</title>
2474    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2475      <address>
2476        <email>klensin+ietf@jck.com</email>
2477      </address>
2478    </author>
2479    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2480      <organization>MIT</organization>
2481      <address>
2482        <email>hartmans-ietf@mit.edu</email>
2483      </address>
2484    </author>
2485    <date year='2007' month='June' />
2486  </front>
2487  <seriesInfo name='BCP' value='97' />
2488  <seriesInfo name='RFC' value='4897' />
2489</reference>
2490
2491
2492</references>
2493
2494<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2495<t>
2496   HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC5322"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2497   allow a message-body to be transmitted in an open variety of
2498   representations and with extensible mechanisms. However, RFC 2045
2499   discusses mail, and HTTP has a few features that are different from
2500   those described in MIME. These differences were carefully chosen
2501   to optimize performance over binary connections, to allow greater
2502   freedom in the use of new media types, to make date comparisons
2503   easier, and to acknowledge the practice of some early HTTP servers
2504   and clients.
2505</t>
2506<t>
2507   This appendix describes specific areas where HTTP differs from MIME.
2508   Proxies and gateways to strict MIME environments &SHOULD; be
2509   aware of these differences and provide the appropriate conversions
2510   where necessary. Proxies and gateways from MIME environments to HTTP
2511   also need to be aware of the differences because some conversions
2512   might be required.
2513</t>
2514
2515<section title="MIME-Version" anchor="mime-version">
2516  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2517  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2518  <x:anchor-alias value="MIME-Version"/>
2519  <x:anchor-alias value="MIME-Version-v"/>
2520<t>
2521   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2522   include a single MIME-Version general-header field to indicate what
2523   version of the MIME protocol was used to construct the message. Use
2524   of the MIME-Version header field indicates that the message is in
2525   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2526   Proxies/gateways are responsible for ensuring full compliance (where
2527   possible) when exporting HTTP messages to strict MIME environments.
2528</t>
2529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2530  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2531  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2532</artwork></figure>
2533<t>
2534   MIME version "1.0" is the default for use in HTTP/1.1. However,
2535   HTTP/1.1 message parsing and semantics are defined by this document
2536   and not the MIME specification.
2537</t>
2538</section>
2539
2540<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2541<t>
2542   MIME requires that an Internet mail body-part be converted to
2543   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2544   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2545   allowed for subtypes of the "text" media type when transmitted over
2546   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2547   line breaks as CRLF and forbids the use of CR or LF outside of line
2548   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2549   line break within text content when a message is transmitted over
2550   HTTP.
2551</t>
2552<t>
2553   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2554   environment &SHOULD; translate all line breaks within the text media
2555   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2556   canonical form of CRLF. Note, however, that this might be complicated
2557   by the presence of a Content-Encoding and by the fact that HTTP
2558   allows the use of some character sets which do not use octets 13 and
2559   10 to represent CR and LF, as is the case for some multi-byte
2560   character sets.
2561</t>
2562<t>
2563   Conversion will break any cryptographic
2564   checksums applied to the original content unless the original content
2565   is already in canonical form. Therefore, the canonical form is
2566   recommended for any content that uses such checksums in HTTP.
2567</t>
2568</section>
2569
2570
2571<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2572<t>
2573   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2574   simplify the process of date comparison. Proxies and gateways from
2575   other protocols &SHOULD; ensure that any Date header field present in a
2576   message conforms to one of the HTTP/1.1 formats and rewrite the date
2577   if necessary.
2578</t>
2579</section>
2580
2581<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2582<t>
2583   MIME does not include any concept equivalent to HTTP/1.1's
2584   Content-Encoding header field. Since this acts as a modifier on the
2585   media type, proxies and gateways from HTTP to MIME-compliant
2586   protocols &MUST; either change the value of the Content-Type header
2587   field or decode the representation before forwarding the message. (Some
2588   experimental applications of Content-Type for Internet mail have used
2589   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2590   a function equivalent to Content-Encoding. However, this parameter is
2591   not part of the MIME standards).
2592</t>
2593</section>
2594
2595<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2596<t>
2597   HTTP does not use the Content-Transfer-Encoding field of MIME.
2598   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2599   remove any Content-Transfer-Encoding
2600   prior to delivering the response message to an HTTP client.
