source: draft-ietf-httpbis/latest/p3-payload.xml @ 1103

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "February">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc rfcedstyle="yes"?>
52<?rfc-ext allow-markup-in-artwork="yes" ?>
53<?rfc-ext include-references-in-index="yes" ?>
54<rfc obsoletes="2616" category="std" x:maturity-level="draft"
55     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
56     xmlns:x='http://purl.org/net/xml2rfc/ext'>
57<front>
58
59  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
60
61  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
62    <organization abbrev="Day Software">Day Software</organization>
63    <address>
64      <postal>
65        <street>23 Corporate Plaza DR, Suite 280</street>
66        <city>Newport Beach</city>
67        <region>CA</region>
68        <code>92660</code>
69        <country>USA</country>
70      </postal>
71      <phone>+1-949-706-5300</phone>
72      <facsimile>+1-949-706-5305</facsimile>
73      <email>fielding@gbiv.com</email>
74      <uri>http://roy.gbiv.com/</uri>
75    </address>
76  </author>
77
78  <author initials="J." surname="Gettys" fullname="Jim Gettys">
79    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
80    <address>
81      <postal>
82        <street>21 Oak Knoll Road</street>
83        <city>Carlisle</city>
84        <region>MA</region>
85        <code>01741</code>
86        <country>USA</country>
87      </postal>
88      <email>jg@freedesktop.org</email>
89      <uri>http://gettys.wordpress.com/</uri>
90    </address>
91  </author>
92 
93  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
94    <organization abbrev="HP">Hewlett-Packard Company</organization>
95    <address>
96      <postal>
97        <street>HP Labs, Large Scale Systems Group</street>
98        <street>1501 Page Mill Road, MS 1177</street>
99        <city>Palo Alto</city>
100        <region>CA</region>
101        <code>94304</code>
102        <country>USA</country>
103      </postal>
104      <email>JeffMogul@acm.org</email>
105    </address>
106  </author>
107
108  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
109    <organization abbrev="Microsoft">Microsoft Corporation</organization>
110    <address>
111      <postal>
112        <street>1 Microsoft Way</street>
113        <city>Redmond</city>
114        <region>WA</region>
115        <code>98052</code>
116        <country>USA</country>
117      </postal>
118      <email>henrikn@microsoft.com</email>
119    </address>
120  </author>
121
122  <author initials="L." surname="Masinter" fullname="Larry Masinter">
123    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
124    <address>
125      <postal>
126        <street>345 Park Ave</street>
127        <city>San Jose</city>
128        <region>CA</region>
129        <code>95110</code>
130        <country>USA</country>
131      </postal>
132      <email>LMM@acm.org</email>
133      <uri>http://larry.masinter.net/</uri>
134    </address>
135  </author>
136 
137  <author initials="P." surname="Leach" fullname="Paul J. Leach">
138    <organization abbrev="Microsoft">Microsoft Corporation</organization>
139    <address>
140      <postal>
141        <street>1 Microsoft Way</street>
142        <city>Redmond</city>
143        <region>WA</region>
144        <code>98052</code>
145      </postal>
146      <email>paulle@microsoft.com</email>
147    </address>
148  </author>
149   
150  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
151    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
152    <address>
153      <postal>
154        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
155        <street>The Stata Center, Building 32</street>
156        <street>32 Vassar Street</street>
157        <city>Cambridge</city>
158        <region>MA</region>
159        <code>02139</code>
160        <country>USA</country>
161      </postal>
162      <email>timbl@w3.org</email>
163      <uri>http://www.w3.org/People/Berners-Lee/</uri>
164    </address>
165  </author>
166
167  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
168    <organization abbrev="W3C">World Wide Web Consortium</organization>
169    <address>
170      <postal>
171        <street>W3C / ERCIM</street>
172        <street>2004, rte des Lucioles</street>
173        <city>Sophia-Antipolis</city>
174        <region>AM</region>
175        <code>06902</code>
176        <country>France</country>
177      </postal>
178      <email>ylafon@w3.org</email>
179      <uri>http://www.raubacapeu.net/people/yves/</uri>
180    </address>
181  </author>
182
183  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
184    <organization abbrev="greenbytes">greenbytes GmbH</organization>
185    <address>
186      <postal>
187        <street>Hafenweg 16</street>
188        <city>Muenster</city><region>NW</region><code>48155</code>
189        <country>Germany</country>
190      </postal>
191      <phone>+49 251 2807760</phone>
192      <facsimile>+49 251 2807761</facsimile>
193      <email>julian.reschke@greenbytes.de</email>
194      <uri>http://greenbytes.de/tech/webdav/</uri>
195    </address>
196  </author>
197
198  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
199  <workgroup>HTTPbis Working Group</workgroup>
200
201<abstract>
202<t>
203   The Hypertext Transfer Protocol (HTTP) is an application-level
204   protocol for distributed, collaborative, hypermedia information
205   systems. HTTP has been in use by the World Wide Web global information
206   initiative since 1990. This document is Part 3 of the seven-part specification
207   that defines the protocol referred to as "HTTP/1.1" and, taken together,
208   obsoletes RFC 2616.  Part 3 defines HTTP message content,
209   metadata, and content negotiation.
