source: draft-ietf-httpbis/18/draft-ietf-httpbis-p3-payload-18.xml @ 1499

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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-18">
20
21
22<front>
23
24  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
25
26  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
27    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
28    <address>
29      <postal>
30        <street>345 Park Ave</street>
31        <city>San Jose</city>
32        <region>CA</region>
33        <code>95110</code>
34        <country>USA</country>
35      </postal>
36      <email>fielding@gbiv.com</email>
37      <uri>http://roy.gbiv.com/</uri>
38    </address>
39  </author>
40
41  <author initials="J." surname="Gettys" fullname="Jim Gettys">
42    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
43    <address>
44      <postal>
45        <street>21 Oak Knoll Road</street>
46        <city>Carlisle</city>
47        <region>MA</region>
48        <code>01741</code>
49        <country>USA</country>
50      </postal>
51      <email>jg@freedesktop.org</email>
52      <uri>http://gettys.wordpress.com/</uri>
53    </address>
54  </author>
55 
56  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
57    <organization abbrev="HP">Hewlett-Packard Company</organization>
58    <address>
59      <postal>
60        <street>HP Labs, Large Scale Systems Group</street>
61        <street>1501 Page Mill Road, MS 1177</street>
62        <city>Palo Alto</city>
63        <region>CA</region>
64        <code>94304</code>
65        <country>USA</country>
66      </postal>
67      <email>JeffMogul@acm.org</email>
68    </address>
69  </author>
70
71  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
72    <organization abbrev="Microsoft">Microsoft Corporation</organization>
73    <address>
74      <postal>
75        <street>1 Microsoft Way</street>
76        <city>Redmond</city>
77        <region>WA</region>
78        <code>98052</code>
79        <country>USA</country>
80      </postal>
81      <email>henrikn@microsoft.com</email>
82    </address>
83  </author>
84
85  <author initials="L." surname="Masinter" fullname="Larry Masinter">
86    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
87    <address>
88      <postal>
89        <street>345 Park Ave</street>
90        <city>San Jose</city>
91        <region>CA</region>
92        <code>95110</code>
93        <country>USA</country>
94      </postal>
95      <email>LMM@acm.org</email>
96      <uri>http://larry.masinter.net/</uri>
97    </address>
98  </author>
99 
100  <author initials="P." surname="Leach" fullname="Paul J. Leach">
101    <organization abbrev="Microsoft">Microsoft Corporation</organization>
102    <address>
103      <postal>
104        <street>1 Microsoft Way</street>
105        <city>Redmond</city>
106        <region>WA</region>
107        <code>98052</code>
108      </postal>
109      <email>paulle@microsoft.com</email>
110    </address>
111  </author>
112   
113  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
114    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
115    <address>
116      <postal>
117        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
118        <street>The Stata Center, Building 32</street>
119        <street>32 Vassar Street</street>
120        <city>Cambridge</city>
121        <region>MA</region>
122        <code>02139</code>
123        <country>USA</country>
124      </postal>
125      <email>timbl@w3.org</email>
126      <uri>http://www.w3.org/People/Berners-Lee/</uri>
127    </address>
128  </author>
129
130  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
131    <organization abbrev="W3C">World Wide Web Consortium</organization>
132    <address>
133      <postal>
134        <street>W3C / ERCIM</street>
135        <street>2004, rte des Lucioles</street>
136        <city>Sophia-Antipolis</city>
137        <region>AM</region>
138        <code>06902</code>
139        <country>France</country>
140      </postal>
141      <email>ylafon@w3.org</email>
142      <uri>http://www.raubacapeu.net/people/yves/</uri>
143    </address>
144  </author>
145
146  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
147    <organization abbrev="greenbytes">greenbytes GmbH</organization>
148    <address>
149      <postal>
150        <street>Hafenweg 16</street>
151        <city>Muenster</city><region>NW</region><code>48155</code>
152        <country>Germany</country>
153      </postal>
154      <phone>+49 251 2807760</phone>
155      <facsimile>+49 251 2807761</facsimile>
156      <email>julian.reschke@greenbytes.de</email>
157      <uri>http://greenbytes.de/tech/webdav/</uri>
158    </address>
159  </author>
160
161  <date month="January" year="2012" day="4"/>
162  <workgroup>HTTPbis Working Group</workgroup>
163
164<abstract>
165<t>
166   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
167   distributed, collaborative, hypertext information systems. HTTP has been in
168   use by the World Wide Web global information initiative since 1990. This
169   document is Part 3 of the seven-part specification that defines the protocol
170   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
171</t>
172<t>
173   Part 3 defines HTTP message content, metadata, and content negotiation.
174</t>
175</abstract>
176
177<note title="Editorial Note (To be removed by RFC Editor)">
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list (ietf-http-wg@w3.org), which is archived at
181    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
182  </t>
183  <t>
184    The current issues list is at
185    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
186    documents (including fancy diffs) can be found at
187    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
188  </t>
189  <t>
190    The changes in this draft are summarized in <xref target="changes.since.17"/>.
191  </t>
192</note>
193</front>
194<middle>
195<section title="Introduction" anchor="introduction">
196<t>
197   This document defines HTTP/1.1 message payloads (a.k.a., content), the
198   associated metadata header fields that define how the payload is intended
199   to be interpreted by a recipient, the request header fields that
200   might influence content selection, and the various selection algorithms
201   that are collectively referred to as HTTP content negotiation.
202</t>
203<t>
204   This document is currently disorganized in order to minimize the changes
205   between drafts and enable reviewers to see the smaller errata changes.
206   A future draft will reorganize the sections to better reflect the content.
207   In particular, the sections on entities will be renamed payload and moved
208   to the first half of the document, while the sections on content negotiation
209   and associated request header fields will be moved to the second half.  The
210   current mess reflects how widely dispersed these topics and associated
211   requirements had become in <xref target="RFC2616"/>.
212</t>
213
214<section title="Terminology" anchor="terminology">
215<t>
216   This specification uses a number of terms to refer to the roles
217   played by participants in, and objects of, the HTTP communication.
218</t>
219<t>
220  <iref item="content negotiation"/>
221  <?rfc needLines="4"?>content negotiation
222  <list>
223    <t>
224      The mechanism for selecting the appropriate representation when
225      servicing a request. The representation in any response
226      can be negotiated (including error responses).
227    </t>
228  </list>
229</t>
230</section>
231
232<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
233<t>
234   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
235   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
236   document are to be interpreted as described in <xref target="RFC2119"/>.
237</t>
238<t>
239   This document defines conformance criteria for several roles in HTTP
240   communication, including Senders, Recipients, Clients, Servers, User-Agents,
241   Origin Servers, Intermediaries, Proxies and Gateways. See Section 2 of <xref target="Part1"/>
242   for definitions of these terms.
243</t>
244<t>
245   An implementation is considered conformant if it complies with all of the
246   requirements associated with its role(s). Note that SHOULD-level requirements
247   are relevant here, unless one of the documented exceptions is applicable.
248</t>
249<t>
250   This document also uses ABNF to define valid protocol elements
251   (<xref target="notation"/>). In addition to the prose requirements placed
252   upon them, Senders MUST NOT generate protocol elements that are invalid.
253</t>
254<t>
255   Unless noted otherwise, Recipients MAY take steps to recover a usable
256   protocol element from an invalid construct. However, HTTP does not define
257   specific error handling mechanisms, except in cases where it has direct
258   impact on security. This is because different uses of the protocol require
259   different error handling strategies; for example, a Web browser may wish to
260   transparently recover from a response where the Location header field
261   doesn't parse according to the ABNF, whereby in a systems control protocol
262   using HTTP, this type of error recovery could lead to dangerous consequences.
263</t>
264</section>
265
266<section title="Syntax Notation" anchor="notation">
267 
268 
269 
270 
271 
272 
273<t>
274  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
275  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
276  <xref target="collected.abnf"/> shows the collected ABNF, with the list
277  rule expanded.
278</t>
279<t>
280  The following core rules are included by
281  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
282  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
283  DIGIT (decimal 0-9), DQUOTE (double quote),
284  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
285  OCTET (any 8-bit sequence of data), SP (space), and
286  VCHAR (any visible US-ASCII character).
287</t>
288
289<section title="Core Rules" anchor="core.rules">
290 
291 
292 
293<t>
294  The core rules below are defined in <xref target="Part1"/>:
295</t>
296<figure><artwork type="abnf2616"><![CDATA[
297  OWS            = <OWS, defined in [Part1], Section 1.2.2>
298  token          = <token, defined in [Part1], Section 3.2.3>
299  word           = <word, defined in [Part1], Section 3.2.3>
300]]></artwork></figure>
301</section>
302
303<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
304 
305 
306 
307<t>
308  The ABNF rules below are defined in other parts:
309</t>
310<figure><artwork type="abnf2616"><![CDATA[
311  absolute-URI   = <absolute-URI, defined in [Part1], Section 2.7>
312  partial-URI    = <partial-URI, defined in [Part1], Section 2.7>
313  qvalue         = <qvalue, defined in [Part1], Section 5.3>
314]]></artwork></figure>
315</section>
316
317</section>
318
319</section>
320
321<section title="Protocol Parameters" anchor="protocol.parameters">
322
323<section title="Character Encodings (charset)" anchor="character.sets">
324<t>
325   HTTP uses charset names to indicate the character encoding of a
326   textual representation.
327</t>
328<t anchor="rule.charset">
329 
330   A character encoding is identified by a case-insensitive token. The
331   complete set of tokens is defined by the IANA Character Set registry
332   (<eref target="http://www.iana.org/assignments/character-sets"/>).
333</t>
334<figure><iref primary="true" item="Grammar" subitem="charset"/><artwork type="abnf2616"><![CDATA[
335  charset = token
336]]></artwork></figure>
337<t>
338   Although HTTP allows an arbitrary token to be used as a charset
339   value, any token that has a predefined value within the IANA
340   Character Set registry MUST represent the character encoding defined
341   by that registry. Applications SHOULD limit their use of character
342   encodings to those defined within the IANA registry.
343</t>
344<t>
345   HTTP uses charset in two contexts: within an Accept-Charset request
346   header field (in which the charset value is an unquoted token) and as the
347   value of a parameter in a Content-Type header field (within a request or
348   response), in which case the parameter value of the charset parameter
349   can be quoted.
350</t>
351<t>
352   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
353   <xref target="RFC2277"/>.
354</t>
355</section>
356
357<section title="Content Codings" anchor="content.codings">
358 
359<t>
360   Content coding values indicate an encoding transformation that has
361   been or can be applied to a representation. Content codings are primarily
362   used to allow a representation to be compressed or otherwise usefully
363   transformed without losing the identity of its underlying media type
364   and without loss of information. Frequently, the representation is stored in
365   coded form, transmitted directly, and only decoded by the recipient.
366</t>
367<figure><iref primary="true" item="Grammar" subitem="content-coding"/><artwork type="abnf2616"><![CDATA[
368  content-coding   = token
369]]></artwork></figure>
370<t>
371   All content-coding values are case-insensitive. HTTP/1.1 uses
372   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
373   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
374   describes the content-coding, what is more important is that it
375   indicates what decoding mechanism will be required to remove the
376   encoding.
377</t>
378<t>
379   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
380  <list>
381    <t>
382      See Section 5.1.2.1 of <xref target="Part1"/>.
383    </t>
384  </list>
385</t>
386<t>
387   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
388  <list>
389    <t>
390      See Section 5.1.2.2 of <xref target="Part1"/>.
391    </t>
392  </list>
393</t>
394<t>
395   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
396  <list>
397    <t>
398      See Section 5.1.2.3 of <xref target="Part1"/>.
399    </t>
400  </list>
401</t>
402
403<section title="Content Coding Registry" anchor="content.coding.registry">
404<t>
405   The HTTP Content Coding Registry defines the name space for the content
406   coding names.
407</t>
408<t>
409   Registrations MUST include the following fields:
410   <list style="symbols">
411     <t>Name</t>
412     <t>Description</t>
413     <t>Pointer to specification text</t>
414   </list>
415</t>
416<t>
417   Names of content codings MUST NOT overlap with names of transfer codings
418   (Section 5.1 of <xref target="Part1"/>), unless the encoding transformation is identical (as it
419   is the case for the compression codings defined in
420   Section 5.1.2 of <xref target="Part1"/>).
421</t>
422<t>
423   Values to be added to this name space require a specification
424   (see "Specification Required" in
425   Section 4.1 of <xref target="RFC5226"/>), and MUST
426   conform to the purpose of content coding defined in this section.
