source: draft-ietf-httpbis/17/draft-ietf-httpbis-p3-payload-17.xml @ 1529

Last change on this file since 1529 was 1500, checked in by julian.reschke@…, 8 years ago

fix mime types

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc obsoletes="2616" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-17">
20<front>
21
22  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
23
24  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
25    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
26    <address>
27      <postal>
28        <street>345 Park Ave</street>
29        <city>San Jose</city>
30        <region>CA</region>
31        <code>95110</code>
32        <country>USA</country>
33      </postal>
34      <email>fielding@gbiv.com</email>
35      <uri>http://roy.gbiv.com/</uri>
36    </address>
37  </author>
38
39  <author initials="J." surname="Gettys" fullname="Jim Gettys">
40    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
41    <address>
42      <postal>
43        <street>21 Oak Knoll Road</street>
44        <city>Carlisle</city>
45        <region>MA</region>
46        <code>01741</code>
47        <country>USA</country>
48      </postal>
49      <email>jg@freedesktop.org</email>
50      <uri>http://gettys.wordpress.com/</uri>
51    </address>
52  </author>
53 
54  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
55    <organization abbrev="HP">Hewlett-Packard Company</organization>
56    <address>
57      <postal>
58        <street>HP Labs, Large Scale Systems Group</street>
59        <street>1501 Page Mill Road, MS 1177</street>
60        <city>Palo Alto</city>
61        <region>CA</region>
62        <code>94304</code>
63        <country>USA</country>
64      </postal>
65      <email>JeffMogul@acm.org</email>
66    </address>
67  </author>
68
69  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
70    <organization abbrev="Microsoft">Microsoft Corporation</organization>
71    <address>
72      <postal>
73        <street>1 Microsoft Way</street>
74        <city>Redmond</city>
75        <region>WA</region>
76        <code>98052</code>
77        <country>USA</country>
78      </postal>
79      <email>henrikn@microsoft.com</email>
80    </address>
81  </author>
82
83  <author initials="L." surname="Masinter" fullname="Larry Masinter">
84    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
85    <address>
86      <postal>
87        <street>345 Park Ave</street>
88        <city>San Jose</city>
89        <region>CA</region>
90        <code>95110</code>
91        <country>USA</country>
92      </postal>
93      <email>LMM@acm.org</email>
94      <uri>http://larry.masinter.net/</uri>
95    </address>
96  </author>
97 
98  <author initials="P." surname="Leach" fullname="Paul J. Leach">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106      </postal>
107      <email>paulle@microsoft.com</email>
108    </address>
109  </author>
110   
111  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
112    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
113    <address>
114      <postal>
115        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
116        <street>The Stata Center, Building 32</street>
117        <street>32 Vassar Street</street>
118        <city>Cambridge</city>
119        <region>MA</region>
120        <code>02139</code>
121        <country>USA</country>
122      </postal>
123      <email>timbl@w3.org</email>
124      <uri>http://www.w3.org/People/Berners-Lee/</uri>
125    </address>
126  </author>
127
128  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="October" year="2011" day="31"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
165   distributed, collaborative, hypertext information systems. HTTP has been in
166   use by the World Wide Web global information initiative since 1990. This
167   document is Part 3 of the seven-part specification that defines the protocol
168   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
169</t>
170<t>
171   Part 3 defines HTTP message content, metadata, and content negotiation.
172</t>
173</abstract>
174
175<note title="Editorial Note (To be removed by RFC Editor)">
176  <t>
177    Discussion of this draft should take place on the HTTPBIS working group
178    mailing list (ietf-http-wg@w3.org), which is archived at
179    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
180  </t>
181  <t>
182    The current issues list is at
183    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
184    documents (including fancy diffs) can be found at
185    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
186  </t>
187  <t>
188    The changes in this draft are summarized in <xref target="changes.since.16"/>.
189  </t>
190</note>
191</front>
192<middle>
193<section title="Introduction" anchor="introduction">
194<t>
195   This document defines HTTP/1.1 message payloads (a.k.a., content), the
196   associated metadata header fields that define how the payload is intended
197   to be interpreted by a recipient, the request header fields that
198   might influence content selection, and the various selection algorithms
199   that are collectively referred to as HTTP content negotiation.
200</t>
201<t>
202   This document is currently disorganized in order to minimize the changes
203   between drafts and enable reviewers to see the smaller errata changes.
204   A future draft will reorganize the sections to better reflect the content.
205   In particular, the sections on entities will be renamed payload and moved
206   to the first half of the document, while the sections on content negotiation
207   and associated request header fields will be moved to the second half.  The
208   current mess reflects how widely dispersed these topics and associated
209   requirements had become in <xref target="RFC2616"/>.
210</t>
211
212<section title="Terminology" anchor="terminology">
213<t>
214   This specification uses a number of terms to refer to the roles
215   played by participants in, and objects of, the HTTP communication.
216</t>
217<t>
218  <iref item="content negotiation"/>
219  <?rfc needLines="4"?>content negotiation
220  <list>
221    <t>
222      The mechanism for selecting the appropriate representation when
223      servicing a request. The representation in any response
224      can be negotiated (including error responses).
225    </t>
226  </list>
227</t>
228</section>
229
230<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
231<t>
232   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
233   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
234   document are to be interpreted as described in <xref target="RFC2119"/>.
235</t>
236<t>
237   This document defines conformance criteria for several roles in HTTP
238   communication, including Senders, Recipients, Clients, Servers, User-Agents,
239   Origin Servers, Intermediaries, Proxies and Gateways. See Section 2 of <xref target="Part1"/>
240   for definitions of these terms.
241</t>
242<t>
243   An implementation is considered conformant if it complies with all of the
244   requirements associated with its role(s). Note that SHOULD-level requirements
245   are relevant here, unless one of the documented exceptions is applicable.
246</t>
247<t>
248   This document also uses ABNF to define valid protocol elements
249   (<xref target="notation"/>). In addition to the prose requirements placed
250   upon them, Senders MUST NOT generate protocol elements that are invalid.
251</t>
252<t>
253   Unless noted otherwise, Recipients MAY take steps to recover a usable
254   protocol element from an invalid construct. However, HTTP does not define
255   specific error handling mechanisms, except in cases where it has direct
256   impact on security. This is because different uses of the protocol require
257   different error handling strategies; for example, a Web browser may wish to
258   transparently recover from a response where the Location header field
259   doesn't parse according to the ABNF, whereby in a systems control protocol
260   using HTTP, this type of error recovery could lead to dangerous consequences.
261</t>
262</section>
263
264<section title="Syntax Notation" anchor="notation">
265 
266 
267 
268 
269 
270 
271<t>
272  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
273  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
274  <xref target="collected.abnf"/> shows the collected ABNF, with the list
275  rule expanded.
276</t>
277<t>
278  The following core rules are included by
279  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
280  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
281  DIGIT (decimal 0-9), DQUOTE (double quote),
282  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
283  OCTET (any 8-bit sequence of data), SP (space), and
284  VCHAR (any visible US-ASCII character).
285</t>
286
287<section title="Core Rules" anchor="core.rules">
288 
289 
290 
291<t>
292  The core rules below are defined in <xref target="Part1"/>:
293</t>
294<figure><artwork type="abnf2616"><![CDATA[
295  OWS            = <OWS, defined in [Part1], Section 1.2.2>
296  token          = <token, defined in [Part1], Section 3.2.3>
297  word           = <word, defined in [Part1], Section 3.2.3>
298]]></artwork></figure>
299</section>
300
301<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
302 
303 
304 
305<t>
306  The ABNF rules below are defined in other parts:
307</t>
308<figure><artwork type="abnf2616"><![CDATA[
309  absolute-URI   = <absolute-URI, defined in [Part1], Section 2.7>
310  partial-URI    = <partial-URI, defined in [Part1], Section 2.7>
311  qvalue         = <qvalue, defined in [Part1], Section 5.3>
312]]></artwork></figure>
313</section>
314
315</section>
316
317</section>
318
319<section title="Protocol Parameters" anchor="protocol.parameters">
320
321<section title="Character Encodings (charset)" anchor="character.sets">
322<t>
323   HTTP uses charset names to indicate the character encoding of a
324   textual representation.
325</t>
326<t anchor="rule.charset">
327 
328   A character encoding is identified by a case-insensitive token. The
329   complete set of tokens is defined by the IANA Character Set registry
330   (<eref target="http://www.iana.org/assignments/character-sets"/>).
331</t>
332<figure><iref primary="true" item="Grammar" subitem="charset"/><artwork type="abnf2616"><![CDATA[
333  charset = token
334]]></artwork></figure>
335<t>
336   Although HTTP allows an arbitrary token to be used as a charset
337   value, any token that has a predefined value within the IANA
338   Character Set registry MUST represent the character encoding defined
339   by that registry. Applications SHOULD limit their use of character
340   encodings to those defined within the IANA registry.
341</t>
342<t>
343   HTTP uses charset in two contexts: within an Accept-Charset request
344   header field (in which the charset value is an unquoted token) and as the
345   value of a parameter in a Content-Type header field (within a request or
346   response), in which case the parameter value of the charset parameter
347   can be quoted.
348</t>
349<t>
350   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
351   <xref target="RFC2277"/>.
352</t>
353</section>
354
355<section title="Content Codings" anchor="content.codings">
356 
357<t>
358   Content coding values indicate an encoding transformation that has
359   been or can be applied to a representation. Content codings are primarily
360   used to allow a representation to be compressed or otherwise usefully
361   transformed without losing the identity of its underlying media type
362   and without loss of information. Frequently, the representation is stored in
363   coded form, transmitted directly, and only decoded by the recipient.
364</t>
365<figure><iref primary="true" item="Grammar" subitem="content-coding"/><artwork type="abnf2616"><![CDATA[
366  content-coding   = token
367]]></artwork></figure>
368<t>
369   All content-coding values are case-insensitive. HTTP/1.1 uses
370   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
371   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
372   describes the content-coding, what is more important is that it
373   indicates what decoding mechanism will be required to remove the
374   encoding.
375</t>
376<t>
377   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
378  <list>
379    <t>
380      See Section 5.1.2.1 of <xref target="Part1"/>.
381    </t>
382  </list>
383</t>
384<t>
385   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
386  <list>
387    <t>
388      See Section 5.1.2.2 of <xref target="Part1"/>.
389    </t>
390  </list>
391</t>
392<t>
393   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
394  <list>
395    <t>
396      See Section 5.1.2.3 of <xref target="Part1"/>.
397    </t>
398  </list>
399</t>
400
401<section title="Content Coding Registry" anchor="content.coding.registry">
402<t>
403   The HTTP Content Coding Registry defines the name space for the content
404   coding names.
405</t>
406<t>
407   Registrations MUST include the following fields:
408   <list style="symbols">
409     <t>Name</t>
410     <t>Description</t>
411     <t>Pointer to specification text</t>
412   </list>
413</t>
414<t>
415   Names of content codings MUST NOT overlap with names of transfer codings
416   (Section 5.1 of <xref target="Part1"/>), unless the encoding transformation is identical (as it
417   is the case for the compression codings defined in
418   Section 5.1.2 of <xref target="Part1"/>).
419</t>
420<t>
421   Values to be added to this name space require a specification
422   (see "Specification Required" in
423   Section 4.1 of <xref target="RFC5226"/>), and MUST
424   conform to the purpose of content coding defined in this section.
425</t>
426<t>
427   The registry itself is maintained at
428   <eref target="http://www.iana.org/assignments/http-parameters"/>.
429</t>
430</section>
431
432</section>
433
434<section title="Media Types" anchor="media.types">
435 
436 
437 
438<t>
439   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
440   and Accept (<xref target="header.accept"/>) header fields in order to provide
441   open and extensible data typing and type negotiation.
442</t>
443<figure><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/><artwork type="abnf2616"><![CDATA[
444  media-type = type "/" subtype *( OWS ";" OWS parameter )
445  type       = token
446  subtype    = token
447]]></artwork></figure>
448<t anchor="rule.parameter">
449 
450 
451 
452   The type/subtype MAY be followed by parameters in the form of
453   attribute/value pairs.
