source: draft-ietf-httpbis/latest/p3-payload.xml @ 1167

Last change on this file since 1167 was 1167, checked in by julian.reschke@…, 9 years ago

remove unused ABNF imports (see #276)

  • Property svn:eol-style set to native
File size: 129.9 KB
Line 
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.12"/>.
221  </t>
222</note>
223</front>
224<middle>
225<section title="Introduction" anchor="introduction">
226<t>
227   This document defines HTTP/1.1 message payloads (a.k.a., content), the
228   associated metadata header fields that define how the payload is intended
229   to be interpreted by a recipient, the request header fields that
230   might influence content selection, and the various selection algorithms
231   that are collectively referred to as HTTP content negotiation.
232</t>
233<t>
234   This document is currently disorganized in order to minimize the changes
235   between drafts and enable reviewers to see the smaller errata changes.
236   A future draft will reorganize the sections to better reflect the content.
237   In particular, the sections on entities will be renamed payload and moved
238   to the first half of the document, while the sections on content negotiation
239   and associated request header fields will be moved to the second half.  The
240   current mess reflects how widely dispersed these topics and associated
241   requirements had become in <xref target="RFC2616"/>.
242</t>
243
244<section title="Terminology" anchor="terminology">
245<t>
246   This specification uses a number of terms to refer to the roles
247   played by participants in, and objects of, the HTTP communication.
248</t>
249<t>
250  <iref item="content negotiation"/>
251  <x:dfn>content negotiation</x:dfn>
252  <list>
253    <t>
254      The mechanism for selecting the appropriate representation when
255      servicing a request. The representation in any response
256      can be negotiated (including error responses).
257    </t>
258  </list>
259</t>
260</section>
261
262<section title="Requirements" anchor="intro.requirements">
263<t>
264   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
265   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
266   document are to be interpreted as described in <xref target="RFC2119"/>.
267</t>
268<t>
269   An implementation is not compliant if it fails to satisfy one or more
270   of the "MUST" or "REQUIRED" level requirements for the protocols it
271   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
272   level and all the "SHOULD" level requirements for its protocols is said
273   to be "unconditionally compliant"; one that satisfies all the "MUST"
274   level requirements but not all the "SHOULD" level requirements for its
275   protocols is said to be "conditionally compliant".
276</t>
277</section>
278
279<section title="Syntax Notation" anchor="notation">
280  <x:anchor-alias value="ALPHA"/>
281  <x:anchor-alias value="CR"/>
282  <x:anchor-alias value="DIGIT"/>
283  <x:anchor-alias value="LF"/>
284  <x:anchor-alias value="OCTET"/>
285  <x:anchor-alias value="VCHAR"/>
286  <x:anchor-alias value="WSP"/>
287<t>
288  This specification uses the ABNF syntax defined in &notation; (which
289  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
290  <xref target="collected.abnf"/> shows the collected ABNF, with the list
291  rule expanded.
292</t>
293<t>
294  The following core rules are included by
295  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
296  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
297  DIGIT (decimal 0-9), DQUOTE (double quote),
298  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
299  OCTET (any 8-bit sequence of data), SP (space),
300  VCHAR (any visible USASCII character),
301  and WSP (whitespace).
302</t>
303
304<section title="Core Rules" anchor="core.rules">
305  <x:anchor-alias value="token"/>
306  <x:anchor-alias value="word"/>
307  <x:anchor-alias value="OWS"/>
308<t>
309  The core rules below are defined in &basic-rules;:
310</t>
311<figure><artwork type="abnf2616">
312  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
313  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
314  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
315</artwork></figure>
316</section>
317
318<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
319  <x:anchor-alias value="absolute-URI"/>
320  <x:anchor-alias value="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 Sets" anchor="character.sets">
339<t>
340   HTTP uses the same definition of the term "character set" as that
341   described for MIME:
342</t>
343<t>
344   The term "character set" is used in this document to refer to a
345   method used with one or more tables to convert a sequence of octets
346   into a sequence of characters. Note that unconditional conversion in
347   the other direction is not required, in that not all characters might
348   be available in a given character set and a character set might provide
349   more than one sequence of octets to represent a particular character.
350   This definition is intended to allow various kinds of character
351   encoding, from simple single-table mappings such as US-ASCII to
352   complex table switching methods such as those that use ISO-2022's
353   techniques. However, the definition associated with a MIME character
354   set name &MUST; fully specify the mapping to be performed from octets
355   to characters. In particular, use of external profiling information
356   to determine the exact mapping is not permitted.
357</t>
358<x:note>
359  <t>
360    <x:h>Note:</x:h> This use of the term "character set" is more commonly
361    referred to as a "character encoding". However, since HTTP and
362    MIME share the same registry, it is important that the terminology
363    also be shared.
364  </t>
365</x:note>
366<t anchor="rule.charset">
367  <x:anchor-alias value="charset"/>
368   HTTP character sets are identified by case-insensitive tokens. The
369   complete set of tokens is defined by the IANA Character Set registry
370   (<eref target="http://www.iana.org/assignments/character-sets"/>).
371</t>
372<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
373  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
374</artwork></figure>
375<t>
376   Although HTTP allows an arbitrary token to be used as a charset
377   value, any token that has a predefined value within the IANA
378   Character Set registry &MUST; represent the character set defined
379   by that registry. Applications &SHOULD; limit their use of character
380   sets to those defined by the IANA registry.
381</t>
382<t>
383   HTTP uses charset in two contexts: within an Accept-Charset request
384   header field (in which the charset value is an unquoted token) and as the
385   value of a parameter in a Content-Type header field (within a request or
386   response), in which case the parameter value of the charset parameter
387   can be quoted.
388</t>
389<t>
390   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
391   <xref target="RFC2277"/>.
392</t>
393
394<section title="Missing Charset" anchor="missing.charset">
395<t>
396   Some HTTP/1.0 software has interpreted a Content-Type header field without
397   charset parameter incorrectly to mean "recipient should guess".
398   Senders wishing to defeat this behavior &MAY; include a charset
399   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
400   it is known that it will not confuse the recipient.
401</t>
402<t>
403   Unfortunately, some older HTTP/1.0 clients did not deal properly with
404   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
405   charset label provided by the sender; and those user agents that have
406   a provision to "guess" a charset &MUST; use the charset from the
407   content-type field if they support that charset, rather than the
408   recipient's preference, when initially displaying a document. See
409   <xref target="canonicalization.and.text.defaults"/>.
410</t>
411</section>
412</section>
413
414<section title="Content Codings" anchor="content.codings">
415  <x:anchor-alias value="content-coding"/>
416<t>
417   Content coding values indicate an encoding transformation that has
418   been or can be applied to a representation. Content codings are primarily
419   used to allow a representation to be compressed or otherwise usefully
420   transformed without losing the identity of its underlying media type
421   and without loss of information. Frequently, the representation is stored in
422   coded form, transmitted directly, and only decoded by the recipient.
423</t>
424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
425  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
426</artwork></figure>
427<t>
428   All content-coding values are case-insensitive. HTTP/1.1 uses
429   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
430   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
431   describes the content-coding, what is more important is that it
432   indicates what decoding mechanism will be required to remove the
433   encoding.
434</t>
435<t>
436   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
437  <list>
438    <t>
439      See &compress-coding;.
440    </t>
441  </list>
442</t>
443<t>
444   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
445  <list>
446    <t>
447      See &deflate-coding;.
448    </t>
449  </list>
450</t>
451<t>
452   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
453  <list>
454    <t>
455      See &gzip-coding;.
456    </t>
457  </list>
458</t>
459<t>
460   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
461  <list><t>
462        The default (identity) encoding; the use of no transformation
463        whatsoever. This content-coding is used only in the Accept-Encoding
464        header field, and &SHOULD-NOT;  be used in the Content-Encoding
465        header field.
466  </t></list>
467</t>
468
469<section title="Content Coding Registry" anchor="content.coding.registry">
470<t>
471   The HTTP Content Coding Registry defines the name space for the content
472   coding names.
473</t>
474<t>
475   Registrations &MUST; include the following fields:
476   <list style="symbols">
477     <t>Name</t>
478     <t>Description</t>
479     <t>Pointer to specification text</t>
480   </list>
481</t>
482<t>
483   Names of content codings &MUST-NOT; overlap with names of transfer codings
484   (&transfer-codings;), unless the encoding transformation is identical (as it
485   is the case for the compression codings defined in
486   &compression-codings;).
487</t>
488<t>
489   Values to be added to this name space require a specification
490   (see "Specification Required" in
491   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
492   conform to the purpose of content coding defined in this section.
493</t>
494<t>
495   The registry itself is maintained at
496   <eref target="http://www.iana.org/assignments/http-parameters"/>.
497</t>
498</section>
499
500</section>
501
502<section title="Media Types" anchor="media.types">
503  <x:anchor-alias value="media-type"/>
504  <x:anchor-alias value="type"/>
505  <x:anchor-alias value="subtype"/>
506<t>
507   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
508   and Accept (<xref target="header.accept"/>) header fields in order to provide
509   open and extensible data typing and type negotiation.
510</t>
511<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"/>
512  <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> )
513  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
514  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
515</artwork></figure>
516<t anchor="rule.parameter">
517  <x:anchor-alias value="attribute"/>
518  <x:anchor-alias value="parameter"/>
519  <x:anchor-alias value="value"/>
520   The type/subtype &MAY; be followed by parameters in the form of
521   attribute/value pairs.
522</t>
523<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"/>
524  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
525  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
526  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
527</artwork></figure>
528<t>
529   The type, subtype, and parameter attribute names are case-insensitive.
530   Parameter values might or might not be case-sensitive, depending on the
531   semantics of the parameter name.  The presence or absence of a parameter might
532   be significant to the processing of a media-type, depending on its
533   definition within the media type registry.
534</t>
535<t>
536   A parameter value that matches the <x:ref>token</x:ref> production can be
537   transmitted as either a token or within a quoted-string. The quoted and
538   unquoted values are equivalent.
539</t>
540<t>
541   Note that some older HTTP applications do not recognize media type
542   parameters. When sending data to older HTTP applications,
543   implementations &SHOULD; only use media type parameters when they are
544   required by that type/subtype definition.
545</t>
546<t>
547   Media-type values are registered with the Internet Assigned Number
548   Authority (IANA). The media type registration process is
549   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
550   discouraged.
551</t>
552
553<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
554<t>
555   Internet media types are registered with a canonical form. A
556   representation transferred via HTTP messages &MUST; be in the
557   appropriate canonical form prior to its transmission except for
558   "text" types, as defined in the next paragraph.
559</t>
560<t>
561   When in canonical form, media subtypes of the "text" type use CRLF as
562   the text line break. HTTP relaxes this requirement and allows the
563   transport of text media with plain CR or LF alone representing a line
564   break when it is done consistently for an entire representation. HTTP
565   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
566   a line break in text media received via HTTP. In
567   addition, if the text is in a character encoding that does not
568   use octets 13 and 10 for CR and LF respectively, as is the case for
569   some multi-byte character encodings, HTTP allows the use of whatever octet
570   sequences are defined by that character encoding to represent the
571   equivalent of CR and LF for line breaks. This flexibility regarding
572   line breaks applies only to text media in the payload body; a bare CR
573   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
574   structures (such as header fields and multipart boundaries).
575</t>
576<t>
577   If a representation is encoded with a content-coding, the underlying
578   data &MUST; be in a form defined above prior to being encoded.