427</t>
428<t>
429   The registry itself is maintained at
430   <eref target="http://www.iana.org/assignments/http-parameters"/>.
431</t>
432</section>
433
434</section>
435
436<section title="Media Types" anchor="media.types">
437 
438 
439 
440<t>
441   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
442   and Accept (<xref target="header.accept"/>) header fields in order to provide
443   open and extensible data typing and type negotiation.
444</t>
445<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[
446  media-type = type "/" subtype *( OWS ";" OWS parameter )
447  type       = token
448  subtype    = token
449]]></artwork></figure>
450<t anchor="rule.parameter">
451 
452 
453 
454   The type/subtype MAY be followed by parameters in the form of
455   attribute/value pairs.
456</t>
457<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[
458  parameter      = attribute "=" value
459  attribute      = token
460  value          = word
461]]></artwork></figure>
462<t>
463   The type, subtype, and parameter attribute names are case-insensitive.
464   Parameter values might or might not be case-sensitive, depending on the
465   semantics of the parameter name.  The presence or absence of a parameter might
466   be significant to the processing of a media-type, depending on its
467   definition within the media type registry.
468</t>
469<t>
470   A parameter value that matches the <xref target="core.rules" format="none">token</xref> production can be
471   transmitted as either a token or within a quoted-string. The quoted and
472   unquoted values are equivalent.
473</t>
474<t>
475   Note that some older HTTP applications do not recognize media type
476   parameters. When sending data to older HTTP applications,
477   implementations SHOULD only use media type parameters when they are
478   required by that type/subtype definition.
479</t>
480<t>
481   Media-type values are registered with the Internet Assigned Number
482   Authority (IANA). The media type registration process is
483   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
484   discouraged.
485</t>
486
487<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
488<t>
489   Internet media types are registered with a canonical form. A
490   representation transferred via HTTP messages MUST be in the
491   appropriate canonical form prior to its transmission except for
492   "text" types, as defined in the next paragraph.
493</t>
494<t>
495   When in canonical form, media subtypes of the "text" type use CRLF as
496   the text line break. HTTP relaxes this requirement and allows the
497   transport of text media with plain CR or LF alone representing a line
498   break when it is done consistently for an entire representation. HTTP
499   applications MUST accept CRLF, bare CR, and bare LF as indicating
500   a line break in text media received via HTTP. In
501   addition, if the text is in a character encoding that does not
502   use octets 13 and 10 for CR and LF respectively, as is the case for
503   some multi-byte character encodings, HTTP allows the use of whatever octet
504   sequences are defined by that character encoding to represent the
505   equivalent of CR and LF for line breaks. This flexibility regarding
506   line breaks applies only to text media in the payload body; a bare CR
507   or LF MUST NOT be substituted for CRLF within any of the HTTP control
508   structures (such as header fields and multipart boundaries).
509</t>
510<t>
511   If a representation is encoded with a content-coding, the underlying
512   data MUST be in a form defined above prior to being encoded.
513</t>
514</section>
515
516<section title="Multipart Types" anchor="multipart.types">
517<t>
518   MIME provides for a number of "multipart" types — encapsulations of
519   one or more representations within a single message-body. All multipart
520   types share a common syntax, as defined in Section 5.1.1 of <xref target="RFC2046"/>,
521   and MUST include a boundary parameter as part of the media type
522   value. The message body is itself a protocol element and MUST
523   therefore use only CRLF to represent line breaks between body-parts.
524</t>
525<t>
526   In general, HTTP treats a multipart message-body no differently than
527   any other media type: strictly as payload.  HTTP does not use the
528   multipart boundary as an indicator of message-body length.
529   <!-- jre: re-insert removed text pointing to caching? -->
530   In all other respects, an HTTP user agent SHOULD follow the same or similar
531   behavior as a MIME user agent would upon receipt of a multipart type.
532   The MIME header fields within each body-part of a multipart message-body
533   do not have any significance to HTTP beyond that defined by
534   their MIME semantics.
535</t>
536<t>
537   If an application receives an unrecognized multipart subtype, the
538   application MUST treat it as being equivalent to "multipart/mixed".
539</t>
540<t><list>
541  <t>
542    Note: The "multipart/form-data" type has been specifically defined
543    for carrying form data suitable for processing via the POST
544    request method, as described in <xref target="RFC2388"/>.
545  </t>
546</list></t>
547</section>
548</section>
549
550<section title="Language Tags" anchor="language.tags">
551 
552<t>
553   A language tag, as defined in <xref target="RFC5646"/>, identifies a
554   natural language spoken, written, or otherwise conveyed by human beings for
555   communication of information to other human beings. Computer languages are
556   explicitly excluded. HTTP uses language tags within the Accept-Language and
557   Content-Language fields.
558</t>
559<t>
560   In summary, a language tag is composed of one or more parts: A primary
561   language subtag followed by a possibly empty series of subtags:
562</t>
563<figure><iref primary="true" item="Grammar" subitem="language-tag"/><artwork type="abnf2616"><![CDATA[
564  language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
565]]></artwork></figure>
566<t>
567   White space is not allowed within the tag and all tags are case-insensitive.
568   The name space of language subtags is administered by the IANA (see
569   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
570</t>
571<figure>
572  <preamble>Example tags include:</preamble>
573<artwork type="example"><![CDATA[
574  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
575]]></artwork>
576</figure>
577<t>
578   See <xref target="RFC5646"/> for further information.
579</t>
580</section>
581</section>
582
583<section title="Payload" anchor="payload">
584<t>
585   HTTP messages MAY transfer a payload if not otherwise restricted by
586   the request method or response status code.  The payload consists of
587   metadata, in the form of header fields, and data, in the form of the
588   sequence of octets in the message-body after any transfer-coding has
589   been decoded.
590</t>
591<iref item="payload"/>
592<t>   
593   A "payload" in HTTP is always a partial or complete
594   representation of some resource.  We use separate terms for payload
595   and representation because some messages contain only the associated
596   representation's header fields (e.g., responses to HEAD) or only some
597   part(s) of the representation (e.g., the 206 status code).
598</t>
599<section title="Payload Header Fields" anchor="payload.header.fields">
600 
601<t>
602   HTTP header fields that specifically define the payload, rather than the
603   associated representation, are referred to as "payload header fields".
604   The following payload header fields are defined by HTTP/1.1:
605</t>
606<texttable align="left">
607  <ttcol>Header Field Name</ttcol>
608  <ttcol>Defined in...</ttcol>
609
610  <c>Content-Length</c> <c>Section 8.2 of <xref target="Part1"/></c>
611  <c>Content-Range</c> <c>Section 5.2 of <xref target="Part5"/></c>
612</texttable>
613</section>
614
615<section title="Payload Body" anchor="payload.body">
616 
617<t>
618   A payload body is only present in a message when a message-body is
619   present, as described in Section 3.3 of <xref target="Part1"/>. The payload body is obtained
620   from the message-body by decoding any Transfer-Encoding that might
621   have been applied to ensure safe and proper transfer of the message.
622</t>
623</section>
624</section>
625
626<section title="Representation" anchor="representation">
627<iref item="representation"/>
628<t>
629   A "representation" is information in a format that can be readily
630   communicated from one party to another.  A resource representation
631   is information that reflects the state of that resource, as observed
632   at some point in the past (e.g., in a response to GET) or to be
633   desired at some point in the future (e.g., in a PUT request).
634</t>
635<t>
636   Most, but not all, representations transferred via HTTP are intended
637   to be a representation of the target resource (the resource identified
638   by the effective request URI).  The precise semantics of a representation
639   are determined by the type of message (request or response), the request
640   method, the response status code, and the representation metadata.
641   For example, the above semantic is true for the representation in any
642   200 (OK) response to GET and for the representation in any PUT request.
643   A 200 response to PUT, in contrast, contains either a representation
644   that describes the successful action or a representation of the target
645   resource, with the latter indicated by a Content-Location header field
646   with the same value as the effective request URI.  Likewise, response
647   messages with an error status code usually contain a representation that
648   describes the error and what next steps are suggested for resolving it.
649</t>
650
651<section title="Representation Header Fields" anchor="representation.header.fields">
652 
653<t>
654   Representation header fields define metadata about the representation data
655   enclosed in the message-body or, if no message-body is present, about
656   the representation that would have been transferred in a 200 response
657   to a simultaneous GET request with the same effective request URI.
658</t>
659<t>
660   The following header fields are defined as representation metadata:
661</t>
662<texttable align="left">
663  <ttcol>Header Field Name</ttcol>
664  <ttcol>Defined in...</ttcol>
665
666  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
667  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
668  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
669  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
670  <c>Expires</c> <c>Section 3.3 of <xref target="Part6"/></c>
671  <c>Last-Modified</c> <c>Section 2.2 of <xref target="Part4"/></c>
672</texttable>
673</section>
674
675<section title="Representation Data" anchor="representation.data">
676 
677<t>
678   The representation body associated with an HTTP message is
679   either provided as the payload body of the message or
680   referred to by the message semantics and the effective request
681   URI.  The representation data is in a format and encoding defined by
682   the representation metadata header fields.
683</t>
684<t>
685   The data type of the representation data
686   is determined via the header fields Content-Type and Content-Encoding.
687   These define a two-layer, ordered encoding model:
688</t>
689<figure><artwork type="example"><![CDATA[
690  representation-data := Content-Encoding( Content-Type( bits ) )
691]]></artwork></figure>
692<t>
693   Content-Type specifies the media type of the underlying data, which
694   defines both the data format and how that data SHOULD be processed
695   by the recipient (within the scope of the request method semantics).
696   Any HTTP/1.1 message containing a payload body SHOULD include a
697   Content-Type header field defining the media type of the associated
698   representation unless that metadata is unknown to the sender.
699   If the Content-Type header field is not present, it indicates that
700   the sender does not know the media type of the representation;
701   recipients MAY either assume that the media type is
702   "application/octet-stream" (<xref target="RFC2046"/>, Section 4.5.1)
703   or examine the content to determine its type.
704</t>
705<t>
706   In practice, resource owners do not always properly configure their origin
707   server to provide the correct Content-Type for a given representation,
708   with the result that some clients will examine a response body's content
709   and override the specified type.
710   Clients that do so risk drawing incorrect conclusions, which might expose
711   additional security risks (e.g., "privilege escalation").  Furthermore,
712   it is impossible to determine the sender's intent by examining the data
713   format: many data formats match multiple media types that differ only in
714   processing semantics.  Implementers are encouraged to provide a means of
715   disabling such "content sniffing" when it is used.
716</t>
717<t>
718   Content-Encoding is used to indicate any additional content
719   codings applied to the data, usually for the purpose of data
720   compression, that are a property of the representation.  If
721   Content-Encoding is not present, then there is no additional
722   encoding beyond that defined by the Content-Type.
723</t>
724</section>
725</section>
726
727<section title="Content Negotiation" anchor="content.negotiation">
728<t>
729   HTTP responses include a representation which contains information for
730   interpretation, whether by a human user or for further processing.
731   Often, the server has different ways of representing the
732   same information; for example, in different formats, languages,
733   or using different character encodings.
734</t>
735<t>
736   HTTP clients and their users might have different or variable
737   capabilities, characteristics or preferences which would influence
738   which representation, among those available from the server,
739   would be best for the server to deliver. For this reason, HTTP
740   provides mechanisms for "content negotiation" — a process of
741   allowing selection of a representation of a given resource,
742   when more than one is available.
743</t>
744<t>
745   This specification defines two patterns of content negotiation;
746   "server-driven", where the server selects the representation based
747   upon the client's stated preferences, and "agent-driven" negotiation,
748   where the server provides a list of representations for the client to
749   choose from, based upon their metadata. In addition,  there are
750   other patterns: some applications use an "active content" pattern,
751   where the server returns active content which runs on the client
752   and, based on client available parameters, selects additional
753   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
754   has also been proposed.
