source: draft-ietf-httpbis/latest/p3-payload.xml @ 1244

Last change on this file since 1244 was 1244, checked in by julian.reschke@…, 9 years ago

use a real parameter in Accept param example (see #281)

  • Property svn:eol-style set to native
File size: 125.0 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 "March">
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.13"/>.
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="partial-URI"/>
321  <x:anchor-alias value="qvalue"/>
322<t>
323  The ABNF rules below are defined in other parts:
324</t>
325<figure><!--Part1--><artwork type="abnf2616">
326  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
327  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
328  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
329</artwork></figure>
330</section>
331
332</section>
333
334</section>
335
336<section title="Protocol Parameters" anchor="protocol.parameters">
337
338<section title="Character Encodings (charset)" anchor="character.sets">
339<t>
340   HTTP uses charset names to indicate the character encoding of a
341   textual representation.
342</t>
343<t anchor="rule.charset">
344  <x:anchor-alias value="charset"/>
345   A character encoding is identified by a case-insensitive token. The
346   complete set of tokens is defined by the IANA Character Set registry
347   (<eref target="http://www.iana.org/assignments/character-sets"/>).
348</t>
349<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
350  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
351</artwork></figure>
352<t>
353   Although HTTP allows an arbitrary token to be used as a charset
354   value, any token that has a predefined value within the IANA
355   Character Set registry &MUST; represent the character encoding defined
356   by that registry. Applications &SHOULD; limit their use of character
357   encodings to those defined within the IANA registry.
358</t>
359<t>
360   HTTP uses charset in two contexts: within an Accept-Charset request
361   header field (in which the charset value is an unquoted token) and as the
362   value of a parameter in a Content-Type header field (within a request or
363   response), in which case the parameter value of the charset parameter
364   can be quoted.
365</t>
366<t>
367   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
368   <xref target="RFC2277"/>.
369</t>
370</section>
371
372<section title="Content Codings" anchor="content.codings">
373  <x:anchor-alias value="content-coding"/>
374<t>
375   Content coding values indicate an encoding transformation that has
376   been or can be applied to a representation. Content codings are primarily
377   used to allow a representation to be compressed or otherwise usefully
378   transformed without losing the identity of its underlying media type
379   and without loss of information. Frequently, the representation is stored in
380   coded form, transmitted directly, and only decoded by the recipient.
381</t>
382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
383  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
384</artwork></figure>
385<t>
386   All content-coding values are case-insensitive. HTTP/1.1 uses
387   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
388   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
389   describes the content-coding, what is more important is that it
390   indicates what decoding mechanism will be required to remove the
391   encoding.
392</t>
393<t>
394   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
395  <list>
396    <t>
397      See &compress-coding;.
398    </t>
399  </list>
400</t>
401<t>
402   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
403  <list>
404    <t>
405      See &deflate-coding;.
406    </t>
407  </list>
408</t>
409<t>
410   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
411  <list>
412    <t>
413      See &gzip-coding;.
414    </t>
415  </list>
416</t>
417<t>
418   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
419  <list><t>
420        The default (identity) encoding; the use of no transformation
421        whatsoever. This content-coding is used only in the Accept-Encoding
422        header field, and &SHOULD-NOT;  be used in the Content-Encoding
423        header field.
424  </t></list>
425</t>
426
427<section title="Content Coding Registry" anchor="content.coding.registry">
428<t>
429   The HTTP Content Coding Registry defines the name space for the content
430   coding names.
431</t>
432<t>
433   Registrations &MUST; include the following fields:
434   <list style="symbols">
435     <t>Name</t>
436     <t>Description</t>
437     <t>Pointer to specification text</t>
438   </list>
439</t>
440<t>
441   Names of content codings &MUST-NOT; overlap with names of transfer codings
442   (&transfer-codings;), unless the encoding transformation is identical (as it
443   is the case for the compression codings defined in
444   &compression-codings;).
445</t>
446<t>
447   Values to be added to this name space require a specification
448   (see "Specification Required" in
449   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
450   conform to the purpose of content coding defined in this section.
451</t>
452<t>
453   The registry itself is maintained at
454   <eref target="http://www.iana.org/assignments/http-parameters"/>.
455</t>
456</section>
457
458</section>
459
460<section title="Media Types" anchor="media.types">
461  <x:anchor-alias value="media-type"/>
462  <x:anchor-alias value="type"/>
463  <x:anchor-alias value="subtype"/>
464<t>
465   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
466   and Accept (<xref target="header.accept"/>) header fields in order to provide
467   open and extensible data typing and type negotiation.
468</t>
469<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"/>
470  <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> )
471  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
472  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
473</artwork></figure>
474<t anchor="rule.parameter">
475  <x:anchor-alias value="attribute"/>
476  <x:anchor-alias value="parameter"/>
477  <x:anchor-alias value="value"/>
478   The type/subtype &MAY; be followed by parameters in the form of
479   attribute/value pairs.
480</t>
481<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"/>
482  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
483  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
484  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
485</artwork></figure>
486<t>
487   The type, subtype, and parameter attribute names are case-insensitive.
488   Parameter values might or might not be case-sensitive, depending on the
489   semantics of the parameter name.  The presence or absence of a parameter might
490   be significant to the processing of a media-type, depending on its
491   definition within the media type registry.
492</t>
493<t>
494   A parameter value that matches the <x:ref>token</x:ref> production can be
495   transmitted as either a token or within a quoted-string. The quoted and
496   unquoted values are equivalent.
497</t>
498<t>
499   Note that some older HTTP applications do not recognize media type
500   parameters. When sending data to older HTTP applications,
501   implementations &SHOULD; only use media type parameters when they are
502   required by that type/subtype definition.
503</t>
504<t>
505   Media-type values are registered with the Internet Assigned Number
506   Authority (IANA). The media type registration process is
507   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
508   discouraged.
509</t>
510
511<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
512<t>
513   Internet media types are registered with a canonical form. A
514   representation transferred via HTTP messages &MUST; be in the
515   appropriate canonical form prior to its transmission except for
516   "text" types, as defined in the next paragraph.
517</t>
518<t>
519   When in canonical form, media subtypes of the "text" type use CRLF as
520   the text line break. HTTP relaxes this requirement and allows the
521   transport of text media with plain CR or LF alone representing a line
522   break when it is done consistently for an entire representation. HTTP
523   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
524   a line break in text media received via HTTP. In
525   addition, if the text is in a character encoding that does not
526   use octets 13 and 10 for CR and LF respectively, as is the case for
527   some multi-byte character encodings, HTTP allows the use of whatever octet
528   sequences are defined by that character encoding to represent the
529   equivalent of CR and LF for line breaks. This flexibility regarding
530   line breaks applies only to text media in the payload body; a bare CR
531   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
532   structures (such as header fields and multipart boundaries).
533</t>
534<t>
535   If a representation is encoded with a content-coding, the underlying
536   data &MUST; be in a form defined above prior to being encoded.
537</t>
538</section>
539
540<section title="Multipart Types" anchor="multipart.types">
541<t>
542   MIME provides for a number of "multipart" types &mdash; encapsulations of
543   one or more representations within a single message-body. All multipart
544   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
545   and &MUST; include a boundary parameter as part of the media type
546   value. The message body is itself a protocol element and &MUST;
547   therefore use only CRLF to represent line breaks between body-parts.
548</t>
549<t>
550   In general, HTTP treats a multipart message-body no differently than
551   any other media type: strictly as payload.  HTTP does not use the
552   multipart boundary as an indicator of message-body length.
553   <!-- jre: re-insert removed text pointing to caching? -->
554   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
555   behavior as a MIME user agent would upon receipt of a multipart type.
556   The MIME header fields within each body-part of a multipart message-body
557   do not have any significance to HTTP beyond that defined by
558   their MIME semantics.
559</t>
560<t>
561   If an application receives an unrecognized multipart subtype, the
562   application &MUST; treat it as being equivalent to "multipart/mixed".
563</t>
564<x:note>
565  <t>
566    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
567    for carrying form data suitable for processing via the POST
568    request method, as described in <xref target="RFC2388"/>.
569  </t>
570</x:note>
571</section>
572</section>
573
574<section title="Language Tags" anchor="language.tags">
575  <x:anchor-alias value="language-tag"/>
576<t>
577   A language tag, as defined in <xref target="RFC5646"/>, identifies a
578   natural language spoken, written, or otherwise conveyed by human beings for
579   communication of information to other human beings. Computer languages are
580   explicitly excluded. HTTP uses language tags within the Accept-Language and
581   Content-Language fields.
582</t>
583<t>
584   In summary, a language tag is composed of one or more parts: A primary
585   language subtag followed by a possibly empty series of subtags:
586</t>
587<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
588  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
589</artwork></figure>
590<t>
591   White space is not allowed within the tag and all tags are case-insensitive.
592   The name space of language subtags is administered by the IANA (see
593   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
594</t>
595<figure>
596  <preamble>Example tags include:</preamble>
597<artwork type="example">
598  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
599</artwork>
600</figure>
601<t>
602   See <xref target="RFC5646"/> for further information.
603</t>
604</section>
605</section>
606
607<section title="Payload" anchor="payload">
608<t>
609   HTTP messages &MAY; transfer a payload if not otherwise restricted by
610   the request method or response status code.  The payload consists of
611   metadata, in the form of header fields, and data, in the form of the
612   sequence of octets in the message-body after any transfer-coding has
613   been decoded.
614</t>
615<iref item="payload"/>
616<t>   
617   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
618   representation of some resource.  We use separate terms for payload
619   and representation because some messages contain only the associated
620   representation's header fields (e.g., responses to HEAD) or only some
621   part(s) of the representation (e.g., the 206 status code).
622</t>
623<section title="Payload Header Fields" anchor="payload.header.fields">
624  <x:anchor-alias value="payload-header"/>
625<t>
626   HTTP header fields that specifically define the payload, rather than the
627   associated representation, are referred to as "payload header fields".
628   The following payload header fields are defined by HTTP/1.1:
629</t>
630<texttable align="left">
631  <ttcol>Header Field Name</ttcol>
632  <ttcol>Defined in...</ttcol>
633
634  <c>Content-Length</c> <c>&header-content-length;</c>
635  <c>Content-MD5</c> <c><xref target="header.content-md5"/></c>
636  <c>Content-Range</c> <c>&header-content-range;</c>
637</texttable>
638</section>
639
640<section title="Payload Body" anchor="payload.body">
641  <x:anchor-alias value="payload-body"/>
642<t>
643   A payload body is only present in a message when a message-body is
644   present, as described in &message-body;. The payload body is obtained
645   from the message-body by decoding any Transfer-Encoding that might
646   have been applied to ensure safe and proper transfer of the message.