579</t>
580<t>
581   The "charset" parameter is used with some media types to define the
582   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
583   parameter is provided by the sender, media subtypes of the "text"
584   type are defined to have a default charset value of "ISO-8859-1" when
585   received via HTTP. Data in character encodings other than "ISO-8859-1" or
586   its subsets &MUST; be labeled with an appropriate charset value. See
587   <xref target="missing.charset"/> for compatibility problems.
588</t>
589</section>
590
591<section title="Multipart Types" anchor="multipart.types">
592<t>
593   MIME provides for a number of "multipart" types &mdash; encapsulations of
594   one or more representations within a single message-body. All multipart
595   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
596   and &MUST; include a boundary parameter as part of the media type
597   value. The message body is itself a protocol element and &MUST;
598   therefore use only CRLF to represent line breaks between body-parts.
599</t>
600<t>
601   In general, HTTP treats a multipart message-body no differently than
602   any other media type: strictly as payload.  HTTP does not use the
603   multipart boundary as an indicator of message-body length.
604   <!-- jre: re-insert removed text pointing to caching? -->
605   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
606   behavior as a MIME user agent would upon receipt of a multipart type.
607   The MIME header fields within each body-part of a multipart message-body
608   do not have any significance to HTTP beyond that defined by
609   their MIME semantics.
610</t>
611<t>
612   If an application receives an unrecognized multipart subtype, the
613   application &MUST; treat it as being equivalent to "multipart/mixed".
614</t>
615<x:note>
616  <t>
617    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
618    for carrying form data suitable for processing via the POST
619    request method, as described in <xref target="RFC2388"/>.
620  </t>
621</x:note>
622</section>
623</section>
624
625<section title="Language Tags" anchor="language.tags">
626  <x:anchor-alias value="language-tag"/>
627<t>
628   A language tag, as defined in <xref target="RFC5646"/>, identifies a
629   natural language spoken, written, or otherwise conveyed by human beings for
630   communication of information to other human beings. Computer languages are
631   explicitly excluded. HTTP uses language tags within the Accept-Language and
632   Content-Language fields.
633</t>
634<t>
635   In summary, a language tag is composed of one or more parts: A primary
636   language subtag followed by a possibly empty series of subtags:
637</t>
638<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
639  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
640</artwork></figure>
641<t>
642   White space is not allowed within the tag and all tags are case-insensitive.
643   The name space of language subtags is administered by the IANA (see
644   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
645</t>
646<figure>
647  <preamble>Example tags include:</preamble>
648<artwork type="example">
649  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
650</artwork>
651</figure>
652<t>
653   See <xref target="RFC5646"/> for further information.
654</t>
655</section>
656</section>
657
658<section title="Payload" anchor="payload">
659<t>
660   HTTP messages &MAY; transfer a payload if not otherwise restricted by
661   the request method or response status code.  The payload consists of
662   metadata, in the form of header fields, and data, in the form of the
663   sequence of octets in the message-body after any transfer-coding has
664   been decoded.
665</t>
666<iref item="payload"/>
667<t>   
668   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
669   representation of some resource.  We use separate terms for payload
670   and representation because some messages contain only the associated
671   representation's header fields (e.g., responses to HEAD) or only some
672   part(s) of the representation (e.g., the 206 status code).
673</t>
674<section title="Payload Header Fields" anchor="payload.header.fields">
675  <x:anchor-alias value="payload-header"/>
676<t>
677   HTTP header fields that specifically define the payload, rather than the
678   associated representation, are referred to as "payload header fields".
679   The following payload header fields are defined by HTTP/1.1:
680</t>
681<texttable align="left">
682  <ttcol>Header Field Name</ttcol>
683  <ttcol>Defined in...</ttcol>
684
685  <c>Content-Length</c> <c>&header-content-length;</c>
686  <c>Content-MD5</c> <c><xref target="header.content-md5"/></c>
687  <c>Content-Range</c> <c>&header-content-range;</c>
688</texttable>
689</section>
690
691<section title="Payload Body" anchor="payload.body">
692  <x:anchor-alias value="payload-body"/>
693<t>
694   A payload body is only present in a message when a message-body is
695   present, as described in &message-body;. The payload body is obtained
696   from the message-body by decoding any Transfer-Encoding that might
697   have been applied to ensure safe and proper transfer of the message.
698</t>
699</section>
700</section>
701
702<section title="Representation" anchor="representation">
703<iref item="representation"/>
704<t>
705   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
706   communicated from one party to another.  A resource representation
707   is information that reflects the state of that resource, as observed
708   at some point in the past (e.g., in a response to GET) or to be
709   desired at some point in the future (e.g., in a PUT request).
710</t>
711<t>
712   Most, but not all, representations transferred via HTTP are intended
713   to be a representation of the target resource (the resource identified
714   by the effective request URI).  The precise semantics of a representation
715   are determined by the type of message (request or response), the request
716   method, the response status code, and the representation metadata.
717   For example, the above semantic is true for the representation in any
718   200 (OK) response to GET and for the representation in any PUT request.
719   A 200 response to PUT, in contrast, contains either a representation
720   that describes the successful action or a representation of the target
721   resource, with the latter indicated by a Content-Location header field
722   with the same value as the effective request URI.  Likewise, response
723   messages with an error status code usually contain a representation that
724   describes the error and what next steps are suggested for resolving it.
725</t>
726
727<section title="Representation Header Fields" anchor="representation.header.fields">
728  <x:anchor-alias value="representation-header"/>
729<t>
730   Representation header fields define metadata about the representation data
731   enclosed in the message-body or, if no message-body is present, about
732   the representation that would have been transferred in a 200 response
733   to a simultaneous GET request with the same effective request URI.
734</t>
735<t>
736   The following header fields are defined as representation metadata:
737</t>
738<texttable align="left">
739  <ttcol>Header Field Name</ttcol>
740  <ttcol>Defined in...</ttcol>
741
742  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
743  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
744  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
745  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
746  <c>Expires</c> <c>&header-expires;</c>
747  <c>Last-Modified</c> <c>&header-last-modified;</c>
748</texttable>
749</section>
750
751<section title="Representation Data" anchor="representation.data">
752  <x:anchor-alias value="representation-data"/>
753<t>
754   The representation body associated with an HTTP message is
755   either provided as the payload body of the message or
756   referred to by the message semantics and the effective request
757   URI.  The representation data is in a format and encoding defined by
758   the representation metadata header fields.
759</t>
760<t>
761   The data type of the representation data
762   is determined via the header fields Content-Type and Content-Encoding.
763   These define a two-layer, ordered encoding model:
764</t>
765<figure><artwork type="example">
766  representation-data := Content-Encoding( Content-Type( bits ) )
767</artwork></figure>
768<t>
769   Content-Type specifies the media type of the underlying data, which
770   defines both the data format and how that data &SHOULD; be processed
771   by the recipient (within the scope of the request method semantics).
772   Any HTTP/1.1 message containing a payload body &SHOULD; include a
773   Content-Type header field defining the media type of the associated
774   representation unless that metadata is unknown to the sender.
775   If the Content-Type header field is not present, it indicates that
776   the sender does not know the media type of the representation;
777   recipients &MAY; either assume that the media type is
778   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
779   or examine the content to determine its type.
780</t>
781<t>
782   In practice, resource owners do not always properly configure their origin
783   server to provide the correct Content-Type for a given representation,
784   with the result that some clients will examine a response body's content
785   and override the specified type.
786   Clients that do so risk drawing incorrect conclusions, which might expose
787   additional security risks (e.g., "privilege escalation").  Furthermore,
788   it is impossible to determine the sender's intent by examining the data
789   format: many data formats match multiple media types that differ only in
790   processing semantics.  Implementers are encouraged to provide a means of
791   disabling such "content sniffing" when it is used.
792</t>
793<t>
794   Content-Encoding is used to indicate any additional content
795   codings applied to the data, usually for the purpose of data
796   compression, that are a property of the representation.  If
797   Content-Encoding is not present, then there is no additional
798   encoding beyond that defined by the Content-Type.
799</t>
800</section>
801</section>
802
803<section title="Content Negotiation" anchor="content.negotiation">
804<t>
805   HTTP responses include a representation which contains information for
806   interpretation, whether by a human user or for further processing.
807   Often, the server has different ways of representing the
808   same information; for example, in different formats, languages,
809   or using different character encodings.
810</t>
811<t>
812   HTTP clients and their users might have different or variable
813   capabilities, characteristics or preferences which would influence
814   which representation, among those available from the server,
815   would be best for the server to deliver. For this reason, HTTP
816   provides mechanisms for "content negotiation" &mdash; a process of
817   allowing selection of a representation of a given resource,
818   when more than one is available.
819</t>
820<t>
821   This specification defines two patterns of content negotiation;
822   "server-driven", where the server selects the representation based
823   upon the client's stated preferences, and "agent-driven" negotiation,
824   where the server provides a list of representations for the client to
825   choose from, based upon their metadata. In addition,  there are
826   other patterns: some applications use an "active content" pattern,
827   where the server returns active content which runs on the client
828   and, based on client available parameters, selects additional
829   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
830   has also been proposed.
831</t>
832<t>
833   These patterns are all widely used, and have trade-offs in applicability
834   and practicality. In particular, when the number of preferences or
835   capabilities to be expressed by a client are large (such as when many
836   different formats are supported by a user-agent), server-driven
837   negotiation becomes unwieldy, and might not be appropriate. Conversely,
838   when the number of representations to choose from is very large,
839   agent-driven negotiation might not be appropriate.
840</t>
841<t>
842   Note that in all cases, the supplier of representations has the
843   responsibility for determining which representations might be
844   considered to be the "same information".
845</t>
846
847<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
848<t>
849   If the selection of the best representation for a response is made by
850   an algorithm located at the server, it is called server-driven
851   negotiation. Selection is based on the available representations of
852   the response (the dimensions over which it can vary; e.g., language,
853   content-coding, etc.) and the contents of particular header fields in
854   the request message or on other information pertaining to the request
855   (such as the network address of the client).
856</t>
857<t>
858   Server-driven negotiation is advantageous when the algorithm for
859   selecting from among the available representations is difficult to
860   describe to the user agent, or when the server desires to send its
861   "best guess" to the client along with the first response (hoping to
862   avoid the round-trip delay of a subsequent request if the "best
863   guess" is good enough for the user). In order to improve the server's
864   guess, the user agent &MAY; include request header fields (Accept,
865   Accept-Language, Accept-Encoding, etc.) which describe its
866   preferences for such a response.
867</t>
868<t>
869   Server-driven negotiation has disadvantages:
870  <list style="numbers">
871    <t>
872         It is impossible for the server to accurately determine what
873         might be "best" for any given user, since that would require
874         complete knowledge of both the capabilities of the user agent
875         and the intended use for the response (e.g., does the user want
876         to view it on screen or print it on paper?).
877    </t>
878    <t>
879         Having the user agent describe its capabilities in every
880         request can be both very inefficient (given that only a small
881         percentage of responses have multiple representations) and a
882         potential violation of the user's privacy.
883    </t>
884    <t>
885         It complicates the implementation of an origin server and the
886         algorithms for generating responses to a request.
887    </t>
888    <t>
889         It might limit a public cache's ability to use the same response
890         for multiple user's requests.