755</t>
756<t>
757   These patterns are all widely used, and have trade-offs in applicability
758   and practicality. In particular, when the number of preferences or
759   capabilities to be expressed by a client are large (such as when many
760   different formats are supported by a user-agent), server-driven
761   negotiation becomes unwieldy, and might not be appropriate. Conversely,
762   when the number of representations to choose from is very large,
763   agent-driven negotiation might not be appropriate.
764</t>
765<t>
766   Note that in all cases, the supplier of representations has the
767   responsibility for determining which representations might be
768   considered to be the "same information".
769</t>
770
771<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
772<t>
773   If the selection of the best representation for a response is made by
774   an algorithm located at the server, it is called server-driven
775   negotiation. Selection is based on the available representations of
776   the response (the dimensions over which it can vary; e.g., language,
777   content-coding, etc.) and the contents of particular header fields in
778   the request message or on other information pertaining to the request
779   (such as the network address of the client).
780</t>
781<t>
782   Server-driven negotiation is advantageous when the algorithm for
783   selecting from among the available representations is difficult to
784   describe to the user agent, or when the server desires to send its
785   "best guess" to the client along with the first response (hoping to
786   avoid the round-trip delay of a subsequent request if the "best
787   guess" is good enough for the user). In order to improve the server's
788   guess, the user agent MAY include request header fields (Accept,
789   Accept-Language, Accept-Encoding, etc.) which describe its
790   preferences for such a response.
791</t>
792<t>
793   Server-driven negotiation has disadvantages:
794  <list style="numbers">
795    <t>
796         It is impossible for the server to accurately determine what
797         might be "best" for any given user, since that would require
798         complete knowledge of both the capabilities of the user agent
799         and the intended use for the response (e.g., does the user want
800         to view it on screen or print it on paper?).
801    </t>
802    <t>
803         Having the user agent describe its capabilities in every
804         request can be both very inefficient (given that only a small
805         percentage of responses have multiple representations) and a
806         potential violation of the user's privacy.
807    </t>
808    <t>
809         It complicates the implementation of an origin server and the
810         algorithms for generating responses to a request.
811    </t>
812    <t>
813         It might limit a public cache's ability to use the same response
814         for multiple user's requests.
815    </t>
816  </list>
817</t>
818<t>
819   Server-driven negotiation allows the user agent to specify its preferences,
820   but it cannot expect responses to always honour them. For example, the origin
821   server might not implement server-driven negotiation, or it might decide that
822   sending a response that doesn't conform to them is better than sending a 406
823   (Not Acceptable) response.
824</t>
825<t>
826   Many of the mechanisms for expressing preferences use quality values to
827   declare relative preference. See Section 5.3 of <xref target="Part1"/> for more information.
828</t>
829<t>
830   HTTP/1.1 includes the following header fields for enabling
831   server-driven negotiation through description of user agent
832   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
833   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
834   (<xref target="header.accept-language"/>), and User-Agent (Section 9.10 of <xref target="Part2"/>).
835   However, an origin server is not limited to these dimensions and MAY vary
836   the response based on any aspect of the request, including aspects
837   of the connection (e.g., IP address) or information within extension
838   header fields not defined by this specification.
839</t>
840<t><list>
841  <t>
842    Note: In practice, User-Agent based negotiation is fragile,
843    because new clients might not be recognized.
844  </t>
845</list></t>
846<t>
847   The Vary header field (Section 3.5 of <xref target="Part6"/>) can be used to express the parameters the
848   server uses to select a representation that is subject to server-driven
849   negotiation.
850</t>
851</section>
852
853<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
854<t>
855   With agent-driven negotiation, selection of the best representation
856   for a response is performed by the user agent after receiving an
857   initial response from the origin server. Selection is based on a list
858   of the available representations of the response included within the
859   header fields or body of the initial response, with each
860   representation identified by its own URI. Selection from among the
861   representations can be performed automatically (if the user agent is
862   capable of doing so) or manually by the user selecting from a
863   generated (possibly hypertext) menu.
864</t>
865<t>
866   Agent-driven negotiation is advantageous when the response would vary
867   over commonly-used dimensions (such as type, language, or encoding),
868   when the origin server is unable to determine a user agent's
869   capabilities from examining the request, and generally when public
870   caches are used to distribute server load and reduce network usage.
871</t>
872<t>
873   Agent-driven negotiation suffers from the disadvantage of needing a
874   second request to obtain the best alternate representation. This
875   second request is only efficient when caching is used. In addition,
876   this specification does not define any mechanism for supporting
877   automatic selection, though it also does not prevent any such
878   mechanism from being developed as an extension and used within
879   HTTP/1.1.
880</t>
881<t>
882   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
883   status codes for enabling agent-driven negotiation when the server is
884   unwilling or unable to provide a varying response using server-driven
885   negotiation.
886</t>
887</section>
888</section>
889
890<section title="Header Field Definitions" anchor="header.field.definitions">
891<t>
892   This section defines the syntax and semantics of HTTP/1.1 header fields
893   related to the payload of messages.
894</t>
895
896<section title="Accept" anchor="header.accept">
897  <iref primary="true" item="Accept header field"/>
898  <iref primary="true" item="Header Fields" subitem="Accept"/>
899 
900 
901 
902 
903<t>
904   The "Accept" header field can be used by user agents to specify
905   response media types that are acceptable. Accept header fields can be used to
906   indicate that the request is specifically limited to a small set of desired
907   types, as in the case of a request for an in-line image.
908</t>
909<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[
910  Accept = #( media-range [ accept-params ] )
911 
912  media-range    = ( "*/*"
913                   / ( type "/" "*" )
914                   / ( type "/" subtype )
915                   ) *( OWS ";" OWS parameter )
916  accept-params  = OWS ";" OWS "q=" qvalue *( accept-ext )
917  accept-ext     = OWS ";" OWS token [ "=" word ]
918]]></artwork></figure>
919<t>
920   The asterisk "*" character is used to group media types into ranges,
921   with "*/*" indicating all media types and "type/*" indicating all
922   subtypes of that type. The media-range MAY include media type
923   parameters that are applicable to that range.
924</t>
925<t>
926   Each media-range MAY be followed by one or more accept-params,
927   beginning with the "q" parameter for indicating a relative quality
928   factor. The first "q" parameter (if any) separates the media-range
929   parameter(s) from the accept-params. Quality factors allow the user
930   or user agent to indicate the relative degree of preference for that
931   media-range, using the qvalue scale from 0 to 1 (Section 5.3 of <xref target="Part1"/>). The
932   default value is q=1.
933</t>
934<t><list>
935  <t>
936    Note: Use of the "q" parameter name to separate media type
937    parameters from Accept extension parameters is due to historical
938    practice. Although this prevents any media type parameter named
939    "q" from being used with a media range, such an event is believed
940    to be unlikely given the lack of any "q" parameters in the IANA
941    media type registry and the rare usage of any media type
942    parameters in Accept. Future media types are discouraged from
943    registering any parameter named "q".
944  </t>
945</list></t>
946<t>
947   The example
948</t>
949<figure><artwork type="example"><![CDATA[
950  Accept: audio/*; q=0.2, audio/basic
951]]></artwork></figure>
952<t>
953   SHOULD be interpreted as "I prefer audio/basic, but send me any audio
954   type if it is the best available after an 80% mark-down in quality".
955</t>
956<t>
957   A request without any Accept header field implies that the user agent
958   will accept any media type in response.
959   If an Accept header field is present in a request and none of the
960   available representations for the response have a media type that is
961   listed as acceptable, the origin server MAY either
962   honor the Accept header field by sending a 406 (Not Acceptable) response
963   or disregard the Accept header field by treating the response as if
964   it is not subject to content negotiation.
965</t>
966<t>
967   A more elaborate example is
968</t>
969<figure><artwork type="example"><![CDATA[
970  Accept: text/plain; q=0.5, text/html,
971          text/x-dvi; q=0.8, text/x-c
972]]></artwork></figure>
973<t>
974   Verbally, this would be interpreted as "text/html and text/x-c are
975   the preferred media types, but if they do not exist, then send the
976   text/x-dvi representation, and if that does not exist, send the text/plain
977   representation".
978</t>
979<t>
980   Media ranges can be overridden by more specific media ranges or
981   specific media types. If more than one media range applies to a given
982   type, the most specific reference has precedence. For example,
983</t>
984<figure><artwork type="example"><![CDATA[
985  Accept: text/*, text/plain, text/plain;format=flowed, */*
986]]></artwork></figure>
987<t>
988   have the following precedence:
989   <list style="numbers">
990    <t>text/plain;format=flowed</t>
991    <t>text/plain</t>
992    <t>text/*</t>
993    <t>*/*</t>
994   </list>
995</t>
996<t>
997   The media type quality factor associated with a given type is
998   determined by finding the media range with the highest precedence
999   which matches that type. For example,
1000</t>
1001<figure><artwork type="example"><![CDATA[
1002  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1003          text/html;level=2;q=0.4, */*;q=0.5
1004]]></artwork></figure>
1005<t>
1006   would cause the following values to be associated:
1007</t>
1008<texttable align="left">
1009  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1010  <c>text/html;level=1</c>    <c>1</c>
1011  <c>text/html</c>            <c>0.7</c>
1012  <c>text/plain</c>           <c>0.3</c>
1013  <c>image/jpeg</c>           <c>0.5</c>
1014  <c>text/html;level=2</c>    <c>0.4</c>
1015  <c>text/html;level=3</c>    <c>0.7</c>
1016</texttable>
1017<t>
1018      Note: A user agent might be provided with a default set of quality
1019      values for certain media ranges. However, unless the user agent is
1020      a closed system which cannot interact with other rendering agents,
1021      this default set ought to be configurable by the user.
1022</t>
1023</section>
1024
1025<section title="Accept-Charset" anchor="header.accept-charset">
1026  <iref primary="true" item="Accept-Charset header field"/>
1027  <iref primary="true" item="Header Fields" subitem="Accept-Charset"/>
1028 
1029<t>
1030   The "Accept-Charset" header field can be used by user agents to
1031   indicate what character encodings are acceptable in a response
1032   payload. This field allows
1033   clients capable of understanding more comprehensive or special-purpose
1034   character encodings to signal that capability to a server which is capable of
1035   representing documents in those character encodings.
1036</t>
1037<figure><iref primary="true" item="Grammar" subitem="Accept-Charset"/><artwork type="abnf2616"><![CDATA[
1038  Accept-Charset = 1#( ( charset / "*" )
1039                         [ OWS ";" OWS "q=" qvalue ] )
1040]]></artwork></figure>
1041<t>
1042   Character encoding values (a.k.a., charsets) are described in
1043   <xref target="character.sets"/>. Each charset MAY be given an
1044   associated quality value which represents the user's preference
1045   for that charset. The default value is q=1. An example is
1046</t>
1047<figure><artwork type="example"><![CDATA[
1048  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1049]]></artwork></figure>
1050<t>
1051   The special value "*", if present in the Accept-Charset field,
1052   matches every character encoding which is not mentioned elsewhere in the
1053   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
1054   all character encodings not explicitly mentioned get a quality value of 0.
1055</t>
1056<t>
1057   A request without any Accept-Charset header field implies that the user
1058   agent will accept any character encoding in response.
1059   If an Accept-Charset header field is present in a request and none of the
1060   available representations for the response have a character encoding that
1061   is listed as acceptable, the origin server MAY either honor the
1062   Accept-Charset header field by sending a 406 (Not Acceptable) response or
1063   disregard the Accept-Charset header field by treating the response as if
1064   it is not subject to content negotiation.
1065</t>
1066</section>
1067
1068<section title="Accept-Encoding" anchor="header.accept-encoding">
1069  <iref primary="true" item="Accept-Encoding header field"/>
1070  <iref primary="true" item="Header Fields" subitem="Accept-Encoding"/>
1071 
1072 
1073<t>
1074   The "Accept-Encoding" header field can be used by user agents to
1075   indicate what response content-codings (<xref target="content.codings"/>)
1076   are acceptable in the response.  An "identity" token is used as a synonym
1077   for "no encoding" in order to communicate when no encoding is preferred.
1078</t>
1079<figure><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/><artwork type="abnf2616"><![CDATA[
1080  Accept-Encoding  = #( codings [ OWS ";" OWS "q=" qvalue ] )
1081  codings          = content-coding / "identity" / "*"
1082]]></artwork></figure>
1083<t>
1084   Each codings value MAY be given an associated quality value which
1085   represents the preference for that encoding. The default value is q=1.