454</t>
455<figure><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><artwork type="abnf2616"><![CDATA[
456  parameter      = attribute "=" value
457  attribute      = token
458  value          = word
459]]></artwork></figure>
460<t>
461   The type, subtype, and parameter attribute names are case-insensitive.
462   Parameter values might or might not be case-sensitive, depending on the
463   semantics of the parameter name.  The presence or absence of a parameter might
464   be significant to the processing of a media-type, depending on its
465   definition within the media type registry.
466</t>
467<t>
468   A parameter value that matches the <xref target="core.rules" format="none">token</xref> production can be
469   transmitted as either a token or within a quoted-string. The quoted and
470   unquoted values are equivalent.
471</t>
472<t>
473   Note that some older HTTP applications do not recognize media type
474   parameters. When sending data to older HTTP applications,
475   implementations SHOULD only use media type parameters when they are
476   required by that type/subtype definition.
477</t>
478<t>
479   Media-type values are registered with the Internet Assigned Number
480   Authority (IANA). The media type registration process is
481   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
482   discouraged.
483</t>
484
485<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
486<t>
487   Internet media types are registered with a canonical form. A
488   representation transferred via HTTP messages MUST be in the
489   appropriate canonical form prior to its transmission except for
490   "text" types, as defined in the next paragraph.
491</t>
492<t>
493   When in canonical form, media subtypes of the "text" type use CRLF as
494   the text line break. HTTP relaxes this requirement and allows the
495   transport of text media with plain CR or LF alone representing a line
496   break when it is done consistently for an entire representation. HTTP
497   applications MUST accept CRLF, bare CR, and bare LF as indicating
498   a line break in text media received via HTTP. In
499   addition, if the text is in a character encoding that does not
500   use octets 13 and 10 for CR and LF respectively, as is the case for
501   some multi-byte character encodings, HTTP allows the use of whatever octet
502   sequences are defined by that character encoding to represent the
503   equivalent of CR and LF for line breaks. This flexibility regarding
504   line breaks applies only to text media in the payload body; a bare CR
505   or LF MUST NOT be substituted for CRLF within any of the HTTP control
506   structures (such as header fields and multipart boundaries).
507</t>
508<t>
509   If a representation is encoded with a content-coding, the underlying
510   data MUST be in a form defined above prior to being encoded.
511</t>
512</section>
513
514<section title="Multipart Types" anchor="multipart.types">
515<t>
516   MIME provides for a number of "multipart" types — encapsulations of
517   one or more representations within a single message-body. All multipart
518   types share a common syntax, as defined in Section 5.1.1 of <xref target="RFC2046"/>,
519   and MUST include a boundary parameter as part of the media type
520   value. The message body is itself a protocol element and MUST
521   therefore use only CRLF to represent line breaks between body-parts.
522</t>
523<t>
524   In general, HTTP treats a multipart message-body no differently than
525   any other media type: strictly as payload.  HTTP does not use the
526   multipart boundary as an indicator of message-body length.
527   <!-- jre: re-insert removed text pointing to caching? -->
528   In all other respects, an HTTP user agent SHOULD follow the same or similar
529   behavior as a MIME user agent would upon receipt of a multipart type.
530   The MIME header fields within each body-part of a multipart message-body
531   do not have any significance to HTTP beyond that defined by
532   their MIME semantics.
533</t>
534<t>
535   If an application receives an unrecognized multipart subtype, the
536   application MUST treat it as being equivalent to "multipart/mixed".
537</t>
538<t><list>
539  <t>
540    Note: The "multipart/form-data" type has been specifically defined
541    for carrying form data suitable for processing via the POST
542    request method, as described in <xref target="RFC2388"/>.
543  </t>
544</list></t>
545</section>
546</section>
547
548<section title="Language Tags" anchor="language.tags">
549 
550<t>
551   A language tag, as defined in <xref target="RFC5646"/>, identifies a
552   natural language spoken, written, or otherwise conveyed by human beings for
553   communication of information to other human beings. Computer languages are
554   explicitly excluded. HTTP uses language tags within the Accept-Language and
555   Content-Language fields.
556</t>
557<t>
558   In summary, a language tag is composed of one or more parts: A primary
559   language subtag followed by a possibly empty series of subtags:
560</t>
561<figure><iref primary="true" item="Grammar" subitem="language-tag"/><artwork type="abnf2616"><![CDATA[
562  language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
563]]></artwork></figure>
564<t>
565   White space is not allowed within the tag and all tags are case-insensitive.
566   The name space of language subtags is administered by the IANA (see
567   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
568</t>
569<figure>
570  <preamble>Example tags include:</preamble>
571<artwork type="example"><![CDATA[
572  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
573]]></artwork>
574</figure>
575<t>
576   See <xref target="RFC5646"/> for further information.
577</t>
578</section>
579</section>
580
581<section title="Payload" anchor="payload">
582<t>
583   HTTP messages MAY transfer a payload if not otherwise restricted by
584   the request method or response status code.  The payload consists of
585   metadata, in the form of header fields, and data, in the form of the
586   sequence of octets in the message-body after any transfer-coding has
587   been decoded.
588</t>
589<iref item="payload"/>
590<t>   
591   A "payload" in HTTP is always a partial or complete
592   representation of some resource.  We use separate terms for payload
593   and representation because some messages contain only the associated
594   representation's header fields (e.g., responses to HEAD) or only some
595   part(s) of the representation (e.g., the 206 status code).
596</t>
597<section title="Payload Header Fields" anchor="payload.header.fields">
598 
599<t>
600   HTTP header fields that specifically define the payload, rather than the
601   associated representation, are referred to as "payload header fields".
602   The following payload header fields are defined by HTTP/1.1:
603</t>
604<texttable align="left">
605  <ttcol>Header Field Name</ttcol>
606  <ttcol>Defined in...</ttcol>
607
608  <c>Content-Length</c> <c>Section 8.2 of <xref target="Part1"/></c>
609  <c>Content-Range</c> <c>Section 5.2 of <xref target="Part5"/></c>
610</texttable>
611</section>
612
613<section title="Payload Body" anchor="payload.body">
614 
615<t>
616   A payload body is only present in a message when a message-body is
617   present, as described in Section 3.3 of <xref target="Part1"/>. The payload body is obtained
618   from the message-body by decoding any Transfer-Encoding that might
619   have been applied to ensure safe and proper transfer of the message.
620</t>
621</section>
622</section>
623
624<section title="Representation" anchor="representation">
625<iref item="representation"/>
626<t>
627   A "representation" is information in a format that can be readily
628   communicated from one party to another.  A resource representation
629   is information that reflects the state of that resource, as observed
630   at some point in the past (e.g., in a response to GET) or to be
631   desired at some point in the future (e.g., in a PUT request).
632</t>
633<t>
634   Most, but not all, representations transferred via HTTP are intended
635   to be a representation of the target resource (the resource identified
636   by the effective request URI).  The precise semantics of a representation
637   are determined by the type of message (request or response), the request
638   method, the response status code, and the representation metadata.
639   For example, the above semantic is true for the representation in any
640   200 (OK) response to GET and for the representation in any PUT request.
641   A 200 response to PUT, in contrast, contains either a representation
642   that describes the successful action or a representation of the target
643   resource, with the latter indicated by a Content-Location header field
644   with the same value as the effective request URI.  Likewise, response
645   messages with an error status code usually contain a representation that
646   describes the error and what next steps are suggested for resolving it.
647</t>
648
649<section title="Representation Header Fields" anchor="representation.header.fields">
650 
651<t>
652   Representation header fields define metadata about the representation data
653   enclosed in the message-body or, if no message-body is present, about
654   the representation that would have been transferred in a 200 response
655   to a simultaneous GET request with the same effective request URI.
656</t>
657<t>
658   The following header fields are defined as representation metadata:
659</t>
660<texttable align="left">
661  <ttcol>Header Field Name</ttcol>
662  <ttcol>Defined in...</ttcol>
663
664  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
665  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
666  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
667  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
668  <c>Expires</c> <c>Section 3.3 of <xref target="Part6"/></c>
669  <c>Last-Modified</c> <c>Section 2.2 of <xref target="Part4"/></c>
670</texttable>
671</section>
672
673<section title="Representation Data" anchor="representation.data">
674 
675<t>
676   The representation body associated with an HTTP message is
677   either provided as the payload body of the message or
678   referred to by the message semantics and the effective request
679   URI.  The representation data is in a format and encoding defined by
680   the representation metadata header fields.
681</t>
682<t>
683   The data type of the representation data
684   is determined via the header fields Content-Type and Content-Encoding.
685   These define a two-layer, ordered encoding model:
686</t>
687<figure><artwork type="example"><![CDATA[
688  representation-data := Content-Encoding( Content-Type( bits ) )
689]]></artwork></figure>
690<t>
691   Content-Type specifies the media type of the underlying data, which
692   defines both the data format and how that data SHOULD be processed
693   by the recipient (within the scope of the request method semantics).
694   Any HTTP/1.1 message containing a payload body SHOULD include a
695   Content-Type header field defining the media type of the associated
696   representation unless that metadata is unknown to the sender.
697   If the Content-Type header field is not present, it indicates that
698   the sender does not know the media type of the representation;
699   recipients MAY either assume that the media type is
700   "application/octet-stream" (<xref target="RFC2046"/>, Section 4.5.1)
701   or examine the content to determine its type.
702</t>
703<t>
704   In practice, resource owners do not always properly configure their origin
705   server to provide the correct Content-Type for a given representation,
706   with the result that some clients will examine a response body's content
707   and override the specified type.
708   Clients that do so risk drawing incorrect conclusions, which might expose
709   additional security risks (e.g., "privilege escalation").  Furthermore,
710   it is impossible to determine the sender's intent by examining the data
711   format: many data formats match multiple media types that differ only in
712   processing semantics.  Implementers are encouraged to provide a means of
713   disabling such "content sniffing" when it is used.
714</t>
715<t>
716   Content-Encoding is used to indicate any additional content
717   codings applied to the data, usually for the purpose of data
718   compression, that are a property of the representation.  If
719   Content-Encoding is not present, then there is no additional
720   encoding beyond that defined by the Content-Type.
721</t>
722</section>
723</section>
724
725<section title="Content Negotiation" anchor="content.negotiation">
726<t>
727   HTTP responses include a representation which contains information for
728   interpretation, whether by a human user or for further processing.
729   Often, the server has different ways of representing the
730   same information; for example, in different formats, languages,
731   or using different character encodings.
732</t>
733<t>
734   HTTP clients and their users might have different or variable
735   capabilities, characteristics or preferences which would influence
736   which representation, among those available from the server,
737   would be best for the server to deliver. For this reason, HTTP
738   provides mechanisms for "content negotiation" — a process of
739   allowing selection of a representation of a given resource,
740   when more than one is available.
741</t>
742<t>
743   This specification defines two patterns of content negotiation;
744   "server-driven", where the server selects the representation based
745   upon the client's stated preferences, and "agent-driven" negotiation,
746   where the server provides a list of representations for the client to
747   choose from, based upon their metadata. In addition,  there are
748   other patterns: some applications use an "active content" pattern,
749   where the server returns active content which runs on the client
750   and, based on client available parameters, selects additional
751   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
752   has also been proposed.
753</t>
754<t>
755   These patterns are all widely used, and have trade-offs in applicability
756   and practicality. In particular, when the number of preferences or
757   capabilities to be expressed by a client are large (such as when many
758   different formats are supported by a user-agent), server-driven
759   negotiation becomes unwieldy, and might not be appropriate. Conversely,
760   when the number of representations to choose from is very large,
761   agent-driven negotiation might not be appropriate.
762</t>
763<t>
764   Note that in all cases, the supplier of representations has the
765   responsibility for determining which representations might be
766   considered to be the "same information".
767</t>
768
769<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
770<t>
771   If the selection of the best representation for a response is made by
772   an algorithm located at the server, it is called server-driven
773   negotiation. Selection is based on the available representations of
774   the response (the dimensions over which it can vary; e.g., language,
775   content-coding, etc.) and the contents of particular header fields in
776   the request message or on other information pertaining to the request
777   (such as the network address of the client).