891    </t>
892  </list>
893</t>
894<t>
895   HTTP/1.1 includes the following header fields for enabling
896   server-driven negotiation through description of user agent
897   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
898   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
899   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
900   However, an origin server is not limited to these dimensions and &MAY; vary
901   the response based on any aspect of the request, including aspects
902   of the connection (e.g., IP address) or information within extension
903   header fields not defined by this specification.
904</t>
905<x:note>
906  <t>
907    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
908    because new clients might not be recognized.
909  </t>
910</x:note>
911<t>
912   The Vary header field (&header-vary;) can be used to express the parameters the
913   server uses to select a representation that is subject to server-driven
914   negotiation.
915</t>
916</section>
917
918<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
919<t>
920   With agent-driven negotiation, selection of the best representation
921   for a response is performed by the user agent after receiving an
922   initial response from the origin server. Selection is based on a list
923   of the available representations of the response included within the
924   header fields or body of the initial response, with each
925   representation identified by its own URI. Selection from among the
926   representations can be performed automatically (if the user agent is
927   capable of doing so) or manually by the user selecting from a
928   generated (possibly hypertext) menu.
929</t>
930<t>
931   Agent-driven negotiation is advantageous when the response would vary
932   over commonly-used dimensions (such as type, language, or encoding),
933   when the origin server is unable to determine a user agent's
934   capabilities from examining the request, and generally when public
935   caches are used to distribute server load and reduce network usage.
936</t>
937<t>
938   Agent-driven negotiation suffers from the disadvantage of needing a
939   second request to obtain the best alternate representation. This
940   second request is only efficient when caching is used. In addition,
941   this specification does not define any mechanism for supporting
942   automatic selection, though it also does not prevent any such
943   mechanism from being developed as an extension and used within
944   HTTP/1.1.
945</t>
946<t>
947   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
948   status codes for enabling agent-driven negotiation when the server is
949   unwilling or unable to provide a varying response using server-driven
950   negotiation.
951</t>
952</section>
953</section>
954
955<section title="Header Field Definitions" anchor="header.fields">
956<t>
957   This section defines the syntax and semantics of HTTP/1.1 header fields
958   related to the payload of messages.
959</t>
960
961<section title="Accept" anchor="header.accept">
962  <iref primary="true" item="Accept header field" x:for-anchor=""/>
963  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
964  <x:anchor-alias value="Accept"/>
965  <x:anchor-alias value="Accept-v"/>
966  <x:anchor-alias value="accept-ext"/>
967  <x:anchor-alias value="accept-params"/>
968  <x:anchor-alias value="media-range"/>
969<t>
970   The "Accept" header field can be used by user agents to specify
971   response media types that are acceptable. Accept header fields can be used to
972   indicate that the request is specifically limited to a small set of desired
973   types, as in the case of a request for an in-line image.
974</t>
975<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
976  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
977  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
978 
979  <x:ref>media-range</x:ref>    = ( "*/*"
980                   / ( <x:ref>type</x:ref> "/" "*" )
981                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
982                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
983  <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> )
984  <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> ]
985</artwork></figure>
986<t>
987   The asterisk "*" character is used to group media types into ranges,
988   with "*/*" indicating all media types and "type/*" indicating all
989   subtypes of that type. The media-range &MAY; include media type
990   parameters that are applicable to that range.
991</t>
992<t>
993   Each media-range &MAY; be followed by one or more accept-params,
994   beginning with the "q" parameter for indicating a relative quality
995   factor. The first "q" parameter (if any) separates the media-range
996   parameter(s) from the accept-params. Quality factors allow the user
997   or user agent to indicate the relative degree of preference for that
998   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
999   default value is q=1.
1000</t>
1001<x:note>
1002  <t>
1003    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1004    parameters from Accept extension parameters is due to historical
1005    practice. Although this prevents any media type parameter named
1006    "q" from being used with a media range, such an event is believed
1007    to be unlikely given the lack of any "q" parameters in the IANA
1008    media type registry and the rare usage of any media type
1009    parameters in Accept. Future media types are discouraged from
1010    registering any parameter named "q".
1011  </t>
1012</x:note>
1013<t>
1014   The example
1015</t>
1016<figure><artwork type="example">
1017  Accept: audio/*; q=0.2, audio/basic
1018</artwork></figure>
1019<t>
1020   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1021   type if it is the best available after an 80% mark-down in quality".
1022</t>
1023<t>
1024   If no Accept header field is present, then it is assumed that the
1025   client accepts all media types. If an Accept header field is present,
1026   and if the server cannot send a response which is acceptable
1027   according to the combined Accept field value, then the server &SHOULD;
1028   send a 406 (Not Acceptable) response.
1029</t>
1030<t>
1031   A more elaborate example is
1032</t>
1033<figure><artwork type="example">
1034  Accept: text/plain; q=0.5, text/html,
1035          text/x-dvi; q=0.8, text/x-c
1036</artwork></figure>
1037<t>
1038   Verbally, this would be interpreted as "text/html and text/x-c are
1039   the preferred media types, but if they do not exist, then send the
1040   text/x-dvi representation, and if that does not exist, send the text/plain
1041   representation".
1042</t>
1043<t>
1044   Media ranges can be overridden by more specific media ranges or
1045   specific media types. If more than one media range applies to a given
1046   type, the most specific reference has precedence. For example,
1047</t>
1048<figure><artwork type="example">
1049  Accept: text/*, text/html, text/html;level=1, */*
1050</artwork></figure>
1051<t>
1052   have the following precedence:
1053   <list style="numbers">
1054    <t>text/html;level=1</t>
1055    <t>text/html</t>
1056    <t>text/*</t>
1057    <t>*/*</t>
1058   </list>
1059</t>
1060<t>
1061   The media type quality factor associated with a given type is
1062   determined by finding the media range with the highest precedence
1063   which matches that type. For example,
1064</t>
1065<figure><artwork type="example">
1066  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1067          text/html;level=2;q=0.4, */*;q=0.5
1068</artwork></figure>
1069<t>
1070   would cause the following values to be associated:
1071</t>
1072<texttable align="left">
1073  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1074  <c>text/html;level=1</c>    <c>1</c>
1075  <c>text/html</c>            <c>0.7</c>
1076  <c>text/plain</c>           <c>0.3</c>
1077  <c>image/jpeg</c>           <c>0.5</c>
1078  <c>text/html;level=2</c>    <c>0.4</c>
1079  <c>text/html;level=3</c>    <c>0.7</c>
1080</texttable>
1081<t>
1082      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1083      values for certain media ranges. However, unless the user agent is
1084      a closed system which cannot interact with other rendering agents,
1085      this default set ought to be configurable by the user.
1086</t>
1087</section>
1088
1089<section title="Accept-Charset" anchor="header.accept-charset">
1090  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
1091  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
1092  <x:anchor-alias value="Accept-Charset"/>
1093  <x:anchor-alias value="Accept-Charset-v"/>
1094<t>
1095   The "Accept-Charset" header field can be used by user agents to
1096   indicate what response character sets are acceptable. This field allows
1097   clients capable of understanding more comprehensive or special-purpose
1098   character sets to signal that capability to a server which is capable of
1099   representing documents in those character sets.
1100</t>
1101<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1102  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1103          <x:ref>Accept-Charset-v</x:ref>
1104  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1105                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1106</artwork></figure>
1107<t>
1108   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1109   be given an associated quality value which represents the user's
1110   preference for that charset. The default value is q=1. An example is
1111</t>
1112<figure><artwork type="example">
1113  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1114</artwork></figure>
1115<t>
1116   The special value "*", if present in the Accept-Charset field,
1117   matches every character set (including ISO-8859-1) which is not
1118   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1119   in an Accept-Charset field, then all character sets not explicitly
1120   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1121   a quality value of 1 if not explicitly mentioned.
1122</t>
1123<t>
1124   If no Accept-Charset header field is present, the default is that any
1125   character set is acceptable. If an Accept-Charset header field is present,
1126   and if the server cannot send a response which is acceptable
1127   according to the Accept-Charset header field, then the server &SHOULD; send
1128   an error response with the 406 (Not Acceptable) status code, though
1129   the sending of an unacceptable response is also allowed.
1130</t>
1131</section>
1132
1133<section title="Accept-Encoding" anchor="header.accept-encoding">
1134  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
1135  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
1136  <x:anchor-alias value="Accept-Encoding"/>
1137  <x:anchor-alias value="Accept-Encoding-v"/>
1138  <x:anchor-alias value="codings"/>
1139<t>
1140   The "Accept-Encoding" header field can be used by user agents to
1141   indicate what response content-codings (<xref target="content.codings"/>)
1142   are acceptable in the response.
1143</t>
1144<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1145  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1146                     <x:ref>Accept-Encoding-v</x:ref>
1147  <x:ref>Accept-Encoding-v</x:ref>  =
1148                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1149  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1150</artwork></figure>
1151<t>
1152   Each codings value &MAY; be given an associated quality value which
1153   represents the preference for that encoding. The default value is q=1.
1154</t>
1155<t>
1156   Examples of its use are:
1157</t>
1158<figure><artwork type="example">
1159  Accept-Encoding: compress, gzip
1160  Accept-Encoding:
1161  Accept-Encoding: *
1162  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1163  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1164</artwork></figure>
1165<t>
1166   A server tests whether a content-coding is acceptable, according to
1167   an Accept-Encoding field, using these rules:
1168  <list style="numbers">
1169      <t>If the content-coding is one of the content-codings listed in
1170         the Accept-Encoding field, then it is acceptable, unless it is
1171         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1172         qvalue of 0 means "not acceptable".)</t>
1173
1174      <t>The special "*" symbol in an Accept-Encoding field matches any
1175         available content-coding not explicitly listed in the header
1176         field.</t>
1177
1178      <t>If multiple content-codings are acceptable, then the acceptable
1179         content-coding with the highest non-zero qvalue is preferred.</t>
1180
1181      <t>The "identity" content-coding is always acceptable, unless
1182         specifically refused because the Accept-Encoding field includes
1183         "identity;q=0", or because the field includes "*;q=0" and does
1184         not explicitly include the "identity" content-coding. If the
1185         Accept-Encoding field-value is empty, then only the "identity"
1186         encoding is acceptable.</t>
1187  </list>
1188</t>
1189<t>
1190   If an Accept-Encoding field is present in a request, and if the
1191   server cannot send a response which is acceptable according to the
1192   Accept-Encoding header field, then the server &SHOULD; send an error response
1193   with the 406 (Not Acceptable) status code.
1194</t>
1195<t>
1196   If no Accept-Encoding field is present in a request, the server &MAY;
1197   assume that the client will accept any content coding. In this case,
1198   if "identity" is one of the available content-codings, then the
1199   server &SHOULD; use the "identity" content-coding, unless it has
1200   additional information that a different content-coding is meaningful
1201   to the client.
1202</t>
1203<x:note>
1204  <t>
1205    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1206    and if the "identity" content-coding is unavailable, then
1207    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1208    "gzip" and "compress") are preferred; some older clients
1209    improperly display messages sent with other content-codings.  The
1210    server might also make this decision based on information about
1211    the particular user-agent or client.
1212  </t>
1213</x:note>
1214<x:note>
1215  <t>
1216    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1217    associated with content-codings. This means that qvalues will not
1218    work and are not permitted with x-gzip or x-compress.