1086</t>
1087<t>
1088   For example,
1089</t>
1090<figure><artwork type="example"><![CDATA[
1091  Accept-Encoding: compress, gzip
1092  Accept-Encoding:
1093  Accept-Encoding: *
1094  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1095  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1096]]></artwork></figure>
1097<t>
1098   A server tests whether a content-coding for a given representation is
1099   acceptable, according to an Accept-Encoding field, using these rules:
1100  <list style="numbers">
1101      <t>The special "*" symbol in an Accept-Encoding field matches any
1102         available content-coding not explicitly listed in the header
1103         field.</t>
1104
1105      <t>If the representation has no content-coding, then it is acceptable
1106         by default unless specifically excluded by the Accept-Encoding field
1107         stating either "identity;q=0" or "*;q=0" without a more specific
1108         entry for "identity".</t>
1109
1110      <t>If the representation's content-coding is one of the content-codings
1111         listed in the Accept-Encoding field, then it is acceptable unless
1112         it is accompanied by a qvalue of 0. (As defined in Section 5.3 of <xref target="Part1"/>, a
1113         qvalue of 0 means "not acceptable".)</t>
1114
1115      <t>If multiple content-codings are acceptable, then the acceptable
1116         content-coding with the highest non-zero qvalue is preferred.</t>
1117  </list>
1118</t>
1119<t>
1120   An Accept-Encoding header field with a combined field-value that is empty
1121   implies that the user agent does not want any content-coding in response.
1122   If an Accept-Encoding header field is present in a request and none of the
1123   available representations for the response have a content-coding that
1124   is listed as acceptable, the origin server SHOULD send a response
1125   without any content-coding.
1126</t>
1127<t>
1128   A request without an Accept-Encoding header field implies that the user
1129   agent will accept any content-coding in response, but a representation
1130   without content-coding is preferred for compatibility with the widest
1131   variety of user agents.
1132</t>
1133<t><list>
1134  <t>
1135    Note: Most HTTP/1.0 applications do not recognize or obey qvalues
1136    associated with content-codings. This means that qvalues will not
1137    work and are not permitted with x-gzip or x-compress.
1138  </t>
1139</list></t>
1140</section>
1141
1142<section title="Accept-Language" anchor="header.accept-language">
1143  <iref primary="true" item="Accept-Language header field"/>
1144  <iref primary="true" item="Header Fields" subitem="Accept-Language"/>
1145 
1146 
1147<t>
1148   The "Accept-Language" header field can be used by user agents to
1149   indicate the set of natural languages that are preferred in the response.
1150   Language tags are defined in <xref target="language.tags"/>.
1151</t>
1152<figure><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/><artwork type="abnf2616"><![CDATA[
1153  Accept-Language =
1154                    1#( language-range [ OWS ";" OWS "q=" qvalue ] )
1155  language-range  =
1156            <language-range, defined in [RFC4647], Section 2.1>
1157]]></artwork></figure>
1158<t>
1159   Each language-range can be given an associated quality value which
1160   represents an estimate of the user's preference for the languages
1161   specified by that range. The quality value defaults to "q=1". For
1162   example,
1163</t>
1164<figure><artwork type="example"><![CDATA[
1165  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1166]]></artwork></figure>
1167<t>
1168   would mean: "I prefer Danish, but will accept British English and
1169   other types of English".
1170   (see also Section 2.3 of <xref target="RFC4647"/>)
1171</t>
1172<t>
1173   For matching, Section 3 of <xref target="RFC4647"/> defines
1174   several matching schemes. Implementations can offer the most appropriate
1175   matching scheme for their requirements.
1176</t>
1177<t><list>
1178  <t>
1179    Note: The "Basic Filtering" scheme (<xref target="RFC4647"/>, Section 3.3.1) is identical to the matching scheme that was
1180    previously defined in Section 14.4 of <xref target="RFC2616"/>.
1181  </t>
1182</list></t>
1183<t>
1184   It might be contrary to the privacy expectations of the user to send
1185   an Accept-Language header field with the complete linguistic preferences of
1186   the user in every request. For a discussion of this issue, see
1187   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1188</t>
1189<t>
1190   As intelligibility is highly dependent on the individual user, it is
1191   recommended that client applications make the choice of linguistic
1192   preference available to the user. If the choice is not made
1193   available, then the Accept-Language header field MUST NOT be given in
1194   the request.
1195</t>
1196<t><list>
1197  <t>
1198    Note: When making the choice of linguistic preference available to
1199    the user, we remind implementors of  the fact that users are not
1200    familiar with the details of language matching as described above,
1201    and ought to be provided appropriate guidance. As an example, users
1202    might assume that on selecting "en-gb", they will be served any
1203    kind of English document if British English is not available. A
1204    user agent might suggest in such a case to add "en" to get the
1205    best matching behavior.
1206  </t>
1207</list></t>
1208</section>
1209
1210<section title="Content-Encoding" anchor="header.content-encoding">
1211  <iref primary="true" item="Content-Encoding header field"/>
1212  <iref primary="true" item="Header Fields" subitem="Content-Encoding"/>
1213 
1214<t>
1215   The "Content-Encoding" header field indicates what content-codings
1216   have been applied to the representation beyond those inherent in the media
1217   type, and thus what decoding mechanisms must be applied in order to obtain
1218   the media-type referenced by the Content-Type header field.
1219   Content-Encoding is primarily used to allow a representation to be
1220   compressed without losing the identity of its underlying media type.
1221</t>
1222<figure><iref primary="true" item="Grammar" subitem="Content-Encoding"/><artwork type="abnf2616"><![CDATA[
1223  Content-Encoding = 1#content-coding
1224]]></artwork></figure>
1225<t>
1226   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1227</t>
1228<figure><artwork type="example"><![CDATA[
1229  Content-Encoding: gzip
1230]]></artwork></figure>
1231<t>
1232   The content-coding is a characteristic of the representation.
1233   Typically, the representation body is stored with this
1234   encoding and is only decoded before rendering or analogous usage.
1235   However, a transforming proxy MAY modify the content-coding if the
1236   new coding is known to be acceptable to the recipient, unless the
1237   "no-transform" cache-control directive is present in the message.
1238</t>
1239<t>
1240   If the media type includes an inherent encoding, such as a data format
1241   that is always compressed, then that encoding would not be restated as
1242   a Content-Encoding even if it happens to be the same algorithm as one
1243   of the content-codings.  Such a content-coding would only be listed if,
1244   for some bizarre reason, it is applied a second time to form the
1245   representation.  Likewise, an origin server might choose to publish the
1246   same payload data as multiple representations that differ only in whether
1247   the coding is defined as part of Content-Type or Content-Encoding, since
1248   some user agents will behave differently in their handling of each
1249   response (e.g., open a "Save as ..." dialog instead of automatic
1250   decompression and rendering of content).
1251</t>
1252<t>
1253   A representation that has a content-coding applied to it MUST include
1254   a Content-Encoding header field (<xref target="header.content-encoding"/>)
1255   that lists the content-coding(s) applied.
1256</t>
1257<t>
1258   If multiple encodings have been applied to a representation, the content
1259   codings MUST be listed in the order in which they were applied.
1260   Additional information about the encoding parameters MAY be provided
1261   by other header fields not defined by this specification.
1262</t>
1263<t>
1264   If the content-coding of a representation in a request message is not
1265   acceptable to the origin server, the server SHOULD respond with a
1266   status code of 415 (Unsupported Media Type).
1267</t>
1268</section>
1269
1270<section title="Content-Language" anchor="header.content-language">
1271  <iref primary="true" item="Content-Language header field"/>
1272  <iref primary="true" item="Header Fields" subitem="Content-Language"/>
1273 
1274<t>
1275   The "Content-Language" header field describes the natural
1276   language(s) of the intended audience for the representation. Note that this might
1277   not be equivalent to all the languages used within the representation.
1278</t>
1279<figure><iref primary="true" item="Grammar" subitem="Content-Language"/><artwork type="abnf2616"><![CDATA[
1280  Content-Language = 1#language-tag
1281]]></artwork></figure>
1282<t>
1283   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1284   Content-Language is to allow a user to identify and differentiate
1285   representations according to the user's own preferred language. Thus, if the
1286   body content is intended only for a Danish-literate audience, the
1287   appropriate field is
1288</t>
1289<figure><artwork type="example"><![CDATA[
1290  Content-Language: da
1291]]></artwork></figure>
1292<t>
1293   If no Content-Language is specified, the default is that the content
1294   is intended for all language audiences. This might mean that the
1295   sender does not consider it to be specific to any natural language,
1296   or that the sender does not know for which language it is intended.
1297</t>
1298<t>
1299   Multiple languages MAY be listed for content that is intended for
1300   multiple audiences. For example, a rendition of the "Treaty of
1301   Waitangi", presented simultaneously in the original Maori and English
1302   versions, would call for
1303</t>
1304<figure><artwork type="example"><![CDATA[
1305  Content-Language: mi, en
1306]]></artwork></figure>
1307<t>
1308   However, just because multiple languages are present within a representation
1309   does not mean that it is intended for multiple linguistic audiences.
1310   An example would be a beginner's language primer, such as "A First
1311   Lesson in Latin", which is clearly intended to be used by an
1312   English-literate audience. In this case, the Content-Language would
1313   properly only include "en".
1314</t>
1315<t>
1316   Content-Language MAY be applied to any media type — it is not
1317   limited to textual documents.
1318</t>
1319</section>
1320
1321<section title="Content-Location" anchor="header.content-location">
1322  <iref primary="true" item="Content-Location header field"/>
1323  <iref primary="true" item="Header Fields" subitem="Content-Location"/>
1324 
1325<t>
1326   The "Content-Location" header field supplies a URI that can be used
1327   as a specific identifier for the representation in this message.
1328   In other words, if one were to perform a GET on this URI at the time
1329   of this message's generation, then a 200 response would contain the
1330   same representation that is enclosed as payload in this message.
1331</t>
1332<figure><iref primary="true" item="Grammar" subitem="Content-Location"/><artwork type="abnf2616"><![CDATA[
1333  Content-Location = absolute-URI / partial-URI
1334]]></artwork></figure>
1335<t>
1336   The Content-Location value is not a replacement for the effective
1337   Request URI (Section 4.3 of <xref target="Part1"/>).  It is representation metadata.
1338   It has the same syntax and semantics as the header field of the same name
1339   defined for MIME body parts in Section 4 of <xref target="RFC2557"/>.
1340   However, its appearance in an HTTP message has some special implications
1341   for HTTP recipients.
1342</t>
1343<t>
1344   If Content-Location is included in a response message and its value
1345   is the same as the effective request URI, then the response payload
1346   SHOULD be considered the current representation of that resource.
1347   For a GET or HEAD request, this is the same as the default semantics
1348   when no Content-Location is provided by the server.  For a state-changing
1349   request like PUT or POST, it implies that the server's response contains
1350   the new representation of that resource, thereby distinguishing it from
1351   representations that might only report about the action (e.g., "It worked!").
1352   This allows authoring applications to update their local copies without
1353   the need for a subsequent GET request.
1354</t>
1355<t>
1356   If Content-Location is included in a response message and its value
1357   differs from the effective request URI, then the origin server is
1358   informing recipients that this representation has its own, presumably
1359   more specific, identifier.  For a GET or HEAD request, this is an
1360   indication that the effective request URI identifies a resource that
1361   is subject to content negotiation and the representation selected for
1362   this response can also be found at the identified URI.  For other
1363   methods, such a Content-Location indicates that this representation
1364   contains a report on the action's status and the same report is
1365   available (for future access with GET) at the given URI.  For
1366   example, a purchase transaction made via a POST request might
1367   include a receipt document as the payload of the 200 response;
1368   the Content-Location value provides an identifier for retrieving
1369   a copy of that same receipt in the future.
1370</t>
1371<t>
1372   If Content-Location is included in a request message, then it MAY
1373   be interpreted by the origin server as an indication of where the
1374   user agent originally obtained the content of the enclosed
1375   representation (prior to any subsequent modification of the content
1376   by that user agent).  In other words, the user agent is providing
1377   the same representation metadata that it received with the original
1378   representation.  However, such interpretation MUST NOT be used to
1379   alter the semantics of the method requested by the client.  For
1380   example, if a client makes a PUT request on a negotiated resource
1381   and the origin server accepts that PUT (without redirection), then the
1382   new set of values for that resource is expected to be consistent with
1383   the one representation supplied in that PUT; the Content-Location
1384   cannot be used as a form of reverse content selection that
1385   identifies only one of the negotiated representations to be updated.