210</t>
211</abstract>
212
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (ietf-http-wg@w3.org). The current issues list is
217    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
218    and related documents (including fancy diffs) can be found at
219    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.12"/>.
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   This document defines HTTP/1.1 message payloads (a.k.a., content), the
230   associated metadata header fields that define how the payload is intended
231   to be interpreted by a recipient, the request header fields that
232   might influence content selection, and the various selection algorithms
233   that are collectively referred to as HTTP content negotiation.
234</t>
235<t>
236   This document is currently disorganized in order to minimize the changes
237   between drafts and enable reviewers to see the smaller errata changes.
238   A future draft will reorganize the sections to better reflect the content.
239   In particular, the sections on entities will be renamed payload and moved
240   to the first half of the document, while the sections on content negotiation
241   and associated request header fields will be moved to the second half.  The
242   current mess reflects how widely dispersed these topics and associated
243   requirements had become in <xref target="RFC2616"/>.
244</t>
245
246<section title="Terminology" anchor="terminology">
247<t>
248   This specification uses a number of terms to refer to the roles
249   played by participants in, and objects of, the HTTP communication.
250</t>
251<t>
252  <iref item="content negotiation"/>
253  <x:dfn>content negotiation</x:dfn>
254  <list>
255    <t>
256      The mechanism for selecting the appropriate representation when
257      servicing a request. The representation in any response
258      can be negotiated (including error responses).
259    </t>
260  </list>
261</t>
262</section>
263
264<section title="Requirements" anchor="intro.requirements">
265<t>
266   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
267   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
268   document are to be interpreted as described in <xref target="RFC2119"/>.
269</t>
270<t>
271   An implementation is not compliant if it fails to satisfy one or more
272   of the "MUST" or "REQUIRED" level requirements for the protocols it
273   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
274   level and all the "SHOULD" level requirements for its protocols is said
275   to be "unconditionally compliant"; one that satisfies all the "MUST"
276   level requirements but not all the "SHOULD" level requirements for its
277   protocols is said to be "conditionally compliant".
278</t>
279</section>
280
281<section title="Syntax Notation" anchor="notation">
282  <x:anchor-alias value="ALPHA"/>
283  <x:anchor-alias value="CR"/>
284  <x:anchor-alias value="DIGIT"/>
285  <x:anchor-alias value="LF"/>
286  <x:anchor-alias value="OCTET"/>
287  <x:anchor-alias value="VCHAR"/>
288  <x:anchor-alias value="WSP"/>
289<t>
290  This specification uses the ABNF syntax defined in &notation; (which
291  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
292  <xref target="collected.abnf"/> shows the collected ABNF, with the list
293  rule expanded.
294</t>
295<t>
296  The following core rules are included by
297  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
298  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
299  DIGIT (decimal 0-9), DQUOTE (double quote),
300  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
301  OCTET (any 8-bit sequence of data), SP (space),
302  VCHAR (any visible USASCII character),
303  and WSP (whitespace).