1219  </t>
1220</x:note>
1221</section>
1222
1223<section title="Accept-Language" anchor="header.accept-language">
1224  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
1225  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
1226  <x:anchor-alias value="Accept-Language"/>
1227  <x:anchor-alias value="Accept-Language-v"/>
1228  <x:anchor-alias value="language-range"/>
1229<t>
1230   The "Accept-Language" header field can be used by user agents to
1231   indicate the set of natural languages that are preferred in the response.
1232   Language tags are defined in <xref target="language.tags"/>.
1233</t>
1234<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1235  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1236                    <x:ref>Accept-Language-v</x:ref>
1237  <x:ref>Accept-Language-v</x:ref> =
1238                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1239  <x:ref>language-range</x:ref>    =
1240            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1241</artwork></figure>
1242<t>
1243   Each language-range can be given an associated quality value which
1244   represents an estimate of the user's preference for the languages
1245   specified by that range. The quality value defaults to "q=1". For
1246   example,
1247</t>
1248<figure><artwork type="example">
1249  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1250</artwork></figure>
1251<t>
1252   would mean: "I prefer Danish, but will accept British English and
1253   other types of English".
1254   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1255</t>
1256<t>
1257   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1258   several matching schemes. Implementations can offer the most appropriate
1259   matching scheme for their requirements.
1260</t>
1261<x:note>
1262  <t>
1263    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1264    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1265    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1266  </t>
1267</x:note>
1268<t>
1269   It might be contrary to the privacy expectations of the user to send
1270   an Accept-Language header field with the complete linguistic preferences of
1271   the user in every request. For a discussion of this issue, see
1272   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1273</t>
1274<t>
1275   As intelligibility is highly dependent on the individual user, it is
1276   recommended that client applications make the choice of linguistic
1277   preference available to the user. If the choice is not made
1278   available, then the Accept-Language header field &MUST-NOT; be given in
1279   the request.
1280</t>
1281<x:note>
1282  <t>
1283    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1284    the user, we remind implementors of  the fact that users are not
1285    familiar with the details of language matching as described above,
1286    and ought to be provided appropriate guidance. As an example, users
1287    might assume that on selecting "en-gb", they will be served any
1288    kind of English document if British English is not available. A
1289    user agent might suggest in such a case to add "en" to get the
1290    best matching behavior.
1291  </t>
1292</x:note>
1293</section>
1294
1295<section title="Content-Encoding" anchor="header.content-encoding">
1296  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1297  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
1298  <x:anchor-alias value="Content-Encoding"/>
1299  <x:anchor-alias value="Content-Encoding-v"/>
1300<t>
1301   The "Content-Encoding" header field indicates what content-codings
1302   have been applied to the representation, and thus what decoding mechanisms
1303   must be applied in order to obtain the media-type referenced by the
1304   Content-Type header field. Content-Encoding is primarily used to allow a
1305   representation to be compressed without losing the identity of its underlying
1306   media type.
1307</t>
1308<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1309  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1310  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1311</artwork></figure>
1312<t>
1313   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1314</t>
1315<figure><artwork type="example">
1316  Content-Encoding: gzip
1317</artwork></figure>
1318<t>
1319   The content-coding is a characteristic of the representation.
1320   Typically, the representation body is stored with this
1321   encoding and is only decoded before rendering or analogous usage.
1322   However, a transforming proxy &MAY; modify the content-coding if the
1323   new coding is known to be acceptable to the recipient, unless the
1324   "no-transform" cache-control directive is present in the message.
1325</t>
1326<t>
1327   If the content-coding of a representation is not "identity", then the
1328   representation metadata &MUST; include a Content-Encoding header
1329   field (<xref target="header.content-encoding"/>)
1330   that lists the non-identity content-coding(s) used.
1331</t>
1332<t>
1333   If the content-coding of a representation in a request message is not
1334   acceptable to the origin server, the server &SHOULD; respond with a
1335   status code of 415 (Unsupported Media Type).
1336</t>
1337<t>
1338   If multiple encodings have been applied to a representation, the content
1339   codings &MUST; be listed in the order in which they were applied.
1340   Additional information about the encoding parameters &MAY; be provided
1341   by other header fields not defined by this specification.
1342</t>
1343</section>
1344
1345<section title="Content-Language" anchor="header.content-language">
1346  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1347  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
1348  <x:anchor-alias value="Content-Language"/>
1349  <x:anchor-alias value="Content-Language-v"/>
1350<t>
1351   The "Content-Language" header field describes the natural
1352   language(s) of the intended audience for the representation. Note that this might
1353   not be equivalent to all the languages used within the representation.
1354</t>
1355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1356  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1357  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1358</artwork></figure>
1359<t>
1360   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1361   Content-Language is to allow a user to identify and differentiate
1362   representations according to the user's own preferred language. Thus, if the
1363   body content is intended only for a Danish-literate audience, the
1364   appropriate field is
1365</t>
1366<figure><artwork type="example">
1367  Content-Language: da
1368</artwork></figure>
1369<t>
1370   If no Content-Language is specified, the default is that the content
1371   is intended for all language audiences. This might mean that the
1372   sender does not consider it to be specific to any natural language,
1373   or that the sender does not know for which language it is intended.
1374</t>
1375<t>
1376   Multiple languages &MAY; be listed for content that is intended for
1377   multiple audiences. For example, a rendition of the "Treaty of
1378   Waitangi", presented simultaneously in the original Maori and English
1379   versions, would call for
1380</t>
1381<figure><artwork type="example">
1382  Content-Language: mi, en
1383</artwork></figure>
1384<t>
1385   However, just because multiple languages are present within a representation
1386   does not mean that it is intended for multiple linguistic audiences.
1387   An example would be a beginner's language primer, such as "A First
1388   Lesson in Latin", which is clearly intended to be used by an
1389   English-literate audience. In this case, the Content-Language would
1390   properly only include "en".
1391</t>
1392<t>
1393   Content-Language &MAY; be applied to any media type &mdash; it is not
1394   limited to textual documents.
1395</t>
1396</section>
1397
1398<section title="Content-Location" anchor="header.content-location">
1399  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1400  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
1401  <x:anchor-alias value="Content-Location"/>
1402  <x:anchor-alias value="Content-Location-v"/>
1403<t>
1404   The "Content-Location" header field supplies a URI that can be used
1405   as a specific identifier for the representation in this message.
1406   In other words, if one were to perform a GET on this URI at the time
1407   of this message's generation, then a 200 response would contain the
1408   same representation that is enclosed as payload in this message.
1409</t>
1410<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1411  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1412                    <x:ref>Content-Location-v</x:ref>
1413  <x:ref>Content-Location-v</x:ref> =
1414                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1415</artwork></figure>
1416<t>
1417   The Content-Location value is not a replacement for the effective
1418   Request URI (&effective-request-uri;).  It is representation metadata.
1419   It has the same syntax and semantics as the header field of the same name
1420   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1421   However, its appearance in an HTTP message has some special implications
1422   for HTTP recipients.
1423</t>
1424<t>
1425   If Content-Location is included in a response message and its value
1426   is the same as the effective request URI, then the response payload
1427   &SHOULD; be considered the current representation of that resource.
1428   For a GET or HEAD request, this is the same as the default semantics
1429   when no Content-Location is provided by the server.  For a state-changing
1430   request like PUT or POST, it implies that the server's response contains
1431   the new representation of that resource, thereby distinguishing it from
1432   representations that might only report about the action (e.g., "It worked!").
1433   This allows authoring applications to update their local copies without
1434   the need for a subsequent GET request.
1435</t>
1436<t>
1437   If Content-Location is included in a response message and its value
1438   differs from the effective request URI, then the origin server is
1439   informing recipients that this representation has its own, presumably
1440   more specific, identifier.  For a GET or HEAD request, this is an
1441   indication that the effective request URI identifies a resource that
1442   is subject to content negotiation and the representation selected for
1443   this response can also be found at the identified URI.  For other
1444   methods, such a Content-Location indicates that this representation
1445   contains a report on the action's status and the same report is
1446   available (for future access with GET) at the given URI.  For
1447   example, a purchase transaction made via a POST request might
1448   include a receipt document as the payload of the 200 response;
1449   the Content-Location value provides an identifier for retrieving
1450   a copy of that same receipt in the future.
1451</t>
1452<t>
1453   If Content-Location is included in a request message, then it &MAY;
1454   be interpreted by the origin server as an indication of where the
1455   user agent originally obtained the content of the enclosed
1456   representation (prior to any subsequent modification of the content
1457   by that user agent).  In other words, the user agent is providing
1458   the same representation metadata that it received with the original
1459   representation.  However, such interpretation &MUST-NOT; be used to
1460   alter the semantics of the method requested by the client.  For
1461   example, if a client makes a PUT request on a negotiated resource
1462   and the origin server accepts that PUT (without redirection), then the
1463   new set of values for that resource is expected to be consistent with
1464   the one representation supplied in that PUT; the Content-Location
1465   cannot be used as a form of reverse content selection that
1466   identifies only one of the negotiated representations to be updated.
1467   If the user agent had wanted the latter semantics, it would have applied
1468   the PUT directly to the Content-Location URI.
1469</t>
1470<t>
1471   A Content-Location field received in a request message is transitory
1472   information that &SHOULD-NOT; be saved with other representation
1473   metadata for use in later responses.  The Content-Location's value
1474   might be saved for use in other contexts, such as within source links
1475   or other metadata.
1476</t>
1477<t>
1478   A cache cannot assume that a representation with a Content-Location
1479   different from the URI used to retrieve it can be used to respond to
1480   later requests on that Content-Location URI.
1481</t>
1482<t>
1483   If the Content-Location value is a partial URI, the partial URI is
1484   interpreted relative to the effective request URI.
1485</t>
1486</section>
1487
1488<section title="Content-MD5" anchor="header.content-md5">
1489  <iref primary="true" item="Content-MD5 header field" x:for-anchor=""/>
1490  <iref primary="true" item="Header Fields" subitem="Content-MD5" x:for-anchor=""/>
1491  <x:anchor-alias value="Content-MD5"/>
1492  <x:anchor-alias value="Content-MD5-v"/>
1493<t>
1494   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
1495   an MD5 digest of the payload body that provides an end-to-end message
1496   integrity check (MIC) of the payload body (the message-body after any
1497   transfer-coding is decoded). Note that a MIC is good for
1498   detecting accidental modification of the payload body in transit, but is not
1499   proof against malicious attacks.
1500</t>
1501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1502  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1503  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1504</artwork></figure>
1505<t>
1506   The Content-MD5 header field &MAY; be generated by an origin server or
1507   client to function as an integrity check of the payload body. Only
1508   origin servers or user agents &MAY; generate the Content-MD5 header field;
1509   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1510   value as an end-to-end integrity check. Any recipient &MAY; check that
1511   the digest value in this header field matches a corresponding digest
1512   calculated on payload body as received.
1513</t>
1514<t>
1515   The MD5 digest is computed based on the content of the payload body,
1516   including any content-coding, but not including any transfer-coding
1517   applied to the message-body because such transfer-codings might be
1518   applied or removed anywhere along the request/response chain.
1519   If the message is received with a transfer-coding, that encoding &MUST;
1520   be decoded prior to checking the Content-MD5 value against the received
1521   payload.
1522</t>
1523<t>
1524   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1525   composite media-types (e.g., multipart/* and message/rfc822), but
1526   this does not change how the digest is computed as defined in the
1527   preceding paragraph.