1386   If the user agent had wanted the latter semantics, it would have applied
1387   the PUT directly to the Content-Location URI.
1388</t>
1389<t>
1390   A Content-Location field received in a request message is transitory
1391   information that SHOULD NOT be saved with other representation
1392   metadata for use in later responses.  The Content-Location's value
1393   might be saved for use in other contexts, such as within source links
1394   or other metadata.
1395</t>
1396<t>
1397   A cache cannot assume that a representation with a Content-Location
1398   different from the URI used to retrieve it can be used to respond to
1399   later requests on that Content-Location URI.
1400</t>
1401<t>
1402   If the Content-Location value is a partial URI, the partial URI is
1403   interpreted relative to the effective request URI.
1404</t>
1405</section>
1406
1407<section title="Content-Type" anchor="header.content-type">
1408  <iref primary="true" item="Content-Type header field"/>
1409  <iref primary="true" item="Header Fields" subitem="Content-Type"/>
1410 
1411<t>
1412   The "Content-Type" header field indicates the media type of the
1413   representation. In the case of responses to the HEAD method, the media type is
1414   that which would have been sent had the request been a GET.
1415</t>
1416<figure><iref primary="true" item="Grammar" subitem="Content-Type"/><artwork type="abnf2616"><![CDATA[
1417  Content-Type = media-type
1418]]></artwork></figure>
1419<t>
1420   Media types are defined in <xref target="media.types"/>. An example of the field is
1421</t>
1422<figure><artwork type="example"><![CDATA[
1423  Content-Type: text/html; charset=ISO-8859-4
1424]]></artwork></figure>
1425<t>
1426   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1427</t>
1428</section>
1429
1430</section>
1431
1432<section title="IANA Considerations" anchor="IANA.considerations">
1433<section title="Header Field Registration" anchor="header.field.registration">
1434<t>
1435   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1436   with the permanent registrations below (see <xref target="RFC3864"/>):
1437</t>
1438
1439<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1440<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1441   <ttcol>Header Field Name</ttcol>
1442   <ttcol>Protocol</ttcol>
1443   <ttcol>Status</ttcol>
1444   <ttcol>Reference</ttcol>
1445
1446   <c>Accept</c>
1447   <c>http</c>
1448   <c>standard</c>
1449   <c>
1450      <xref target="header.accept"/>
1451   </c>
1452   <c>Accept-Charset</c>
1453   <c>http</c>
1454   <c>standard</c>
1455   <c>
1456      <xref target="header.accept-charset"/>
1457   </c>
1458   <c>Accept-Encoding</c>
1459   <c>http</c>
1460   <c>standard</c>
1461   <c>
1462      <xref target="header.accept-encoding"/>
1463   </c>
1464   <c>Accept-Language</c>
1465   <c>http</c>
1466   <c>standard</c>
1467   <c>
1468      <xref target="header.accept-language"/>
1469   </c>
1470   <c>Content-Encoding</c>
1471   <c>http</c>
1472   <c>standard</c>
1473   <c>
1474      <xref target="header.content-encoding"/>
1475   </c>
1476   <c>Content-Language</c>
1477   <c>http</c>
1478   <c>standard</c>
1479   <c>
1480      <xref target="header.content-language"/>
1481   </c>
1482   <c>Content-Location</c>
1483   <c>http</c>
1484   <c>standard</c>
1485   <c>
1486      <xref target="header.content-location"/>
1487   </c>
1488   <c>Content-Type</c>
1489   <c>http</c>
1490   <c>standard</c>
1491   <c>
1492      <xref target="header.content-type"/>
1493   </c>
1494   <c>MIME-Version</c>
1495   <c>http</c>
1496   <c>standard</c>
1497   <c>
1498      <xref target="mime-version"/>
1499   </c>
1500</texttable>
1501<!--(END)-->
1502
1503<t>
1504   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1505</t>
1506</section>
1507
1508<section title="Content Coding Registry" anchor="content.coding.registration">
1509<t>
1510   The registration procedure for HTTP Content Codings is now defined
1511   by <xref target="content.coding.registry"/> of this document.
1512</t>
1513<t>
1514   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1515   shall be updated with the registration below:
1516</t>
1517<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1518   <ttcol>Name</ttcol>
1519   <ttcol>Description</ttcol>
1520   <ttcol>Reference</ttcol>
1521   <c>compress</c>
1522   <c>UNIX "compress" program method</c>
1523   <c>
1524      Section 5.1.2.1 of <xref target="Part1"/>
1525   </c>
1526   <c>deflate</c>
1527   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1528   the "zlib" data format (<xref target="RFC1950"/>)
1529   </c>
1530   <c>
1531      Section 5.1.2.2 of <xref target="Part1"/>
1532   </c>
1533   <c>gzip</c>
1534   <c>Same as GNU zip <xref target="RFC1952"/></c>
1535   <c>
1536      Section 5.1.2.3 of <xref target="Part1"/>
1537   </c>
1538   <c>identity</c>
1539   <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
1540   <c>
1541      <xref target="header.accept-encoding"/>
1542   </c>
1543</texttable>
1544</section>
1545
1546</section>
1547
1548<section title="Security Considerations" anchor="security.considerations">
1549<t>
1550   This section is meant to inform application developers, information
1551   providers, and users of the security limitations in HTTP/1.1 as
1552   described by this document. The discussion does not include
1553   definitive solutions to the problems revealed, though it does make
1554   some suggestions for reducing security risks.
1555</t>
1556
1557<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1558<t>
1559   Accept headers fields can reveal information about the user to all
1560   servers which are accessed. The Accept-Language header field in particular
1561   can reveal information the user would consider to be of a private
1562   nature, because the understanding of particular languages is often
1563   strongly correlated to the membership of a particular ethnic group.
1564   User agents which offer the option to configure the contents of an
1565   Accept-Language header field to be sent in every request are strongly
1566   encouraged to let the configuration process include a message which
1567   makes the user aware of the loss of privacy involved.
1568</t>
1569<t>
1570   An approach that limits the loss of privacy would be for a user agent
1571   to omit the sending of Accept-Language header fields by default, and to ask
1572   the user whether or not to start sending Accept-Language header fields to a
1573   server if it detects, by looking for any Vary header fields
1574   generated by the server, that such sending could improve the quality
1575   of service.
1576</t>
1577<t>
1578   Elaborate user-customized accept header fields sent in every request,
1579   in particular if these include quality values, can be used by servers
1580   as relatively reliable and long-lived user identifiers. Such user
1581   identifiers would allow content providers to do click-trail tracking,
1582   and would allow collaborating content providers to match cross-server
1583   click-trails or form submissions of individual users. Note that for
1584   many users not behind a proxy, the network address of the host
1585   running the user agent will also serve as a long-lived user
1586   identifier. In environments where proxies are used to enhance
1587   privacy, user agents ought to be conservative in offering accept
1588   header configuration options to end users. As an extreme privacy
1589   measure, proxies could filter the accept header fields in relayed requests.
1590   General purpose user agents which provide a high degree of header
1591   configurability SHOULD warn users about the loss of privacy which can
1592   be involved.
1593</t>
1594</section>
1595
1596</section>
1597
1598<section title="Acknowledgments" anchor="acks">
1599<t>
1600  See Section 11 of <xref target="Part1"/>.
1601</t>
1602</section>
1603</middle>
1604<back>
1605
1606<references title="Normative References">
1607
1608<reference anchor="Part1">
1609  <front>
1610    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1611    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1612      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1613      <address><email>fielding@gbiv.com</email></address>
1614    </author>
1615    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1616      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1617      <address><email>jg@freedesktop.org</email></address>
1618    </author>
1619    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1620      <organization abbrev="HP">Hewlett-Packard Company</organization>
1621      <address><email>JeffMogul@acm.org</email></address>
1622    </author>
1623    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1624      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1625      <address><email>henrikn@microsoft.com</email></address>
1626    </author>
1627    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1628      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1629      <address><email>LMM@acm.org</email></address>
1630    </author>
1631    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1632      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1633      <address><email>paulle@microsoft.com</email></address>
1634    </author>
1635    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1636      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1637      <address><email>timbl@w3.org</email></address>
1638    </author>
1639    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1640      <organization abbrev="W3C">World Wide Web Consortium</organization>
1641      <address><email>ylafon@w3.org</email></address>
1642    </author>
1643    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1644      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1645      <address><email>julian.reschke@greenbytes.de</email></address>
1646    </author>
1647    <date month="January" year="2012"/>
1648  </front>
1649  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-18"/>
1650 
1651</reference>
1652
1653<reference anchor="Part2">
1654  <front>
1655    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1656    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1657      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1658      <address><email>fielding@gbiv.com</email></address>
1659    </author>
1660    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1661      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1662      <address><email>jg@freedesktop.org</email></address>
1663    </author>
1664    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1665      <organization abbrev="HP">Hewlett-Packard Company</organization>
1666      <address><email>JeffMogul@acm.org</email></address>
1667    </author>
1668    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1669      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1670      <address><email>henrikn@microsoft.com</email></address>
1671    </author>
1672    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1673      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1674      <address><email>LMM@acm.org</email></address>
1675    </author>
1676    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1677      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1678      <address><email>paulle@microsoft.com</email></address>
1679    </author>
1680    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1681      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1682      <address><email>timbl@w3.org</email></address>
1683    </author>
1684    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1685      <organization abbrev="W3C">World Wide Web Consortium</organization>
1686      <address><email>ylafon@w3.org</email></address>
1687    </author>
1688    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1689      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1690      <address><email>julian.reschke@greenbytes.de</email></address>
1691    </author>
1692    <date month="January" year="2012"/>
1693  </front>
1694  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-18"/>
1695 
1696</reference>
1697
1698<reference anchor="Part4">
1699  <front>
1700    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1701    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1702      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1703      <address><email>fielding@gbiv.com</email></address>
1704    </author>
1705    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1706      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1707      <address><email>jg@freedesktop.org</email></address>
1708    </author>
1709    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1710      <organization abbrev="HP">Hewlett-Packard Company</organization>
1711      <address><email>JeffMogul@acm.org</email></address>
1712    </author>
1713    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1714      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1715      <address><email>henrikn@microsoft.com</email></address>
1716    </author>
1717    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1718      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1719      <address><email>LMM@acm.org</email></address>
1720    </author>
1721    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1722      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1723      <address><email>paulle@microsoft.com</email></address>
1724    </author>
1725    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1726      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1727      <address><email>timbl@w3.org</email></address>
1728    </author>
1729    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1730      <organization abbrev="W3C">World Wide Web Consortium</organization>
1731      <address><email>ylafon@w3.org</email></address>
1732    </author>
1733    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1734      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1735      <address><email>julian.reschke@greenbytes.de</email></address>
1736    </author>
1737    <date month="January" year="2012"/>
1738  </front>
1739  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-18"/>
1740 
1741</reference>
1742
1743<reference anchor="Part5">
1744  <front>
1745    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1746    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1747      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1748      <address><email>fielding@gbiv.com</email></address>
1749    </author>
1750    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1751      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1752      <address><email>jg@freedesktop.org</email></address>
1753    </author>
1754    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1755      <organization abbrev="HP">Hewlett-Packard Company</organization>
1756      <address><email>JeffMogul@acm.org</email></address>
1757    </author>
1758    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1759      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1760      <address><email>henrikn@microsoft.com</email></address>
1761    </author>
1762    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1763      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1764      <address><email>LMM@acm.org</email></address>
1765    </author>
1766    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1767      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1768      <address><email>paulle@microsoft.com</email></address>
1769    </author>
1770    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1771      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1772      <address><email>timbl@w3.org</email></address>
1773    </author>
1774    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1775      <organization abbrev="W3C">World Wide Web Consortium</organization>
1776      <address><email>ylafon@w3.org</email></address>
1777    </author>
1778    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1779      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1780      <address><email>julian.reschke@greenbytes.de</email></address>
1781    </author>
1782    <date month="January" year="2012"/>
1783  </front>
1784  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-18"/>
1785 
1786</reference>
1787
1788<reference anchor="Part6">
1789  <front>
1790    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1791    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1792      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1793      <address><email>fielding@gbiv.com</email></address>
1794    </author>
1795    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1796      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1797      <address><email>jg@freedesktop.org</email></address>
1798    </author>
1799    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1800      <organization abbrev="HP">Hewlett-Packard Company</organization>
1801      <address><email>JeffMogul@acm.org</email></address>
1802    </author>
1803    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1804      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1805      <address><email>henrikn@microsoft.com</email></address>
1806    </author>
1807    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1808      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1809      <address><email>LMM@acm.org</email></address>
1810    </author>
1811    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1812      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1813      <address><email>paulle@microsoft.com</email></address>
1814    </author>
1815    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1816      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1817      <address><email>timbl@w3.org</email></address>
1818    </author>
1819    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1820      <organization abbrev="W3C">World Wide Web Consortium</organization>
1821      <address><email>ylafon@w3.org</email></address>
1822    </author>
1823    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1824      <organization>Rackspace</organization>
1825      <address><email>mnot@mnot.net</email></address>
1826    </author>
1827    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1828      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1829      <address><email>julian.reschke@greenbytes.de</email></address>
1830    </author>
1831    <date month="January" year="2012"/>
1832  </front>
1833  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-18"/>
1834 
1835</reference>
1836
1837<reference anchor="RFC1950">
1838  <front>
1839    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1840    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1841      <organization>Aladdin Enterprises</organization>
1842      <address><email>ghost@aladdin.com</email></address>
1843    </author>
1844    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1845    <date month="May" year="1996"/>
1846  </front>
1847  <seriesInfo name="RFC" value="1950"/>
1848  <!--<annotation>
1849    RFC 1950 is an Informational RFC, thus it might be less stable than
1850    this specification. On the other hand, this downward reference was
1851    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1852    therefore it is unlikely to cause problems in practice. See also
1853    <xref target="BCP97"/>.