304</t>
305
306<section title="Core Rules" anchor="core.rules">
307  <x:anchor-alias value="token"/>
308  <x:anchor-alias value="word"/>
309  <x:anchor-alias value="OWS"/>
310<t>
311  The core rules below are defined in &basic-rules;:
312</t>
313<figure><artwork type="abnf2616">
314  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
315  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
316  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
317</artwork></figure>
318</section>
319
320<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
321  <x:anchor-alias value="absolute-URI"/>
322  <x:anchor-alias value="Allow"/>
323  <x:anchor-alias value="Content-Length"/>
324  <x:anchor-alias value="Content-Range"/>
325  <x:anchor-alias value="Expires"/>
326  <x:anchor-alias value="Last-Modified"/>
327  <x:anchor-alias value="partial-URI"/>
328  <x:anchor-alias value="qvalue"/>
329<t>
330  The ABNF rules below are defined in other parts:
331</t>
332<figure><!--Part1--><artwork type="abnf2616">
333  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
334  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
335  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
336  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
337</artwork></figure>
338<figure><!--Part4--><artwork type="abnf2616">
339  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
340</artwork></figure>
341<figure><!--Part5--><artwork type="abnf2616">
342  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
343</artwork></figure>
344<figure><!--Part6--><artwork type="abnf2616">
345  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
346</artwork></figure>
347</section>
348
349</section>
350
351</section>
352
353<section title="Protocol Parameters" anchor="protocol.parameters">
354
355<section title="Character Sets" anchor="character.sets">
356<t>
357   HTTP uses the same definition of the term "character set" as that
358   described for MIME:
359</t>
360<t>
361   The term "character set" is used in this document to refer to a
362   method used with one or more tables to convert a sequence of octets
363   into a sequence of characters. Note that unconditional conversion in
364   the other direction is not required, in that not all characters might
365   be available in a given character set and a character set might provide
366   more than one sequence of octets to represent a particular character.
367   This definition is intended to allow various kinds of character
368   encoding, from simple single-table mappings such as US-ASCII to
369   complex table switching methods such as those that use ISO-2022's
370   techniques. However, the definition associated with a MIME character
371   set name &MUST; fully specify the mapping to be performed from octets
372   to characters. In particular, use of external profiling information
373   to determine the exact mapping is not permitted.
374</t>
375<x:note>
376  <t>
377    <x:h>Note:</x:h> This use of the term "character set" is more commonly
378    referred to as a "character encoding". However, since HTTP and
379    MIME share the same registry, it is important that the terminology
380    also be shared.
381  </t>
382</x:note>
383<t anchor="rule.charset">
384  <x:anchor-alias value="charset"/>
385   HTTP character sets are identified by case-insensitive tokens. The
386   complete set of tokens is defined by the IANA Character Set registry
387   (<eref target="http://www.iana.org/assignments/character-sets"/>).
388</t>
389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
390  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
391</artwork></figure>
392<t>
393   Although HTTP allows an arbitrary token to be used as a charset
394   value, any token that has a predefined value within the IANA
395   Character Set registry &MUST; represent the character set defined
396   by that registry. Applications &SHOULD; limit their use of character
397   sets to those defined by the IANA registry.
398</t>
399<t>
400   HTTP uses charset in two contexts: within an Accept-Charset request
401   header field (in which the charset value is an unquoted token) and as the
402   value of a parameter in a Content-Type header field (within a request or
403   response), in which case the parameter value of the charset parameter
404   can be quoted.
405</t>
406<t>
407   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
408   <xref target="RFC2277"/>.
409</t>
410
411<section title="Missing Charset" anchor="missing.charset">
412<t>
413   Some HTTP/1.0 software has interpreted a Content-Type header field without
414   charset parameter incorrectly to mean "recipient should guess".
415   Senders wishing to defeat this behavior &MAY; include a charset
416   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
417   it is known that it will not confuse the recipient.
418</t>
419<t>
420   Unfortunately, some older HTTP/1.0 clients did not deal properly with
421   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
422   charset label provided by the sender; and those user agents that have
423   a provision to "guess" a charset &MUST; use the charset from the
424   content-type field if they support that charset, rather than the
425   recipient's preference, when initially displaying a document. See
426   <xref target="canonicalization.and.text.defaults"/>.
427</t>
428</section>
429</section>
430
431<section title="Content Codings" anchor="content.codings">
432  <x:anchor-alias value="content-coding"/>
433<t>
434   Content coding values indicate an encoding transformation that has
435   been or can be applied to a representation. Content codings are primarily
436   used to allow a representation to be compressed or otherwise usefully
437   transformed without losing the identity of its underlying media type
438   and without loss of information. Frequently, the representation is stored in
439   coded form, transmitted directly, and only decoded by the recipient.
440</t>
441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
442  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
443</artwork></figure>
444<t>
445   All content-coding values are case-insensitive. HTTP/1.1 uses
446   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
447   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
448   describes the content-coding, what is more important is that it
449   indicates what decoding mechanism will be required to remove the
450   encoding.