778</t>
779<t>
780   Server-driven negotiation is advantageous when the algorithm for
781   selecting from among the available representations is difficult to
782   describe to the user agent, or when the server desires to send its
783   "best guess" to the client along with the first response (hoping to
784   avoid the round-trip delay of a subsequent request if the "best
785   guess" is good enough for the user). In order to improve the server's
786   guess, the user agent MAY include request header fields (Accept,
787   Accept-Language, Accept-Encoding, etc.) which describe its
788   preferences for such a response.
789</t>
790<t>
791   Server-driven negotiation has disadvantages:
792  <list style="numbers">
793    <t>
794         It is impossible for the server to accurately determine what
795         might be "best" for any given user, since that would require
796         complete knowledge of both the capabilities of the user agent
797         and the intended use for the response (e.g., does the user want
798         to view it on screen or print it on paper?).
799    </t>
800    <t>
801         Having the user agent describe its capabilities in every
802         request can be both very inefficient (given that only a small
803         percentage of responses have multiple representations) and a
804         potential violation of the user's privacy.
805    </t>
806    <t>
807         It complicates the implementation of an origin server and the
808         algorithms for generating responses to a request.
809    </t>
810    <t>
811         It might limit a public cache's ability to use the same response
812         for multiple user's requests.
813    </t>
814  </list>
815</t>
816<t>
817   Server-driven negotiation allows the user agent to specify its preferences,
818   but it cannot expect responses to always honour them. For example, the origin
819   server might not implement server-driven negotiation, or it might decide that
820   sending a response that doesn't conform to them is better than sending a 406
821   (Not Acceptable) response.
822</t>
823<t>
824   Many of the mechanisms for expressing preferences use quality values to
825   declare relative preference. See Section 5.3 of <xref target="Part1"/> for more information.
826</t>
827<t>
828   HTTP/1.1 includes the following header fields for enabling
829   server-driven negotiation through description of user agent
830   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
831   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
832   (<xref target="header.accept-language"/>), and User-Agent (Section 9.10 of <xref target="Part2"/>).
833   However, an origin server is not limited to these dimensions and MAY vary
834   the response based on any aspect of the request, including aspects
835   of the connection (e.g., IP address) or information within extension
836   header fields not defined by this specification.
837</t>
838<t><list>
839  <t>
840    Note: In practice, User-Agent based negotiation is fragile,
841    because new clients might not be recognized.
842  </t>
843</list></t>
844<t>
845   The Vary header field (Section 3.5 of <xref target="Part6"/>) can be used to express the parameters the
846   server uses to select a representation that is subject to server-driven
847   negotiation.
848</t>
849</section>
850
851<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
852<t>
853   With agent-driven negotiation, selection of the best representation
854   for a response is performed by the user agent after receiving an
855   initial response from the origin server. Selection is based on a list
856   of the available representations of the response included within the
857   header fields or body of the initial response, with each
858   representation identified by its own URI. Selection from among the
859   representations can be performed automatically (if the user agent is
860   capable of doing so) or manually by the user selecting from a
861   generated (possibly hypertext) menu.
862</t>
863<t>
864   Agent-driven negotiation is advantageous when the response would vary
865   over commonly-used dimensions (such as type, language, or encoding),
866   when the origin server is unable to determine a user agent's
867   capabilities from examining the request, and generally when public
868   caches are used to distribute server load and reduce network usage.
869</t>
870<t>
871   Agent-driven negotiation suffers from the disadvantage of needing a
872   second request to obtain the best alternate representation. This
873   second request is only efficient when caching is used. In addition,
874   this specification does not define any mechanism for supporting
875   automatic selection, though it also does not prevent any such
876   mechanism from being developed as an extension and used within
877   HTTP/1.1.
878</t>
879<t>
880   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
881   status codes for enabling agent-driven negotiation when the server is
882   unwilling or unable to provide a varying response using server-driven
883   negotiation.
884</t>
885</section>
886</section>
887
888<section title="Header Field Definitions" anchor="header.field.definitions">
889<t>
890   This section defines the syntax and semantics of HTTP/1.1 header fields
891   related to the payload of messages.
892</t>
893
894<section title="Accept" anchor="header.accept">
895  <iref primary="true" item="Accept header field"/>
896  <iref primary="true" item="Header Fields" subitem="Accept"/>
897 
898 
899 
900 
901<t>
902   The "Accept" header field can be used by user agents to specify
903   response media types that are acceptable. Accept header fields can be used to
904   indicate that the request is specifically limited to a small set of desired
905   types, as in the case of a request for an in-line image.
906</t>
907<figure><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/><artwork type="abnf2616"><![CDATA[
908  Accept = #( media-range [ accept-params ] )
909 
910  media-range    = ( "*/*"
911                   / ( type "/" "*" )
912                   / ( type "/" subtype )
913                   ) *( OWS ";" OWS parameter )
914  accept-params  = OWS ";" OWS "q=" qvalue *( accept-ext )
915  accept-ext     = OWS ";" OWS token [ "=" word ]
916]]></artwork></figure>
917<t>
918   The asterisk "*" character is used to group media types into ranges,
919   with "*/*" indicating all media types and "type/*" indicating all
920   subtypes of that type. The media-range MAY include media type
921   parameters that are applicable to that range.
922</t>
923<t>
924   Each media-range MAY be followed by one or more accept-params,
925   beginning with the "q" parameter for indicating a relative quality
926   factor. The first "q" parameter (if any) separates the media-range
927   parameter(s) from the accept-params. Quality factors allow the user
928   or user agent to indicate the relative degree of preference for that
929   media-range, using the qvalue scale from 0 to 1 (Section 5.3 of <xref target="Part1"/>). The
930   default value is q=1.
931</t>
932<t><list>
933  <t>
934    Note: Use of the "q" parameter name to separate media type
935    parameters from Accept extension parameters is due to historical
936    practice. Although this prevents any media type parameter named
937    "q" from being used with a media range, such an event is believed
938    to be unlikely given the lack of any "q" parameters in the IANA
939    media type registry and the rare usage of any media type
940    parameters in Accept. Future media types are discouraged from
941    registering any parameter named "q".
942  </t>
943</list></t>
944<t>
945   The example
946</t>
947<figure><artwork type="example"><![CDATA[
948  Accept: audio/*; q=0.2, audio/basic
949]]></artwork></figure>
950<t>
951   SHOULD be interpreted as "I prefer audio/basic, but send me any audio
952   type if it is the best available after an 80% mark-down in quality".
953</t>
954<t>
955   A request without any Accept header field implies that the user agent
956   will accept any media type in response.
957   If an Accept header field is present in a request and none of the
958   available representations for the response have a media type that is
959   listed as acceptable, the origin server MAY either
960   honor the Accept header field by sending a 406 (Not Acceptable) response
961   or disregard the Accept header field by treating the response as if
962   it is not subject to content negotiation.
963</t>
964<t>
965   A more elaborate example is
966</t>
967<figure><artwork type="example"><![CDATA[
968  Accept: text/plain; q=0.5, text/html,
969          text/x-dvi; q=0.8, text/x-c
970]]></artwork></figure>
971<t>
972   Verbally, this would be interpreted as "text/html and text/x-c are
973   the preferred media types, but if they do not exist, then send the
974   text/x-dvi representation, and if that does not exist, send the text/plain
975   representation".
976</t>
977<t>
978   Media ranges can be overridden by more specific media ranges or
979   specific media types. If more than one media range applies to a given
980   type, the most specific reference has precedence. For example,
981</t>
982<figure><artwork type="example"><![CDATA[
983  Accept: text/*, text/plain, text/plain;format=flowed, */*
984]]></artwork></figure>
985<t>
986   have the following precedence:
987   <list style="numbers">
988    <t>text/plain;format=flowed</t>
989    <t>text/plain</t>
990    <t>text/*</t>
991    <t>*/*</t>
992   </list>
993</t>
994<t>
995   The media type quality factor associated with a given type is
996   determined by finding the media range with the highest precedence
997   which matches that type. For example,
998</t>
999<figure><artwork type="example"><![CDATA[
1000  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1001          text/html;level=2;q=0.4, */*;q=0.5
1002]]></artwork></figure>
1003<t>
1004   would cause the following values to be associated:
1005</t>
1006<texttable align="left">
1007  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1008  <c>text/html;level=1</c>    <c>1</c>
1009  <c>text/html</c>            <c>0.7</c>
1010  <c>text/plain</c>           <c>0.3</c>
1011  <c>image/jpeg</c>           <c>0.5</c>
1012  <c>text/html;level=2</c>    <c>0.4</c>
1013  <c>text/html;level=3</c>    <c>0.7</c>
1014</texttable>
1015<t>
1016      Note: A user agent might be provided with a default set of quality
1017      values for certain media ranges. However, unless the user agent is
1018      a closed system which cannot interact with other rendering agents,
1019      this default set ought to be configurable by the user.
1020</t>
1021</section>
1022
1023<section title="Accept-Charset" anchor="header.accept-charset">
1024  <iref primary="true" item="Accept-Charset header field"/>
1025  <iref primary="true" item="Header Fields" subitem="Accept-Charset"/>
1026 
1027<t>
1028   The "Accept-Charset" header field can be used by user agents to
1029   indicate what character encodings are acceptable in a response
1030   payload. This field allows
1031   clients capable of understanding more comprehensive or special-purpose
1032   character encodings to signal that capability to a server which is capable of
1033   representing documents in those character encodings.
1034</t>
1035<figure><iref primary="true" item="Grammar" subitem="Accept-Charset"/><artwork type="abnf2616"><![CDATA[
1036  Accept-Charset = 1#( ( charset / "*" )
1037                         [ OWS ";" OWS "q=" qvalue ] )
1038]]></artwork></figure>
1039<t>
1040   Character encoding values (a.k.a., charsets) are described in
1041   <xref target="character.sets"/>. Each charset MAY be given an
1042   associated quality value which represents the user's preference
1043   for that charset. The default value is q=1. An example is
1044</t>
1045<figure><artwork type="example"><![CDATA[
1046  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1047]]></artwork></figure>
1048<t>
1049   The special value "*", if present in the Accept-Charset field,
1050   matches every character encoding which is not mentioned elsewhere in the
1051   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
1052   all character encodings not explicitly mentioned get a quality value of 0.
1053</t>
1054<t>
1055   A request without any Accept-Charset header field implies that the user
1056   agent will accept any character encoding in response.
1057   If an Accept-Charset header field is present in a request and none of the
1058   available representations for the response have a character encoding that
1059   is listed as acceptable, the origin server MAY either honor the
1060   Accept-Charset header field by sending a 406 (Not Acceptable) response or
1061   disregard the Accept-Charset header field by treating the response as if
1062   it is not subject to content negotiation.
1063</t>
1064</section>
1065
1066<section title="Accept-Encoding" anchor="header.accept-encoding">
1067  <iref primary="true" item="Accept-Encoding header field"/>
1068  <iref primary="true" item="Header Fields" subitem="Accept-Encoding"/>
1069 
1070 
1071<t>
1072   The "Accept-Encoding" header field can be used by user agents to
1073   indicate what response content-codings (<xref target="content.codings"/>)
1074   are acceptable in the response.  An "identity" token is used as a synonym
1075   for "no encoding" in order to communicate when no encoding is preferred.
1076</t>
1077<figure><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/><artwork type="abnf2616"><![CDATA[
1078  Accept-Encoding  = #( codings [ OWS ";" OWS "q=" qvalue ] )
1079  codings          = content-coding / "identity" / "*"
1080]]></artwork></figure>
1081<t>
1082   Each codings value MAY be given an associated quality value which
1083   represents the preference for that encoding. The default value is q=1.