1854  </annotation>-->
1855</reference>
1856
1857<reference anchor="RFC1951">
1858  <front>
1859    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1860    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1861      <organization>Aladdin Enterprises</organization>
1862      <address><email>ghost@aladdin.com</email></address>
1863    </author>
1864    <date month="May" year="1996"/>
1865  </front>
1866  <seriesInfo name="RFC" value="1951"/>
1867  <!--<annotation>
1868    RFC 1951 is an Informational RFC, thus it might be less stable than
1869    this specification. On the other hand, this downward reference was
1870    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1871    therefore it is unlikely to cause problems in practice. See also
1872    <xref target="BCP97"/>.
1873  </annotation>-->
1874</reference>
1875
1876<reference anchor="RFC1952">
1877  <front>
1878    <title>GZIP file format specification version 4.3</title>
1879    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1880      <organization>Aladdin Enterprises</organization>
1881      <address><email>ghost@aladdin.com</email></address>
1882    </author>
1883    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1884      <address><email>gzip@prep.ai.mit.edu</email></address>
1885    </author>
1886    <author initials="M." surname="Adler" fullname="Mark Adler">
1887      <address><email>madler@alumni.caltech.edu</email></address>
1888    </author>
1889    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1890      <address><email>ghost@aladdin.com</email></address>
1891    </author>
1892    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1893      <address><email>randeg@alumni.rpi.edu</email></address>
1894    </author>
1895    <date month="May" year="1996"/>
1896  </front>
1897  <seriesInfo name="RFC" value="1952"/>
1898  <!--<annotation>
1899    RFC 1952 is an Informational RFC, thus it might be less stable than
1900    this specification. On the other hand, this downward reference was
1901    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1902    therefore it is unlikely to cause problems in practice. See also
1903    <xref target="BCP97"/>.
1904  </annotation>-->
1905</reference>
1906
1907<reference anchor="RFC2045">
1908  <front>
1909    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1910    <author initials="N." surname="Freed" fullname="Ned Freed">
1911      <organization>Innosoft International, Inc.</organization>
1912      <address><email>ned@innosoft.com</email></address>
1913    </author>
1914    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1915      <organization>First Virtual Holdings</organization>
1916      <address><email>nsb@nsb.fv.com</email></address>
1917    </author>
1918    <date month="November" year="1996"/>
1919  </front>
1920  <seriesInfo name="RFC" value="2045"/>
1921</reference>
1922
1923<reference anchor="RFC2046">
1924  <front>
1925    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1926    <author initials="N." surname="Freed" fullname="Ned Freed">
1927      <organization>Innosoft International, Inc.</organization>
1928      <address><email>ned@innosoft.com</email></address>
1929    </author>
1930    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1931      <organization>First Virtual Holdings</organization>
1932      <address><email>nsb@nsb.fv.com</email></address>
1933    </author>
1934    <date month="November" year="1996"/>
1935  </front>
1936  <seriesInfo name="RFC" value="2046"/>
1937</reference>
1938
1939<reference anchor="RFC2119">
1940  <front>
1941    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1942    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1943      <organization>Harvard University</organization>
1944      <address><email>sob@harvard.edu</email></address>
1945    </author>
1946    <date month="March" year="1997"/>
1947  </front>
1948  <seriesInfo name="BCP" value="14"/>
1949  <seriesInfo name="RFC" value="2119"/>
1950</reference>
1951
1952<reference anchor="RFC4647">
1953  <front>
1954    <title>Matching of Language Tags</title>
1955    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
1956      <organization>Yahoo! Inc.</organization>
1957      <address><email>addison@inter-locale.com</email></address>
1958    </author>
1959    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
1960      <organization>Google</organization>
1961      <address><email>mark.davis@macchiato.com</email></address>
1962    </author>
1963    <date year="2006" month="September"/>
1964  </front>
1965  <seriesInfo name="BCP" value="47"/>
1966  <seriesInfo name="RFC" value="4647"/>
1967</reference>
1968
1969<reference anchor="RFC5234">
1970  <front>
1971    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1972    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1973      <organization>Brandenburg InternetWorking</organization>
1974      <address>
1975        <email>dcrocker@bbiw.net</email>
1976      </address> 
1977    </author>
1978    <author initials="P." surname="Overell" fullname="Paul Overell">
1979      <organization>THUS plc.</organization>
1980      <address>
1981        <email>paul.overell@thus.net</email>
1982      </address>
1983    </author>
1984    <date month="January" year="2008"/>
1985  </front>
1986  <seriesInfo name="STD" value="68"/>
1987  <seriesInfo name="RFC" value="5234"/>
1988</reference>
1989
1990<reference anchor="RFC5646">
1991  <front>
1992    <title>Tags for Identifying Languages</title>
1993    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
1994      <organization>Lab126</organization>
1995      <address><email>addison@inter-locale.com</email></address>
1996    </author>
1997    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
1998      <organization>Google</organization>
1999      <address><email>mark.davis@google.com</email></address>
2000    </author>
2001    <date month="September" year="2009"/>
2002  </front>
2003  <seriesInfo name="BCP" value="47"/>
2004  <seriesInfo name="RFC" value="5646"/>
2005</reference>
2006
2007</references>
2008
2009<references title="Informative References">
2010
2011<reference anchor="RFC1945">
2012  <front>
2013    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2014    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2015      <organization>MIT, Laboratory for Computer Science</organization>
2016      <address><email>timbl@w3.org</email></address>
2017    </author>
2018    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2019      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2020      <address><email>fielding@ics.uci.edu</email></address>
2021    </author>
2022    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2023      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2024      <address><email>frystyk@w3.org</email></address>
2025    </author>
2026    <date month="May" year="1996"/>
2027  </front>
2028  <seriesInfo name="RFC" value="1945"/>
2029</reference>
2030
2031<reference anchor="RFC2049">
2032  <front>
2033    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2034    <author initials="N." surname="Freed" fullname="Ned Freed">
2035      <organization>Innosoft International, Inc.</organization>
2036      <address><email>ned@innosoft.com</email></address>
2037    </author>
2038    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2039      <organization>First Virtual Holdings</organization>
2040      <address><email>nsb@nsb.fv.com</email></address>
2041    </author>
2042    <date month="November" year="1996"/>
2043  </front>
2044  <seriesInfo name="RFC" value="2049"/>
2045</reference>
2046
2047<reference anchor="RFC2068">
2048  <front>
2049    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2050    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2051      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2052      <address><email>fielding@ics.uci.edu</email></address>
2053    </author>
2054    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2055      <organization>MIT Laboratory for Computer Science</organization>
2056      <address><email>jg@w3.org</email></address>
2057    </author>
2058    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2059      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2060      <address><email>mogul@wrl.dec.com</email></address>
2061    </author>
2062    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2063      <organization>MIT Laboratory for Computer Science</organization>
2064      <address><email>frystyk@w3.org</email></address>
2065    </author>
2066    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2067      <organization>MIT Laboratory for Computer Science</organization>
2068      <address><email>timbl@w3.org</email></address>
2069    </author>
2070    <date month="January" year="1997"/>
2071  </front>
2072  <seriesInfo name="RFC" value="2068"/>
2073</reference>
2074
2075<reference anchor="RFC2076">
2076  <front>
2077    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2078    <author initials="J." surname="Palme" fullname="Jacob Palme">
2079      <organization>Stockholm University/KTH</organization>
2080      <address><email>jpalme@dsv.su.se</email></address>
2081    </author>
2082    <date month="February" year="1997"/>
2083  </front>
2084  <seriesInfo name="RFC" value="2076"/>
2085</reference>
2086
2087<reference anchor="RFC2277">
2088  <front>
2089    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2090    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2091      <organization>UNINETT</organization>
2092      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2093    </author>
2094    <date month="January" year="1998"/>
2095  </front>
2096  <seriesInfo name="BCP" value="18"/>
2097  <seriesInfo name="RFC" value="2277"/>
2098</reference>
2099
2100<reference anchor="RFC2295">
2101  <front>
2102    <title abbrev="HTTP Content Negotiation">Transparent Content Negotiation in HTTP</title>
2103    <author initials="K." surname="Holtman" fullname="Koen Holtman">
2104      <organization>Technische Universiteit Eindhoven</organization>
2105      <address>
2106        <email>koen@win.tue.nl</email>
2107      </address>
2108    </author>
2109    <author initials="A.H." surname="Mutz" fullname="Andrew H. Mutz">
2110      <organization>Hewlett-Packard Company</organization>
2111      <address>
2112        <email>mutz@hpl.hp.com</email>
2113      </address>
2114    </author>
2115    <date year="1998" month="March"/>
2116  </front>
2117  <seriesInfo name="RFC" value="2295"/>
2118</reference>
2119
2120<reference anchor="RFC2388">
2121  <front>
2122    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2123    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2124      <organization>Xerox Palo Alto Research Center</organization>
2125      <address><email>masinter@parc.xerox.com</email></address>
2126    </author>
2127    <date year="1998" month="August"/>
2128  </front>
2129  <seriesInfo name="RFC" value="2388"/>
2130</reference>
2131
2132<reference anchor="RFC2557">
2133  <front>
2134    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2135    <author initials="F." surname="Palme" fullname="Jacob Palme">
2136      <organization>Stockholm University and KTH</organization>
2137      <address><email>jpalme@dsv.su.se</email></address>
2138    </author>
2139    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2140      <organization>Microsoft Corporation</organization>
2141      <address><email>alexhop@microsoft.com</email></address>
2142    </author>
2143    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2144      <organization>Lotus Development Corporation</organization>
2145      <address><email>Shelness@lotus.com</email></address>
2146    </author>
2147    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2148      <address><email>stef@nma.com</email></address>
2149    </author>
2150    <date year="1999" month="March"/>
2151  </front>
2152  <seriesInfo name="RFC" value="2557"/>
2153</reference>
2154
2155<reference anchor="RFC2616">
2156  <front>
2157    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2158    <author initials="R." surname="Fielding" fullname="R. Fielding">
2159      <organization>University of California, Irvine</organization>
2160      <address><email>fielding@ics.uci.edu</email></address>
2161    </author>
2162    <author initials="J." surname="Gettys" fullname="J. Gettys">
2163      <organization>W3C</organization>
2164      <address><email>jg@w3.org</email></address>
2165    </author>
2166    <author initials="J." surname="Mogul" fullname="J. Mogul">
2167      <organization>Compaq Computer Corporation</organization>
2168      <address><email>mogul@wrl.dec.com</email></address>
2169    </author>
2170    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2171      <organization>MIT Laboratory for Computer Science</organization>
2172      <address><email>frystyk@w3.org</email></address>
2173    </author>
2174    <author initials="L." surname="Masinter" fullname="L. Masinter">
2175      <organization>Xerox Corporation</organization>
2176      <address><email>masinter@parc.xerox.com</email></address>
2177    </author>
2178    <author initials="P." surname="Leach" fullname="P. Leach">
2179      <organization>Microsoft Corporation</organization>
2180      <address><email>paulle@microsoft.com</email></address>
2181    </author>
2182    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2183      <organization>W3C</organization>
2184      <address><email>timbl@w3.org</email></address>
2185    </author>
2186    <date month="June" year="1999"/>