1528</t>
1529<t>
1530   There are several consequences of this. The payload for composite
1531   types &MAY; contain many body-parts, each with its own MIME and HTTP
1532   header fields (including Content-MD5, Content-Transfer-Encoding, and
1533   Content-Encoding header fields). If a body-part has a Content-Transfer-Encoding
1534   or Content-Encoding header field, it is assumed that the content
1535   of the body-part has had the encoding applied, and the body-part is
1536   included in the Content-MD5 digest as is &mdash; i.e., after the
1537   application. The Transfer-Encoding header field is not allowed within
1538   body-parts.
1539</t>
1540<t>
1541   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1542   computing or checking the digest: the line break convention used in
1543   the text actually transmitted &MUST; be left unaltered when computing
1544   the digest.
1545</t>
1546<x:note>
1547  <t>
1548    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1549    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1550    in which the application of Content-MD5 to HTTP entity-bodies
1551    differs from its application to MIME entity-bodies. One is that
1552    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1553    does use Transfer-Encoding and Content-Encoding. Another is that
1554    HTTP more frequently uses binary content types than MIME, so it is
1555    worth noting that, in such cases, the byte order used to compute
1556    the digest is the transmission byte order defined for the type.
1557    Lastly, HTTP allows transmission of text types with any of several
1558    line break conventions and not just the canonical form using CRLF.
1559  </t>
1560</x:note>
1561</section>
1562
1563<section title="Content-Type" anchor="header.content-type">
1564  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1565  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
1566  <x:anchor-alias value="Content-Type"/>
1567  <x:anchor-alias value="Content-Type-v"/>
1568<t>
1569   The "Content-Type" header field indicates the media type of the
1570   representation. In the case of responses to the HEAD method, the media type is
1571   that which would have been sent had the request been a GET.
1572</t>
1573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1574  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1575  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1576</artwork></figure>
1577<t>
1578   Media types are defined in <xref target="media.types"/>. An example of the field is
1579</t>
1580<figure><artwork type="example">
1581  Content-Type: text/html; charset=ISO-8859-4
1582</artwork></figure>
1583<t>
1584   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1585</t>
1586</section>
1587
1588</section>
1589
1590<section title="IANA Considerations" anchor="IANA.considerations">
1591<section title="Header Field Registration" anchor="header.field.registration">
1592<t>
1593   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1594   with the permanent registrations below (see <xref target="RFC3864"/>):
1595</t>
1596<?BEGININC p3-payload.iana-headers ?>
1597<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1598<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1599   <ttcol>Header Field Name</ttcol>
1600   <ttcol>Protocol</ttcol>
1601   <ttcol>Status</ttcol>
1602   <ttcol>Reference</ttcol>
1603
1604   <c>Accept</c>
1605   <c>http</c>
1606   <c>standard</c>
1607   <c>
1608      <xref target="header.accept"/>
1609   </c>
1610   <c>Accept-Charset</c>
1611   <c>http</c>
1612   <c>standard</c>
1613   <c>
1614      <xref target="header.accept-charset"/>
1615   </c>
1616   <c>Accept-Encoding</c>
1617   <c>http</c>
1618   <c>standard</c>
1619   <c>
1620      <xref target="header.accept-encoding"/>
1621   </c>
1622   <c>Accept-Language</c>
1623   <c>http</c>
1624   <c>standard</c>
1625   <c>
1626      <xref target="header.accept-language"/>
1627   </c>
1628   <c>Content-Encoding</c>
1629   <c>http</c>
1630   <c>standard</c>
1631   <c>
1632      <xref target="header.content-encoding"/>
1633   </c>
1634   <c>Content-Language</c>
1635   <c>http</c>
1636   <c>standard</c>
1637   <c>
1638      <xref target="header.content-language"/>
1639   </c>
1640   <c>Content-Location</c>
1641   <c>http</c>
1642   <c>standard</c>
1643   <c>
1644      <xref target="header.content-location"/>
1645   </c>
1646   <c>Content-MD5</c>
1647   <c>http</c>
1648   <c>standard</c>
1649   <c>
1650      <xref target="header.content-md5"/>
1651   </c>
1652   <c>Content-Type</c>
1653   <c>http</c>
1654   <c>standard</c>
1655   <c>
1656      <xref target="header.content-type"/>
1657   </c>
1658   <c>MIME-Version</c>
1659   <c>http</c>
1660   <c>standard</c>
1661   <c>
1662      <xref target="mime-version"/>
1663   </c>
1664</texttable>
1665<!--(END)-->
1666<?ENDINC p3-payload.iana-headers ?>
1667<t>
1668   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1669</t>
1670</section>
1671
1672<section title="Content Coding Registry" anchor="content.coding.registration">
1673<t>
1674   The registration procedure for HTTP Content Codings is now defined
1675   by <xref target="content.coding.registry"/> of this document.
1676</t>
1677<t>
1678   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1679   shall be updated with the registration below:
1680</t>
1681<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1682   <ttcol>Name</ttcol>
1683   <ttcol>Description</ttcol>
1684   <ttcol>Reference</ttcol>
1685   <c>compress</c>
1686   <c>UNIX "compress" program method</c>
1687   <c>
1688      &compress-coding;
1689   </c>
1690   <c>deflate</c>
1691   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1692   the "zlib" data format (<xref target="RFC1950"/>)
1693   </c>
1694   <c>
1695      &deflate-coding;
1696   </c>
1697   <c>gzip</c>
1698   <c>Same as GNU zip <xref target="RFC1952"/></c>
1699   <c>
1700      &gzip-coding;
1701   </c>
1702   <c>identity</c>
1703   <c>No transformation</c>
1704   <c>
1705      <xref target="content.codings"/>
1706   </c>
1707</texttable>
1708</section>
1709
1710</section>
1711
1712<section title="Security Considerations" anchor="security.considerations">
1713<t>
1714   This section is meant to inform application developers, information
1715   providers, and users of the security limitations in HTTP/1.1 as
1716   described by this document. The discussion does not include
1717   definitive solutions to the problems revealed, though it does make
1718   some suggestions for reducing security risks.
1719</t>
1720
1721<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1722<t>
1723   Accept headers fields can reveal information about the user to all
1724   servers which are accessed. The Accept-Language header field in particular
1725   can reveal information the user would consider to be of a private
1726   nature, because the understanding of particular languages is often
1727   strongly correlated to the membership of a particular ethnic group.
1728   User agents which offer the option to configure the contents of an
1729   Accept-Language header field to be sent in every request are strongly
1730   encouraged to let the configuration process include a message which
1731   makes the user aware of the loss of privacy involved.
1732</t>
1733<t>
1734   An approach that limits the loss of privacy would be for a user agent
1735   to omit the sending of Accept-Language header fields by default, and to ask
1736   the user whether or not to start sending Accept-Language header fields to a
1737   server if it detects, by looking for any Vary header fields
1738   generated by the server, that such sending could improve the quality
1739   of service.
1740</t>
1741<t>
1742   Elaborate user-customized accept header fields sent in every request,
1743   in particular if these include quality values, can be used by servers
1744   as relatively reliable and long-lived user identifiers. Such user
1745   identifiers would allow content providers to do click-trail tracking,
1746   and would allow collaborating content providers to match cross-server
1747   click-trails or form submissions of individual users. Note that for
1748   many users not behind a proxy, the network address of the host
1749   running the user agent will also serve as a long-lived user
1750   identifier. In environments where proxies are used to enhance
1751   privacy, user agents ought to be conservative in offering accept
1752   header configuration options to end users. As an extreme privacy
1753   measure, proxies could filter the accept header fields in relayed requests.
1754   General purpose user agents which provide a high degree of header
1755   configurability &SHOULD; warn users about the loss of privacy which can
1756   be involved.
1757</t>
1758</section>
1759
1760</section>
1761
1762<section title="Acknowledgments" anchor="ack">
1763</section>
1764</middle>
1765<back>
1766
1767<references title="Normative References">
1768
1769<reference anchor="ISO-8859-1">
1770  <front>
1771    <title>
1772     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1773    </title>
1774    <author>
1775      <organization>International Organization for Standardization</organization>
1776    </author>
1777    <date year="1998"/>
1778  </front>
1779  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1780</reference>
1781
1782<reference anchor="Part1">
1783  <front>
1784    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1785    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1786      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1787      <address><email>fielding@gbiv.com</email></address>
1788    </author>
1789    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1790      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1791      <address><email>jg@freedesktop.org</email></address>
1792    </author>
1793    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1794      <organization abbrev="HP">Hewlett-Packard Company</organization>
1795      <address><email>JeffMogul@acm.org</email></address>
1796    </author>
1797    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1798      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1799      <address><email>henrikn@microsoft.com</email></address>
1800    </author>
1801    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1802      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1803      <address><email>LMM@acm.org</email></address>
1804    </author>
1805    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1806      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1807      <address><email>paulle@microsoft.com</email></address>
1808    </author>
1809    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1810      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1811      <address><email>timbl@w3.org</email></address>
1812    </author>
1813    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1814      <organization abbrev="W3C">World Wide Web Consortium</organization>
1815      <address><email>ylafon@w3.org</email></address>
1816    </author>
1817    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1818      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1819      <address><email>julian.reschke@greenbytes.de</email></address>
1820    </author>
1821    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1822  </front>
1823  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1824  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1825</reference>
1826
1827<reference anchor="Part2">
1828  <front>
1829    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1830    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1831      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1832      <address><email>fielding@gbiv.com</email></address>
1833    </author>
1834    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1835      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1836      <address><email>jg@freedesktop.org</email></address>
1837    </author>
1838    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1839      <organization abbrev="HP">Hewlett-Packard Company</organization>
1840      <address><email>JeffMogul@acm.org</email></address>
1841    </author>
1842    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1843      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1844      <address><email>henrikn@microsoft.com</email></address>
1845    </author>
1846    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1847      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1848      <address><email>LMM@acm.org</email></address>
1849    </author>
1850    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1851      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1852      <address><email>paulle@microsoft.com</email></address>
1853    </author>
1854    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1855      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1856      <address><email>timbl@w3.org</email></address>
1857    </author>
1858    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1859      <organization abbrev="W3C">World Wide Web Consortium</organization>
1860      <address><email>ylafon@w3.org</email></address>
1861    </author>
1862    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1863      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1864      <address><email>julian.reschke@greenbytes.de</email></address>
1865    </author>
1866    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1867  </front>
1868  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1869  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1870</reference>
1871
1872<reference anchor="Part4">
1873  <front>
1874    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1875    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1876      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1877      <address><email>fielding@gbiv.com</email></address>
1878    </author>
1879    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1880      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1881      <address><email>jg@freedesktop.org</email></address>
1882    </author>
1883    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1884      <organization abbrev="HP">Hewlett-Packard Company</organization>
1885      <address><email>JeffMogul@acm.org</email></address>
1886    </author>
1887    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1888      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1889      <address><email>henrikn@microsoft.com</email></address>
1890    </author>
1891    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1892      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1893      <address><email>LMM@acm.org</email></address>
1894    </author>
1895    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1896      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1897      <address><email>paulle@microsoft.com</email></address>
1898    </author>
1899    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1900      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1901      <address><email>timbl@w3.org</email></address>
1902    </author>