1084</t>
1085<t>
1086   For example,
1087</t>
1088<figure><artwork type="example"><![CDATA[
1089  Accept-Encoding: compress, gzip
1090  Accept-Encoding:
1091  Accept-Encoding: *
1092  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1093  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1094]]></artwork></figure>
1095<t>
1096   A server tests whether a content-coding for a given representation is
1097   acceptable, according to an Accept-Encoding field, using these rules:
1098  <list style="numbers">
1099      <t>The special "*" symbol in an Accept-Encoding field matches any
1100         available content-coding not explicitly listed in the header
1101         field.</t>
1102
1103      <t>If the representation has no content-coding, then it is acceptable
1104         by default unless specifically excluded by the Accept-Encoding field
1105         stating either "identity;q=0" or "*;q=0" without a more specific
1106         entry for "identity".</t>
1107
1108      <t>If the representation's content-coding is one of the content-codings
1109         listed in the Accept-Encoding field, then it is acceptable unless
1110         it is accompanied by a qvalue of 0. (As defined in Section 5.3 of <xref target="Part1"/>, a
1111         qvalue of 0 means "not acceptable".)</t>
1112
1113      <t>If multiple content-codings are acceptable, then the acceptable
1114         content-coding with the highest non-zero qvalue is preferred.</t>
1115  </list>
1116</t>
1117<t>
1118   An Accept-Encoding header field with a combined field-value that is empty
1119   implies that the user agent does not want any content-coding in response.
1120   If an Accept-Encoding header field is present in a request and none of the
1121   available representations for the response have a content-coding that
1122   is listed as acceptable, the origin server SHOULD send a response
1123   without any content-coding.
1124</t>
1125<t>
1126   A request without an Accept-Encoding header field implies that the user
1127   agent will accept any content-coding in response, but a representation
1128   without content-coding is preferred for compatibility with the widest
1129   variety of user agents.
1130</t>
1131<t><list>
1132  <t>
1133    Note: Most HTTP/1.0 applications do not recognize or obey qvalues
1134    associated with content-codings. This means that qvalues will not
1135    work and are not permitted with x-gzip or x-compress.
1136  </t>
1137</list></t>
1138</section>
1139
1140<section title="Accept-Language" anchor="header.accept-language">
1141  <iref primary="true" item="Accept-Language header field"/>
1142  <iref primary="true" item="Header Fields" subitem="Accept-Language"/>
1143 
1144 
1145<t>
1146   The "Accept-Language" header field can be used by user agents to
1147   indicate the set of natural languages that are preferred in the response.
1148   Language tags are defined in <xref target="language.tags"/>.
1149</t>
1150<figure><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/><artwork type="abnf2616"><![CDATA[
1151  Accept-Language =
1152                    1#( language-range [ OWS ";" OWS "q=" qvalue ] )
1153  language-range  =
1154            <language-range, defined in [RFC4647], Section 2.1>
1155]]></artwork></figure>
1156<t>
1157   Each language-range can be given an associated quality value which
1158   represents an estimate of the user's preference for the languages
1159   specified by that range. The quality value defaults to "q=1". For
1160   example,
1161</t>
1162<figure><artwork type="example"><![CDATA[
1163  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1164]]></artwork></figure>
1165<t>
1166   would mean: "I prefer Danish, but will accept British English and
1167   other types of English".
1168   (see also Section 2.3 of <xref target="RFC4647"/>)
1169</t>
1170<t>
1171   For matching, Section 3 of <xref target="RFC4647"/> defines
1172   several matching schemes. Implementations can offer the most appropriate
1173   matching scheme for their requirements.
1174</t>
1175<t><list>
1176  <t>
1177    Note: The "Basic Filtering" scheme (<xref target="RFC4647"/>, Section 3.3.1) is identical to the matching scheme that was
1178    previously defined in Section 14.4 of <xref target="RFC2616"/>.
1179  </t>
1180</list></t>
1181<t>
1182   It might be contrary to the privacy expectations of the user to send
1183   an Accept-Language header field with the complete linguistic preferences of
1184   the user in every request. For a discussion of this issue, see
1185   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1186</t>
1187<t>
1188   As intelligibility is highly dependent on the individual user, it is
1189   recommended that client applications make the choice of linguistic
1190   preference available to the user. If the choice is not made
1191   available, then the Accept-Language header field MUST NOT be given in
1192   the request.
1193</t>
1194<t><list>
1195  <t>
1196    Note: When making the choice of linguistic preference available to
1197    the user, we remind implementors of  the fact that users are not
1198    familiar with the details of language matching as described above,
1199    and ought to be provided appropriate guidance. As an example, users
1200    might assume that on selecting "en-gb", they will be served any
1201    kind of English document if British English is not available. A
1202    user agent might suggest in such a case to add "en" to get the
1203    best matching behavior.
1204  </t>
1205</list></t>
1206</section>
1207
1208<section title="Content-Encoding" anchor="header.content-encoding">
1209  <iref primary="true" item="Content-Encoding header field"/>
1210  <iref primary="true" item="Header Fields" subitem="Content-Encoding"/>
1211 
1212<t>
1213   The "Content-Encoding" header field indicates what content-codings
1214   have been applied to the representation beyond those inherent in the media
1215   type, and thus what decoding mechanisms must be applied in order to obtain
1216   the media-type referenced by the Content-Type header field.
1217   Content-Encoding is primarily used to allow a representation to be
1218   compressed without losing the identity of its underlying media type.
1219</t>
1220<figure><iref primary="true" item="Grammar" subitem="Content-Encoding"/><artwork type="abnf2616"><![CDATA[
1221  Content-Encoding = 1#content-coding
1222]]></artwork></figure>
1223<t>
1224   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1225</t>
1226<figure><artwork type="example"><![CDATA[
1227  Content-Encoding: gzip
1228]]></artwork></figure>
1229<t>
1230   The content-coding is a characteristic of the representation.
1231   Typically, the representation body is stored with this
1232   encoding and is only decoded before rendering or analogous usage.
1233   However, a transforming proxy MAY modify the content-coding if the
1234   new coding is known to be acceptable to the recipient, unless the
1235   "no-transform" cache-control directive is present in the message.
1236</t>
1237<t>
1238   If the media type includes an inherent encoding, such as a data format
1239   that is always compressed, then that encoding would not be restated as
1240   a Content-Encoding even if it happens to be the same algorithm as one
1241   of the content-codings.  Such a content-coding would only be listed if,
1242   for some bizarre reason, it is applied a second time to form the
1243   representation.  Likewise, an origin server might choose to publish the
1244   same payload data as multiple representations that differ only in whether
1245   the coding is defined as part of Content-Type or Content-Encoding, since
1246   some user agents will behave differently in their handling of each
1247   response (e.g., open a "Save as ..." dialog instead of automatic
1248   decompression and rendering of content).
1249</t>
1250<t>
1251   A representation that has a content-coding applied to it MUST include
1252   a Content-Encoding header field (<xref target="header.content-encoding"/>)
1253   that lists the content-coding(s) applied.
1254</t>
1255<t>
1256   If multiple encodings have been applied to a representation, the content
1257   codings MUST be listed in the order in which they were applied.
1258   Additional information about the encoding parameters MAY be provided
1259   by other header fields not defined by this specification.
1260</t>
1261<t>
1262   If the content-coding of a representation in a request message is not
1263   acceptable to the origin server, the server SHOULD respond with a
1264   status code of 415 (Unsupported Media Type).
1265</t>
1266</section>
1267
1268<section title="Content-Language" anchor="header.content-language">
1269  <iref primary="true" item="Content-Language header field"/>
1270  <iref primary="true" item="Header Fields" subitem="Content-Language"/>
1271 
1272<t>
1273   The "Content-Language" header field describes the natural
1274   language(s) of the intended audience for the representation. Note that this might
1275   not be equivalent to all the languages used within the representation.
1276</t>
1277<figure><iref primary="true" item="Grammar" subitem="Content-Language"/><artwork type="abnf2616"><![CDATA[
1278  Content-Language = 1#language-tag
1279]]></artwork></figure>
1280<t>
1281   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1282   Content-Language is to allow a user to identify and differentiate
1283   representations according to the user's own preferred language. Thus, if the
1284   body content is intended only for a Danish-literate audience, the
1285   appropriate field is
1286</t>
1287<figure><artwork type="example"><![CDATA[
1288  Content-Language: da
1289]]></artwork></figure>
1290<t>
1291   If no Content-Language is specified, the default is that the content
1292   is intended for all language audiences. This might mean that the
1293   sender does not consider it to be specific to any natural language,
1294   or that the sender does not know for which language it is intended.
1295</t>
1296<t>
1297   Multiple languages MAY be listed for content that is intended for
1298   multiple audiences. For example, a rendition of the "Treaty of
1299   Waitangi", presented simultaneously in the original Maori and English
1300   versions, would call for
1301</t>
1302<figure><artwork type="example"><![CDATA[
1303  Content-Language: mi, en
1304]]></artwork></figure>
1305<t>
1306   However, just because multiple languages are present within a representation
1307   does not mean that it is intended for multiple linguistic audiences.
1308   An example would be a beginner's language primer, such as "A First
1309   Lesson in Latin", which is clearly intended to be used by an
1310   English-literate audience. In this case, the Content-Language would
1311   properly only include "en".
1312</t>
1313<t>
1314   Content-Language MAY be applied to any media type — it is not
1315   limited to textual documents.
1316</t>
1317</section>
1318
1319<section title="Content-Location" anchor="header.content-location">
1320  <iref primary="true" item="Content-Location header field"/>
1321  <iref primary="true" item="Header Fields" subitem="Content-Location"/>
1322 
1323<t>
1324   The "Content-Location" header field supplies a URI that can be used
1325   as a specific identifier for the representation in this message.
1326   In other words, if one were to perform a GET on this URI at the time
1327   of this message's generation, then a 200 response would contain the
1328   same representation that is enclosed as payload in this message.
1329</t>
1330<figure><iref primary="true" item="Grammar" subitem="Content-Location"/><artwork type="abnf2616"><![CDATA[
1331  Content-Location = absolute-URI / partial-URI
1332]]></artwork></figure>
1333<t>
1334   The Content-Location value is not a replacement for the effective
1335   Request URI (Section 4.3 of <xref target="Part1"/>).  It is representation metadata.
1336   It has the same syntax and semantics as the header field of the same name
1337   defined for MIME body parts in Section 4 of <xref target="RFC2557"/>.
1338   However, its appearance in an HTTP message has some special implications
1339   for HTTP recipients.
1340</t>
1341<t>
1342   If Content-Location is included in a response message and its value
1343   is the same as the effective request URI, then the response payload
1344   SHOULD be considered the current representation of that resource.
1345   For a GET or HEAD request, this is the same as the default semantics
1346   when no Content-Location is provided by the server.  For a state-changing
1347   request like PUT or POST, it implies that the server's response contains
1348   the new representation of that resource, thereby distinguishing it from
1349   representations that might only report about the action (e.g., "It worked!").
1350   This allows authoring applications to update their local copies without
1351   the need for a subsequent GET request.
1352</t>
1353<t>
1354   If Content-Location is included in a response message and its value
1355   differs from the effective request URI, then the origin server is
1356   informing recipients that this representation has its own, presumably
1357   more specific, identifier.  For a GET or HEAD request, this is an
1358   indication that the effective request URI identifies a resource that
1359   is subject to content negotiation and the representation selected for
1360   this response can also be found at the identified URI.  For other
1361   methods, such a Content-Location indicates that this representation
1362   contains a report on the action's status and the same report is
1363   available (for future access with GET) at the given URI.  For
1364   example, a purchase transaction made via a POST request might
1365   include a receipt document as the payload of the 200 response;
1366   the Content-Location value provides an identifier for retrieving
1367   a copy of that same receipt in the future.
1368</t>
1369<t>
1370   If Content-Location is included in a request message, then it MAY
1371   be interpreted by the origin server as an indication of where the
1372   user agent originally obtained the content of the enclosed
1373   representation (prior to any subsequent modification of the content
1374   by that user agent).  In other words, the user agent is providing
1375   the same representation metadata that it received with the original
1376   representation.  However, such interpretation MUST NOT be used to
1377   alter the semantics of the method requested by the client.  For
1378   example, if a client makes a PUT request on a negotiated resource
1379   and the origin server accepts that PUT (without redirection), then the
1380   new set of values for that resource is expected to be consistent with
1381   the one representation supplied in that PUT; the Content-Location
1382   cannot be used as a form of reverse content selection that
1383   identifies only one of the negotiated representations to be updated.
1384   If the user agent had wanted the latter semantics, it would have applied
1385   the PUT directly to the Content-Location URI.