2601</t>
2602<t>
2603   Proxies and gateways from HTTP to MIME-compliant protocols are
2604   responsible for ensuring that the message is in the correct format
2605   and encoding for safe transport on that protocol, where "safe
2606   transport" is defined by the limitations of the protocol being used.
2607   Such a proxy or gateway &SHOULD; label the data with an appropriate
2608   Content-Transfer-Encoding if doing so will improve the likelihood of
2609   safe transport over the destination protocol.
2610</t>
2611</section>
2612
2613<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2614<t>
2615   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2616   Proxies/gateways &MUST; remove any transfer-coding prior to
2617   forwarding a message via a MIME-compliant protocol.
2618</t>
2619</section>
2620
2621<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2622<t>
2623   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2624   need to be aware of MIME line length limitations. Since HTTP does not
2625   have this limitation, HTTP does not fold long lines. MHTML messages
2626   being transported by HTTP follow all conventions of MHTML, including
2627   line length limitations and folding, canonicalization, etc., since
2628   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2629   does not interpret the content or any MIME header lines that might be
2630   contained therein.
2631</t>
2632</section>
2633</section>
2634
2635<section title="Additional Features" anchor="additional.features">
2636<t>
2637   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2638   existing HTTP implementations, but not consistently and correctly
2639   across most HTTP/1.1 applications. Implementors are advised to be
2640   aware of these features, but cannot rely upon their presence in, or
2641   interoperability with, other HTTP/1.1 applications. Some of these
2642   describe proposed experimental features, and some describe features
2643   that experimental deployment found lacking that are now addressed in
2644   the base HTTP/1.1 specification.
2645</t>
2646<t>
2647   A number of other header fields, such as Content-Disposition and Title,
2648   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2649</t>
2650</section>
2651
2652<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2653<t>
2654  Clarify contexts that charset is used in.
2655  (<xref target="character.sets"/>)
2656</t>
2657<t>
2658  Remove base URI setting semantics for Content-Location due to poor
2659  implementation support, which was caused by too many broken servers emitting
2660  bogus Content-Location header fields, and also the potentially undesirable effect
2661  of potentially breaking relative links in content-negotiated resources.
2662  (<xref target="header.content-location"/>)
2663</t>
2664<t>
2665  Remove reference to non-existant identity transfer-coding value tokens.
2666  (<xref target="no.content-transfer-encoding"/>)
2667</t>
2668</section>
2669
2670<?BEGININC p3-payload.abnf-appendix ?>
2671<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2672<figure>
2673<artwork type="abnf" name="p3-payload.parsed-abnf">
2674<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2675<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2676<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2677 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2678 qvalue ] ] )
2679<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2680<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2681 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2682<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2683<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2684 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2685 ] )
2686<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2687 OWS media-range [ accept-params ] ] ) ]
2688
2689<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2690<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2691 content-coding ] )
2692<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2693<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2694 language-tag ] )
2695<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2696<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2697<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2698<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2699<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2700<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2701<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2702<x:ref>Content-Type-v</x:ref> = media-type
2703
2704<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2705
2706<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2707
2708<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2709<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2710
2711<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2712
2713<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2714<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2715<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2716<x:ref>attribute</x:ref> = token
2717
2718<x:ref>charset</x:ref> = token
2719<x:ref>codings</x:ref> = ( content-coding / "*" )
2720<x:ref>content-coding</x:ref> = token
2721
2722<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2723<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2724
2725<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2726 ";" OWS parameter )
2727<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2728
2729<x:ref>parameter</x:ref> = attribute "=" value
2730<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2731
2732<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2733
2734<x:ref>subtype</x:ref> = token
2735
2736<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2737<x:ref>type</x:ref> = token
2738
2739<x:ref>value</x:ref> = word
2740
2741<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2742</artwork>
2743</figure>
2744<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2745; Accept defined but not used