647</t>
648</section>
649</section>
650
651<section title="Representation" anchor="representation">
652<iref item="representation"/>
653<t>
654   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
655   communicated from one party to another.  A resource representation
656   is information that reflects the state of that resource, as observed
657   at some point in the past (e.g., in a response to GET) or to be
658   desired at some point in the future (e.g., in a PUT request).
659</t>
660<t>
661   Most, but not all, representations transferred via HTTP are intended
662   to be a representation of the target resource (the resource identified
663   by the effective request URI).  The precise semantics of a representation
664   are determined by the type of message (request or response), the request
665   method, the response status code, and the representation metadata.
666   For example, the above semantic is true for the representation in any
667   200 (OK) response to GET and for the representation in any PUT request.
668   A 200 response to PUT, in contrast, contains either a representation
669   that describes the successful action or a representation of the target
670   resource, with the latter indicated by a Content-Location header field
671   with the same value as the effective request URI.  Likewise, response
672   messages with an error status code usually contain a representation that
673   describes the error and what next steps are suggested for resolving it.
674</t>
675
676<section title="Representation Header Fields" anchor="representation.header.fields">
677  <x:anchor-alias value="representation-header"/>
678<t>
679   Representation header fields define metadata about the representation data
680   enclosed in the message-body or, if no message-body is present, about
681   the representation that would have been transferred in a 200 response
682   to a simultaneous GET request with the same effective request URI.
683</t>
684<t>
685   The following header fields are defined as representation metadata:
686</t>
687<texttable align="left">
688  <ttcol>Header Field Name</ttcol>
689  <ttcol>Defined in...</ttcol>
690
691  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
692  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
693  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
694  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
695  <c>Expires</c> <c>&header-expires;</c>
696  <c>Last-Modified</c> <c>&header-last-modified;</c>
697</texttable>
698</section>
699
700<section title="Representation Data" anchor="representation.data">
701  <x:anchor-alias value="representation-data"/>
702<t>
703   The representation body associated with an HTTP message is
704   either provided as the payload body of the message or
705   referred to by the message semantics and the effective request
706   URI.  The representation data is in a format and encoding defined by
707   the representation metadata header fields.
708</t>
709<t>
710   The data type of the representation data
711   is determined via the header fields Content-Type and Content-Encoding.
712   These define a two-layer, ordered encoding model:
713</t>
714<figure><artwork type="example">
715  representation-data := Content-Encoding( Content-Type( bits ) )
716</artwork></figure>
717<t>
718   Content-Type specifies the media type of the underlying data, which
719   defines both the data format and how that data &SHOULD; be processed
720   by the recipient (within the scope of the request method semantics).
721   Any HTTP/1.1 message containing a payload body &SHOULD; include a
722   Content-Type header field defining the media type of the associated
723   representation unless that metadata is unknown to the sender.
724   If the Content-Type header field is not present, it indicates that
725   the sender does not know the media type of the representation;
726   recipients &MAY; either assume that the media type is
727   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
728   or examine the content to determine its type.
729</t>
730<t>
731   In practice, resource owners do not always properly configure their origin
732   server to provide the correct Content-Type for a given representation,
733   with the result that some clients will examine a response body's content
734   and override the specified type.
735   Clients that do so risk drawing incorrect conclusions, which might expose
736   additional security risks (e.g., "privilege escalation").  Furthermore,
737   it is impossible to determine the sender's intent by examining the data
738   format: many data formats match multiple media types that differ only in
739   processing semantics.  Implementers are encouraged to provide a means of
740   disabling such "content sniffing" when it is used.
741</t>
742<t>
743   Content-Encoding is used to indicate any additional content
744   codings applied to the data, usually for the purpose of data
745   compression, that are a property of the representation.  If
746   Content-Encoding is not present, then there is no additional
747   encoding beyond that defined by the Content-Type.
748</t>
749</section>
750</section>
751
752<section title="Content Negotiation" anchor="content.negotiation">
753<t>
754   HTTP responses include a representation which contains information for
755   interpretation, whether by a human user or for further processing.
756   Often, the server has different ways of representing the
757   same information; for example, in different formats, languages,
758   or using different character encodings.
759</t>
760<t>
761   HTTP clients and their users might have different or variable
762   capabilities, characteristics or preferences which would influence
763   which representation, among those available from the server,
764   would be best for the server to deliver. For this reason, HTTP
765   provides mechanisms for "content negotiation" &mdash; a process of
766   allowing selection of a representation of a given resource,
767   when more than one is available.
768</t>
769<t>
770   This specification defines two patterns of content negotiation;
771   "server-driven", where the server selects the representation based
772   upon the client's stated preferences, and "agent-driven" negotiation,
773   where the server provides a list of representations for the client to
774   choose from, based upon their metadata. In addition,  there are
775   other patterns: some applications use an "active content" pattern,
776   where the server returns active content which runs on the client
777   and, based on client available parameters, selects additional
778   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
779   has also been proposed.
780</t>
781<t>
782   These patterns are all widely used, and have trade-offs in applicability
783   and practicality. In particular, when the number of preferences or
784   capabilities to be expressed by a client are large (such as when many
785   different formats are supported by a user-agent), server-driven
786   negotiation becomes unwieldy, and might not be appropriate. Conversely,
787   when the number of representations to choose from is very large,
788   agent-driven negotiation might not be appropriate.
789</t>
790<t>
791   Note that in all cases, the supplier of representations has the
792   responsibility for determining which representations might be
793   considered to be the "same information".
794</t>
795
796<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
797<t>
798   If the selection of the best representation for a response is made by
799   an algorithm located at the server, it is called server-driven
800   negotiation. Selection is based on the available representations of
801   the response (the dimensions over which it can vary; e.g., language,
802   content-coding, etc.) and the contents of particular header fields in
803   the request message or on other information pertaining to the request
804   (such as the network address of the client).
805</t>
806<t>
807   Server-driven negotiation is advantageous when the algorithm for
808   selecting from among the available representations is difficult to
809   describe to the user agent, or when the server desires to send its
810   "best guess" to the client along with the first response (hoping to
811   avoid the round-trip delay of a subsequent request if the "best
812   guess" is good enough for the user). In order to improve the server's
813   guess, the user agent &MAY; include request header fields (Accept,
814   Accept-Language, Accept-Encoding, etc.) which describe its
815   preferences for such a response.
816</t>
817<t>
818   Server-driven negotiation has disadvantages:
819  <list style="numbers">
820    <t>
821         It is impossible for the server to accurately determine what
822         might be "best" for any given user, since that would require
823         complete knowledge of both the capabilities of the user agent
824         and the intended use for the response (e.g., does the user want
825         to view it on screen or print it on paper?).
826    </t>
827    <t>
828         Having the user agent describe its capabilities in every
829         request can be both very inefficient (given that only a small
830         percentage of responses have multiple representations) and a
831         potential violation of the user's privacy.
832    </t>
833    <t>
834         It complicates the implementation of an origin server and the
835         algorithms for generating responses to a request.
836    </t>
837    <t>
838         It might limit a public cache's ability to use the same response
839         for multiple user's requests.
840    </t>
841  </list>
842</t>
843<t>
844   HTTP/1.1 includes the following header fields for enabling
845   server-driven negotiation through description of user agent
846   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
847   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
848   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
849   However, an origin server is not limited to these dimensions and &MAY; vary
850   the response based on any aspect of the request, including aspects
851   of the connection (e.g., IP address) or information within extension
852   header fields not defined by this specification.
853</t>
854<x:note>
855  <t>
856    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
857    because new clients might not be recognized.
858  </t>
859</x:note>
860<t>
861   The Vary header field (&header-vary;) can be used to express the parameters the
862   server uses to select a representation that is subject to server-driven
863   negotiation.
864</t>
865</section>
866
867<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
868<t>
869   With agent-driven negotiation, selection of the best representation
870   for a response is performed by the user agent after receiving an
871   initial response from the origin server. Selection is based on a list
872   of the available representations of the response included within the
873   header fields or body of the initial response, with each
874   representation identified by its own URI. Selection from among the
875   representations can be performed automatically (if the user agent is
876   capable of doing so) or manually by the user selecting from a
877   generated (possibly hypertext) menu.
878</t>
879<t>
880   Agent-driven negotiation is advantageous when the response would vary
881   over commonly-used dimensions (such as type, language, or encoding),
882   when the origin server is unable to determine a user agent's
883   capabilities from examining the request, and generally when public
884   caches are used to distribute server load and reduce network usage.
885</t>
886<t>
887   Agent-driven negotiation suffers from the disadvantage of needing a
888   second request to obtain the best alternate representation. This
889   second request is only efficient when caching is used. In addition,
890   this specification does not define any mechanism for supporting
891   automatic selection, though it also does not prevent any such
892   mechanism from being developed as an extension and used within
893   HTTP/1.1.
894</t>
895<t>
896   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
897   status codes for enabling agent-driven negotiation when the server is
898   unwilling or unable to provide a varying response using server-driven
899   negotiation.
900</t>
901</section>
902</section>
903
904<section title="Header Field Definitions" anchor="header.fields">
905<t>
906   This section defines the syntax and semantics of HTTP/1.1 header fields
907   related to the payload of messages.
908</t>
909
910<section title="Accept" anchor="header.accept">
911  <iref primary="true" item="Accept header field" x:for-anchor=""/>
912  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
913  <x:anchor-alias value="Accept"/>
914  <x:anchor-alias value="accept-ext"/>
915  <x:anchor-alias value="accept-params"/>
916  <x:anchor-alias value="media-range"/>
917<t>
918   The "Accept" header field can be used by user agents to specify
919   response media types that are acceptable. Accept header fields can be used to
920   indicate that the request is specifically limited to a small set of desired
921   types, as in the case of a request for an in-line image.
922</t>
923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
924  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
925 
926  <x:ref>media-range</x:ref>    = ( "*/*"
927                   / ( <x:ref>type</x:ref> "/" "*" )
928                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
929                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
930  <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> )
931  <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> ]
932</artwork></figure>
933<t>
934   The asterisk "*" character is used to group media types into ranges,
935   with "*/*" indicating all media types and "type/*" indicating all
936   subtypes of that type. The media-range &MAY; include media type
937   parameters that are applicable to that range.
938</t>
939<t>
940   Each media-range &MAY; be followed by one or more accept-params,
941   beginning with the "q" parameter for indicating a relative quality
942   factor. The first "q" parameter (if any) separates the media-range
943   parameter(s) from the accept-params. Quality factors allow the user
944   or user agent to indicate the relative degree of preference for that
945   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
946   default value is q=1.
947</t>
948<x:note>
949  <t>
950    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
951    parameters from Accept extension parameters is due to historical
952    practice. Although this prevents any media type parameter named
953    "q" from being used with a media range, such an event is believed
954    to be unlikely given the lack of any "q" parameters in the IANA
955    media type registry and the rare usage of any media type
956    parameters in Accept. Future media types are discouraged from
957    registering any parameter named "q".