1386</t>
1387<t>
1388   A Content-Location field received in a request message is transitory
1389   information that SHOULD NOT be saved with other representation
1390   metadata for use in later responses.  The Content-Location's value
1391   might be saved for use in other contexts, such as within source links
1392   or other metadata.
1393</t>
1394<t>
1395   A cache cannot assume that a representation with a Content-Location
1396   different from the URI used to retrieve it can be used to respond to
1397   later requests on that Content-Location URI.
1398</t>
1399<t>
1400   If the Content-Location value is a partial URI, the partial URI is
1401   interpreted relative to the effective request URI.
1402</t>
1403</section>
1404
1405<section title="Content-Type" anchor="header.content-type">
1406  <iref primary="true" item="Content-Type header field"/>
1407  <iref primary="true" item="Header Fields" subitem="Content-Type"/>
1408 
1409<t>
1410   The "Content-Type" header field indicates the media type of the
1411   representation. In the case of responses to the HEAD method, the media type is
1412   that which would have been sent had the request been a GET.
1413</t>
1414<figure><iref primary="true" item="Grammar" subitem="Content-Type"/><artwork type="abnf2616"><![CDATA[
1415  Content-Type = media-type
1416]]></artwork></figure>
1417<t>
1418   Media types are defined in <xref target="media.types"/>. An example of the field is
1419</t>
1420<figure><artwork type="example"><![CDATA[
1421  Content-Type: text/html; charset=ISO-8859-4
1422]]></artwork></figure>
1423<t>
1424   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1425</t>
1426</section>
1427
1428</section>
1429
1430<section title="IANA Considerations" anchor="IANA.considerations">
1431<section title="Header Field Registration" anchor="header.field.registration">
1432<t>
1433   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1434   with the permanent registrations below (see <xref target="RFC3864"/>):
1435</t>
1436
1437<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1438<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1439   <ttcol>Header Field Name</ttcol>
1440   <ttcol>Protocol</ttcol>
1441   <ttcol>Status</ttcol>
1442   <ttcol>Reference</ttcol>
1443
1444   <c>Accept</c>
1445   <c>http</c>
1446   <c>standard</c>
1447   <c>
1448      <xref target="header.accept"/>
1449   </c>
1450   <c>Accept-Charset</c>
1451   <c>http</c>
1452   <c>standard</c>
1453   <c>
1454      <xref target="header.accept-charset"/>
1455   </c>
1456   <c>Accept-Encoding</c>
1457   <c>http</c>
1458   <c>standard</c>
1459   <c>
1460      <xref target="header.accept-encoding"/>
1461   </c>
1462   <c>Accept-Language</c>
1463   <c>http</c>
1464   <c>standard</c>
1465   <c>
1466      <xref target="header.accept-language"/>
1467   </c>
1468   <c>Content-Encoding</c>
1469   <c>http</c>
1470   <c>standard</c>
1471   <c>
1472      <xref target="header.content-encoding"/>
1473   </c>
1474   <c>Content-Language</c>
1475   <c>http</c>
1476   <c>standard</c>
1477   <c>
1478      <xref target="header.content-language"/>
1479   </c>
1480   <c>Content-Location</c>
1481   <c>http</c>
1482   <c>standard</c>
1483   <c>
1484      <xref target="header.content-location"/>
1485   </c>
1486   <c>Content-Type</c>
1487   <c>http</c>
1488   <c>standard</c>
1489   <c>
1490      <xref target="header.content-type"/>
1491   </c>
1492   <c>MIME-Version</c>
1493   <c>http</c>
1494   <c>standard</c>
1495   <c>
1496      <xref target="mime-version"/>
1497   </c>
1498</texttable>
1499<!--(END)-->
1500
1501<t>
1502   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1503</t>
1504</section>
1505
1506<section title="Content Coding Registry" anchor="content.coding.registration">
1507<t>
1508   The registration procedure for HTTP Content Codings is now defined
1509   by <xref target="content.coding.registry"/> of this document.
1510</t>
1511<t>
1512   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1513   shall be updated with the registration below:
1514</t>
1515<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1516   <ttcol>Name</ttcol>
1517   <ttcol>Description</ttcol>
1518   <ttcol>Reference</ttcol>
1519   <c>compress</c>
1520   <c>UNIX "compress" program method</c>
1521   <c>
1522      Section 5.1.2.1 of <xref target="Part1"/>
1523   </c>
1524   <c>deflate</c>
1525   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1526   the "zlib" data format (<xref target="RFC1950"/>)
1527   </c>
1528   <c>
1529      Section 5.1.2.2 of <xref target="Part1"/>
1530   </c>
1531   <c>gzip</c>
1532   <c>Same as GNU zip <xref target="RFC1952"/></c>
1533   <c>
1534      Section 5.1.2.3 of <xref target="Part1"/>
1535   </c>
1536   <c>identity</c>
1537   <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
1538   <c>
1539      <xref target="header.accept-encoding"/>
1540   </c>
1541</texttable>
1542</section>
1543
1544</section>
1545
1546<section title="Security Considerations" anchor="security.considerations">
1547<t>
1548   This section is meant to inform application developers, information
1549   providers, and users of the security limitations in HTTP/1.1 as
1550   described by this document. The discussion does not include
1551   definitive solutions to the problems revealed, though it does make
1552   some suggestions for reducing security risks.
1553</t>
1554
1555<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1556<t>
1557   Accept headers fields can reveal information about the user to all
1558   servers which are accessed. The Accept-Language header field in particular
1559   can reveal information the user would consider to be of a private
1560   nature, because the understanding of particular languages is often
1561   strongly correlated to the membership of a particular ethnic group.
1562   User agents which offer the option to configure the contents of an
1563   Accept-Language header field to be sent in every request are strongly
1564   encouraged to let the configuration process include a message which
1565   makes the user aware of the loss of privacy involved.
1566</t>
1567<t>
1568   An approach that limits the loss of privacy would be for a user agent
1569   to omit the sending of Accept-Language header fields by default, and to ask
1570   the user whether or not to start sending Accept-Language header fields to a
1571   server if it detects, by looking for any Vary header fields
1572   generated by the server, that such sending could improve the quality
1573   of service.
1574</t>
1575<t>
1576   Elaborate user-customized accept header fields sent in every request,
1577   in particular if these include quality values, can be used by servers
1578   as relatively reliable and long-lived user identifiers. Such user
1579   identifiers would allow content providers to do click-trail tracking,
1580   and would allow collaborating content providers to match cross-server
1581   click-trails or form submissions of individual users. Note that for
1582   many users not behind a proxy, the network address of the host
1583   running the user agent will also serve as a long-lived user
1584   identifier. In environments where proxies are used to enhance
1585   privacy, user agents ought to be conservative in offering accept
1586   header configuration options to end users. As an extreme privacy
1587   measure, proxies could filter the accept header fields in relayed requests.
1588   General purpose user agents which provide a high degree of header
1589   configurability SHOULD warn users about the loss of privacy which can
1590   be involved.
1591</t>
1592</section>
1593
1594</section>
1595
1596<section title="Acknowledgments" anchor="acks">
1597<t>
1598  See Section 11 of <xref target="Part1"/>.
1599</t>
1600</section>
1601</middle>
1602<back>
1603
1604<references title="Normative References">
1605
1606<reference anchor="Part1">
1607  <front>
1608    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1609    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1610      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1611      <address><email>fielding@gbiv.com</email></address>
1612    </author>
1613    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1614      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1615      <address><email>jg@freedesktop.org</email></address>
1616    </author>
1617    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1618      <organization abbrev="HP">Hewlett-Packard Company</organization>
1619      <address><email>JeffMogul@acm.org</email></address>
1620    </author>
1621    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1622      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1623      <address><email>henrikn@microsoft.com</email></address>
1624    </author>
1625    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1626      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1627      <address><email>LMM@acm.org</email></address>
1628    </author>
1629    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1630      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1631      <address><email>paulle@microsoft.com</email></address>
1632    </author>
1633    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1634      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1635      <address><email>timbl@w3.org</email></address>
1636    </author>
1637    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1638      <organization abbrev="W3C">World Wide Web Consortium</organization>
1639      <address><email>ylafon@w3.org</email></address>
1640    </author>
1641    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1642      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1643      <address><email>julian.reschke@greenbytes.de</email></address>
1644    </author>
1645    <date month="October" year="2011"/>
1646  </front>
1647  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-17"/>
1648 
1649</reference>
1650
1651<reference anchor="Part2">
1652  <front>
1653    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1654    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1655      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1656      <address><email>fielding@gbiv.com</email></address>
1657    </author>
1658    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1659      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1660      <address><email>jg@freedesktop.org</email></address>
1661    </author>
1662    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1663      <organization abbrev="HP">Hewlett-Packard Company</organization>
1664      <address><email>JeffMogul@acm.org</email></address>
1665    </author>
1666    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1667      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1668      <address><email>henrikn@microsoft.com</email></address>
1669    </author>
1670    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1671      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1672      <address><email>LMM@acm.org</email></address>
1673    </author>
1674    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1675      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1676      <address><email>paulle@microsoft.com</email></address>
1677    </author>
1678    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1679      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1680      <address><email>timbl@w3.org</email></address>
1681    </author>
1682    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1683      <organization abbrev="W3C">World Wide Web Consortium</organization>
1684      <address><email>ylafon@w3.org</email></address>
1685    </author>
1686    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1687      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1688      <address><email>julian.reschke@greenbytes.de</email></address>
1689    </author>
1690    <date month="October" year="2011"/>
1691  </front>
1692  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-17"/>
1693 
1694</reference>
1695
1696<reference anchor="Part4">
1697  <front>
1698    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1699    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1700      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1701      <address><email>fielding@gbiv.com</email></address>
1702    </author>
1703    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1704      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1705      <address><email>jg@freedesktop.org</email></address>
1706    </author>
1707    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1708      <organization abbrev="HP">Hewlett-Packard Company</organization>
1709      <address><email>JeffMogul@acm.org</email></address>
1710    </author>
1711    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1712      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1713      <address><email>henrikn@microsoft.com</email></address>
1714    </author>
1715    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1716      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1717      <address><email>LMM@acm.org</email></address>
1718    </author>
1719    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1720      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1721      <address><email>paulle@microsoft.com</email></address>
1722    </author>
1723    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1724      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1725      <address><email>timbl@w3.org</email></address>
1726    </author>
1727    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1728      <organization abbrev="W3C">World Wide Web Consortium</organization>
1729      <address><email>ylafon@w3.org</email></address>
1730    </author>
1731    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1732      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1733      <address><email>julian.reschke@greenbytes.de</email></address>
1734    </author>
1735    <date month="October" year="2011"/>
1736  </front>
1737  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-17"/>
1738 
1739</reference>
1740
1741<reference anchor="Part5">
1742  <front>
1743    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1744    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1745      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1746      <address><email>fielding@gbiv.com</email></address>
1747    </author>
1748    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1749      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1750      <address><email>jg@freedesktop.org</email></address>
1751    </author>
1752    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1753      <organization abbrev="HP">Hewlett-Packard Company</organization>
1754      <address><email>JeffMogul@acm.org</email></address>
1755    </author>
1756    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1757      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1758      <address><email>henrikn@microsoft.com</email></address>
1759    </author>
1760    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1761      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1762      <address><email>LMM@acm.org</email></address>
1763    </author>
1764    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1765      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1766      <address><email>paulle@microsoft.com</email></address>
1767    </author>
1768    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1769      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1770      <address><email>timbl@w3.org</email></address>
1771    </author>
1772    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1773      <organization abbrev="W3C">World Wide Web Consortium</organization>
1774      <address><email>ylafon@w3.org</email></address>
1775    </author>
1776    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1777      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1778      <address><email>julian.reschke@greenbytes.de</email></address>
1779    </author>
1780    <date month="October" year="2011"/>
1781  </front>
1782  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-17"/>
1783 
1784</reference>
1785
1786<reference anchor="Part6">
1787  <front>
1788    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1789    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1790      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1791      <address><email>fielding@gbiv.com</email></address>
1792    </author>
1793    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1794      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1795      <address><email>jg@freedesktop.org</email></address>
1796    </author>
1797    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1798      <organization abbrev="HP">Hewlett-Packard Company</organization>
1799      <address><email>JeffMogul@acm.org</email></address>
1800    </author>
1801    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1802      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1803      <address><email>henrikn@microsoft.com</email></address>
1804    </author>
1805    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1806      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1807      <address><email>LMM@acm.org</email></address>
1808    </author>
1809    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1810      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1811      <address><email>paulle@microsoft.com</email></address>
1812    </author>
1813    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1814      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1815      <address><email>timbl@w3.org</email></address>
1816    </author>
1817    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1818      <organization abbrev="W3C">World Wide Web Consortium</organization>
1819      <address><email>ylafon@w3.org</email></address>
1820    </author>
1821    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1822      <organization>Rackspace</organization>
1823      <address><email>mnot@mnot.net</email></address>
1824    </author>
1825    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1826      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1827      <address><email>julian.reschke@greenbytes.de</email></address>
1828    </author>
1829    <date month="October" year="2011"/>
1830  </front>
1831  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-17"/>
1832 
1833</reference>
1834
1835<reference anchor="RFC1950">
1836  <front>
1837    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1838    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1839      <organization>Aladdin Enterprises</organization>
1840      <address><email>ghost@aladdin.com</email></address>
1841    </author>
1842    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1843    <date month="May" year="1996"/>
1844  </front>
1845  <seriesInfo name="RFC" value="1950"/>
1846  <annotation>
1847    RFC 1950 is an Informational RFC, thus it might be less stable than
1848    this specification. On the other hand, this downward reference was
1849    present since the publication of RFC 2068 in 1997,
1850    therefore it is unlikely to cause problems in practice. See also
1851    <xref target="BCP97"/>.