2746; Accept-Charset defined but not used
2747; Accept-Encoding defined but not used
2748; Accept-Language defined but not used
2749; Content-Encoding defined but not used
2750; Content-Language defined but not used
2751; Content-Length defined but not used
2752; Content-Location defined but not used
2753; Content-MD5 defined but not used
2754; Content-Range defined but not used
2755; Content-Type defined but not used
2756; Expires defined but not used
2757; Last-Modified defined but not used
2758; MIME-Version defined but not used
2759</artwork></figure></section>
2760<?ENDINC p3-payload.abnf-appendix ?>
2761
2762<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2763
2764<section title="Since RFC 2616">
2765<t>
2766  Extracted relevant partitions from <xref target="RFC2616"/>.
2767</t>
2768</section>
2769
2770<section title="Since draft-ietf-httpbis-p3-payload-00">
2771<t>
2772  Closed issues:
2773  <list style="symbols"> 
2774    <t>
2775      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2776      "Media Type Registrations"
2777      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2778    </t>
2779    <t>
2780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2781      "Clarification regarding quoting of charset values"
2782      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2783    </t>
2784    <t>
2785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2786      "Remove 'identity' token references"
2787      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2788    </t>
2789    <t>
2790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2791      "Accept-Encoding BNF"
2792    </t>
2793    <t>
2794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2795      "Normative and Informative references"
2796    </t>
2797    <t>
2798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2799      "RFC1700 references"
2800    </t>
2801    <t>
2802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2803      "Updating to RFC4288"
2804    </t>
2805    <t>
2806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2807      "Informative references"
2808    </t>
2809    <t>
2810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2811      "ISO-8859-1 Reference"
2812    </t>
2813    <t>
2814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2815      "Encoding References Normative"
2816    </t>
2817    <t>
2818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2819      "Normative up-to-date references"
2820    </t>
2821  </list>
2822</t>
2823</section>
2824
2825<section title="Since draft-ietf-httpbis-p3-payload-01">
2826<t>
2827  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2828  <list style="symbols"> 
2829    <t>
2830      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2831    </t>
2832  </list>
2833</t>
2834</section>
2835
2836<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2837<t>
2838  Closed issues:
2839  <list style="symbols"> 
2840    <t>
2841      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2842      "Quoting Charsets"
2843    </t>
2844    <t>
2845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2846      "Classification for Allow header"
2847    </t>
2848    <t>
2849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2850      "missing default for qvalue in description of Accept-Encoding"
2851    </t>
2852  </list>
2853</t>
2854<t>
2855  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2856  <list style="symbols"> 
2857    <t>
2858      Reference RFC 3984, and update header field registrations for headers defined
2859      in this document.
2860    </t>
2861  </list>
2862</t>
2863</section>
2864
2865<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2866<t>
2867  Closed issues:
2868  <list style="symbols"> 
2869    <t>
2870      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2871      "Quoting Charsets"
2872    </t>
2873    <t>
2874      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2875      "language tag matching (Accept-Language) vs RFC4647"
2876    </t>
2877    <t>
2878      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2879      "RFC 1806 has been replaced by RFC2183"
2880    </t>
2881  </list>
2882</t>
2883<t>
2884  Other changes:
2885  <list style="symbols"> 
2886    <t>
2887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2888      "Encoding References Normative" &mdash; rephrase the annotation and reference
2889      <xref target="BCP97"/>.
2890    </t>
2891  </list>
2892</t>
2893 </section>
2894
2895<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2896<t>
2897  Closed issues:
2898  <list style="symbols"> 
2899    <t>
2900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2901      "RFC 2822 is updated by RFC 5322"
2902    </t>
2903  </list>
2904</t>
2905<t>
2906  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2907  <list style="symbols"> 
2908    <t>
2909      Use "/" instead of "|" for alternatives.
2910    </t>
2911    <t>
2912      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2913      whitespace ("OWS") and required whitespace ("RWS").
2914    </t>
2915    <t>
2916      Rewrite ABNFs to spell out whitespace rules, factor out
2917      header field value format definitions.