2187  </front>
2188  <seriesInfo name="RFC" value="2616"/>
2189</reference>
2190
2191<reference anchor="RFC3629">
2192  <front>
2193    <title>UTF-8, a transformation format of ISO 10646</title>
2194    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2195      <organization>Alis Technologies</organization>
2196      <address><email>fyergeau@alis.com</email></address>
2197    </author>
2198    <date month="November" year="2003"/>
2199  </front>
2200  <seriesInfo name="STD" value="63"/>
2201  <seriesInfo name="RFC" value="3629"/>
2202</reference>
2203
2204<reference anchor="RFC3864">
2205  <front>
2206    <title>Registration Procedures for Message Header Fields</title>
2207    <author initials="G." surname="Klyne" fullname="G. Klyne">
2208      <organization>Nine by Nine</organization>
2209      <address><email>GK-IETF@ninebynine.org</email></address>
2210    </author>
2211    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
2212      <organization>BEA Systems</organization>
2213      <address><email>mnot@pobox.com</email></address>
2214    </author>
2215    <author initials="J." surname="Mogul" fullname="J. Mogul">
2216      <organization>HP Labs</organization>
2217      <address><email>JeffMogul@acm.org</email></address>
2218    </author>
2219    <date year="2004" month="September"/>
2220  </front>
2221  <seriesInfo name="BCP" value="90"/>
2222  <seriesInfo name="RFC" value="3864"/>
2223</reference>
2224
2225<reference anchor="RFC4288">
2226  <front>
2227    <title>Media Type Specifications and Registration Procedures</title>
2228    <author initials="N." surname="Freed" fullname="N. Freed">
2229      <organization>Sun Microsystems</organization>
2230      <address>
2231        <email>ned.freed@mrochek.com</email>
2232      </address>
2233    </author>
2234    <author initials="J." surname="Klensin" fullname="J. Klensin">
2235      <address>
2236        <email>klensin+ietf@jck.com</email>
2237      </address>
2238    </author>
2239    <date year="2005" month="December"/>
2240  </front>
2241  <seriesInfo name="BCP" value="13"/>
2242  <seriesInfo name="RFC" value="4288"/>
2243</reference>
2244
2245<reference anchor="RFC5226">
2246  <front>
2247    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2248    <author initials="T." surname="Narten" fullname="T. Narten">
2249      <organization>IBM</organization>
2250      <address><email>narten@us.ibm.com</email></address>
2251    </author>
2252    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
2253      <organization>Google</organization>
2254      <address><email>Harald@Alvestrand.no</email></address>
2255    </author>
2256    <date year="2008" month="May"/>
2257  </front>
2258  <seriesInfo name="BCP" value="26"/>
2259  <seriesInfo name="RFC" value="5226"/>
2260</reference>
2261
2262<reference anchor="RFC5322">
2263  <front>
2264    <title>Internet Message Format</title>
2265    <author initials="P." surname="Resnick" fullname="P. Resnick">
2266      <organization>Qualcomm Incorporated</organization>
2267    </author>
2268    <date year="2008" month="October"/>
2269  </front> 
2270  <seriesInfo name="RFC" value="5322"/>
2271</reference>
2272
2273<reference anchor="RFC6151">
2274  <front>
2275    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
2276    <author initials="S." surname="Turner" fullname="S. Turner"/>
2277    <author initials="L." surname="Chen" fullname="L. Chen"/>
2278    <date year="2011" month="March"/>
2279  </front>
2280  <seriesInfo name="RFC" value="6151"/>
2281</reference>
2282
2283<!--<reference anchor='BCP97'>
2284  <front>
2285    <title>Handling Normative References to Standards-Track Documents</title>
2286    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2287      <address>
2288        <email>klensin+ietf@jck.com</email>
2289      </address>
2290    </author>
2291    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2292      <organization>MIT</organization>
2293      <address>
2294        <email>hartmans-ietf@mit.edu</email>
2295      </address>
2296    </author>
2297    <date year='2007' month='June' />
2298  </front>
2299  <seriesInfo name='BCP' value='97' />
2300  <seriesInfo name='RFC' value='4897' />
2301</reference>-->
2302
2303<reference anchor="RFC6266">
2304  <front>
2305    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
2306    in the Hypertext Transfer Protocol (HTTP)</title>
2307    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
2308      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2309      <address>
2310        <email>julian.reschke@greenbytes.de</email>
2311      </address>
2312    </author>
2313    <date month="June" year="2011"/>
2314  </front>
2315  <seriesInfo name="RFC" value="6266"/>
2316</reference>
2317
2318</references>
2319
2320<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2321<t>
2322   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
2323   allow a message-body to be transmitted in an open variety of
2324   representations and with extensible mechanisms. However, RFC 2045
2325   discusses mail, and HTTP has a few features that are different from
2326   those described in MIME. These differences were carefully chosen
2327   to optimize performance over binary connections, to allow greater
2328   freedom in the use of new media types, to make date comparisons
2329   easier, and to acknowledge the practice of some early HTTP servers
2330   and clients.
2331</t>
2332<t>
2333   This appendix describes specific areas where HTTP differs from MIME.
2334   Proxies and gateways to strict MIME environments SHOULD be
2335   aware of these differences and provide the appropriate conversions
2336   where necessary. Proxies and gateways from MIME environments to HTTP
2337   also need to be aware of the differences because some conversions
2338   might be required.
2339</t>
2340
2341<section title="MIME-Version" anchor="mime-version">
2342  <iref primary="true" item="MIME-Version header field"/>
2343  <iref primary="true" item="Header Fields" subitem="MIME-Version"/>
2344 
2345<t>
2346   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages MAY
2347   include a single MIME-Version header field to indicate what
2348   version of the MIME protocol was used to construct the message. Use
2349   of the MIME-Version header field indicates that the message is in
2350   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2351   Proxies/gateways are responsible for ensuring full compliance (where
2352   possible) when exporting HTTP messages to strict MIME environments.
2353</t>
2354<figure><iref primary="true" item="Grammar" subitem="MIME-Version"/><artwork type="abnf2616"><![CDATA[
2355  MIME-Version = 1*DIGIT "." 1*DIGIT
2356]]></artwork></figure>
2357<t>
2358   MIME version "1.0" is the default for use in HTTP/1.1. However,
2359   HTTP/1.1 message parsing and semantics are defined by this document
2360   and not the MIME specification.
2361</t>
2362</section>
2363
2364<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2365<t>
2366   MIME requires that an Internet mail body-part be converted to
2367   canonical form prior to being transferred, as described in Section 4 of <xref target="RFC2049"/>.
2368   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2369   allowed for subtypes of the "text" media type when transmitted over
2370   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2371   line breaks as CRLF and forbids the use of CR or LF outside of line
2372   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2373   line break within text content when a message is transmitted over
2374   HTTP.
2375</t>
2376<t>
2377   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2378   environment SHOULD translate all line breaks within the text media
2379   types described in <xref target="canonicalization.and.text.defaults"/>
2380   of this document to the RFC 2049
2381   canonical form of CRLF. Note, however, that this might be complicated
2382   by the presence of a Content-Encoding and by the fact that HTTP
2383   allows the use of some character encodings which do not use octets 13 and
2384   10 to represent CR and LF, respectively, as is the case for some multi-byte
2385   character encodings.
2386</t>
2387<t>
2388   Conversion will break any cryptographic
2389   checksums applied to the original content unless the original content
2390   is already in canonical form. Therefore, the canonical form is
2391   recommended for any content that uses such checksums in HTTP.
2392</t>
2393</section>
2394
2395
2396<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2397<t>
2398   HTTP/1.1 uses a restricted set of date formats (Section 8 of <xref target="Part2"/>) to
2399   simplify the process of date comparison. Proxies and gateways from
2400   other protocols SHOULD ensure that any Date header field present in a
2401   message conforms to one of the HTTP/1.1 formats and rewrite the date
2402   if necessary.
2403</t>
2404</section>
2405
2406<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2407<t>
2408   MIME does not include any concept equivalent to HTTP/1.1's
2409   Content-Encoding header field. Since this acts as a modifier on the
2410   media type, proxies and gateways from HTTP to MIME-compliant
2411   protocols MUST either change the value of the Content-Type header
2412   field or decode the representation before forwarding the message. (Some
2413   experimental applications of Content-Type for Internet mail have used
2414   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2415   a function equivalent to Content-Encoding. However, this parameter is
2416   not part of the MIME standards).
2417</t>
2418</section>
2419
2420<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2421<t>
2422   HTTP does not use the Content-Transfer-Encoding field of MIME.
2423   Proxies and gateways from MIME-compliant protocols to HTTP MUST
2424   remove any Content-Transfer-Encoding
2425   prior to delivering the response message to an HTTP client.
2426</t>
2427<t>
2428   Proxies and gateways from HTTP to MIME-compliant protocols are
2429   responsible for ensuring that the message is in the correct format
2430   and encoding for safe transport on that protocol, where "safe
2431   transport" is defined by the limitations of the protocol being used.
2432   Such a proxy or gateway SHOULD label the data with an appropriate
2433   Content-Transfer-Encoding if doing so will improve the likelihood of
2434   safe transport over the destination protocol.
2435</t>
2436</section>
2437
2438<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2439<t>
2440   HTTP/1.1 introduces the Transfer-Encoding header field (Section 8.6 of <xref target="Part1"/>).
2441   Proxies/gateways MUST remove any transfer-coding prior to
2442   forwarding a message via a MIME-compliant protocol.
2443</t>
2444</section>
2445
2446<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2447<t>
2448   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2449   need to be aware of MIME line length limitations. Since HTTP does not
2450   have this limitation, HTTP does not fold long lines. MHTML messages
2451   being transported by HTTP follow all conventions of MHTML, including
2452   line length limitations and folding, canonicalization, etc., since
2453   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2454   does not interpret the content or any MIME header lines that might be
2455   contained therein.
2456</t>
2457</section>
2458</section>
2459
2460<section title="Additional Features" anchor="additional.features">
2461<t>
2462   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2463   existing HTTP implementations, but not consistently and correctly
2464   across most HTTP/1.1 applications. Implementors are advised to be
2465   aware of these features, but cannot rely upon their presence in, or
2466   interoperability with, other HTTP/1.1 applications. Some of these
2467   describe proposed experimental features, and some describe features
2468   that experimental deployment found lacking that are now addressed in
2469   the base HTTP/1.1 specification.
2470</t>
2471<t>
2472   A number of other header fields, such as Content-Disposition and Title,
2473   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
2474   and <xref target="RFC2076"/>).
2475</t>
2476</section>
2477
2478<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2479<t>
2480  Clarify contexts that charset is used in.
2481  (<xref target="character.sets"/>)
2482</t>
2483<t>
2484  Remove the default character encoding for text media types; the default
2485  now is whatever the media type definition says.
2486  (<xref target="canonicalization.and.text.defaults"/>)
2487</t>
2488<t>
2489  Change ABNF productions for header fields to only define the field value.
2490  (<xref target="header.field.definitions"/>)
2491</t>
2492<t>
2493  Remove definition of Content-MD5 header field because it was inconsistently
2494  implemented with respect to partial responses, and also because of known
2495  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
2496  (<xref target="header.field.definitions"/>)
2497</t>
2498<t>
2499  Remove ISO-8859-1 special-casing in Accept-Charset.
2500  (<xref target="header.accept-charset"/>)
2501</t>
2502<t>
2503  Remove base URI setting semantics for Content-Location due to poor
2504  implementation support, which was caused by too many broken servers emitting
2505  bogus Content-Location header fields, and also the potentially undesirable effect
2506  of potentially breaking relative links in content-negotiated resources.