1852  </annotation>
1853</reference>
1854
1855<reference anchor="RFC1951">
1856  <front>
1857    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1858    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1859      <organization>Aladdin Enterprises</organization>
1860      <address><email>ghost@aladdin.com</email></address>
1861    </author>
1862    <date month="May" year="1996"/>
1863  </front>
1864  <seriesInfo name="RFC" value="1951"/>
1865  <annotation>
1866    RFC 1951 is an Informational RFC, thus it might be less stable than
1867    this specification. On the other hand, this downward reference was
1868    present since the publication of RFC 2068 in 1997,
1869    therefore it is unlikely to cause problems in practice. See also
1870    <xref target="BCP97"/>.
1871  </annotation>
1872</reference>
1873
1874<reference anchor="RFC1952">
1875  <front>
1876    <title>GZIP file format specification version 4.3</title>
1877    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1878      <organization>Aladdin Enterprises</organization>
1879      <address><email>ghost@aladdin.com</email></address>
1880    </author>
1881    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1882      <address><email>gzip@prep.ai.mit.edu</email></address>
1883    </author>
1884    <author initials="M." surname="Adler" fullname="Mark Adler">
1885      <address><email>madler@alumni.caltech.edu</email></address>
1886    </author>
1887    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1888      <address><email>ghost@aladdin.com</email></address>
1889    </author>
1890    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1891      <address><email>randeg@alumni.rpi.edu</email></address>
1892    </author>
1893    <date month="May" year="1996"/>
1894  </front>
1895  <seriesInfo name="RFC" value="1952"/>
1896  <annotation>
1897    RFC 1952 is an Informational RFC, thus it might be less stable than
1898    this specification. On the other hand, this downward reference was
1899    present since the publication of RFC 2068 in 1997,
1900    therefore it is unlikely to cause problems in practice. See also
1901    <xref target="BCP97"/>.
1902  </annotation>
1903</reference>
1904
1905<reference anchor="RFC2045">
1906  <front>
1907    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1908    <author initials="N." surname="Freed" fullname="Ned Freed">
1909      <organization>Innosoft International, Inc.</organization>
1910      <address><email>ned@innosoft.com</email></address>
1911    </author>
1912    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1913      <organization>First Virtual Holdings</organization>
1914      <address><email>nsb@nsb.fv.com</email></address>
1915    </author>
1916    <date month="November" year="1996"/>
1917  </front>
1918  <seriesInfo name="RFC" value="2045"/>
1919</reference>
1920
1921<reference anchor="RFC2046">
1922  <front>
1923    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1924    <author initials="N." surname="Freed" fullname="Ned Freed">
1925      <organization>Innosoft International, Inc.</organization>
1926      <address><email>ned@innosoft.com</email></address>
1927    </author>
1928    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1929      <organization>First Virtual Holdings</organization>
1930      <address><email>nsb@nsb.fv.com</email></address>
1931    </author>
1932    <date month="November" year="1996"/>
1933  </front>
1934  <seriesInfo name="RFC" value="2046"/>
1935</reference>
1936
1937<reference anchor="RFC2119">
1938  <front>
1939    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1940    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1941      <organization>Harvard University</organization>
1942      <address><email>sob@harvard.edu</email></address>
1943    </author>
1944    <date month="March" year="1997"/>
1945  </front>
1946  <seriesInfo name="BCP" value="14"/>
1947  <seriesInfo name="RFC" value="2119"/>
1948</reference>
1949
1950<reference anchor="RFC4647">
1951  <front>
1952    <title>Matching of Language Tags</title>
1953    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
1954      <organization>Yahoo! Inc.</organization>
1955      <address><email>addison@inter-locale.com</email></address>
1956    </author>
1957    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
1958      <organization>Google</organization>
1959      <address><email>mark.davis@macchiato.com</email></address>
1960    </author>
1961    <date year="2006" month="September"/>
1962  </front>
1963  <seriesInfo name="BCP" value="47"/>
1964  <seriesInfo name="RFC" value="4647"/>
1965</reference>
1966
1967<reference anchor="RFC5234">
1968  <front>
1969    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1970    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1971      <organization>Brandenburg InternetWorking</organization>
1972      <address>
1973        <email>dcrocker@bbiw.net</email>
1974      </address> 
1975    </author>
1976    <author initials="P." surname="Overell" fullname="Paul Overell">
1977      <organization>THUS plc.</organization>
1978      <address>
1979        <email>paul.overell@thus.net</email>
1980      </address>
1981    </author>
1982    <date month="January" year="2008"/>
1983  </front>
1984  <seriesInfo name="STD" value="68"/>
1985  <seriesInfo name="RFC" value="5234"/>
1986</reference>
1987
1988<reference anchor="RFC5646">
1989  <front>
1990    <title>Tags for Identifying Languages</title>
1991    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
1992      <organization>Lab126</organization>
1993      <address><email>addison@inter-locale.com</email></address>
1994    </author>
1995    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
1996      <organization>Google</organization>
1997      <address><email>mark.davis@google.com</email></address>
1998    </author>
1999    <date month="September" year="2009"/>
2000  </front>
2001  <seriesInfo name="BCP" value="47"/>
2002  <seriesInfo name="RFC" value="5646"/>
2003</reference>
2004
2005</references>
2006
2007<references title="Informative References">
2008
2009<reference anchor="RFC1945">
2010  <front>
2011    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2012    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2013      <organization>MIT, Laboratory for Computer Science</organization>
2014      <address><email>timbl@w3.org</email></address>
2015    </author>
2016    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2017      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2018      <address><email>fielding@ics.uci.edu</email></address>
2019    </author>
2020    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2021      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2022      <address><email>frystyk@w3.org</email></address>
2023    </author>
2024    <date month="May" year="1996"/>
2025  </front>
2026  <seriesInfo name="RFC" value="1945"/>
2027</reference>
2028
2029<reference anchor="RFC2049">
2030  <front>
2031    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2032    <author initials="N." surname="Freed" fullname="Ned Freed">
2033      <organization>Innosoft International, Inc.</organization>
2034      <address><email>ned@innosoft.com</email></address>
2035    </author>
2036    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2037      <organization>First Virtual Holdings</organization>
2038      <address><email>nsb@nsb.fv.com</email></address>
2039    </author>
2040    <date month="November" year="1996"/>
2041  </front>
2042  <seriesInfo name="RFC" value="2049"/>
2043</reference>
2044
2045<reference anchor="RFC2068">
2046  <front>
2047    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2048    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2049      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2050      <address><email>fielding@ics.uci.edu</email></address>
2051    </author>
2052    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2053      <organization>MIT Laboratory for Computer Science</organization>
2054      <address><email>jg@w3.org</email></address>
2055    </author>
2056    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2057      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2058      <address><email>mogul@wrl.dec.com</email></address>
2059    </author>
2060    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2061      <organization>MIT Laboratory for Computer Science</organization>
2062      <address><email>frystyk@w3.org</email></address>
2063    </author>
2064    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2065      <organization>MIT Laboratory for Computer Science</organization>
2066      <address><email>timbl@w3.org</email></address>
2067    </author>
2068    <date month="January" year="1997"/>
2069  </front>
2070  <seriesInfo name="RFC" value="2068"/>
2071</reference>
2072
2073<reference anchor="RFC2076">
2074  <front>
2075    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2076    <author initials="J." surname="Palme" fullname="Jacob Palme">
2077      <organization>Stockholm University/KTH</organization>
2078      <address><email>jpalme@dsv.su.se</email></address>
2079    </author>
2080    <date month="February" year="1997"/>
2081  </front>
2082  <seriesInfo name="RFC" value="2076"/>
2083</reference>
2084
2085<reference anchor="RFC2277">
2086  <front>
2087    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2088    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2089      <organization>UNINETT</organization>
2090      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2091    </author>
2092    <date month="January" year="1998"/>
2093  </front>
2094  <seriesInfo name="BCP" value="18"/>
2095  <seriesInfo name="RFC" value="2277"/>
2096</reference>
2097
2098<reference anchor="RFC2295">
2099  <front>
2100    <title abbrev="HTTP Content Negotiation">Transparent Content Negotiation in HTTP</title>
2101    <author initials="K." surname="Holtman" fullname="Koen Holtman">
2102      <organization>Technische Universiteit Eindhoven</organization>
2103      <address>
2104        <email>koen@win.tue.nl</email>
2105      </address>
2106    </author>
2107    <author initials="A.H." surname="Mutz" fullname="Andrew H. Mutz">
2108      <organization>Hewlett-Packard Company</organization>
2109      <address>
2110        <email>mutz@hpl.hp.com</email>
2111      </address>
2112    </author>
2113    <date year="1998" month="March"/>
2114  </front>
2115  <seriesInfo name="RFC" value="2295"/>
2116</reference>
2117
2118<reference anchor="RFC2388">
2119  <front>
2120    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2121    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2122      <organization>Xerox Palo Alto Research Center</organization>
2123      <address><email>masinter@parc.xerox.com</email></address>
2124    </author>
2125    <date year="1998" month="August"/>
2126  </front>
2127  <seriesInfo name="RFC" value="2388"/>
2128</reference>
2129
2130<reference anchor="RFC2557">
2131  <front>
2132    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2133    <author initials="F." surname="Palme" fullname="Jacob Palme">
2134      <organization>Stockholm University and KTH</organization>
2135      <address><email>jpalme@dsv.su.se</email></address>
2136    </author>
2137    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2138      <organization>Microsoft Corporation</organization>
2139      <address><email>alexhop@microsoft.com</email></address>
2140    </author>
2141    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2142      <organization>Lotus Development Corporation</organization>
2143      <address><email>Shelness@lotus.com</email></address>
2144    </author>
2145    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2146      <address><email>stef@nma.com</email></address>
2147    </author>
2148    <date year="1999" month="March"/>
2149  </front>
2150  <seriesInfo name="RFC" value="2557"/>
2151</reference>
2152
2153<reference anchor="RFC2616">
2154  <front>
2155    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2156    <author initials="R." surname="Fielding" fullname="R. Fielding">
2157      <organization>University of California, Irvine</organization>
2158      <address><email>fielding@ics.uci.edu</email></address>
2159    </author>
2160    <author initials="J." surname="Gettys" fullname="J. Gettys">
2161      <organization>W3C</organization>
2162      <address><email>jg@w3.org</email></address>
2163    </author>
2164    <author initials="J." surname="Mogul" fullname="J. Mogul">
2165      <organization>Compaq Computer Corporation</organization>
2166      <address><email>mogul@wrl.dec.com</email></address>
2167    </author>
2168    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2169      <organization>MIT Laboratory for Computer Science</organization>
2170      <address><email>frystyk@w3.org</email></address>
2171    </author>
2172    <author initials="L." surname="Masinter" fullname="L. Masinter">
2173      <organization>Xerox Corporation</organization>
2174      <address><email>masinter@parc.xerox.com</email></address>
2175    </author>
2176    <author initials="P." surname="Leach" fullname="P. Leach">
2177      <organization>Microsoft Corporation</organization>
2178      <address><email>paulle@microsoft.com</email></address>
2179    </author>
2180    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2181      <organization>W3C</organization>
2182      <address><email>timbl@w3.org</email></address>
2183    </author>
2184    <date month="June" year="1999"/>
2185  </front>