958  </t>
959</x:note>
960<t>
961   The example
962</t>
963<figure><artwork type="example">
964  Accept: audio/*; q=0.2, audio/basic
965</artwork></figure>
966<t>
967   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
968   type if it is the best available after an 80% mark-down in quality".
969</t>
970<t>
971   If no Accept header field is present, then it is assumed that the
972   client accepts all media types. If an Accept header field is present,
973   and if the server cannot send a response which is acceptable
974   according to the combined Accept field value, then the server &SHOULD;
975   send a 406 (Not Acceptable) response.
976</t>
977<t>
978   A more elaborate example is
979</t>
980<figure><artwork type="example">
981  Accept: text/plain; q=0.5, text/html,
982          text/x-dvi; q=0.8, text/x-c
983</artwork></figure>
984<t>
985   Verbally, this would be interpreted as "text/html and text/x-c are
986   the preferred media types, but if they do not exist, then send the
987   text/x-dvi representation, and if that does not exist, send the text/plain
988   representation".
989</t>
990<t>
991   Media ranges can be overridden by more specific media ranges or
992   specific media types. If more than one media range applies to a given
993   type, the most specific reference has precedence. For example,
994</t>
995<figure><artwork type="example">
996  Accept: text/*, text/plain, text/plain;format=flowed, */*
997</artwork></figure>
998<t>
999   have the following precedence:
1000   <list style="numbers">
1001    <t>text/plain;format=flowed</t>
1002    <t>text/plain</t>
1003    <t>text/*</t>
1004    <t>*/*</t>
1005   </list>
1006</t>
1007<t>
1008   The media type quality factor associated with a given type is
1009   determined by finding the media range with the highest precedence
1010   which matches that type. For example,
1011</t>
1012<figure><artwork type="example">
1013  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1014          text/html;level=2;q=0.4, */*;q=0.5
1015</artwork></figure>
1016<t>
1017   would cause the following values to be associated:
1018</t>
1019<texttable align="left">
1020  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1021  <c>text/html;level=1</c>    <c>1</c>
1022  <c>text/html</c>            <c>0.7</c>
1023  <c>text/plain</c>           <c>0.3</c>
1024  <c>image/jpeg</c>           <c>0.5</c>
1025  <c>text/html;level=2</c>    <c>0.4</c>
1026  <c>text/html;level=3</c>    <c>0.7</c>
1027</texttable>
1028<t>
1029      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1030      values for certain media ranges. However, unless the user agent is
1031      a closed system which cannot interact with other rendering agents,
1032      this default set ought to be configurable by the user.
1033</t>
1034</section>
1035
1036<section title="Accept-Charset" anchor="header.accept-charset">
1037  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
1038  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
1039  <x:anchor-alias value="Accept-Charset"/>
1040<t>
1041   The "Accept-Charset" header field can be used by user agents to
1042   indicate what character encodings are acceptable in a response
1043   payload. This field allows
1044   clients capable of understanding more comprehensive or special-purpose
1045   character encodings to signal that capability to a server which is capable of
1046   representing documents in those character encodings.
1047</t>
1048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
1049  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1050                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1051</artwork></figure>
1052<t>
1053   Character encoding values (a.k.a., charsets) are described in
1054   <xref target="character.sets"/>. Each charset &MAY; be given an
1055   associated quality value which represents the user's preference
1056   for that charset. The default value is q=1. An example is
1057</t>
1058<figure><artwork type="example">
1059  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1060</artwork></figure>
1061<t>
1062   The special value "*", if present in the Accept-Charset field,
1063   matches every character encoding which is not mentioned elsewhere in the
1064   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
1065   all character encodings not explicitly mentioned get a quality value of 0.
1066</t>
1067<t>
1068   If no Accept-Charset header field is present, the default is that any
1069   character encoding is acceptable. If an Accept-Charset header field is present,
1070   and if the server cannot send a response which is acceptable
1071   according to the Accept-Charset header field, then the server &SHOULD; send
1072   an error response with the 406 (Not Acceptable) status code, though
1073   the sending of an unacceptable response is also allowed.
1074</t>
1075</section>
1076
1077<section title="Accept-Encoding" anchor="header.accept-encoding">
1078  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
1079  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
1080  <x:anchor-alias value="Accept-Encoding"/>
1081  <x:anchor-alias value="codings"/>
1082<t>
1083   The "Accept-Encoding" header field can be used by user agents to
1084   indicate what response content-codings (<xref target="content.codings"/>)
1085   are acceptable in the response.
1086</t>
1087<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
1088  <x:ref>Accept-Encoding</x:ref>  = #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1089  <x:ref>codings</x:ref>          = ( <x:ref>content-coding</x:ref> / "*" )
1090</artwork></figure>
1091<t>
1092   Each codings value &MAY; be given an associated quality value which
1093   represents the preference for that encoding. The default value is q=1.
1094</t>
1095<t>
1096   Examples of its use are:
1097</t>
1098<figure><artwork type="example">
1099  Accept-Encoding: compress, gzip
1100  Accept-Encoding:
1101  Accept-Encoding: *
1102  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1103  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1104</artwork></figure>
1105<t>
1106   A server tests whether a content-coding is acceptable, according to
1107   an Accept-Encoding field, using these rules:
1108  <list style="numbers">
1109      <t>If the content-coding is one of the content-codings listed in
1110         the Accept-Encoding field, then it is acceptable, unless it is
1111         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1112         qvalue of 0 means "not acceptable".)</t>
1113
1114      <t>The special "*" symbol in an Accept-Encoding field matches any
1115         available content-coding not explicitly listed in the header
1116         field.</t>
1117
1118      <t>If multiple content-codings are acceptable, then the acceptable
1119         content-coding with the highest non-zero qvalue is preferred.</t>
1120
1121      <t>The "identity" content-coding is always acceptable, unless
1122         specifically refused because the Accept-Encoding field includes
1123         "identity;q=0", or because the field includes "*;q=0" and does
1124         not explicitly include the "identity" content-coding. If the
1125         Accept-Encoding field-value is empty, then only the "identity"
1126         encoding is acceptable.</t>
1127  </list>
1128</t>
1129<t>
1130   If an Accept-Encoding field is present in a request, and if the
1131   server cannot send a response which is acceptable according to the
1132   Accept-Encoding header field, then the server &SHOULD; send an error response
1133   with the 406 (Not Acceptable) status code.
1134</t>
1135<t>
1136   If no Accept-Encoding field is present in a request, the server &MAY;
1137   assume that the client will accept any content coding. In this case,
1138   if "identity" is one of the available content-codings, then the
1139   server &SHOULD; use the "identity" content-coding, unless it has
1140   additional information that a different content-coding is meaningful
1141   to the client.
1142</t>
1143<x:note>
1144  <t>
1145    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1146    and if the "identity" content-coding is unavailable, then
1147    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1148    "gzip" and "compress") are preferred; some older clients
1149    improperly display messages sent with other content-codings.  The
1150    server might also make this decision based on information about
1151    the particular user-agent or client.
1152  </t>
1153</x:note>
1154<x:note>
1155  <t>
1156    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1157    associated with content-codings. This means that qvalues will not
1158    work and are not permitted with x-gzip or x-compress.
1159  </t>
1160</x:note>
1161</section>
1162
1163<section title="Accept-Language" anchor="header.accept-language">
1164  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
1165  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
1166  <x:anchor-alias value="Accept-Language"/>
1167  <x:anchor-alias value="language-range"/>
1168<t>
1169   The "Accept-Language" header field can be used by user agents to
1170   indicate the set of natural languages that are preferred in the response.
1171   Language tags are defined in <xref target="language.tags"/>.
1172</t>
1173<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1174  <x:ref>Accept-Language</x:ref> =
1175                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1176  <x:ref>language-range</x:ref>  =
1177            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1178</artwork></figure>
1179<t>
1180   Each language-range can be given an associated quality value which
1181   represents an estimate of the user's preference for the languages
1182   specified by that range. The quality value defaults to "q=1". For
1183   example,
1184</t>
1185<figure><artwork type="example">
1186  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1187</artwork></figure>
1188<t>
1189   would mean: "I prefer Danish, but will accept British English and
1190   other types of English".
1191   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1192</t>
1193<t>
1194   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1195   several matching schemes. Implementations can offer the most appropriate
1196   matching scheme for their requirements.
1197</t>
1198<x:note>
1199  <t>
1200    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1201    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1202    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1203  </t>
1204</x:note>
1205<t>
1206   It might be contrary to the privacy expectations of the user to send
1207   an Accept-Language header field with the complete linguistic preferences of
1208   the user in every request. For a discussion of this issue, see
1209   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1210</t>
1211<t>
1212   As intelligibility is highly dependent on the individual user, it is
1213   recommended that client applications make the choice of linguistic
1214   preference available to the user. If the choice is not made
1215   available, then the Accept-Language header field &MUST-NOT; be given in
1216   the request.
1217</t>
1218<x:note>
1219  <t>
1220    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1221    the user, we remind implementors of  the fact that users are not
1222    familiar with the details of language matching as described above,
1223    and ought to be provided appropriate guidance. As an example, users
1224    might assume that on selecting "en-gb", they will be served any
1225    kind of English document if British English is not available. A
1226    user agent might suggest in such a case to add "en" to get the
1227    best matching behavior.
1228  </t>
1229</x:note>
1230</section>
1231
1232<section title="Content-Encoding" anchor="header.content-encoding">
1233  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1234  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
1235  <x:anchor-alias value="Content-Encoding"/>
1236<t>
1237   The "Content-Encoding" header field indicates what content-codings
1238   have been applied to the representation, and thus what decoding mechanisms
1239   must be applied in order to obtain the media-type referenced by the
1240   Content-Type header field. Content-Encoding is primarily used to allow a
1241   representation to be compressed without losing the identity of its underlying
1242   media type.
1243</t>
1244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1245  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
1246</artwork></figure>
1247<t>
1248   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1249</t>
1250<figure><artwork type="example">
1251  Content-Encoding: gzip
1252</artwork></figure>
1253<t>
1254   The content-coding is a characteristic of the representation.
1255   Typically, the representation body is stored with this
1256   encoding and is only decoded before rendering or analogous usage.
1257   However, a transforming proxy &MAY; modify the content-coding if the
1258   new coding is known to be acceptable to the recipient, unless the
1259   "no-transform" cache-control directive is present in the message.
1260</t>
1261<t>
1262   If the content-coding of a representation is not "identity", then the
1263   representation metadata &MUST; include a Content-Encoding header
1264   field (<xref target="header.content-encoding"/>)
1265   that lists the non-identity content-coding(s) used.
1266</t>
1267<t>
1268   If the content-coding of a representation in a request message is not
1269   acceptable to the origin server, the server &SHOULD; respond with a
1270   status code of 415 (Unsupported Media Type).