1903    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1904      <organization abbrev="W3C">World Wide Web Consortium</organization>
1905      <address><email>ylafon@w3.org</email></address>
1906    </author>
1907    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1908      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1909      <address><email>julian.reschke@greenbytes.de</email></address>
1910    </author>
1911    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1912  </front>
1913  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1914  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1915</reference>
1916
1917<reference anchor="Part5">
1918  <front>
1919    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1920    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1921      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1922      <address><email>fielding@gbiv.com</email></address>
1923    </author>
1924    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1925      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1926      <address><email>jg@freedesktop.org</email></address>
1927    </author>
1928    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1929      <organization abbrev="HP">Hewlett-Packard Company</organization>
1930      <address><email>JeffMogul@acm.org</email></address>
1931    </author>
1932    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1933      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1934      <address><email>henrikn@microsoft.com</email></address>
1935    </author>
1936    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1937      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1938      <address><email>LMM@acm.org</email></address>
1939    </author>
1940    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1941      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1942      <address><email>paulle@microsoft.com</email></address>
1943    </author>
1944    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1945      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1946      <address><email>timbl@w3.org</email></address>
1947    </author>
1948    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1949      <organization abbrev="W3C">World Wide Web Consortium</organization>
1950      <address><email>ylafon@w3.org</email></address>
1951    </author>
1952    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1953      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1954      <address><email>julian.reschke@greenbytes.de</email></address>
1955    </author>
1956    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1957  </front>
1958  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1959  <x:source href="p5-range.xml" basename="p5-range"/>
1960</reference>
1961
1962<reference anchor="Part6">
1963  <front>
1964    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1965    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1966      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1967      <address><email>fielding@gbiv.com</email></address>
1968    </author>
1969    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1970      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1971      <address><email>jg@freedesktop.org</email></address>
1972    </author>
1973    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1974      <organization abbrev="HP">Hewlett-Packard Company</organization>
1975      <address><email>JeffMogul@acm.org</email></address>
1976    </author>
1977    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1978      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1979      <address><email>henrikn@microsoft.com</email></address>
1980    </author>
1981    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1982      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1983      <address><email>LMM@acm.org</email></address>
1984    </author>
1985    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1986      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1987      <address><email>paulle@microsoft.com</email></address>
1988    </author>
1989    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1990      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1991      <address><email>timbl@w3.org</email></address>
1992    </author>
1993    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1994      <organization abbrev="W3C">World Wide Web Consortium</organization>
1995      <address><email>ylafon@w3.org</email></address>
1996    </author>
1997    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1998      <address><email>mnot@mnot.net</email></address>
1999    </author>
2000    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2001      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2002      <address><email>julian.reschke@greenbytes.de</email></address>
2003    </author>
2004    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2005  </front>
2006  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2007  <x:source href="p6-cache.xml" basename="p6-cache"/>
2008</reference>
2009
2010<reference anchor="RFC1864">
2011  <front>
2012    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2013    <author initials="J." surname="Myers" fullname="John G. Myers">
2014      <organization>Carnegie Mellon University</organization>
2015      <address><email>jgm+@cmu.edu</email></address>
2016    </author>
2017    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2018      <organization>Dover Beach Consulting, Inc.</organization>
2019      <address><email>mrose@dbc.mtview.ca.us</email></address>
2020    </author>
2021    <date month="October" year="1995"/>
2022  </front>
2023  <seriesInfo name="RFC" value="1864"/>
2024</reference>
2025
2026<reference anchor="RFC1950">
2027  <front>
2028    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2029    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2030      <organization>Aladdin Enterprises</organization>
2031      <address><email>ghost@aladdin.com</email></address>
2032    </author>
2033    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2034    <date month="May" year="1996"/>
2035  </front>
2036  <seriesInfo name="RFC" value="1950"/>
2037  <annotation>
2038    RFC 1950 is an Informational RFC, thus it might be less stable than
2039    this specification. On the other hand, this downward reference was
2040    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2041    therefore it is unlikely to cause problems in practice. See also
2042    <xref target="BCP97"/>.
2043  </annotation>
2044</reference>
2045
2046<reference anchor="RFC1951">
2047  <front>
2048    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2049    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2050      <organization>Aladdin Enterprises</organization>
2051      <address><email>ghost@aladdin.com</email></address>
2052    </author>
2053    <date month="May" year="1996"/>
2054  </front>
2055  <seriesInfo name="RFC" value="1951"/>
2056  <annotation>
2057    RFC 1951 is an Informational RFC, thus it might be less stable than
2058    this specification. On the other hand, this downward reference was
2059    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2060    therefore it is unlikely to cause problems in practice. See also
2061    <xref target="BCP97"/>.
2062  </annotation>
2063</reference>
2064
2065<reference anchor="RFC1952">
2066  <front>
2067    <title>GZIP file format specification version 4.3</title>
2068    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2069      <organization>Aladdin Enterprises</organization>
2070      <address><email>ghost@aladdin.com</email></address>
2071    </author>
2072    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2073      <address><email>gzip@prep.ai.mit.edu</email></address>
2074    </author>
2075    <author initials="M." surname="Adler" fullname="Mark Adler">
2076      <address><email>madler@alumni.caltech.edu</email></address>
2077    </author>
2078    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2079      <address><email>ghost@aladdin.com</email></address>
2080    </author>
2081    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2082      <address><email>randeg@alumni.rpi.edu</email></address>
2083    </author>
2084    <date month="May" year="1996"/>
2085  </front>
2086  <seriesInfo name="RFC" value="1952"/>
2087  <annotation>
2088    RFC 1952 is an Informational RFC, thus it might be less stable than
2089    this specification. On the other hand, this downward reference was
2090    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2091    therefore it is unlikely to cause problems in practice. See also
2092    <xref target="BCP97"/>.
2093  </annotation>
2094</reference>
2095
2096<reference anchor="RFC2045">
2097  <front>
2098    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2099    <author initials="N." surname="Freed" fullname="Ned Freed">
2100      <organization>Innosoft International, Inc.</organization>
2101      <address><email>ned@innosoft.com</email></address>
2102    </author>
2103    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2104      <organization>First Virtual Holdings</organization>
2105      <address><email>nsb@nsb.fv.com</email></address>
2106    </author>
2107    <date month="November" year="1996"/>
2108  </front>
2109  <seriesInfo name="RFC" value="2045"/>
2110</reference>
2111
2112<reference anchor="RFC2046">
2113  <front>
2114    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2115    <author initials="N." surname="Freed" fullname="Ned Freed">
2116      <organization>Innosoft International, Inc.</organization>
2117      <address><email>ned@innosoft.com</email></address>
2118    </author>
2119    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2120      <organization>First Virtual Holdings</organization>
2121      <address><email>nsb@nsb.fv.com</email></address>
2122    </author>
2123    <date month="November" year="1996"/>
2124  </front>
2125  <seriesInfo name="RFC" value="2046"/>
2126</reference>
2127
2128<reference anchor="RFC2119">
2129  <front>
2130    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2131    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2132      <organization>Harvard University</organization>
2133      <address><email>sob@harvard.edu</email></address>
2134    </author>
2135    <date month="March" year="1997"/>
2136  </front>
2137  <seriesInfo name="BCP" value="14"/>
2138  <seriesInfo name="RFC" value="2119"/>
2139</reference>
2140
2141<reference anchor='RFC4647'>
2142  <front>
2143    <title>Matching of Language Tags</title>
2144    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2145      <organization>Yahoo! Inc.</organization>
2146      <address><email>addison@inter-locale.com</email></address>
2147    </author>
2148    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2149      <organization>Google</organization>
2150      <address><email>mark.davis@macchiato.com</email></address>
2151    </author>
2152    <date year='2006' month='September' />
2153  </front>
2154  <seriesInfo name='BCP' value='47' />
2155  <seriesInfo name='RFC' value='4647' />
2156</reference>
2157
2158<reference anchor="RFC5234">
2159  <front>
2160    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2161    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2162      <organization>Brandenburg InternetWorking</organization>
2163      <address>
2164        <email>dcrocker@bbiw.net</email>
2165      </address> 
2166    </author>
2167    <author initials="P." surname="Overell" fullname="Paul Overell">
2168      <organization>THUS plc.</organization>
2169      <address>
2170        <email>paul.overell@thus.net</email>
2171      </address>
2172    </author>
2173    <date month="January" year="2008"/>
2174  </front>
2175  <seriesInfo name="STD" value="68"/>
2176  <seriesInfo name="RFC" value="5234"/>
2177</reference>
2178
2179<reference anchor='RFC5646'>
2180  <front>
2181    <title>Tags for Identifying Languages</title>
2182    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2183      <organization>Lab126</organization>
2184      <address><email>addison@inter-locale.com</email></address>
2185    </author>
2186    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2187      <organization>Google</organization>
2188      <address><email>mark.davis@google.com</email></address>
2189    </author>
2190    <date month='September' year='2009' />
2191  </front>
2192  <seriesInfo name='BCP' value='47' />
2193  <seriesInfo name='RFC' value='5646' />
2194</reference>
2195
2196</references>
2197
2198<references title="Informative References">
2199
2200<reference anchor="RFC1945">
2201  <front>
2202    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2203    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2204      <organization>MIT, Laboratory for Computer Science</organization>
2205      <address><email>timbl@w3.org</email></address>
2206    </author>
2207    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2208      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2209      <address><email>fielding@ics.uci.edu</email></address>
2210    </author>
2211    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2212      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2213      <address><email>frystyk@w3.org</email></address>
2214    </author>
2215    <date month="May" year="1996"/>
2216  </front>
2217  <seriesInfo name="RFC" value="1945"/>
2218</reference>
2219
2220<reference anchor="RFC2049">
2221  <front>
2222    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2223    <author initials="N." surname="Freed" fullname="Ned Freed">
2224      <organization>Innosoft International, Inc.</organization>
2225      <address><email>ned@innosoft.com</email></address>
2226    </author>
2227    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2228      <organization>First Virtual Holdings</organization>
2229      <address><email>nsb@nsb.fv.com</email></address>
2230    </author>
2231    <date month="November" year="1996"/>
2232  </front>
2233  <seriesInfo name="RFC" value="2049"/>
2234</reference>
2235
2236<reference anchor="RFC2068">
2237  <front>
2238    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2239    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2240      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2241      <address><email>fielding@ics.uci.edu</email></address>
2242    </author>
2243    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2244      <organization>MIT Laboratory for Computer Science</organization>
2245      <address><email>jg@w3.org</email></address>
2246    </author>
2247    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2248      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2249      <address><email>mogul@wrl.dec.com</email></address>
2250    </author>
2251    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2252      <organization>MIT Laboratory for Computer Science</organization>
2253      <address><email>frystyk@w3.org</email></address>
2254    </author>
2255    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2256      <organization>MIT Laboratory for Computer Science</organization>