451</t>
452<t>
453   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
454  <list>
455    <t>
456      See &compress-coding;.
457    </t>
458  </list>
459</t>
460<t>
461   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
462  <list>
463    <t>
464      See &deflate-coding;.
465    </t>
466  </list>
467</t>
468<t>
469   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
470  <list>
471    <t>
472      See &gzip-coding;.
473    </t>
474  </list>
475</t>
476<t>
477   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
478  <list><t>
479        The default (identity) encoding; the use of no transformation
480        whatsoever. This content-coding is used only in the Accept-Encoding
481        header field, and &SHOULD-NOT;  be used in the Content-Encoding
482        header field.
483  </t></list>
484</t>
485
486<section title="Content Coding Registry" anchor="content.coding.registry">
487<t>
488   The HTTP Content Coding Registry defines the name space for the content
489   coding names.
490</t>
491<t>
492   Registrations &MUST; include the following fields:
493   <list style="symbols">
494     <t>Name</t>
495     <t>Description</t>
496     <t>Pointer to specification text</t>
497   </list>
498</t>
499<t>
500   Names of content codings &MUST-NOT; overlap with names of transfer codings
501   (&transfer-codings;), unless the encoding transformation is identical (as it
502   is the case for the compression codings defined in
503   &compression-codings;).
504</t>
505<t>
506   Values to be added to this name space require a specification
507   (see "Specification Required" in
508   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
509   conform to the purpose of content coding defined in this section.
510</t>
511<t>
512   The registry itself is maintained at
513   <eref target="http://www.iana.org/assignments/http-parameters"/>.
514</t>
515</section>
516
517</section>
518
519<section title="Media Types" anchor="media.types">
520  <x:anchor-alias value="media-type"/>
521  <x:anchor-alias value="type"/>
522  <x:anchor-alias value="subtype"/>
523<t>
524   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
525   and Accept (<xref target="header.accept"/>) header fields in order to provide
526   open and extensible data typing and type negotiation.
527</t>
528<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/>
529  <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
530  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
531  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
532</artwork></figure>
533<t anchor="rule.parameter">
534  <x:anchor-alias value="attribute"/>
535  <x:anchor-alias value="parameter"/>
536  <x:anchor-alias value="value"/>
537   Parameters &MAY; follow the type/subtype in the form of attribute/value
538   pairs.
539</t>
540<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
541  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
542  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
543  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
544</artwork></figure>
545<t>
546   The type, subtype, and parameter attribute names are case-insensitive.
547   Parameter values might or might not be case-sensitive, depending on the
548   semantics of the parameter name.  The presence or absence of a parameter might
549   be significant to the processing of a media-type, depending on its
550   definition within the media type registry.
551</t>
552<t>
553   A parameter value that matches the <x:ref>token</x:ref> production can be
554   transmitted as either a token or within a quoted-string. The quoted and
555   unquoted values are equivalent.
556</t>
557<t>
558   Note that some older HTTP applications do not recognize media type
559   parameters. When sending data to older HTTP applications,
560   implementations &SHOULD; only use media type parameters when they are
561   required by that type/subtype definition.
562</t>
563<t>
564   Media-type values are registered with the Internet Assigned Number
565   Authority (IANA). The media type registration process is
566   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
567   discouraged.
568</t>
569
570<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
571<t>
572   Internet media types are registered with a canonical form. A
573   representation transferred via HTTP messages &MUST; be in the
574   appropriate canonical form prior to its transmission except for
575   "text" types, as defined in the next paragraph.
576</t>
577<t>
578   When in canonical form, media subtypes of the "text" type use CRLF as
579   the text line break. HTTP relaxes this requirement and allows the
580   transport of text media with plain CR or LF alone representing a line
581   break when it is done consistently for an entire representation. HTTP
582   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
583   a line break in text media received via HTTP. In
584   addition, if the text is in a character encoding that does not
585   use octets 13 and 10 for CR and LF respectively, as is the case for
586   some multi-byte character encodings, HTTP allows the use of whatever octet
587   sequences are defined by that character encoding to represent the
588   equivalent of CR and LF for line breaks. This flexibility regarding
589   line breaks applies only to text media in the payload body; a bare CR
590   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
591   structures (such as header fields and multipart boundaries).
592</t>
593<t>
594   If a representation is encoded with a content-coding, the underlying
595   data &MUST; be in a form defined above prior to being encoded.