2186  <seriesInfo name="RFC" value="2616"/>
2187</reference>
2188
2189<reference anchor="RFC3629">
2190  <front>
2191    <title>UTF-8, a transformation format of ISO 10646</title>
2192    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2193      <organization>Alis Technologies</organization>
2194      <address><email>fyergeau@alis.com</email></address>
2195    </author>
2196    <date month="November" year="2003"/>
2197  </front>
2198  <seriesInfo name="STD" value="63"/>
2199  <seriesInfo name="RFC" value="3629"/>
2200</reference>
2201
2202<reference anchor="RFC3864">
2203  <front>
2204    <title>Registration Procedures for Message Header Fields</title>
2205    <author initials="G." surname="Klyne" fullname="G. Klyne">
2206      <organization>Nine by Nine</organization>
2207      <address><email>GK-IETF@ninebynine.org</email></address>
2208    </author>
2209    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
2210      <organization>BEA Systems</organization>
2211      <address><email>mnot@pobox.com</email></address>
2212    </author>
2213    <author initials="J." surname="Mogul" fullname="J. Mogul">
2214      <organization>HP Labs</organization>
2215      <address><email>JeffMogul@acm.org</email></address>
2216    </author>
2217    <date year="2004" month="September"/>
2218  </front>
2219  <seriesInfo name="BCP" value="90"/>
2220  <seriesInfo name="RFC" value="3864"/>
2221</reference>
2222
2223<reference anchor="RFC4288">
2224  <front>
2225    <title>Media Type Specifications and Registration Procedures</title>
2226    <author initials="N." surname="Freed" fullname="N. Freed">
2227      <organization>Sun Microsystems</organization>
2228      <address>
2229        <email>ned.freed@mrochek.com</email>
2230      </address>
2231    </author>
2232    <author initials="J." surname="Klensin" fullname="J. Klensin">
2233      <address>
2234        <email>klensin+ietf@jck.com</email>
2235      </address>
2236    </author>
2237    <date year="2005" month="December"/>
2238  </front>
2239  <seriesInfo name="BCP" value="13"/>
2240  <seriesInfo name="RFC" value="4288"/>
2241</reference>
2242
2243<reference anchor="RFC5226">
2244  <front>
2245    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2246    <author initials="T." surname="Narten" fullname="T. Narten">
2247      <organization>IBM</organization>
2248      <address><email>narten@us.ibm.com</email></address>
2249    </author>
2250    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
2251      <organization>Google</organization>
2252      <address><email>Harald@Alvestrand.no</email></address>
2253    </author>
2254    <date year="2008" month="May"/>
2255  </front>
2256  <seriesInfo name="BCP" value="26"/>
2257  <seriesInfo name="RFC" value="5226"/>
2258</reference>
2259
2260<reference anchor="RFC5322">
2261  <front>
2262    <title>Internet Message Format</title>
2263    <author initials="P." surname="Resnick" fullname="P. Resnick">
2264      <organization>Qualcomm Incorporated</organization>
2265    </author>
2266    <date year="2008" month="October"/>
2267  </front> 
2268  <seriesInfo name="RFC" value="5322"/>
2269</reference>
2270
2271<reference anchor="RFC6151">
2272  <front>
2273    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
2274    <author initials="S." surname="Turner" fullname="S. Turner"/>
2275    <author initials="L." surname="Chen" fullname="L. Chen"/>
2276    <date year="2011" month="March"/>
2277  </front>
2278  <seriesInfo name="RFC" value="6151"/>
2279</reference>
2280
2281<reference anchor="BCP97">
2282  <front>
2283    <title>Handling Normative References to Standards-Track Documents</title>
2284    <author initials="J." surname="Klensin" fullname="J. Klensin">
2285      <address>
2286        <email>klensin+ietf@jck.com</email>
2287      </address>
2288    </author>
2289    <author initials="S." surname="Hartman" fullname="S. Hartman">
2290      <organization>MIT</organization>
2291      <address>
2292        <email>hartmans-ietf@mit.edu</email>
2293      </address>
2294    </author>
2295    <date year="2007" month="June"/>
2296  </front>
2297  <seriesInfo name="BCP" value="97"/>
2298  <seriesInfo name="RFC" value="4897"/>
2299</reference>
2300
2301<reference anchor="RFC6266">
2302  <front>
2303    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
2304    in the Hypertext Transfer Protocol (HTTP)</title>
2305    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
2306      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2307      <address>
2308        <email>julian.reschke@greenbytes.de</email>
2309      </address>
2310    </author>
2311    <date month="June" year="2011"/>
2312  </front>
2313  <seriesInfo name="RFC" value="6266"/>
2314</reference>
2315
2316</references>
2317
2318<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2319<t>
2320   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
2321   allow a message-body to be transmitted in an open variety of
2322   representations and with extensible mechanisms. However, RFC 2045
2323   discusses mail, and HTTP has a few features that are different from
2324   those described in MIME. These differences were carefully chosen
2325   to optimize performance over binary connections, to allow greater
2326   freedom in the use of new media types, to make date comparisons
2327   easier, and to acknowledge the practice of some early HTTP servers
2328   and clients.
2329</t>
2330<t>
2331   This appendix describes specific areas where HTTP differs from MIME.
2332   Proxies and gateways to strict MIME environments SHOULD be
2333   aware of these differences and provide the appropriate conversions
2334   where necessary. Proxies and gateways from MIME environments to HTTP
2335   also need to be aware of the differences because some conversions
2336   might be required.
2337</t>
2338
2339<section title="MIME-Version" anchor="mime-version">
2340  <iref primary="true" item="MIME-Version header field"/>
2341  <iref primary="true" item="Header Fields" subitem="MIME-Version"/>
2342 
2343<t>
2344   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages MAY
2345   include a single MIME-Version header field to indicate what
2346   version of the MIME protocol was used to construct the message. Use
2347   of the MIME-Version header field indicates that the message is in
2348   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2349   Proxies/gateways are responsible for ensuring full compliance (where
2350   possible) when exporting HTTP messages to strict MIME environments.
2351</t>
2352<figure><iref primary="true" item="Grammar" subitem="MIME-Version"/><artwork type="abnf2616"><![CDATA[
2353  MIME-Version = 1*DIGIT "." 1*DIGIT
2354]]></artwork></figure>
2355<t>
2356   MIME version "1.0" is the default for use in HTTP/1.1. However,
2357   HTTP/1.1 message parsing and semantics are defined by this document
2358   and not the MIME specification.
2359</t>
2360</section>
2361
2362<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2363<t>
2364   MIME requires that an Internet mail body-part be converted to
2365   canonical form prior to being transferred, as described in Section 4 of <xref target="RFC2049"/>.
2366   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2367   allowed for subtypes of the "text" media type when transmitted over
2368   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2369   line breaks as CRLF and forbids the use of CR or LF outside of line
2370   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2371   line break within text content when a message is transmitted over
2372   HTTP.
2373</t>
2374<t>
2375   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2376   environment SHOULD translate all line breaks within the text media
2377   types described in <xref target="canonicalization.and.text.defaults"/>
2378   of this document to the RFC 2049
2379   canonical form of CRLF. Note, however, that this might be complicated
2380   by the presence of a Content-Encoding and by the fact that HTTP
2381   allows the use of some character encodings which do not use octets 13 and
2382   10 to represent CR and LF, respectively, as is the case for some multi-byte
2383   character encodings.
2384</t>
2385<t>
2386   Conversion will break any cryptographic
2387   checksums applied to the original content unless the original content
2388   is already in canonical form. Therefore, the canonical form is
2389   recommended for any content that uses such checksums in HTTP.
2390</t>
2391</section>
2392
2393
2394<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2395<t>
2396   HTTP/1.1 uses a restricted set of date formats (Section 8 of <xref target="Part2"/>) to
2397   simplify the process of date comparison. Proxies and gateways from
2398   other protocols SHOULD ensure that any Date header field present in a
2399   message conforms to one of the HTTP/1.1 formats and rewrite the date
2400   if necessary.
2401</t>
2402</section>
2403
2404<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2405<t>
2406   MIME does not include any concept equivalent to HTTP/1.1's
2407   Content-Encoding header field. Since this acts as a modifier on the
2408   media type, proxies and gateways from HTTP to MIME-compliant
2409   protocols MUST either change the value of the Content-Type header
2410   field or decode the representation before forwarding the message. (Some
2411   experimental applications of Content-Type for Internet mail have used
2412   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2413   a function equivalent to Content-Encoding. However, this parameter is
2414   not part of the MIME standards).
2415</t>
2416</section>
2417
2418<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2419<t>
2420   HTTP does not use the Content-Transfer-Encoding field of MIME.
2421   Proxies and gateways from MIME-compliant protocols to HTTP MUST
2422   remove any Content-Transfer-Encoding
2423   prior to delivering the response message to an HTTP client.
2424</t>
2425<t>
2426   Proxies and gateways from HTTP to MIME-compliant protocols are
2427   responsible for ensuring that the message is in the correct format
2428   and encoding for safe transport on that protocol, where "safe
2429   transport" is defined by the limitations of the protocol being used.
2430   Such a proxy or gateway SHOULD label the data with an appropriate
2431   Content-Transfer-Encoding if doing so will improve the likelihood of
2432   safe transport over the destination protocol.
2433</t>
2434</section>
2435
2436<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2437<t>
2438   HTTP/1.1 introduces the Transfer-Encoding header field (Section 8.6 of <xref target="Part1"/>).
2439   Proxies/gateways MUST remove any transfer-coding prior to
2440   forwarding a message via a MIME-compliant protocol.
2441</t>
2442</section>
2443
2444<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2445<t>
2446   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2447   need to be aware of MIME line length limitations. Since HTTP does not
2448   have this limitation, HTTP does not fold long lines. MHTML messages
2449   being transported by HTTP follow all conventions of MHTML, including
2450   line length limitations and folding, canonicalization, etc., since
2451   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2452   does not interpret the content or any MIME header lines that might be
2453   contained therein.
2454</t>
2455</section>
2456</section>
2457
2458<section title="Additional Features" anchor="additional.features">
2459<t>
2460   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2461   existing HTTP implementations, but not consistently and correctly
2462   across most HTTP/1.1 applications. Implementors are advised to be
2463   aware of these features, but cannot rely upon their presence in, or
2464   interoperability with, other HTTP/1.1 applications. Some of these
2465   describe proposed experimental features, and some describe features
2466   that experimental deployment found lacking that are now addressed in
2467   the base HTTP/1.1 specification.
2468</t>
2469<t>
2470   A number of other header fields, such as Content-Disposition and Title,
2471   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
2472   and <xref target="RFC2076"/>).
2473</t>
2474</section>
2475
2476<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2477<t>
2478  Clarify contexts that charset is used in.
2479  (<xref target="character.sets"/>)
2480</t>
2481<t>
2482  Remove the default character encoding for text media types; the default
2483  now is whatever the media type definition says.
2484  (<xref target="canonicalization.and.text.defaults"/>)
2485</t>
2486<t>
2487  Change ABNF productions for header fields to only define the field value.
2488  (<xref target="header.field.definitions"/>)
2489</t>
2490<t>
2491  Remove definition of Content-MD5 header field because it was inconsistently
2492  implemented with respect to partial responses, and also because of known
2493  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
2494  (<xref target="header.field.definitions"/>)
2495</t>
2496<t>
2497  Remove ISO-8859-1 special-casing in Accept-Charset.
2498  (<xref target="header.accept-charset"/>)
2499</t>
2500<t>
2501  Remove base URI setting semantics for Content-Location due to poor
2502  implementation support, which was caused by too many broken servers emitting
2503  bogus Content-Location header fields, and also the potentially undesirable effect
2504  of potentially breaking relative links in content-negotiated resources.