1271</t>
1272<t>
1273   If multiple encodings have been applied to a representation, the content
1274   codings &MUST; be listed in the order in which they were applied.
1275   Additional information about the encoding parameters &MAY; be provided
1276   by other header fields not defined by this specification.
1277</t>
1278</section>
1279
1280<section title="Content-Language" anchor="header.content-language">
1281  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1282  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
1283  <x:anchor-alias value="Content-Language"/>
1284<t>
1285   The "Content-Language" header field describes the natural
1286   language(s) of the intended audience for the representation. Note that this might
1287   not be equivalent to all the languages used within the representation.
1288</t>
1289<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1290  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
1291</artwork></figure>
1292<t>
1293   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1294   Content-Language is to allow a user to identify and differentiate
1295   representations according to the user's own preferred language. Thus, if the
1296   body content is intended only for a Danish-literate audience, the
1297   appropriate field is
1298</t>
1299<figure><artwork type="example">
1300  Content-Language: da
1301</artwork></figure>
1302<t>
1303   If no Content-Language is specified, the default is that the content
1304   is intended for all language audiences. This might mean that the
1305   sender does not consider it to be specific to any natural language,
1306   or that the sender does not know for which language it is intended.
1307</t>
1308<t>
1309   Multiple languages &MAY; be listed for content that is intended for
1310   multiple audiences. For example, a rendition of the "Treaty of
1311   Waitangi", presented simultaneously in the original Maori and English
1312   versions, would call for
1313</t>
1314<figure><artwork type="example">
1315  Content-Language: mi, en
1316</artwork></figure>
1317<t>
1318   However, just because multiple languages are present within a representation
1319   does not mean that it is intended for multiple linguistic audiences.
1320   An example would be a beginner's language primer, such as "A First
1321   Lesson in Latin", which is clearly intended to be used by an
1322   English-literate audience. In this case, the Content-Language would
1323   properly only include "en".
1324</t>
1325<t>
1326   Content-Language &MAY; be applied to any media type &mdash; it is not
1327   limited to textual documents.
1328</t>
1329</section>
1330
1331<section title="Content-Location" anchor="header.content-location">
1332  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1333  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
1334  <x:anchor-alias value="Content-Location"/>
1335<t>
1336   The "Content-Location" header field supplies a URI that can be used
1337   as a specific identifier for the representation in this message.
1338   In other words, if one were to perform a GET on this URI at the time
1339   of this message's generation, then a 200 response would contain the
1340   same representation that is enclosed as payload in this message.
1341</t>
1342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1343  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1344</artwork></figure>
1345<t>
1346   The Content-Location value is not a replacement for the effective
1347   Request URI (&effective-request-uri;).  It is representation metadata.
1348   It has the same syntax and semantics as the header field of the same name
1349   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1350   However, its appearance in an HTTP message has some special implications
1351   for HTTP recipients.
1352</t>
1353<t>
1354   If Content-Location is included in a response message and its value
1355   is the same as the effective request URI, then the response payload
1356   &SHOULD; be considered the current representation of that resource.
1357   For a GET or HEAD request, this is the same as the default semantics
1358   when no Content-Location is provided by the server.  For a state-changing
1359   request like PUT or POST, it implies that the server's response contains
1360   the new representation of that resource, thereby distinguishing it from
1361   representations that might only report about the action (e.g., "It worked!").
1362   This allows authoring applications to update their local copies without
1363   the need for a subsequent GET request.
1364</t>
1365<t>
1366   If Content-Location is included in a response message and its value
1367   differs from the effective request URI, then the origin server is
1368   informing recipients that this representation has its own, presumably
1369   more specific, identifier.  For a GET or HEAD request, this is an
1370   indication that the effective request URI identifies a resource that
1371   is subject to content negotiation and the representation selected for
1372   this response can also be found at the identified URI.  For other
1373   methods, such a Content-Location indicates that this representation
1374   contains a report on the action's status and the same report is
1375   available (for future access with GET) at the given URI.  For
1376   example, a purchase transaction made via a POST request might
1377   include a receipt document as the payload of the 200 response;
1378   the Content-Location value provides an identifier for retrieving
1379   a copy of that same receipt in the future.
1380</t>
1381<t>
1382   If Content-Location is included in a request message, then it &MAY;
1383   be interpreted by the origin server as an indication of where the
1384   user agent originally obtained the content of the enclosed
1385   representation (prior to any subsequent modification of the content
1386   by that user agent).  In other words, the user agent is providing
1387   the same representation metadata that it received with the original
1388   representation.  However, such interpretation &MUST-NOT; be used to
1389   alter the semantics of the method requested by the client.  For
1390   example, if a client makes a PUT request on a negotiated resource
1391   and the origin server accepts that PUT (without redirection), then the
1392   new set of values for that resource is expected to be consistent with
1393   the one representation supplied in that PUT; the Content-Location
1394   cannot be used as a form of reverse content selection that
1395   identifies only one of the negotiated representations to be updated.
1396   If the user agent had wanted the latter semantics, it would have applied
1397   the PUT directly to the Content-Location URI.
1398</t>
1399<t>
1400   A Content-Location field received in a request message is transitory
1401   information that &SHOULD-NOT; be saved with other representation
1402   metadata for use in later responses.  The Content-Location's value
1403   might be saved for use in other contexts, such as within source links
1404   or other metadata.
1405</t>
1406<t>
1407   A cache cannot assume that a representation with a Content-Location
1408   different from the URI used to retrieve it can be used to respond to
1409   later requests on that Content-Location URI.
1410</t>
1411<t>
1412   If the Content-Location value is a partial URI, the partial URI is
1413   interpreted relative to the effective request URI.
1414</t>
1415</section>
1416
1417<section title="Content-MD5" anchor="header.content-md5">
1418  <iref primary="true" item="Content-MD5 header field" x:for-anchor=""/>
1419  <iref primary="true" item="Header Fields" subitem="Content-MD5" x:for-anchor=""/>
1420  <x:anchor-alias value="Content-MD5"/>
1421<t>
1422   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
1423   an MD5 digest of the payload body that provides an end-to-end message
1424   integrity check (MIC) of the payload body (the message-body after any
1425   transfer-coding is decoded). Note that a MIC is good for
1426   detecting accidental modification of the payload body in transit, but is not
1427   proof against malicious attacks.
1428</t>
1429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/>
1430  <x:ref>Content-MD5</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1431</artwork></figure>
1432<t>
1433   The Content-MD5 header field &MAY; be generated by an origin server or
1434   client to function as an integrity check of the payload body. Only
1435   origin servers or user agents &MAY; generate the Content-MD5 header field;
1436   proxies &MUST-NOT; generate it, as this would defeat its
1437   value as an end-to-end integrity check. Any recipient &MAY; check that
1438   the digest value in this header field matches a corresponding digest
1439   calculated on payload body as received.
1440</t>
1441<t>
1442   The MD5 digest is computed based on the content of the payload body,
1443   including any content-coding, but not including any transfer-coding
1444   applied to the message-body because such transfer-codings might be
1445   applied or removed anywhere along the request/response chain.
1446   If the message is received with a transfer-coding, that encoding &MUST;
1447   be decoded prior to checking the Content-MD5 value against the received
1448   payload.
1449</t>
1450<t>
1451   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1452   composite media-types (e.g., multipart/* and message/rfc822), but
1453   this does not change how the digest is computed as defined in the
1454   preceding paragraph.
1455</t>
1456<t>
1457   There are several consequences of this. The payload for composite
1458   types &MAY; contain many body-parts, each with its own MIME and HTTP
1459   header fields (including Content-MD5, Content-Transfer-Encoding, and
1460   Content-Encoding header fields). If a body-part has a Content-Transfer-Encoding
1461   or Content-Encoding header field, it is assumed that the content
1462   of the body-part has had the encoding applied, and the body-part is
1463   included in the Content-MD5 digest as is &mdash; i.e., after the
1464   application. The Transfer-Encoding header field is not allowed within
1465   body-parts.
1466</t>
1467<t>
1468   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1469   computing or checking the digest: the line break convention used in
1470   the text actually transmitted &MUST; be left unaltered when computing
1471   the digest.
1472</t>
1473<x:note>
1474  <t>
1475    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1476    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1477    in which the application of Content-MD5 to HTTP entity-bodies
1478    differs from its application to MIME entity-bodies. One is that
1479    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1480    does use Transfer-Encoding and Content-Encoding. Another is that
1481    HTTP more frequently uses binary content types than MIME, so it is
1482    worth noting that, in such cases, the byte order used to compute
1483    the digest is the transmission byte order defined for the type.
1484    Lastly, HTTP allows transmission of text types with any of several
1485    line break conventions and not just the canonical form using CRLF.
1486  </t>
1487</x:note>
1488</section>
1489
1490<section title="Content-Type" anchor="header.content-type">
1491  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1492  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
1493  <x:anchor-alias value="Content-Type"/>
1494<t>
1495   The "Content-Type" header field indicates the media type of the
1496   representation. In the case of responses to the HEAD method, the media type is
1497   that which would have been sent had the request been a GET.
1498</t>
1499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1500  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
1501</artwork></figure>
1502<t>
1503   Media types are defined in <xref target="media.types"/>. An example of the field is
1504</t>
1505<figure><artwork type="example">
1506  Content-Type: text/html; charset=ISO-8859-4
1507</artwork></figure>
1508<t>
1509   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1510</t>
1511</section>
1512
1513</section>
1514
1515<section title="IANA Considerations" anchor="IANA.considerations">
1516<section title="Header Field Registration" anchor="header.field.registration">
1517<t>
1518   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1519   with the permanent registrations below (see <xref target="RFC3864"/>):
1520</t>
1521<?BEGININC p3-payload.iana-headers ?>
1522<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1523<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1524   <ttcol>Header Field Name</ttcol>
1525   <ttcol>Protocol</ttcol>
1526   <ttcol>Status</ttcol>
1527   <ttcol>Reference</ttcol>
1528
1529   <c>Accept</c>
1530   <c>http</c>
1531   <c>standard</c>
1532   <c>
1533      <xref target="header.accept"/>
1534   </c>
1535   <c>Accept-Charset</c>
1536   <c>http</c>
1537   <c>standard</c>
1538   <c>
1539      <xref target="header.accept-charset"/>
1540   </c>
1541   <c>Accept-Encoding</c>
1542   <c>http</c>
1543   <c>standard</c>
1544   <c>
1545      <xref target="header.accept-encoding"/>
1546   </c>
1547   <c>Accept-Language</c>
1548   <c>http</c>
1549   <c>standard</c>
1550   <c>
1551      <xref target="header.accept-language"/>
1552   </c>
1553   <c>Content-Encoding</c>
1554   <c>http</c>
1555   <c>standard</c>
1556   <c>
1557      <xref target="header.content-encoding"/>
1558   </c>
1559   <c>Content-Language</c>
1560   <c>http</c>
1561   <c>standard</c>
1562   <c>
1563      <xref target="header.content-language"/>
1564   </c>
1565   <c>Content-Location</c>
1566   <c>http</c>
1567   <c>standard</c>
1568   <c>
1569      <xref target="header.content-location"/>
1570   </c>
1571   <c>Content-MD5</c>
1572   <c>http</c>
1573   <c>standard</c>
1574   <c>
1575      <xref target="header.content-md5"/>
1576   </c>
1577   <c>Content-Type</c>
1578   <c>http</c>
1579   <c>standard</c>
1580   <c>
1581      <xref target="header.content-type"/>
1582   </c>
1583   <c>MIME-Version</c>
1584   <c>http</c>
1585   <c>standard</c>
1586   <c>
1587      <xref target="mime-version"/>
1588   </c>
1589</texttable>
1590<!--(END)-->
1591<?ENDINC p3-payload.iana-headers ?>
1592<t>
1593   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1594</t>
1595</section>
1596
1597<section title="Content Coding Registry" anchor="content.coding.registration">
1598<t>
1599   The registration procedure for HTTP Content Codings is now defined
1600   by <xref target="content.coding.registry"/> of this document.