596</t>
597<t>
598   The "charset" parameter is used with some media types to define the
599   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
600   parameter is provided by the sender, media subtypes of the "text"
601   type are defined to have a default charset value of "ISO-8859-1" when
602   received via HTTP. Data in character encodings other than "ISO-8859-1" or
603   its subsets &MUST; be labeled with an appropriate charset value. See
604   <xref target="missing.charset"/> for compatibility problems.
605</t>
606</section>
607
608<section title="Multipart Types" anchor="multipart.types">
609<t>
610   MIME provides for a number of "multipart" types &mdash; encapsulations of
611   one or more representations within a single message-body. All multipart
612   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
613   and &MUST; include a boundary parameter as part of the media type
614   value. The message body is itself a protocol element and &MUST;
615   therefore use only CRLF to represent line breaks between body-parts.
616</t>
617<t>
618   In general, HTTP treats a multipart message-body no differently than
619   any other media type: strictly as payload.  HTTP does not use the
620   multipart boundary as an indicator of message-body length.
621   <!-- jre: re-insert removed text pointing to caching? -->
622   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
623   behavior as a MIME user agent would upon receipt of a multipart type.
624   The MIME header fields within each body-part of a multipart message-body
625   do not have any significance to HTTP beyond that defined by
626   their MIME semantics.
627</t>
628<t>
629   If an application receives an unrecognized multipart subtype, the
630   application &MUST; treat it as being equivalent to "multipart/mixed".
631</t>
632<x:note>
633  <t>
634    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
635    for carrying form data suitable for processing via the POST
636    request method, as described in <xref target="RFC2388"/>.
637  </t>
638</x:note>
639</section>
640</section>
641
642<section title="Language Tags" anchor="language.tags">
643  <x:anchor-alias value="language-tag"/>
644<t>
645   A language tag, as defined in <xref target="RFC5646"/>, identifies a
646   natural language spoken, written, or otherwise conveyed by human beings for
647   communication of information to other human beings. Computer languages are
648   explicitly excluded. HTTP uses language tags within the Accept-Language and
649   Content-Language fields.
650</t>
651<t>
652   In summary, a language tag is composed of one or more parts: A primary
653   language subtag followed by a possibly empty series of subtags:
654</t>
655<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
656  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
657</artwork></figure>
658<t>
659   White space is not allowed within the tag and all tags are case-insensitive.
660   The name space of language subtags is administered by the IANA (see
661   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
662</t>
663<figure>
664  <preamble>Example tags include:</preamble>
665<artwork type="example">
666  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
667</artwork>
668</figure>
669<t>
670   See <xref target="RFC5646"/> for further information.
671</t>
672</section>
673</section>
674
675<section title="Payload" anchor="payload">
676<t>
677   HTTP messages &MAY; transfer a payload if not otherwise restricted by
678   the request method or response status code.  The payload consists of
679   metadata, in the form of header fields, and data, in the form of the
680   sequence of octets in the message-body after any transfer-coding has
681   been decoded.
682</t>
683<iref item="payload"/>
684<t>   
685   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
686   representation of some resource.  We use separate terms for payload
687   and representation because some messages contain only the associated
688   representation's header fields (e.g., responses to HEAD) or only some
689   part(s) of the representation (e.g., the 206 status code).
690</t>
691<section title="Payload Header Fields" anchor="payload.header.fields">
692  <x:anchor-alias value="payload-header"/>
693<t>
694   HTTP header fields that specifically define the payload, rather than the
695   associated representation, are referred to as "payload header fields".
696   The following payload header fields are defined by HTTP/1.1:
697</t>
698<figure><artwork type="inline">
699   <x:ref>Content-Length</x:ref>           ; &header-content-length;
700   <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
701   <x:ref>Content-Range</x:ref>            ; &header-content-range;
702</artwork></figure>
703</section>
704
705<section title="Payload Body" anchor="payload.body">
706  <x:anchor-alias value="payload-body"/>
707<t>
708   A payload body is only present in a message when a message-body is
709   present, as described in &message-body;. The payload body is obtained
710   from the message-body by decoding any Transfer-Encoding that might
711   have been applied to ensure safe and proper transfer of the message.