2918    </t>
2919  </list>
2920</t>
2921</section>
2922
2923<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2924<t>
2925  Closed issues:
2926  <list style="symbols"> 
2927    <t>
2928      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2929      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2930    </t>
2931  </list>
2932</t>
2933<t>
2934  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2935  <list style="symbols"> 
2936    <t>
2937      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2938    </t>
2939  </list>
2940</t>
2941<t>
2942  Other changes:
2943  <list style="symbols"> 
2944    <t>
2945      Move definition of quality values into Part 1.
2946    </t>
2947  </list>
2948</t>
2949</section>
2950
2951<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2952<t>
2953  Closed issues:
2954  <list style="symbols"> 
2955    <t>
2956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2957      "Content-Location isn't special"
2958    </t>
2959    <t>
2960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2961      "Content Sniffing"
2962    </t>
2963  </list>
2964</t>
2965</section>
2966
2967<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2968<t>
2969  Closed issues:
2970  <list style="symbols"> 
2971    <t>
2972      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2973      "Updated reference for language tags"
2974    </t>
2975    <t>
2976      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2977      "Clarify rules for determining what entities a response carries"
2978    </t>
2979    <t>
2980      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2981      "Content-Location base-setting problems"
2982    </t>
2983    <t>
2984      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2985      "Content Sniffing"
2986    </t>
2987    <t>
2988      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2989      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2990    </t>
2991    <t>
2992      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2993      "move definitions of gzip/deflate/compress to part 1"
2994    </t>
2995  </list>
2996</t>
2997<t>
2998  Partly resolved issues:
2999  <list style="symbols"> 
3000    <t>
3001      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3002      "update IANA requirements wrt Transfer-Coding values" (add the
3003      IANA Considerations subsection)
3004    </t>
3005    <t>
3006      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3007      "update IANA requirements wrt Content-Coding values" (add the
3008      IANA Considerations subsection)
3009    </t>
3010  </list>
3011</t>
3012</section>
3013
3014<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3015<t>
3016  Closed issues:
3017  <list style="symbols"> 
3018    <t>
3019      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3020      "Content Negotiation for media types"
3021    </t>
3022    <t>
3023      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3024      "Accept-Language: which RFC4647 filtering?"
3025    </t>
3026  </list>
3027</t>
3028</section>
3029
3030<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3031<t>
3032  Closed issues:
3033  <list style="symbols"> 
3034    <t>
3035      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
3036      "MIME-Version not listed in P1, general header fields"
3037    </t>
3038    <t>
3039      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
3040      "IANA registry for content/transfer encodings"
3041    </t>
3042    <t>
3043      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3044      "Content Sniffing"
3045    </t>
3046    <t>
3047      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
3048      "use of term "word" when talking about header structure"
3049    </t>
3050  </list>
3051</t>
3052<t>
3053  Partly resolved issues:
3054  <list style="symbols"> 
3055    <t>
3056      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
3057      "Term for the requested resource's URI"
3058    </t>
3059  </list>
3060</t>
3061</section>
3062
3063<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
3064<t>
3065  Closed issues:
3066  <list style="symbols"> 
3067    <t>
3068      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
3069      "Clarify 'Requested Variant'"
3070    </t>
3071    <t>
3072      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3073      "Content-Location isn't special"
3074    </t>
3075    <t>
3076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
3077      "Delimiting messages with multipart/byteranges"
3078    </t>
3079    <t>
3080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
3081      "Clarify entity / representation / variant terminology"
3082    </t>
3083    <t>
3084      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
3085      "confusing req. language for Content-Location"
3086    </t>
3087    <t>
3088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
3089      "Content-Location on 304 responses"
3090    </t>
3091    <t>
3092      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
3093      "'requested resource' in content-encoding definition"
3094    </t>
3095    <t>
3096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
3097      "consider removing the 'changes from 2068' sections"
3098    </t>
3099  </list>
3100</t>
3101<t>
3102  Partly resolved issues:
3103  <list style="symbols"> 
3104    <t>
3105      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
3106      "Content-MD5 and partial responses"
3107    </t>
3108  </list>
3109</t>
3110</section>
3111
3112<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
3113<t>
3114  Closed issues:
3115  <list style="symbols"> 
3116    <t>
3117      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
3118      "Factor out Content-Disposition"
3119    </t>
3120  </list>
3121</t>
3122</section>
3123
3124<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
3125<t>
3126  None yet.
3127</t>
3128</section>
3129
3130</section>
3131
3132</back>
3133</rfc>
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