1601</t>
1602<t>
1603   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1604   shall be updated with the registration below:
1605</t>
1606<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1607   <ttcol>Name</ttcol>
1608   <ttcol>Description</ttcol>
1609   <ttcol>Reference</ttcol>
1610   <c>compress</c>
1611   <c>UNIX "compress" program method</c>
1612   <c>
1613      &compress-coding;
1614   </c>
1615   <c>deflate</c>
1616   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1617   the "zlib" data format (<xref target="RFC1950"/>)
1618   </c>
1619   <c>
1620      &deflate-coding;
1621   </c>
1622   <c>gzip</c>
1623   <c>Same as GNU zip <xref target="RFC1952"/></c>
1624   <c>
1625      &gzip-coding;
1626   </c>
1627   <c>identity</c>
1628   <c>No transformation</c>
1629   <c>
1630      <xref target="content.codings"/>
1631   </c>
1632</texttable>
1633</section>
1634
1635</section>
1636
1637<section title="Security Considerations" anchor="security.considerations">
1638<t>
1639   This section is meant to inform application developers, information
1640   providers, and users of the security limitations in HTTP/1.1 as
1641   described by this document. The discussion does not include
1642   definitive solutions to the problems revealed, though it does make
1643   some suggestions for reducing security risks.
1644</t>
1645
1646<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1647<t>
1648   Accept headers fields can reveal information about the user to all
1649   servers which are accessed. The Accept-Language header field in particular
1650   can reveal information the user would consider to be of a private
1651   nature, because the understanding of particular languages is often
1652   strongly correlated to the membership of a particular ethnic group.
1653   User agents which offer the option to configure the contents of an
1654   Accept-Language header field to be sent in every request are strongly
1655   encouraged to let the configuration process include a message which
1656   makes the user aware of the loss of privacy involved.
1657</t>
1658<t>
1659   An approach that limits the loss of privacy would be for a user agent
1660   to omit the sending of Accept-Language header fields by default, and to ask
1661   the user whether or not to start sending Accept-Language header fields to a
1662   server if it detects, by looking for any Vary header fields
1663   generated by the server, that such sending could improve the quality
1664   of service.
1665</t>
1666<t>
1667   Elaborate user-customized accept header fields sent in every request,
1668   in particular if these include quality values, can be used by servers
1669   as relatively reliable and long-lived user identifiers. Such user
1670   identifiers would allow content providers to do click-trail tracking,
1671   and would allow collaborating content providers to match cross-server
1672   click-trails or form submissions of individual users. Note that for
1673   many users not behind a proxy, the network address of the host
1674   running the user agent will also serve as a long-lived user
1675   identifier. In environments where proxies are used to enhance
1676   privacy, user agents ought to be conservative in offering accept
1677   header configuration options to end users. As an extreme privacy
1678   measure, proxies could filter the accept header fields in relayed requests.
1679   General purpose user agents which provide a high degree of header
1680   configurability &SHOULD; warn users about the loss of privacy which can
1681   be involved.
1682</t>
1683</section>
1684
1685</section>
1686
1687<section title="Acknowledgments" anchor="ack">
1688</section>
1689</middle>
1690<back>
1691
1692<references title="Normative References">
1693
1694<reference anchor="Part1">
1695  <front>
1696    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1697    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1698      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1699      <address><email>fielding@gbiv.com</email></address>
1700    </author>
1701    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1702      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1703      <address><email>jg@freedesktop.org</email></address>
1704    </author>
1705    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1706      <organization abbrev="HP">Hewlett-Packard Company</organization>
1707      <address><email>JeffMogul@acm.org</email></address>
1708    </author>
1709    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1710      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1711      <address><email>henrikn@microsoft.com</email></address>
1712    </author>
1713    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1714      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1715      <address><email>LMM@acm.org</email></address>
1716    </author>
1717    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1718      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1719      <address><email>paulle@microsoft.com</email></address>
1720    </author>
1721    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1722      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1723      <address><email>timbl@w3.org</email></address>
1724    </author>
1725    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1726      <organization abbrev="W3C">World Wide Web Consortium</organization>
1727      <address><email>ylafon@w3.org</email></address>
1728    </author>
1729    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1730      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1731      <address><email>julian.reschke@greenbytes.de</email></address>
1732    </author>
1733    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1734  </front>
1735  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1736  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1737</reference>
1738
1739<reference anchor="Part2">
1740  <front>
1741    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1742    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1743      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1744      <address><email>fielding@gbiv.com</email></address>
1745    </author>
1746    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1747      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1748      <address><email>jg@freedesktop.org</email></address>
1749    </author>
1750    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1751      <organization abbrev="HP">Hewlett-Packard Company</organization>
1752      <address><email>JeffMogul@acm.org</email></address>
1753    </author>
1754    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1755      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1756      <address><email>henrikn@microsoft.com</email></address>
1757    </author>
1758    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1759      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1760      <address><email>LMM@acm.org</email></address>
1761    </author>
1762    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1763      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1764      <address><email>paulle@microsoft.com</email></address>
1765    </author>
1766    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1767      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1768      <address><email>timbl@w3.org</email></address>
1769    </author>
1770    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1771      <organization abbrev="W3C">World Wide Web Consortium</organization>
1772      <address><email>ylafon@w3.org</email></address>
1773    </author>
1774    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1775      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1776      <address><email>julian.reschke@greenbytes.de</email></address>
1777    </author>
1778    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1779  </front>
1780  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1781  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1782</reference>
1783
1784<reference anchor="Part4">
1785  <front>
1786    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1787    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1788      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1789      <address><email>fielding@gbiv.com</email></address>
1790    </author>
1791    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1792      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1793      <address><email>jg@freedesktop.org</email></address>
1794    </author>
1795    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1796      <organization abbrev="HP">Hewlett-Packard Company</organization>
1797      <address><email>JeffMogul@acm.org</email></address>
1798    </author>
1799    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1800      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1801      <address><email>henrikn@microsoft.com</email></address>
1802    </author>
1803    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1804      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1805      <address><email>LMM@acm.org</email></address>
1806    </author>
1807    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1808      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1809      <address><email>paulle@microsoft.com</email></address>
1810    </author>
1811    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1812      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1813      <address><email>timbl@w3.org</email></address>
1814    </author>
1815    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1816      <organization abbrev="W3C">World Wide Web Consortium</organization>
1817      <address><email>ylafon@w3.org</email></address>
1818    </author>
1819    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1820      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1821      <address><email>julian.reschke@greenbytes.de</email></address>
1822    </author>
1823    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1824  </front>
1825  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1826  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1827</reference>
1828
1829<reference anchor="Part5">
1830  <front>
1831    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1832    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1833      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1834      <address><email>fielding@gbiv.com</email></address>
1835    </author>
1836    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1837      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1838      <address><email>jg@freedesktop.org</email></address>
1839    </author>
1840    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1841      <organization abbrev="HP">Hewlett-Packard Company</organization>
1842      <address><email>JeffMogul@acm.org</email></address>
1843    </author>
1844    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1845      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1846      <address><email>henrikn@microsoft.com</email></address>
1847    </author>
1848    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1849      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1850      <address><email>LMM@acm.org</email></address>
1851    </author>
1852    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1853      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1854      <address><email>paulle@microsoft.com</email></address>
1855    </author>
1856    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1857      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1858      <address><email>timbl@w3.org</email></address>
1859    </author>
1860    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1861      <organization abbrev="W3C">World Wide Web Consortium</organization>
1862      <address><email>ylafon@w3.org</email></address>
1863    </author>
1864    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1865      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1866      <address><email>julian.reschke@greenbytes.de</email></address>
1867    </author>
1868    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1869  </front>
1870  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1871  <x:source href="p5-range.xml" basename="p5-range"/>
1872</reference>
1873
1874<reference anchor="Part6">
1875  <front>
1876    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1877    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1878      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1879      <address><email>fielding@gbiv.com</email></address>
1880    </author>
1881    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1882      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1883      <address><email>jg@freedesktop.org</email></address>
1884    </author>
1885    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1886      <organization abbrev="HP">Hewlett-Packard Company</organization>
1887      <address><email>JeffMogul@acm.org</email></address>
1888    </author>
1889    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1890      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1891      <address><email>henrikn@microsoft.com</email></address>
1892    </author>
1893    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1894      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1895      <address><email>LMM@acm.org</email></address>
1896    </author>
1897    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1898      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1899      <address><email>paulle@microsoft.com</email></address>
1900    </author>
1901    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1902      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1903      <address><email>timbl@w3.org</email></address>
1904    </author>
1905    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1906      <organization abbrev="W3C">World Wide Web Consortium</organization>
1907      <address><email>ylafon@w3.org</email></address>
1908    </author>
1909    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1910      <address><email>mnot@mnot.net</email></address>
1911    </author>
1912    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1913      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1914      <address><email>julian.reschke@greenbytes.de</email></address>
1915    </author>
1916    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1917  </front>
1918  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1919  <x:source href="p6-cache.xml" basename="p6-cache"/>
1920</reference>
1921
1922<reference anchor="RFC1864">
1923  <front>
1924    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1925    <author initials="J." surname="Myers" fullname="John G. Myers">
1926      <organization>Carnegie Mellon University</organization>
1927      <address><email>jgm+@cmu.edu</email></address>
1928    </author>
1929    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1930      <organization>Dover Beach Consulting, Inc.</organization>
1931      <address><email>mrose@dbc.mtview.ca.us</email></address>
1932    </author>
1933    <date month="October" year="1995"/>
1934  </front>
1935  <seriesInfo name="RFC" value="1864"/>
1936</reference>
1937
1938<reference anchor="RFC1950">
1939  <front>
1940    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1941    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1942      <organization>Aladdin Enterprises</organization>
1943      <address><email>ghost@aladdin.com</email></address>
1944    </author>
1945    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1946    <date month="May" year="1996"/>
1947  </front>
1948  <seriesInfo name="RFC" value="1950"/>
1949  <annotation>
1950    RFC 1950 is an Informational RFC, thus it might be less stable than
1951    this specification. On the other hand, this downward reference was
1952    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1953    therefore it is unlikely to cause problems in practice. See also
1954    <xref target="BCP97"/>.