712</t>
713</section>
714</section>
715
716<section title="Representation" anchor="representation">
717<iref item="representation"/>
718<t>
719   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
720   communicated from one party to another.  A resource representation
721   is information that reflects the state of that resource, as observed
722   at some point in the past (e.g., in a response to GET) or to be
723   desired at some point in the future (e.g., in a PUT request).
724</t>
725<t>
726   Most, but not all, representations transferred via HTTP are intended
727   to be a representation of the target resource (the resource identified
728   by the effective request URI).  The precise semantics of a representation
729   are determined by the type of message (request or response), the request
730   method, the response status code, and the representation metadata.
731   For example, the above semantic is true for the representation in any
732   200 (OK) response to GET and for the representation in any PUT request.
733   A 200 response to PUT, in contrast, contains either a representation
734   that describes the successful action or a representation of the target
735   resource, with the latter indicated by a Content-Location header field
736   with the same value as the effective request URI.  Likewise, response
737   messages with an error status code usually contain a representation that
738   describes the error and what next steps are suggested for resolving it.
739</t>
740
741<section title="Representation Header Fields" anchor="representation.header.fields">
742  <x:anchor-alias value="representation-header"/>
743<t>
744   Representation header fields define metadata about the representation data
745   enclosed in the message-body or, if no message-body is present, about
746   the representation that would have been transferred in a 200 response
747   to a simultaneous GET request with the same effective request URI.
748</t>
749<t>
750   The following header fields are defined as representation metadata:
751</t>
752<figure><artwork type="inline">
753   <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
754   <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
755   <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
756   <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
757   <x:ref>Expires</x:ref>                  ; &header-expires;
758   <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
759</artwork></figure>
760</section>
761
762<section title="Representation Data" anchor="representation.data">
763  <x:anchor-alias value="representation-data"/>
764<t>
765   The representation body associated with an HTTP message is
766   either provided as the payload body of the message or
767   referred to by the message semantics and the effective request
768   URI.  The representation data is in a format and encoding defined by
769   the representation metadata header fields.
770</t>
771<t>
772   The data type of the representation data
773   is determined via the header fields Content-Type and Content-Encoding.
774   These define a two-layer, ordered encoding model:
775</t>
776<figure><artwork type="example">
777  representation-data := Content-Encoding( Content-Type( bits ) )
778</artwork></figure>
779<t>
780   Content-Type specifies the media type of the underlying data, which
781   defines both the data format and how that data &SHOULD; be processed
782   by the recipient (within the scope of the request method semantics).
783   Any HTTP/1.1 message containing a payload body &SHOULD; include a
784   Content-Type header field defining the media type of the associated
785   representation unless that metadata is unknown to the sender.
786   If the Content-Type header field is not present, it indicates that
787   the sender does not know the media type of the representation;
788   recipients &MAY; either assume that the media type is
789   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
790   or examine the content to determine its type.
791</t>
792<t>
793   In practice, resource owners do not always properly configure their origin
794   server to provide the correct Content-Type for a given representation,
795   with the result that some clients will examine a response body's content
796   and override the specified type.
797   Clients that do so risk drawing incorrect conclusions, which might expose
798   additional security risks (e.g., "privilege escalation").  Furthermore,
799   it is impossible to determine the sender's intent by examining the data
800   format: many data formats match multiple media types that differ only in
801   processing semantics.  Implementers are encouraged to provide a means of
802   disabling such "content sniffing" when it is used.
803</t>
804<t>
805   Content-Encoding is used to indicate any additional content
806   codings applied to the data, usually for the purpose of data
807   compression, that are a property of the representation.  If
808   Content-Encoding is not present, then there is no additional
809   encoding beyond that defined by the Content-Type.
810</t>
811</section>
812</section>
813
814<section title="Content Negotiation" anchor="content.negotiation">
815<t>
816   HTTP responses include a representation which contains information for
817   interpretation, whether by a human user or for further processing.
818   Often, the server has different ways of representing the
819   same information; for example, in different formats, languages,
820   or using different character encodings.
821</t>
822<t>
823   HTTP clients and their users might have different or variable
824   capabilities, characteristics or preferences which would influence
825   which representation, among those available from the server,
826   would be best for the server to deliver. For this reason, HTTP
827   provides mechanisms for "content negotiation" &mdash; a process of
828   allowing selection of a representation of a given resource,
829   when more than one is available.