2507  (<xref target="header.content-location"/>)
2508</t>
2509<t>
2510  Remove discussion of Content-Disposition header field, it is now defined
2511  by <xref target="RFC6266"/>.
2512  (<xref target="additional.features"/>)
2513</t>
2514<t>
2515  Remove reference to non-existant identity transfer-coding value tokens.
2516  (<xref target="no.content-transfer-encoding"/>)
2517</t>
2518</section>
2519
2520
2521<section title="Collected ABNF" anchor="collected.abnf">
2522<figure>
2523<artwork type="abnf" name="p3-payload.parsed-abnf"><![CDATA[
2524Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2525 OWS media-range [ accept-params ] ] ) ]
2526Accept-Charset = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2527 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2528 qvalue ] ] )
2529Accept-Encoding = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
2530 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2531Accept-Language = *( "," OWS ) language-range [ OWS ";" OWS "q="
2532 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2533 ] )
2534
2535Content-Encoding = *( "," OWS ) content-coding *( OWS "," [ OWS
2536 content-coding ] )
2537Content-Language = *( "," OWS ) language-tag *( OWS "," [ OWS
2538 language-tag ] )
2539Content-Location = absolute-URI / partial-URI
2540Content-Type = media-type
2541
2542MIME-Version = 1*DIGIT "." 1*DIGIT
2543
2544OWS = <OWS, defined in [Part1], Section 1.2.2>
2545
2546absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
2547accept-ext = OWS ";" OWS token [ "=" word ]
2548accept-params = OWS ";" OWS "q=" qvalue *accept-ext
2549attribute = token
2550
2551charset = token
2552codings = content-coding / "identity" / "*"
2553content-coding = token
2554
2555language-range = <language-range, defined in [RFC4647], Section 2.1>
2556language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
2557
2558media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2559 ";" OWS parameter )
2560media-type = type "/" subtype *( OWS ";" OWS parameter )
2561
2562parameter = attribute "=" value
2563partial-URI = <partial-URI, defined in [Part1], Section 2.7>
2564
2565qvalue = <qvalue, defined in [Part1], Section 5.3>
2566
2567subtype = token
2568
2569token = <token, defined in [Part1], Section 3.2.3>
2570type = token
2571
2572value = word
2573
2574word = <word, defined in [Part1], Section 3.2.3>
2575]]></artwork>
2576</figure>
2577<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
2578; Accept defined but not used
2579; Accept-Charset defined but not used
2580; Accept-Encoding defined but not used
2581; Accept-Language defined but not used
2582; Content-Encoding defined but not used
2583; Content-Language defined but not used
2584; Content-Location defined but not used
2585; Content-Type defined but not used
2586; MIME-Version defined but not used
2587]]></artwork></figure></section>
2588
2589
2590<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2591
2592<section title="Since RFC 2616">
2593<t>
2594  Extracted relevant partitions from <xref target="RFC2616"/>.
2595</t>
2596</section>
2597
2598<section title="Since draft-ietf-httpbis-p3-payload-00">
2599<t>
2600  Closed issues:
2601  <list style="symbols"> 
2602    <t>
2603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2604      "Media Type Registrations"
2605      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2606    </t>
2607    <t>
2608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2609      "Clarification regarding quoting of charset values"
2610      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2611    </t>
2612    <t>
2613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2614      "Remove 'identity' token references"
2615      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2616    </t>
2617    <t>
2618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2619      "Accept-Encoding BNF"
2620    </t>
2621    <t>
2622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2623      "Normative and Informative references"
2624    </t>
2625    <t>
2626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2627      "RFC1700 references"
2628    </t>
2629    <t>
2630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2631      "Updating to RFC4288"
2632    </t>
2633    <t>
2634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2635      "Informative references"
2636    </t>
2637    <t>
2638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2639      "ISO-8859-1 Reference"
2640    </t>
2641    <t>
2642      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2643      "Encoding References Normative"
2644    </t>
2645    <t>
2646      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2647      "Normative up-to-date references"
2648    </t>
2649  </list>
2650</t>
2651</section>
2652
2653<section title="Since draft-ietf-httpbis-p3-payload-01">
2654<t>
2655  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2656  <list style="symbols"> 
2657    <t>
2658      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2659    </t>
2660  </list>
2661</t>
2662</section>
2663
2664<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2665<t>
2666  Closed issues:
2667  <list style="symbols"> 
2668    <t>
2669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2670      "Quoting Charsets"
2671    </t>
2672    <t>
2673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2674      "Classification for Allow header"
2675    </t>
2676    <t>
2677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2678      "missing default for qvalue in description of Accept-Encoding"
2679    </t>
2680  </list>
2681</t>
2682<t>
2683  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2684  <list style="symbols"> 
2685    <t>
2686      Reference RFC 3984, and update header field registrations for headers defined
2687      in this document.
2688    </t>
2689  </list>
2690</t>
2691</section>
2692
2693<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2694<t>
2695  Closed issues:
2696  <list style="symbols"> 
2697    <t>
2698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2699      "Quoting Charsets"
2700    </t>
2701    <t>
2702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2703      "language tag matching (Accept-Language) vs RFC4647"
2704    </t>
2705    <t>
2706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2707      "RFC 1806 has been replaced by RFC2183"
2708    </t>
2709  </list>
2710</t>
2711<t>
2712  Other changes:
2713  <list style="symbols"> 
2714    <t>
2715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2716      "Encoding References Normative" — rephrase the annotation and reference
2717      BCP97.
2718    </t>
2719  </list>
2720</t>
2721 </section>
2722
2723<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2724<t>
2725  Closed issues:
2726  <list style="symbols"> 
2727    <t>
2728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2729      "RFC 2822 is updated by RFC 5322"
2730    </t>
2731  </list>
2732</t>
2733<t>
2734  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2735  <list style="symbols"> 
2736    <t>
2737      Use "/" instead of "|" for alternatives.
2738    </t>
2739    <t>
2740      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2741      whitespace ("OWS") and required whitespace ("RWS").
2742    </t>
2743    <t>
2744      Rewrite ABNFs to spell out whitespace rules, factor out
2745      header field value format definitions.
2746    </t>
2747  </list>
2748</t>
2749</section>
2750
2751<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2752<t>
2753  Closed issues:
2754  <list style="symbols"> 
2755    <t>
2756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2757      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2758    </t>
2759  </list>
2760</t>
2761<t>
2762  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2763  <list style="symbols"> 
2764    <t>
2765      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2766    </t>
2767  </list>
2768</t>
2769<t>
2770  Other changes:
2771  <list style="symbols"> 
2772    <t>
2773      Move definition of quality values into Part 1.
2774    </t>
2775  </list>
2776</t>
2777</section>
2778
2779<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2780<t>
2781  Closed issues:
2782  <list style="symbols"> 
2783    <t>
2784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2785      "Content-Location isn't special"
2786    </t>
2787    <t>
2788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2789      "Content Sniffing"
2790    </t>
2791  </list>
2792</t>
2793</section>
2794
2795<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2796<t>
2797  Closed issues:
2798  <list style="symbols"> 
2799    <t>
2800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2801      "Updated reference for language tags"
2802    </t>
2803    <t>
2804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2805      "Clarify rules for determining what entities a response carries"
2806    </t>
2807    <t>
2808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2809      "Content-Location base-setting problems"
2810    </t>
2811    <t>
2812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2813      "Content Sniffing"
2814    </t>
2815    <t>
2816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2817      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2818    </t>
2819    <t>
2820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2821      "move definitions of gzip/deflate/compress to part 1"
2822    </t>
2823  </list>
2824</t>
2825<t>
2826  Partly resolved issues:
2827  <list style="symbols"> 
2828    <t>
2829      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2830      "update IANA requirements wrt Transfer-Coding values" (add the
2831      IANA Considerations subsection)
2832    </t>
2833    <t>
2834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2835      "update IANA requirements wrt Content-Coding values" (add the
2836      IANA Considerations subsection)
2837    </t>
2838  </list>
2839</t>
2840</section>
2841
2842<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2843<t>
2844  Closed issues:
2845  <list style="symbols"> 
2846    <t>
2847      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
2848      "Content Negotiation for media types"
2849    </t>
2850    <t>
2851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
2852      "Accept-Language: which RFC4647 filtering?"
2853    </t>
2854  </list>
2855</t>
2856</section>
2857
2858<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
2859<t>
2860  Closed issues:
2861  <list style="symbols"> 
2862    <t>
2863      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
2864      "MIME-Version not listed in P1, general header fields"
2865    </t>
2866    <t>
2867      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
2868      "IANA registry for content/transfer encodings"
2869    </t>
2870    <t>
2871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2872      "Content Sniffing"
2873    </t>
2874    <t>
2875      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
2876      "use of term "word" when talking about header structure"
2877    </t>
2878  </list>
2879</t>
2880<t>
2881  Partly resolved issues:
2882  <list style="symbols"> 
2883    <t>
2884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2885      "Term for the requested resource's URI"
2886    </t>
2887  </list>
2888</t>
2889</section>
2890
2891<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
2892<t>
2893  Closed issues:
2894  <list style="symbols"> 
2895    <t>
2896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
2897      "Clarify 'Requested Variant'"
2898    </t>
2899    <t>
2900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2901      "Content-Location isn't special"
2902    </t>
2903    <t>
2904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
2905      "Delimiting messages with multipart/byteranges"
2906    </t>
2907    <t>
2908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
2909      "Clarify entity / representation / variant terminology"
2910    </t>
2911    <t>
2912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
2913      "confusing req. language for Content-Location"
2914    </t>
2915    <t>
2916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
2917      "Content-Location on 304 responses"
2918    </t>
2919    <t>
2920      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
2921      "'requested resource' in content-encoding definition"
2922    </t>
2923    <t>
2924      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
2925      "consider removing the 'changes from 2068' sections"
2926    </t>
2927  </list>
2928</t>
2929<t>
2930  Partly resolved issues:
2931  <list style="symbols"> 
2932    <t>
2933      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2934      "Content-MD5 and partial responses"
2935    </t>
2936  </list>
2937</t>
2938</section>
2939
2940<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
2941<t>
2942  Closed issues:
2943  <list style="symbols"> 
2944    <t>
2945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
2946      "Factor out Content-Disposition"
2947    </t>
2948  </list>
2949</t>
2950</section>
2951
2952<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
2953<t>
2954  Closed issues:
2955  <list style="symbols"> 
2956    <t>
2957      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
2958      "Header Classification"
2959    </t>
2960    <t>
2961      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2962      "untangle ABNFs for header fields"
2963    </t>
2964    <t>
2965      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
2966      "potentially misleading MAY in media-type def"
2967    </t>
2968  </list>
2969</t>
2970</section>
2971
2972<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
2973<t>
2974  Closed issues:
2975  <list style="symbols"> 
2976    <t>
2977      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
2978      "Default charsets for text media types"
2979    </t>
2980    <t>
2981      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2982      "Content-MD5 and partial responses"
2983    </t>
2984    <t>
2985      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2986      "untangle ABNFs for header fields"
2987    </t>
2988    <t>
2989      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
2990      "confusing undefined parameter in media range example"
2991    </t>
2992  </list>
2993</t>
2994</section>
2995
2996<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
2997<t>
2998  None.
2999</t>
3000</section>
3001
3002<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
3003<t>
3004  Closed issues:
3005  <list style="symbols"> 
3006    <t>
3007      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
3008      "Strength of requirements on Accept re: 406"
3009    </t>
3010  </list>
3011</t>
3012</section>
3013
3014<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
3015<t>
3016  Closed issues:
3017  <list style="symbols"> 
3018    <t>
3019      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
3020      "Document HTTP's error-handling philosophy"
3021    </t>
3022  </list>
3023</t>
3024</section>
3025
3026<section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.since.17">
3027<t>
3028  Closed issues:
3029  <list style="symbols"> 
3030    <t>
3031      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
3032      "intended maturity level vs normative references"
3033    </t>
3034  </list>
3035</t>
3036</section>
3037
3038</section>
3039
3040</back>
3041</rfc>
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