1955  </annotation>
1956</reference>
1957
1958<reference anchor="RFC1951">
1959  <front>
1960    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1961    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1962      <organization>Aladdin Enterprises</organization>
1963      <address><email>ghost@aladdin.com</email></address>
1964    </author>
1965    <date month="May" year="1996"/>
1966  </front>
1967  <seriesInfo name="RFC" value="1951"/>
1968  <annotation>
1969    RFC 1951 is an Informational RFC, thus it might be less stable than
1970    this specification. On the other hand, this downward reference was
1971    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1972    therefore it is unlikely to cause problems in practice. See also
1973    <xref target="BCP97"/>.
1974  </annotation>
1975</reference>
1976
1977<reference anchor="RFC1952">
1978  <front>
1979    <title>GZIP file format specification version 4.3</title>
1980    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1981      <organization>Aladdin Enterprises</organization>
1982      <address><email>ghost@aladdin.com</email></address>
1983    </author>
1984    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1985      <address><email>gzip@prep.ai.mit.edu</email></address>
1986    </author>
1987    <author initials="M." surname="Adler" fullname="Mark Adler">
1988      <address><email>madler@alumni.caltech.edu</email></address>
1989    </author>
1990    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1991      <address><email>ghost@aladdin.com</email></address>
1992    </author>
1993    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1994      <address><email>randeg@alumni.rpi.edu</email></address>
1995    </author>
1996    <date month="May" year="1996"/>
1997  </front>
1998  <seriesInfo name="RFC" value="1952"/>
1999  <annotation>
2000    RFC 1952 is an Informational RFC, thus it might be less stable than
2001    this specification. On the other hand, this downward reference was
2002    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2003    therefore it is unlikely to cause problems in practice. See also
2004    <xref target="BCP97"/>.
2005  </annotation>
2006</reference>
2007
2008<reference anchor="RFC2045">
2009  <front>
2010    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2011    <author initials="N." surname="Freed" fullname="Ned Freed">
2012      <organization>Innosoft International, Inc.</organization>
2013      <address><email>ned@innosoft.com</email></address>
2014    </author>
2015    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2016      <organization>First Virtual Holdings</organization>
2017      <address><email>nsb@nsb.fv.com</email></address>
2018    </author>
2019    <date month="November" year="1996"/>
2020  </front>
2021  <seriesInfo name="RFC" value="2045"/>
2022</reference>
2023
2024<reference anchor="RFC2046">
2025  <front>
2026    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2027    <author initials="N." surname="Freed" fullname="Ned Freed">
2028      <organization>Innosoft International, Inc.</organization>
2029      <address><email>ned@innosoft.com</email></address>
2030    </author>
2031    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2032      <organization>First Virtual Holdings</organization>
2033      <address><email>nsb@nsb.fv.com</email></address>
2034    </author>
2035    <date month="November" year="1996"/>
2036  </front>
2037  <seriesInfo name="RFC" value="2046"/>
2038</reference>
2039
2040<reference anchor="RFC2119">
2041  <front>
2042    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2043    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2044      <organization>Harvard University</organization>
2045      <address><email>sob@harvard.edu</email></address>
2046    </author>
2047    <date month="March" year="1997"/>
2048  </front>
2049  <seriesInfo name="BCP" value="14"/>
2050  <seriesInfo name="RFC" value="2119"/>
2051</reference>
2052
2053<reference anchor='RFC4647'>
2054  <front>
2055    <title>Matching of Language Tags</title>
2056    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2057      <organization>Yahoo! Inc.</organization>
2058      <address><email>addison@inter-locale.com</email></address>
2059    </author>
2060    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2061      <organization>Google</organization>
2062      <address><email>mark.davis@macchiato.com</email></address>
2063    </author>
2064    <date year='2006' month='September' />
2065  </front>
2066  <seriesInfo name='BCP' value='47' />
2067  <seriesInfo name='RFC' value='4647' />
2068</reference>
2069
2070<reference anchor="RFC5234">
2071  <front>
2072    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2073    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2074      <organization>Brandenburg InternetWorking</organization>
2075      <address>
2076        <email>dcrocker@bbiw.net</email>
2077      </address> 
2078    </author>
2079    <author initials="P." surname="Overell" fullname="Paul Overell">
2080      <organization>THUS plc.</organization>
2081      <address>
2082        <email>paul.overell@thus.net</email>
2083      </address>
2084    </author>
2085    <date month="January" year="2008"/>
2086  </front>
2087  <seriesInfo name="STD" value="68"/>
2088  <seriesInfo name="RFC" value="5234"/>
2089</reference>
2090
2091<reference anchor='RFC5646'>
2092  <front>
2093    <title>Tags for Identifying Languages</title>
2094    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2095      <organization>Lab126</organization>
2096      <address><email>addison@inter-locale.com</email></address>
2097    </author>
2098    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2099      <organization>Google</organization>
2100      <address><email>mark.davis@google.com</email></address>
2101    </author>
2102    <date month='September' year='2009' />
2103  </front>
2104  <seriesInfo name='BCP' value='47' />
2105  <seriesInfo name='RFC' value='5646' />
2106</reference>
2107
2108</references>
2109
2110<references title="Informative References">
2111
2112<reference anchor="RFC1945">
2113  <front>
2114    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2115    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2116      <organization>MIT, Laboratory for Computer Science</organization>
2117      <address><email>timbl@w3.org</email></address>
2118    </author>
2119    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2120      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2121      <address><email>fielding@ics.uci.edu</email></address>
2122    </author>
2123    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2124      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2125      <address><email>frystyk@w3.org</email></address>
2126    </author>
2127    <date month="May" year="1996"/>
2128  </front>
2129  <seriesInfo name="RFC" value="1945"/>
2130</reference>
2131
2132<reference anchor="RFC2049">
2133  <front>
2134    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2135    <author initials="N." surname="Freed" fullname="Ned Freed">
2136      <organization>Innosoft International, Inc.</organization>
2137      <address><email>ned@innosoft.com</email></address>
2138    </author>
2139    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2140      <organization>First Virtual Holdings</organization>
2141      <address><email>nsb@nsb.fv.com</email></address>
2142    </author>
2143    <date month="November" year="1996"/>
2144  </front>
2145  <seriesInfo name="RFC" value="2049"/>
2146</reference>
2147
2148<reference anchor="RFC2068">
2149  <front>
2150    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2151    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2152      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2153      <address><email>fielding@ics.uci.edu</email></address>
2154    </author>
2155    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2156      <organization>MIT Laboratory for Computer Science</organization>
2157      <address><email>jg@w3.org</email></address>
2158    </author>
2159    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2160      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2161      <address><email>mogul@wrl.dec.com</email></address>
2162    </author>
2163    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2164      <organization>MIT Laboratory for Computer Science</organization>
2165      <address><email>frystyk@w3.org</email></address>
2166    </author>
2167    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2168      <organization>MIT Laboratory for Computer Science</organization>
2169      <address><email>timbl@w3.org</email></address>
2170    </author>
2171    <date month="January" year="1997"/>
2172  </front>
2173  <seriesInfo name="RFC" value="2068"/>
2174</reference>
2175
2176<reference anchor="RFC2076">
2177  <front>
2178    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2179    <author initials="J." surname="Palme" fullname="Jacob Palme">
2180      <organization>Stockholm University/KTH</organization>
2181      <address><email>jpalme@dsv.su.se</email></address>
2182    </author>
2183    <date month="February" year="1997"/>
2184  </front>
2185  <seriesInfo name="RFC" value="2076"/>
2186</reference>
2187
2188<reference anchor="RFC2277">
2189  <front>
2190    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2191    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2192      <organization>UNINETT</organization>
2193      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2194    </author>
2195    <date month="January" year="1998"/>
2196  </front>
2197  <seriesInfo name="BCP" value="18"/>
2198  <seriesInfo name="RFC" value="2277"/>
2199</reference>
2200
2201<reference anchor='RFC2295'>
2202  <front>
2203    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2204    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2205      <organization>Technische Universiteit Eindhoven</organization>
2206      <address>
2207        <email>koen@win.tue.nl</email>
2208      </address>
2209    </author>
2210    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2211      <organization>Hewlett-Packard Company</organization>
2212      <address>
2213        <email>mutz@hpl.hp.com</email>
2214      </address>
2215    </author>
2216    <date year='1998' month='March'/>
2217  </front>
2218  <seriesInfo name='RFC' value='2295'/>
2219</reference>
2220
2221<reference anchor="RFC2388">
2222  <front>
2223    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2224    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2225      <organization>Xerox Palo Alto Research Center</organization>
2226      <address><email>masinter@parc.xerox.com</email></address>
2227    </author>
2228    <date year="1998" month="August"/>
2229  </front>
2230  <seriesInfo name="RFC" value="2388"/>
2231</reference>
2232
2233<reference anchor="RFC2557">
2234  <front>
2235    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2236    <author initials="F." surname="Palme" fullname="Jacob Palme">
2237      <organization>Stockholm University and KTH</organization>
2238      <address><email>jpalme@dsv.su.se</email></address>
2239    </author>
2240    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2241      <organization>Microsoft Corporation</organization>
2242      <address><email>alexhop@microsoft.com</email></address>
2243    </author>
2244    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2245      <organization>Lotus Development Corporation</organization>
2246      <address><email>Shelness@lotus.com</email></address>
2247    </author>
2248    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2249      <address><email>stef@nma.com</email></address>
2250    </author>
2251    <date year="1999" month="March"/>
2252  </front>
2253  <seriesInfo name="RFC" value="2557"/>
2254</reference>
2255
2256<reference anchor="RFC2616">
2257  <front>
2258    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2259    <author initials="R." surname="Fielding" fullname="R. Fielding">
2260      <organization>University of California, Irvine</organization>
2261      <address><email>fielding@ics.uci.edu</email></address>
2262    </author>
2263    <author initials="J." surname="Gettys" fullname="J. Gettys">
2264      <organization>W3C</organization>
2265      <address><email>jg@w3.org</email></address>
2266    </author>
2267    <author initials="J." surname="Mogul" fullname="J. Mogul">
2268      <organization>Compaq Computer Corporation</organization>
2269      <address><email>mogul@wrl.dec.com</email></address>
2270    </author>
2271    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2272      <organization>MIT Laboratory for Computer Science</organization>
2273      <address><email>frystyk@w3.org</email></address>