2257      <address><email>timbl@w3.org</email></address>
2258    </author>
2259    <date month="January" year="1997"/>
2260  </front>
2261  <seriesInfo name="RFC" value="2068"/>
2262</reference>
2263
2264<reference anchor="RFC2076">
2265  <front>
2266    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2267    <author initials="J." surname="Palme" fullname="Jacob Palme">
2268      <organization>Stockholm University/KTH</organization>
2269      <address><email>jpalme@dsv.su.se</email></address>
2270    </author>
2271    <date month="February" year="1997"/>
2272  </front>
2273  <seriesInfo name="RFC" value="2076"/>
2274</reference>
2275
2276<reference anchor="RFC2277">
2277  <front>
2278    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2279    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2280      <organization>UNINETT</organization>
2281      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2282    </author>
2283    <date month="January" year="1998"/>
2284  </front>
2285  <seriesInfo name="BCP" value="18"/>
2286  <seriesInfo name="RFC" value="2277"/>
2287</reference>
2288
2289<reference anchor='RFC2295'>
2290  <front>
2291    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2292    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2293      <organization>Technische Universiteit Eindhoven</organization>
2294      <address>
2295        <email>koen@win.tue.nl</email>
2296      </address>
2297    </author>
2298    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2299      <organization>Hewlett-Packard Company</organization>
2300      <address>
2301        <email>mutz@hpl.hp.com</email>
2302      </address>
2303    </author>
2304    <date year='1998' month='March'/>
2305  </front>
2306  <seriesInfo name='RFC' value='2295'/>
2307</reference>
2308
2309<reference anchor="RFC2388">
2310  <front>
2311    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2312    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2313      <organization>Xerox Palo Alto Research Center</organization>
2314      <address><email>masinter@parc.xerox.com</email></address>
2315    </author>
2316    <date year="1998" month="August"/>
2317  </front>
2318  <seriesInfo name="RFC" value="2388"/>
2319</reference>
2320
2321<reference anchor="RFC2557">
2322  <front>
2323    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2324    <author initials="F." surname="Palme" fullname="Jacob Palme">
2325      <organization>Stockholm University and KTH</organization>
2326      <address><email>jpalme@dsv.su.se</email></address>
2327    </author>
2328    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2329      <organization>Microsoft Corporation</organization>
2330      <address><email>alexhop@microsoft.com</email></address>
2331    </author>
2332    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2333      <organization>Lotus Development Corporation</organization>
2334      <address><email>Shelness@lotus.com</email></address>
2335    </author>
2336    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2337      <address><email>stef@nma.com</email></address>
2338    </author>
2339    <date year="1999" month="March"/>
2340  </front>
2341  <seriesInfo name="RFC" value="2557"/>
2342</reference>
2343
2344<reference anchor="RFC2616">
2345  <front>
2346    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2347    <author initials="R." surname="Fielding" fullname="R. Fielding">
2348      <organization>University of California, Irvine</organization>
2349      <address><email>fielding@ics.uci.edu</email></address>
2350    </author>
2351    <author initials="J." surname="Gettys" fullname="J. Gettys">
2352      <organization>W3C</organization>
2353      <address><email>jg@w3.org</email></address>
2354    </author>
2355    <author initials="J." surname="Mogul" fullname="J. Mogul">
2356      <organization>Compaq Computer Corporation</organization>
2357      <address><email>mogul@wrl.dec.com</email></address>
2358    </author>
2359    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2360      <organization>MIT Laboratory for Computer Science</organization>
2361      <address><email>frystyk@w3.org</email></address>
2362    </author>
2363    <author initials="L." surname="Masinter" fullname="L. Masinter">
2364      <organization>Xerox Corporation</organization>
2365      <address><email>masinter@parc.xerox.com</email></address>
2366    </author>
2367    <author initials="P." surname="Leach" fullname="P. Leach">
2368      <organization>Microsoft Corporation</organization>
2369      <address><email>paulle@microsoft.com</email></address>
2370    </author>
2371    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2372      <organization>W3C</organization>
2373      <address><email>timbl@w3.org</email></address>
2374    </author>
2375    <date month="June" year="1999"/>
2376  </front>
2377  <seriesInfo name="RFC" value="2616"/>
2378</reference>
2379
2380<reference anchor="RFC3629">
2381  <front>
2382    <title>UTF-8, a transformation format of ISO 10646</title>
2383    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2384      <organization>Alis Technologies</organization>
2385      <address><email>fyergeau@alis.com</email></address>
2386    </author>
2387    <date month="November" year="2003"/>
2388  </front>
2389  <seriesInfo name="STD" value="63"/>
2390  <seriesInfo name="RFC" value="3629"/>
2391</reference>
2392
2393<reference anchor='RFC3864'>
2394  <front>
2395    <title>Registration Procedures for Message Header Fields</title>
2396    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2397      <organization>Nine by Nine</organization>
2398      <address><email>GK-IETF@ninebynine.org</email></address>
2399    </author>
2400    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2401      <organization>BEA Systems</organization>
2402      <address><email>mnot@pobox.com</email></address>
2403    </author>
2404    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2405      <organization>HP Labs</organization>
2406      <address><email>JeffMogul@acm.org</email></address>
2407    </author>
2408    <date year='2004' month='September' />
2409  </front>
2410  <seriesInfo name='BCP' value='90' />
2411  <seriesInfo name='RFC' value='3864' />
2412</reference>
2413
2414<reference anchor="RFC4288">
2415  <front>
2416    <title>Media Type Specifications and Registration Procedures</title>
2417    <author initials="N." surname="Freed" fullname="N. Freed">
2418      <organization>Sun Microsystems</organization>
2419      <address>
2420        <email>ned.freed@mrochek.com</email>
2421      </address>
2422    </author>
2423    <author initials="J." surname="Klensin" fullname="J. Klensin">
2424      <address>
2425        <email>klensin+ietf@jck.com</email>
2426      </address>
2427    </author>
2428    <date year="2005" month="December"/>
2429  </front>
2430  <seriesInfo name="BCP" value="13"/>
2431  <seriesInfo name="RFC" value="4288"/>
2432</reference>
2433
2434<reference anchor='RFC5226'>
2435  <front>
2436    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2437    <author initials='T.' surname='Narten' fullname='T. Narten'>
2438      <organization>IBM</organization>
2439      <address><email>narten@us.ibm.com</email></address>
2440    </author>
2441    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2442      <organization>Google</organization>
2443      <address><email>Harald@Alvestrand.no</email></address>
2444    </author>
2445    <date year='2008' month='May' />
2446  </front>
2447  <seriesInfo name='BCP' value='26' />
2448  <seriesInfo name='RFC' value='5226' />
2449</reference>
2450
2451<reference anchor="RFC5322">
2452  <front>
2453    <title>Internet Message Format</title>
2454    <author initials="P." surname="Resnick" fullname="P. Resnick">
2455      <organization>Qualcomm Incorporated</organization>
2456    </author>
2457    <date year="2008" month="October"/>
2458  </front> 
2459  <seriesInfo name="RFC" value="5322"/>
2460</reference>
2461
2462<reference anchor='BCP97'>
2463  <front>
2464    <title>Handling Normative References to Standards-Track Documents</title>
2465    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2466      <address>
2467        <email>klensin+ietf@jck.com</email>
2468      </address>
2469    </author>
2470    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2471      <organization>MIT</organization>
2472      <address>
2473        <email>hartmans-ietf@mit.edu</email>
2474      </address>
2475    </author>
2476    <date year='2007' month='June' />
2477  </front>
2478  <seriesInfo name='BCP' value='97' />
2479  <seriesInfo name='RFC' value='4897' />
2480</reference>
2481
2482
2483</references>
2484
2485<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2486<t>
2487   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
2488   allow a message-body to be transmitted in an open variety of
2489   representations and with extensible mechanisms. However, RFC 2045
2490   discusses mail, and HTTP has a few features that are different from
2491   those described in MIME. These differences were carefully chosen
2492   to optimize performance over binary connections, to allow greater
2493   freedom in the use of new media types, to make date comparisons
2494   easier, and to acknowledge the practice of some early HTTP servers
2495   and clients.
2496</t>
2497<t>
2498   This appendix describes specific areas where HTTP differs from MIME.
2499   Proxies and gateways to strict MIME environments &SHOULD; be
2500   aware of these differences and provide the appropriate conversions
2501   where necessary. Proxies and gateways from MIME environments to HTTP
2502   also need to be aware of the differences because some conversions
2503   might be required.
2504</t>
2505
2506<section title="MIME-Version" anchor="mime-version">
2507  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
2508  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
2509  <x:anchor-alias value="MIME-Version"/>
2510  <x:anchor-alias value="MIME-Version-v"/>
2511<t>
2512   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2513   include a single MIME-Version header field to indicate what
2514   version of the MIME protocol was used to construct the message. Use
2515   of the MIME-Version header field indicates that the message is in
2516   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2517   Proxies/gateways are responsible for ensuring full compliance (where
2518   possible) when exporting HTTP messages to strict MIME environments.
2519</t>
2520<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2521  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2522  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2523</artwork></figure>
2524<t>
2525   MIME version "1.0" is the default for use in HTTP/1.1. However,
2526   HTTP/1.1 message parsing and semantics are defined by this document
2527   and not the MIME specification.
2528</t>
2529</section>
2530
2531<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2532<t>
2533   MIME requires that an Internet mail body-part be converted to
2534   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2535   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2536   allowed for subtypes of the "text" media type when transmitted over
2537   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2538   line breaks as CRLF and forbids the use of CR or LF outside of line
2539   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2540   line break within text content when a message is transmitted over
2541   HTTP.
2542</t>
2543<t>
2544   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2545   environment &SHOULD; translate all line breaks within the text media
2546   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2547   canonical form of CRLF. Note, however, that this might be complicated
2548   by the presence of a Content-Encoding and by the fact that HTTP
2549   allows the use of some character sets which do not use octets 13 and
2550   10 to represent CR and LF, as is the case for some multi-byte
2551   character sets.
2552</t>
2553<t>
2554   Conversion will break any cryptographic
2555   checksums applied to the original content unless the original content
2556   is already in canonical form. Therefore, the canonical form is
2557   recommended for any content that uses such checksums in HTTP.
2558</t>
2559</section>
2560
2561
2562<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2563<t>
2564   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2565   simplify the process of date comparison. Proxies and gateways from
2566   other protocols &SHOULD; ensure that any Date header field present in a
2567   message conforms to one of the HTTP/1.1 formats and rewrite the date
2568   if necessary.
2569</t>
2570</section>
2571
2572<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2573<t>
2574   MIME does not include any concept equivalent to HTTP/1.1's
2575   Content-Encoding header field. Since this acts as a modifier on the
2576   media type, proxies and gateways from HTTP to MIME-compliant
2577   protocols &MUST; either change the value of the Content-Type header
2578   field or decode the representation before forwarding the message. (Some
2579   experimental applications of Content-Type for Internet mail have used
2580   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2581   a function equivalent to Content-Encoding. However, this parameter is
2582   not part of the MIME standards).
2583</t>
2584</section>
2585
2586<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2587<t>
2588   HTTP does not use the Content-Transfer-Encoding field of MIME.
2589   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2590   remove any Content-Transfer-Encoding
2591   prior to delivering the response message to an HTTP client.
2592</t>
2593<t>
2594   Proxies and gateways from HTTP to MIME-compliant protocols are
2595   responsible for ensuring that the message is in the correct format
2596   and encoding for safe transport on that protocol, where "safe
2597   transport" is defined by the limitations of the protocol being used.
2598   Such a proxy or gateway &SHOULD; label the data with an appropriate
2599   Content-Transfer-Encoding if doing so will improve the likelihood of
2600   safe transport over the destination protocol.
2601</t>
2602</section>
2603
2604<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2605<t>
2606   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2607   Proxies/gateways &MUST; remove any transfer-coding prior to
2608   forwarding a message via a MIME-compliant protocol.
2609</t>
2610</section>
2611
2612<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2613<t>
2614   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2615   need to be aware of MIME line length limitations. Since HTTP does not
2616   have this limitation, HTTP does not fold long lines. MHTML messages
2617   being transported by HTTP follow all conventions of MHTML, including
2618   line length limitations and folding, canonicalization, etc., since
2619   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2620   does not interpret the content or any MIME header lines that might be
2621   contained therein.