2505  (<xref target="header.content-location"/>)
2506</t>
2507<t>
2508  Remove discussion of Content-Disposition header field, it is now defined
2509  by <xref target="RFC6266"/>.
2510  (<xref target="additional.features"/>)
2511</t>
2512<t>
2513  Remove reference to non-existant identity transfer-coding value tokens.
2514  (<xref target="no.content-transfer-encoding"/>)
2515</t>
2516</section>
2517
2518
2519<section title="Collected ABNF" anchor="collected.abnf">
2520<figure>
2521<artwork type="abnf" name="p3-payload.parsed-abnf"><![CDATA[
2522Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2523 OWS media-range [ accept-params ] ] ) ]
2524Accept-Charset = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2525 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2526 qvalue ] ] )
2527Accept-Encoding = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
2528 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2529Accept-Language = *( "," OWS ) language-range [ OWS ";" OWS "q="
2530 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2531 ] )
2532
2533Content-Encoding = *( "," OWS ) content-coding *( OWS "," [ OWS
2534 content-coding ] )
2535Content-Language = *( "," OWS ) language-tag *( OWS "," [ OWS
2536 language-tag ] )
2537Content-Location = absolute-URI / partial-URI
2538Content-Type = media-type
2539
2540MIME-Version = 1*DIGIT "." 1*DIGIT
2541
2542OWS = <OWS, defined in [Part1], Section 1.2.2>
2543
2544absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
2545accept-ext = OWS ";" OWS token [ "=" word ]
2546accept-params = OWS ";" OWS "q=" qvalue *accept-ext
2547attribute = token
2548
2549charset = token
2550codings = content-coding / "identity" / "*"
2551content-coding = token
2552
2553language-range = <language-range, defined in [RFC4647], Section 2.1>
2554language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
2555
2556media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2557 ";" OWS parameter )
2558media-type = type "/" subtype *( OWS ";" OWS parameter )
2559
2560parameter = attribute "=" value
2561partial-URI = <partial-URI, defined in [Part1], Section 2.7>
2562
2563qvalue = <qvalue, defined in [Part1], Section 5.3>
2564
2565subtype = token
2566
2567token = <token, defined in [Part1], Section 3.2.3>
2568type = token
2569
2570value = word
2571
2572word = <word, defined in [Part1], Section 3.2.3>
2573]]></artwork>
2574</figure>
2575<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
2576; Accept defined but not used
2577; Accept-Charset defined but not used
2578; Accept-Encoding defined but not used
2579; Accept-Language defined but not used
2580; Content-Encoding defined but not used
2581; Content-Language defined but not used
2582; Content-Location defined but not used
2583; Content-Type defined but not used
2584; MIME-Version defined but not used
2585]]></artwork></figure></section>
2586
2587
2588<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2589
2590<section title="Since RFC 2616">
2591<t>
2592  Extracted relevant partitions from <xref target="RFC2616"/>.
2593</t>
2594</section>
2595
2596<section title="Since draft-ietf-httpbis-p3-payload-00">
2597<t>
2598  Closed issues:
2599  <list style="symbols"> 
2600    <t>
2601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2602      "Media Type Registrations"
2603      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2604    </t>
2605    <t>
2606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2607      "Clarification regarding quoting of charset values"
2608      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2609    </t>
2610    <t>
2611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2612      "Remove 'identity' token references"
2613      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2614    </t>
2615    <t>
2616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2617      "Accept-Encoding BNF"
2618    </t>
2619    <t>
2620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2621      "Normative and Informative references"
2622    </t>
2623    <t>
2624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2625      "RFC1700 references"
2626    </t>
2627    <t>
2628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2629      "Updating to RFC4288"
2630    </t>
2631    <t>
2632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2633      "Informative references"
2634    </t>
2635    <t>
2636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2637      "ISO-8859-1 Reference"
2638    </t>
2639    <t>
2640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2641      "Encoding References Normative"
2642    </t>
2643    <t>
2644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2645      "Normative up-to-date references"
2646    </t>
2647  </list>
2648</t>
2649</section>
2650
2651<section title="Since draft-ietf-httpbis-p3-payload-01">
2652<t>
2653  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2654  <list style="symbols"> 
2655    <t>
2656      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2657    </t>
2658  </list>
2659</t>
2660</section>
2661
2662<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2663<t>
2664  Closed issues:
2665  <list style="symbols"> 
2666    <t>
2667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2668      "Quoting Charsets"
2669    </t>
2670    <t>
2671      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2672      "Classification for Allow header"
2673    </t>
2674    <t>
2675      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2676      "missing default for qvalue in description of Accept-Encoding"
2677    </t>
2678  </list>
2679</t>
2680<t>
2681  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2682  <list style="symbols"> 
2683    <t>
2684      Reference RFC 3984, and update header field registrations for headers defined
2685      in this document.
2686    </t>
2687  </list>
2688</t>
2689</section>
2690
2691<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2692<t>
2693  Closed issues:
2694  <list style="symbols"> 
2695    <t>
2696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2697      "Quoting Charsets"
2698    </t>
2699    <t>
2700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2701      "language tag matching (Accept-Language) vs RFC4647"
2702    </t>
2703    <t>
2704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2705      "RFC 1806 has been replaced by RFC2183"
2706    </t>
2707  </list>
2708</t>
2709<t>
2710  Other changes:
2711  <list style="symbols"> 
2712    <t>
2713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2714      "Encoding References Normative" — rephrase the annotation and reference
2715      <xref target="BCP97"/>.
2716    </t>
2717  </list>
2718</t>
2719 </section>
2720
2721<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2722<t>
2723  Closed issues:
2724  <list style="symbols"> 
2725    <t>
2726      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2727      "RFC 2822 is updated by RFC 5322"
2728    </t>
2729  </list>
2730</t>
2731<t>
2732  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2733  <list style="symbols"> 
2734    <t>
2735      Use "/" instead of "|" for alternatives.
2736    </t>
2737    <t>
2738      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2739      whitespace ("OWS") and required whitespace ("RWS").
2740    </t>
2741    <t>
2742      Rewrite ABNFs to spell out whitespace rules, factor out
2743      header field value format definitions.
2744    </t>
2745  </list>
2746</t>
2747</section>
2748
2749<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2750<t>
2751  Closed issues:
2752  <list style="symbols"> 
2753    <t>
2754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2755      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2756    </t>
2757  </list>
2758</t>
2759<t>
2760  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2761  <list style="symbols"> 
2762    <t>
2763      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2764    </t>
2765  </list>
2766</t>
2767<t>
2768  Other changes:
2769  <list style="symbols"> 
2770    <t>
2771      Move definition of quality values into Part 1.
2772    </t>
2773  </list>
2774</t>
2775</section>
2776
2777<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2778<t>
2779  Closed issues:
2780  <list style="symbols"> 
2781    <t>
2782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2783      "Content-Location isn't special"
2784    </t>
2785    <t>
2786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2787      "Content Sniffing"
2788    </t>
2789  </list>
2790</t>
2791</section>
2792
2793<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2794<t>
2795  Closed issues:
2796  <list style="symbols"> 
2797    <t>
2798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2799      "Updated reference for language tags"
2800    </t>
2801    <t>
2802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2803      "Clarify rules for determining what entities a response carries"
2804    </t>
2805    <t>
2806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2807      "Content-Location base-setting problems"
2808    </t>
2809    <t>
2810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2811      "Content Sniffing"
2812    </t>
2813    <t>
2814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2815      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2816    </t>
2817    <t>
2818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2819      "move definitions of gzip/deflate/compress to part 1"
2820    </t>
2821  </list>
2822</t>
2823<t>
2824  Partly resolved issues:
2825  <list style="symbols"> 
2826    <t>
2827      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2828      "update IANA requirements wrt Transfer-Coding values" (add the
2829      IANA Considerations subsection)
2830    </t>
2831    <t>
2832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2833      "update IANA requirements wrt Content-Coding values" (add the
2834      IANA Considerations subsection)
2835    </t>
2836  </list>
2837</t>
2838</section>
2839
2840<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2841<t>
2842  Closed issues:
2843  <list style="symbols"> 
2844    <t>
2845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
2846      "Content Negotiation for media types"
2847    </t>
2848    <t>
2849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
2850      "Accept-Language: which RFC4647 filtering?"
2851    </t>
2852  </list>
2853</t>
2854</section>
2855
2856<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
2857<t>
2858  Closed issues:
2859  <list style="symbols"> 
2860    <t>
2861      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
2862      "MIME-Version not listed in P1, general header fields"
2863    </t>
2864    <t>
2865      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
2866      "IANA registry for content/transfer encodings"
2867    </t>
2868    <t>
2869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2870      "Content Sniffing"
2871    </t>
2872    <t>
2873      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
2874      "use of term "word" when talking about header structure"
2875    </t>
2876  </list>
2877</t>
2878<t>
2879  Partly resolved issues:
2880  <list style="symbols"> 
2881    <t>
2882      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2883      "Term for the requested resource's URI"
2884    </t>
2885  </list>
2886</t>
2887</section>
2888
2889<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
2890<t>
2891  Closed issues:
2892  <list style="symbols"> 
2893    <t>
2894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
2895      "Clarify 'Requested Variant'"
2896    </t>
2897    <t>
2898      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2899      "Content-Location isn't special"
2900    </t>
2901    <t>
2902      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
2903      "Delimiting messages with multipart/byteranges"
2904    </t>
2905    <t>
2906      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
2907      "Clarify entity / representation / variant terminology"
2908    </t>
2909    <t>
2910      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
2911      "confusing req. language for Content-Location"
2912    </t>
2913    <t>
2914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
2915      "Content-Location on 304 responses"
2916    </t>
2917    <t>
2918      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
2919      "'requested resource' in content-encoding definition"
2920    </t>
2921    <t>
2922      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
2923      "consider removing the 'changes from 2068' sections"
2924    </t>
2925  </list>
2926</t>
2927<t>
2928  Partly resolved issues:
2929  <list style="symbols"> 
2930    <t>
2931      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2932      "Content-MD5 and partial responses"
2933    </t>
2934  </list>
2935</t>
2936</section>
2937
2938<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
2939<t>
2940  Closed issues:
2941  <list style="symbols"> 
2942    <t>
2943      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
2944      "Factor out Content-Disposition"
2945    </t>
2946  </list>
2947</t>
2948</section>
2949
2950<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
2951<t>
2952  Closed issues:
2953  <list style="symbols"> 
2954    <t>
2955      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
2956      "Header Classification"
2957    </t>
2958    <t>
2959      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2960      "untangle ABNFs for header fields"
2961    </t>
2962    <t>
2963      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
2964      "potentially misleading MAY in media-type def"
2965    </t>
2966  </list>
2967</t>
2968</section>
2969
2970<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
2971<t>
2972  Closed issues:
2973  <list style="symbols"> 
2974    <t>
2975      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
2976      "Default charsets for text media types"
2977    </t>
2978    <t>
2979      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2980      "Content-MD5 and partial responses"
2981    </t>
2982    <t>
2983      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2984      "untangle ABNFs for header fields"
2985    </t>
2986    <t>
2987      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
2988      "confusing undefined parameter in media range example"
2989    </t>
2990  </list>
2991</t>
2992</section>
2993
2994<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
2995<t>
2996  None.
2997</t>
2998</section>
2999
3000<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
3001<t>
3002  Closed issues:
3003  <list style="symbols"> 
3004    <t>
3005      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
3006      "Strength of requirements on Accept re: 406"
3007    </t>
3008  </list>
3009</t>
3010</section>
3011
3012<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
3013<t>
3014  Closed issues:
3015  <list style="symbols"> 
3016    <t>
3017      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
3018      "Document HTTP's error-handling philosophy"
3019    </t>
3020  </list>
3021</t>
3022</section>
3023
3024</section>
3025
3026</back>
3027</rfc>
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