2274    </author>
2275    <author initials="L." surname="Masinter" fullname="L. Masinter">
2276      <organization>Xerox Corporation</organization>
2277      <address><email>masinter@parc.xerox.com</email></address>
2278    </author>
2279    <author initials="P." surname="Leach" fullname="P. Leach">
2280      <organization>Microsoft Corporation</organization>
2281      <address><email>paulle@microsoft.com</email></address>
2282    </author>
2283    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2284      <organization>W3C</organization>
2285      <address><email>timbl@w3.org</email></address>
2286    </author>
2287    <date month="June" year="1999"/>
2288  </front>
2289  <seriesInfo name="RFC" value="2616"/>
2290</reference>
2291
2292<reference anchor="RFC3629">
2293  <front>
2294    <title>UTF-8, a transformation format of ISO 10646</title>
2295    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2296      <organization>Alis Technologies</organization>
2297      <address><email>fyergeau@alis.com</email></address>
2298    </author>
2299    <date month="November" year="2003"/>
2300  </front>
2301  <seriesInfo name="STD" value="63"/>
2302  <seriesInfo name="RFC" value="3629"/>
2303</reference>
2304
2305<reference anchor='RFC3864'>
2306  <front>
2307    <title>Registration Procedures for Message Header Fields</title>
2308    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2309      <organization>Nine by Nine</organization>
2310      <address><email>GK-IETF@ninebynine.org</email></address>
2311    </author>
2312    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2313      <organization>BEA Systems</organization>
2314      <address><email>mnot@pobox.com</email></address>
2315    </author>
2316    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2317      <organization>HP Labs</organization>
2318      <address><email>JeffMogul@acm.org</email></address>
2319    </author>
2320    <date year='2004' month='September' />
2321  </front>
2322  <seriesInfo name='BCP' value='90' />
2323  <seriesInfo name='RFC' value='3864' />
2324</reference>
2325
2326<reference anchor="RFC4288">
2327  <front>
2328    <title>Media Type Specifications and Registration Procedures</title>
2329    <author initials="N." surname="Freed" fullname="N. Freed">
2330      <organization>Sun Microsystems</organization>
2331      <address>
2332        <email>ned.freed@mrochek.com</email>
2333      </address>
2334    </author>
2335    <author initials="J." surname="Klensin" fullname="J. Klensin">
2336      <address>
2337        <email>klensin+ietf@jck.com</email>
2338      </address>
2339    </author>
2340    <date year="2005" month="December"/>
2341  </front>
2342  <seriesInfo name="BCP" value="13"/>
2343  <seriesInfo name="RFC" value="4288"/>
2344</reference>
2345
2346<reference anchor='RFC5226'>
2347  <front>
2348    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2349    <author initials='T.' surname='Narten' fullname='T. Narten'>
2350      <organization>IBM</organization>
2351      <address><email>narten@us.ibm.com</email></address>
2352    </author>
2353    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2354      <organization>Google</organization>
2355      <address><email>Harald@Alvestrand.no</email></address>
2356    </author>
2357    <date year='2008' month='May' />
2358  </front>
2359  <seriesInfo name='BCP' value='26' />
2360  <seriesInfo name='RFC' value='5226' />
2361</reference>
2362
2363<reference anchor="RFC5322">
2364  <front>
2365    <title>Internet Message Format</title>
2366    <author initials="P." surname="Resnick" fullname="P. Resnick">
2367      <organization>Qualcomm Incorporated</organization>
2368    </author>
2369    <date year="2008" month="October"/>
2370  </front> 
2371  <seriesInfo name="RFC" value="5322"/>
2372</reference>
2373
2374<reference anchor='BCP97'>
2375  <front>
2376    <title>Handling Normative References to Standards-Track Documents</title>
2377    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2378      <address>
2379        <email>klensin+ietf@jck.com</email>
2380      </address>
2381    </author>
2382    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2383      <organization>MIT</organization>
2384      <address>
2385        <email>hartmans-ietf@mit.edu</email>
2386      </address>
2387    </author>
2388    <date year='2007' month='June' />
2389  </front>
2390  <seriesInfo name='BCP' value='97' />
2391  <seriesInfo name='RFC' value='4897' />
2392</reference>
2393
2394
2395</references>
2396
2397<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2398<t>
2399   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
2400   allow a message-body to be transmitted in an open variety of
2401   representations and with extensible mechanisms. However, RFC 2045
2402   discusses mail, and HTTP has a few features that are different from
2403   those described in MIME. These differences were carefully chosen
2404   to optimize performance over binary connections, to allow greater
2405   freedom in the use of new media types, to make date comparisons
2406   easier, and to acknowledge the practice of some early HTTP servers
2407   and clients.
2408</t>
2409<t>
2410   This appendix describes specific areas where HTTP differs from MIME.
2411   Proxies and gateways to strict MIME environments &SHOULD; be
2412   aware of these differences and provide the appropriate conversions
2413   where necessary. Proxies and gateways from MIME environments to HTTP
2414   also need to be aware of the differences because some conversions
2415   might be required.
2416</t>
2417
2418<section title="MIME-Version" anchor="mime-version">
2419  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
2420  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
2421  <x:anchor-alias value="MIME-Version"/>
2422<t>
2423   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2424   include a single MIME-Version header field to indicate what
2425   version of the MIME protocol was used to construct the message. Use
2426   of the MIME-Version header field indicates that the message is in
2427   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2428   Proxies/gateways are responsible for ensuring full compliance (where
2429   possible) when exporting HTTP messages to strict MIME environments.
2430</t>
2431<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2432  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2433</artwork></figure>
2434<t>
2435   MIME version "1.0" is the default for use in HTTP/1.1. However,
2436   HTTP/1.1 message parsing and semantics are defined by this document
2437   and not the MIME specification.
2438</t>
2439</section>
2440
2441<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2442<t>
2443   MIME requires that an Internet mail body-part be converted to
2444   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2445   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2446   allowed for subtypes of the "text" media type when transmitted over
2447   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2448   line breaks as CRLF and forbids the use of CR or LF outside of line
2449   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2450   line break within text content when a message is transmitted over
2451   HTTP.
2452</t>
2453<t>
2454   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2455   environment &SHOULD; translate all line breaks within the text media
2456   types described in <xref target="canonicalization.and.text.defaults"/>
2457   of this document to the RFC 2049
2458   canonical form of CRLF. Note, however, that this might be complicated
2459   by the presence of a Content-Encoding and by the fact that HTTP
2460   allows the use of some character encodings which do not use octets 13 and
2461   10 to represent CR and LF, respectively, as is the case for some multi-byte
2462   character encodings.
2463</t>
2464<t>
2465   Conversion will break any cryptographic
2466   checksums applied to the original content unless the original content
2467   is already in canonical form. Therefore, the canonical form is
2468   recommended for any content that uses such checksums in HTTP.
2469</t>
2470</section>
2471
2472
2473<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2474<t>
2475   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2476   simplify the process of date comparison. Proxies and gateways from
2477   other protocols &SHOULD; ensure that any Date header field present in a
2478   message conforms to one of the HTTP/1.1 formats and rewrite the date
2479   if necessary.
2480</t>
2481</section>
2482
2483<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2484<t>
2485   MIME does not include any concept equivalent to HTTP/1.1's
2486   Content-Encoding header field. Since this acts as a modifier on the
2487   media type, proxies and gateways from HTTP to MIME-compliant
2488   protocols &MUST; either change the value of the Content-Type header
2489   field or decode the representation before forwarding the message. (Some
2490   experimental applications of Content-Type for Internet mail have used
2491   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2492   a function equivalent to Content-Encoding. However, this parameter is
2493   not part of the MIME standards).
2494</t>
2495</section>
2496
2497<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2498<t>
2499   HTTP does not use the Content-Transfer-Encoding field of MIME.
2500   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2501   remove any Content-Transfer-Encoding
2502   prior to delivering the response message to an HTTP client.
2503</t>
2504<t>
2505   Proxies and gateways from HTTP to MIME-compliant protocols are
2506   responsible for ensuring that the message is in the correct format
2507   and encoding for safe transport on that protocol, where "safe
2508   transport" is defined by the limitations of the protocol being used.
2509   Such a proxy or gateway &SHOULD; label the data with an appropriate
2510   Content-Transfer-Encoding if doing so will improve the likelihood of
2511   safe transport over the destination protocol.
2512</t>
2513</section>
2514
2515<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2516<t>
2517   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2518   Proxies/gateways &MUST; remove any transfer-coding prior to
2519   forwarding a message via a MIME-compliant protocol.
2520</t>
2521</section>
2522
2523<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2524<t>
2525   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2526   need to be aware of MIME line length limitations. Since HTTP does not
2527   have this limitation, HTTP does not fold long lines. MHTML messages
2528   being transported by HTTP follow all conventions of MHTML, including
2529   line length limitations and folding, canonicalization, etc., since
2530   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2531   does not interpret the content or any MIME header lines that might be
2532   contained therein.
2533</t>
2534</section>
2535</section>
2536
2537<section title="Additional Features" anchor="additional.features">
2538<t>
2539   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2540   existing HTTP implementations, but not consistently and correctly
2541   across most HTTP/1.1 applications. Implementors are advised to be
2542   aware of these features, but cannot rely upon their presence in, or
2543   interoperability with, other HTTP/1.1 applications. Some of these
2544   describe proposed experimental features, and some describe features
2545   that experimental deployment found lacking that are now addressed in
2546   the base HTTP/1.1 specification.
2547</t>
2548<t>
2549   A number of other header fields, such as Content-Disposition and Title,
2550   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2551</t>
2552</section>
2553
2554<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2555<t>
2556  Clarify contexts that charset is used in.
2557  (<xref target="character.sets"/>)
2558</t>
2559<t>
2560  Remove the default character encoding for text media types; the default
2561  now is whatever the media type definition says.
2562  (<xref target="canonicalization.and.text.defaults"/>)
2563</t>
2564<t>
2565  Change ABNF productions for header fields to only define the field value.
2566  (<xref target="header.fields"/>)
2567</t>
2568<t>
2569  Remove ISO-8859-1 special-casing in Accept-Charset.
2570  (<xref target="header.accept-charset"/>)
2571</t>
2572<t>
2573  Remove base URI setting semantics for Content-Location due to poor
2574  implementation support, which was caused by too many broken servers emitting
2575  bogus Content-Location header fields, and also the potentially undesirable effect
2576  of potentially breaking relative links in content-negotiated resources.