2622</t>
2623</section>
2624</section>
2625
2626<section title="Additional Features" anchor="additional.features">
2627<t>
2628   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2629   existing HTTP implementations, but not consistently and correctly
2630   across most HTTP/1.1 applications. Implementors are advised to be
2631   aware of these features, but cannot rely upon their presence in, or
2632   interoperability with, other HTTP/1.1 applications. Some of these
2633   describe proposed experimental features, and some describe features
2634   that experimental deployment found lacking that are now addressed in
2635   the base HTTP/1.1 specification.
2636</t>
2637<t>
2638   A number of other header fields, such as Content-Disposition and Title,
2639   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2640</t>
2641</section>
2642
2643<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2644<t>
2645  Clarify contexts that charset is used in.
2646  (<xref target="character.sets"/>)
2647</t>
2648<t>
2649  Remove base URI setting semantics for Content-Location due to poor
2650  implementation support, which was caused by too many broken servers emitting
2651  bogus Content-Location header fields, and also the potentially undesirable effect
2652  of potentially breaking relative links in content-negotiated resources.
2653  (<xref target="header.content-location"/>)
2654</t>
2655<t>
2656  Remove reference to non-existant identity transfer-coding value tokens.
2657  (<xref target="no.content-transfer-encoding"/>)
2658</t>
2659</section>
2660
2661<?BEGININC p3-payload.abnf-appendix ?>
2662<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2663<figure>
2664<artwork type="abnf" name="p3-payload.parsed-abnf">
2665<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2666<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2667<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2668 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2669 qvalue ] ] )
2670<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2671<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2672 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2673<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2674<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2675 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2676 ] )
2677<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2678 OWS media-range [ accept-params ] ] ) ]
2679
2680<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2681<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2682 content-coding ] )
2683<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2684<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2685 language-tag ] )
2686<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2687<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2688<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2689<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2690<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2691<x:ref>Content-Type-v</x:ref> = media-type
2692
2693<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2694<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2695
2696<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2697
2698<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2699<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2700<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2701<x:ref>attribute</x:ref> = token
2702
2703<x:ref>charset</x:ref> = token
2704<x:ref>codings</x:ref> = ( content-coding / "*" )
2705<x:ref>content-coding</x:ref> = token
2706
2707<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2708<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2709
2710<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2711 ";" OWS parameter )
2712<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2713
2714<x:ref>parameter</x:ref> = attribute "=" value
2715<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2716
2717<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2718
2719<x:ref>subtype</x:ref> = token
2720
2721<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2722<x:ref>type</x:ref> = token
2723
2724<x:ref>value</x:ref> = word
2725
2726<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2727</artwork>
2728</figure>
2729<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2730; Accept defined but not used
2731; Accept-Charset defined but not used
2732; Accept-Encoding defined but not used
2733; Accept-Language defined but not used
2734; Content-Encoding defined but not used
2735; Content-Language defined but not used
2736; Content-Location defined but not used
2737; Content-MD5 defined but not used
2738; Content-Type defined but not used
2739; MIME-Version defined but not used
2740</artwork></figure></section>
2741<?ENDINC p3-payload.abnf-appendix ?>
2742
2743<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2744
2745<section title="Since RFC 2616">
2746<t>
2747  Extracted relevant partitions from <xref target="RFC2616"/>.
2748</t>
2749</section>
2750
2751<section title="Since draft-ietf-httpbis-p3-payload-00">
2752<t>
2753  Closed issues:
2754  <list style="symbols"> 
2755    <t>
2756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2757      "Media Type Registrations"
2758      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2759    </t>
2760    <t>
2761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2762      "Clarification regarding quoting of charset values"
2763      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2764    </t>
2765    <t>
2766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2767      "Remove 'identity' token references"
2768      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2769    </t>
2770    <t>
2771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2772      "Accept-Encoding BNF"
2773    </t>
2774    <t>
2775      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2776      "Normative and Informative references"
2777    </t>
2778    <t>
2779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2780      "RFC1700 references"
2781    </t>
2782    <t>
2783      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2784      "Updating to RFC4288"
2785    </t>
2786    <t>
2787      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2788      "Informative references"
2789    </t>
2790    <t>
2791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2792      "ISO-8859-1 Reference"
2793    </t>
2794    <t>
2795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2796      "Encoding References Normative"
2797    </t>
2798    <t>
2799      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2800      "Normative up-to-date references"
2801    </t>
2802  </list>
2803</t>
2804</section>
2805
2806<section title="Since draft-ietf-httpbis-p3-payload-01">
2807<t>
2808  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2809  <list style="symbols"> 
2810    <t>
2811      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2812    </t>
2813  </list>
2814</t>
2815</section>
2816
2817<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2818<t>
2819  Closed issues:
2820  <list style="symbols"> 
2821    <t>
2822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2823      "Quoting Charsets"
2824    </t>
2825    <t>
2826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2827      "Classification for Allow header"
2828    </t>
2829    <t>
2830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2831      "missing default for qvalue in description of Accept-Encoding"
2832    </t>
2833  </list>
2834</t>
2835<t>
2836  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2837  <list style="symbols"> 
2838    <t>
2839      Reference RFC 3984, and update header field registrations for headers defined
2840      in this document.
2841    </t>
2842  </list>
2843</t>
2844</section>
2845
2846<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2847<t>
2848  Closed issues:
2849  <list style="symbols"> 
2850    <t>
2851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2852      "Quoting Charsets"
2853    </t>
2854    <t>
2855      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2856      "language tag matching (Accept-Language) vs RFC4647"
2857    </t>
2858    <t>
2859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2860      "RFC 1806 has been replaced by RFC2183"
2861    </t>
2862  </list>
2863</t>
2864<t>
2865  Other changes:
2866  <list style="symbols"> 
2867    <t>
2868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2869      "Encoding References Normative" &mdash; rephrase the annotation and reference
2870      <xref target="BCP97"/>.
2871    </t>
2872  </list>
2873</t>
2874 </section>
2875
2876<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2877<t>
2878  Closed issues:
2879  <list style="symbols"> 
2880    <t>
2881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2882      "RFC 2822 is updated by RFC 5322"
2883    </t>
2884  </list>
2885</t>
2886<t>
2887  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2888  <list style="symbols"> 
2889    <t>
2890      Use "/" instead of "|" for alternatives.
2891    </t>
2892    <t>
2893      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2894      whitespace ("OWS") and required whitespace ("RWS").
2895    </t>
2896    <t>
2897      Rewrite ABNFs to spell out whitespace rules, factor out
2898      header field value format definitions.
2899    </t>
2900  </list>
2901</t>
2902</section>
2903
2904<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2905<t>
2906  Closed issues:
2907  <list style="symbols"> 
2908    <t>
2909      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2910      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2911    </t>
2912  </list>
2913</t>
2914<t>
2915  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2916  <list style="symbols"> 
2917    <t>
2918      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2919    </t>
2920  </list>
2921</t>
2922<t>
2923  Other changes:
2924  <list style="symbols"> 
2925    <t>
2926      Move definition of quality values into Part 1.
2927    </t>
2928  </list>
2929</t>
2930</section>
2931
2932<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2933<t>
2934  Closed issues:
2935  <list style="symbols"> 
2936    <t>
2937      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2938      "Content-Location isn't special"
2939    </t>
2940    <t>
2941      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2942      "Content Sniffing"
2943    </t>
2944  </list>
2945</t>
2946</section>
2947
2948<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2949<t>
2950  Closed issues:
2951  <list style="symbols"> 
2952    <t>
2953      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2954      "Updated reference for language tags"
2955    </t>
2956    <t>
2957      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2958      "Clarify rules for determining what entities a response carries"
2959    </t>
2960    <t>
2961      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2962      "Content-Location base-setting problems"
2963    </t>
2964    <t>
2965      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2966      "Content Sniffing"
2967    </t>
2968    <t>
2969      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2970      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2971    </t>
2972    <t>
2973      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2974      "move definitions of gzip/deflate/compress to part 1"
2975    </t>
2976  </list>
2977</t>
2978<t>
2979  Partly resolved issues:
2980  <list style="symbols"> 
2981    <t>
2982      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2983      "update IANA requirements wrt Transfer-Coding values" (add the
2984      IANA Considerations subsection)
2985    </t>
2986    <t>
2987      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2988      "update IANA requirements wrt Content-Coding values" (add the
2989      IANA Considerations subsection)
2990    </t>
2991  </list>
2992</t>
2993</section>
2994
2995<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2996<t>
2997  Closed issues:
2998  <list style="symbols"> 
2999    <t>
3000      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3001      "Content Negotiation for media types"
3002    </t>
3003    <t>
3004      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3005      "Accept-Language: which RFC4647 filtering?"
3006    </t>
3007  </list>
3008</t>
3009</section>
3010
3011<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3012<t>
3013  Closed issues:
3014  <list style="symbols"> 
3015    <t>
3016      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
3017      "MIME-Version not listed in P1, general header fields"
3018    </t>
3019    <t>
3020      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
3021      "IANA registry for content/transfer encodings"
3022    </t>
3023    <t>
3024      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3025      "Content Sniffing"
3026    </t>
3027    <t>
3028      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
3029      "use of term "word" when talking about header structure"
3030    </t>
3031  </list>
3032</t>
3033<t>
3034  Partly resolved issues:
3035  <list style="symbols"> 
3036    <t>
3037      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
3038      "Term for the requested resource's URI"
3039    </t>
3040  </list>
3041</t>
3042</section>
3043
3044<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
3045<t>
3046  Closed issues:
3047  <list style="symbols"> 
3048    <t>
3049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
3050      "Clarify 'Requested Variant'"
3051    </t>
3052    <t>
3053      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3054      "Content-Location isn't special"
3055    </t>
3056    <t>
3057      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
3058      "Delimiting messages with multipart/byteranges"
3059    </t>
3060    <t>
3061      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
3062      "Clarify entity / representation / variant terminology"
3063    </t>
3064    <t>
3065      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
3066      "confusing req. language for Content-Location"
3067    </t>
3068    <t>
3069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
3070      "Content-Location on 304 responses"
3071    </t>
3072    <t>
3073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
3074      "'requested resource' in content-encoding definition"
3075    </t>
3076    <t>
3077      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
3078      "consider removing the 'changes from 2068' sections"
3079    </t>
3080  </list>
3081</t>
3082<t>
3083  Partly resolved issues:
3084  <list style="symbols"> 
3085    <t>
3086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
3087      "Content-MD5 and partial responses"
3088    </t>
3089  </list>
3090</t>
3091</section>
3092
3093<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
3094<t>
3095  Closed issues:
3096  <list style="symbols"> 
3097    <t>
3098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
3099      "Factor out Content-Disposition"
3100    </t>
3101  </list>
3102</t>
3103</section>
3104
3105<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
3106<t>
3107  Closed issues:
3108  <list style="symbols"> 
3109    <t>
3110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
3111      "Header Classification"
3112    </t>
3113    <t>
3114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
3115      "untangle ABNFs for header fields"
3116    </t>
3117    <t>
3118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
3119      "potentially misleading MAY in media-type def"
3120    </t>
3121  </list>
3122</t>
3123</section>
3124
3125</section>
3126
3127</back>
3128</rfc>
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