2577  (<xref target="header.content-location"/>)
2578</t>
2579<t>
2580  Remove reference to non-existant identity transfer-coding value tokens.
2581  (<xref target="no.content-transfer-encoding"/>)
2582</t>
2583</section>
2584
2585<?BEGININC p3-payload.abnf-appendix ?>
2586<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2587<figure>
2588<artwork type="abnf" name="p3-payload.parsed-abnf">
2589<x:ref>Accept</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2590 OWS media-range [ accept-params ] ] ) ]
2591<x:ref>Accept-Charset</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2592 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2593 qvalue ] ] )
2594<x:ref>Accept-Encoding</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
2595 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2596<x:ref>Accept-Language</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2597 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2598 ] )
2599
2600<x:ref>Content-Encoding</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2601 content-coding ] )
2602<x:ref>Content-Language</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2603 language-tag ] )
2604<x:ref>Content-Location</x:ref> = absolute-URI / partial-URI
2605<x:ref>Content-MD5</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2606<x:ref>Content-Type</x:ref> = media-type
2607
2608<x:ref>MIME-Version</x:ref> = 1*DIGIT "." 1*DIGIT
2609
2610<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2611
2612<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2613<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2614<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2615<x:ref>attribute</x:ref> = token
2616
2617<x:ref>charset</x:ref> = token
2618<x:ref>codings</x:ref> = ( content-coding / "*" )
2619<x:ref>content-coding</x:ref> = token
2620
2621<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2622<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2623
2624<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2625 ";" OWS parameter )
2626<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2627
2628<x:ref>parameter</x:ref> = attribute "=" value
2629<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2630
2631<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2632
2633<x:ref>subtype</x:ref> = token
2634
2635<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2636<x:ref>type</x:ref> = token
2637
2638<x:ref>value</x:ref> = word
2639
2640<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2641</artwork>
2642</figure>
2643<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2644; Accept defined but not used
2645; Accept-Charset defined but not used
2646; Accept-Encoding defined but not used
2647; Accept-Language defined but not used
2648; Content-Encoding defined but not used
2649; Content-Language defined but not used
2650; Content-Location defined but not used
2651; Content-MD5 defined but not used
2652; Content-Type defined but not used
2653; MIME-Version defined but not used
2654</artwork></figure></section>
2655<?ENDINC p3-payload.abnf-appendix ?>
2656
2657<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2658
2659<section title="Since RFC 2616">
2660<t>
2661  Extracted relevant partitions from <xref target="RFC2616"/>.
2662</t>
2663</section>
2664
2665<section title="Since draft-ietf-httpbis-p3-payload-00">
2666<t>
2667  Closed issues:
2668  <list style="symbols"> 
2669    <t>
2670      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2671      "Media Type Registrations"
2672      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2673    </t>
2674    <t>
2675      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2676      "Clarification regarding quoting of charset values"
2677      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2678    </t>
2679    <t>
2680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2681      "Remove 'identity' token references"
2682      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2683    </t>
2684    <t>
2685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2686      "Accept-Encoding BNF"
2687    </t>
2688    <t>
2689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2690      "Normative and Informative references"
2691    </t>
2692    <t>
2693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2694      "RFC1700 references"
2695    </t>
2696    <t>
2697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2698      "Updating to RFC4288"
2699    </t>
2700    <t>
2701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2702      "Informative references"
2703    </t>
2704    <t>
2705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2706      "ISO-8859-1 Reference"
2707    </t>
2708    <t>
2709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2710      "Encoding References Normative"
2711    </t>
2712    <t>
2713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2714      "Normative up-to-date references"
2715    </t>
2716  </list>
2717</t>
2718</section>
2719
2720<section title="Since draft-ietf-httpbis-p3-payload-01">
2721<t>
2722  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2723  <list style="symbols"> 
2724    <t>
2725      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2726    </t>
2727  </list>
2728</t>
2729</section>
2730
2731<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2732<t>
2733  Closed issues:
2734  <list style="symbols"> 
2735    <t>
2736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2737      "Quoting Charsets"
2738    </t>
2739    <t>
2740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2741      "Classification for Allow header"
2742    </t>
2743    <t>
2744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2745      "missing default for qvalue in description of Accept-Encoding"
2746    </t>
2747  </list>
2748</t>
2749<t>
2750  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2751  <list style="symbols"> 
2752    <t>
2753      Reference RFC 3984, and update header field registrations for headers defined
2754      in this document.
2755    </t>
2756  </list>
2757</t>
2758</section>
2759
2760<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2761<t>
2762  Closed issues:
2763  <list style="symbols"> 
2764    <t>
2765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2766      "Quoting Charsets"
2767    </t>
2768    <t>
2769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2770      "language tag matching (Accept-Language) vs RFC4647"
2771    </t>
2772    <t>
2773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2774      "RFC 1806 has been replaced by RFC2183"
2775    </t>
2776  </list>
2777</t>
2778<t>
2779  Other changes:
2780  <list style="symbols"> 
2781    <t>
2782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2783      "Encoding References Normative" &mdash; rephrase the annotation and reference
2784      <xref target="BCP97"/>.
2785    </t>
2786  </list>
2787</t>
2788 </section>
2789
2790<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2791<t>
2792  Closed issues:
2793  <list style="symbols"> 
2794    <t>
2795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2796      "RFC 2822 is updated by RFC 5322"
2797    </t>
2798  </list>
2799</t>
2800<t>
2801  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2802  <list style="symbols"> 
2803    <t>
2804      Use "/" instead of "|" for alternatives.
2805    </t>
2806    <t>
2807      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2808      whitespace ("OWS") and required whitespace ("RWS").
2809    </t>
2810    <t>
2811      Rewrite ABNFs to spell out whitespace rules, factor out
2812      header field value format definitions.
2813    </t>
2814  </list>
2815</t>
2816</section>
2817
2818<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2819<t>
2820  Closed issues:
2821  <list style="symbols"> 
2822    <t>
2823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2824      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2825    </t>
2826  </list>
2827</t>
2828<t>
2829  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2830  <list style="symbols"> 
2831    <t>
2832      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2833    </t>
2834  </list>
2835</t>
2836<t>
2837  Other changes:
2838  <list style="symbols"> 
2839    <t>
2840      Move definition of quality values into Part 1.
2841    </t>
2842  </list>
2843</t>
2844</section>
2845
2846<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2847<t>
2848  Closed issues:
2849  <list style="symbols"> 
2850    <t>
2851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2852      "Content-Location isn't special"
2853    </t>
2854    <t>
2855      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2856      "Content Sniffing"
2857    </t>
2858  </list>
2859</t>
2860</section>
2861
2862<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2863<t>
2864  Closed issues:
2865  <list style="symbols"> 
2866    <t>
2867      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2868      "Updated reference for language tags"
2869    </t>
2870    <t>
2871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2872      "Clarify rules for determining what entities a response carries"
2873    </t>
2874    <t>
2875      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2876      "Content-Location base-setting problems"
2877    </t>
2878    <t>
2879      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2880      "Content Sniffing"
2881    </t>
2882    <t>
2883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2884      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2885    </t>
2886    <t>
2887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2888      "move definitions of gzip/deflate/compress to part 1"
2889    </t>
2890  </list>
2891</t>
2892<t>
2893  Partly resolved issues:
2894  <list style="symbols"> 
2895    <t>
2896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2897      "update IANA requirements wrt Transfer-Coding values" (add the
2898      IANA Considerations subsection)
2899    </t>
2900    <t>
2901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2902      "update IANA requirements wrt Content-Coding values" (add the
2903      IANA Considerations subsection)
2904    </t>
2905  </list>
2906</t>
2907</section>
2908
2909<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2910<t>
2911  Closed issues:
2912  <list style="symbols"> 
2913    <t>
2914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
2915      "Content Negotiation for media types"
2916    </t>
2917    <t>
2918      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
2919      "Accept-Language: which RFC4647 filtering?"
2920    </t>
2921  </list>
2922</t>
2923</section>
2924
2925<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
2926<t>
2927  Closed issues:
2928  <list style="symbols"> 
2929    <t>
2930      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
2931      "MIME-Version not listed in P1, general header fields"
2932    </t>
2933    <t>
2934      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
2935      "IANA registry for content/transfer encodings"
2936    </t>
2937    <t>
2938      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2939      "Content Sniffing"
2940    </t>
2941    <t>
2942      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
2943      "use of term "word" when talking about header structure"
2944    </t>
2945  </list>
2946</t>
2947<t>
2948  Partly resolved issues:
2949  <list style="symbols"> 
2950    <t>
2951      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2952      "Term for the requested resource's URI"
2953    </t>
2954  </list>
2955</t>
2956</section>
2957
2958<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
2959<t>
2960  Closed issues:
2961  <list style="symbols"> 
2962    <t>
2963      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
2964      "Clarify 'Requested Variant'"
2965    </t>
2966    <t>
2967      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2968      "Content-Location isn't special"
2969    </t>
2970    <t>
2971      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
2972      "Delimiting messages with multipart/byteranges"
2973    </t>
2974    <t>
2975      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
2976      "Clarify entity / representation / variant terminology"
2977    </t>
2978    <t>
2979      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
2980      "confusing req. language for Content-Location"
2981    </t>
2982    <t>
2983      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
2984      "Content-Location on 304 responses"
2985    </t>
2986    <t>
2987      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
2988      "'requested resource' in content-encoding definition"
2989    </t>
2990    <t>
2991      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
2992      "consider removing the 'changes from 2068' sections"
2993    </t>
2994  </list>
2995</t>
2996<t>
2997  Partly resolved issues:
2998  <list style="symbols"> 
2999    <t>
3000      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
3001      "Content-MD5 and partial responses"
3002    </t>
3003  </list>
3004</t>
3005</section>
3006
3007<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
3008<t>
3009  Closed issues:
3010  <list style="symbols"> 
3011    <t>
3012      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
3013      "Factor out Content-Disposition"
3014    </t>
3015  </list>
3016</t>
3017</section>
3018
3019<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
3020<t>
3021  Closed issues:
3022  <list style="symbols"> 
3023    <t>
3024      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
3025      "Header Classification"
3026    </t>
3027    <t>
3028      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
3029      "untangle ABNFs for header fields"
3030    </t>
3031    <t>
3032      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
3033      "potentially misleading MAY in media-type def"
3034    </t>
3035  </list>
3036</t>
3037</section>
3038
3039<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
3040<t>
3041  Closed issues:
3042  <list style="symbols"> 
3043    <t>
3044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
3045      "Default charsets for text media types"
3046    </t>
3047    <t>
3048      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
3049      "untangle ABNFs for header fields"
3050    </t>
3051    <t>
3052      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
3053      "confusing undefined parameter in media range example"
3054    </t>
3055  </list>
3056</t>
3057</section>
3058
3059</section>
3060
3061</back>
3062</rfc>
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