830</t>
831<t>
832   This specification defines two patterns of content negotiation;
833   "server-driven", where the server selects the representation based
834   upon the client's stated preferences, and "agent-driven" negotiation,
835   where the server provides a list of representations for the client to
836   choose from, based upon their metadata. In addition,  there are
837   other patterns: some applications use an "active content" pattern,
838   where the server returns active content which runs on the client
839   and, based on client available parameters, selects additional
840   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
841   has also been proposed.
842</t>
843<t>
844   These patterns are all widely used, and have trade-offs in applicability
845   and practicality. In particular, when the number of preferences or
846   capabilities to be expressed by a client are large (such as when many
847   different formats are supported by a user-agent), server-driven
848   negotiation becomes unwieldy, and might not be appropriate. Conversely,
849   when the number of representations to choose from is very large,
850   agent-driven negotiation might not be appropriate.
851</t>
852<t>
853   Note that in all cases, the supplier of representations has the
854   responsibility for determining which representations might be
855   considered to be the "same information".
856</t>
857
858<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
859<t>
860   If the selection of the best representation for a response is made by
861   an algorithm located at the server, it is called server-driven
862   negotiation. Selection is based on the available representations of
863   the response (the dimensions over which it can vary; e.g., language,
864   content-coding, etc.) and the contents of particular header fields in
865   the request message or on other information pertaining to the request
866   (such as the network address of the client).
867</t>
868<t>
869   Server-driven negotiation is advantageous when the algorithm for
870   selecting from among the available representations is difficult to
871   describe to the user agent, or when the server desires to send its
872   "best guess" to the client along with the first response (hoping to
873   avoid the round-trip delay of a subsequent request if the "best
874   guess" is good enough for the user). In order to improve the server's
875   guess, the user agent &MAY; include request header fields (Accept,
876   Accept-Language, Accept-Encoding, etc.) which describe its
877   preferences for such a response.
878</t>
879<t>
880   Server-driven negotiation has disadvantages:
881  <list style="numbers">
882    <t>
883         It is impossible for the server to accurately determine what
884         might be "best" for any given user, since that would require
885         complete knowledge of both the capabilities of the user agent
886         and the intended use for the response (e.g., does the user want
887         to view it on screen or print it on paper?).
888    </t>
889    <t>
890         Having the user agent describe its capabilities in every
891         request can be both very inefficient (given that only a small
892         percentage of responses have multiple representations) and a
893         potential violation of the user's privacy.
894    </t>
895    <t>
896         It complicates the implementation of an origin server and the
897         algorithms for generating responses to a request.
898    </t>
899    <t>
900         It might limit a public cache's ability to use the same response
901         for multiple user's requests.
902    </t>
903  </list>
904</t>
905<t>
906   HTTP/1.1 includes the following request-header fields for enabling
907   server-driven negotiation through description of user agent
908   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
909   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
910   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
911   However, an origin server is not limited to these dimensions and &MAY; vary
912   the response based on any aspect of the request, including information
913   outside the request-header fields or within extension header fields
914   not defined by this specification.
915</t>
916<x:note>
917  <t>
918    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
919    because new clients might not be recognized.
920  </t>
921</x:note>
922<t>
923   The Vary header field (&header-vary;) can be used to express the parameters the
924   server uses to select a representation that is subject to server-driven
925   negotiation.
926</t>
927</section>
928
929<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
930<t>
931   With agent-driven negotiation, selection of the best representation
932   for a response is performed by the user agent after receiving an
933   initial response from the origin server. Selection is based on a list
934   of the available representations of the response included within the
935   header fields or body of the initial response, with each
936   representation identified by its own URI. Selection from among the
937   representations can be performed automatically (if the user agent is
938   capable of doing so) or manually by the user selecting from a
939   generated (possibly hypertext) menu.
940</t>
941<t>
942   Agent-driven negotiation is advantageous when the response would vary
943   over commonly-used dimensions (such as type, language, or encoding),
944   when the origin server is unable to determine a user agent's
945   capabilities from examining the request, and generally when public
946   caches are used to distribute server load and reduce network usage.
947</t>
948<t>
949   Agent-driven negotiation suffers from the disadvantage of needing a
950   second request to obtain the best alternate representation. This
951   second request is only efficient when caching is used. In addition,
952   this specification does not define any mechanism for supporting
953   automatic selection, though it also does not prevent any such
954   mechanism from being developed as an extension and used within
955   HTTP/1.1.
956</t>
957<t>
958   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
959   status codes for enabling agent-driven negotiation when the server is
960   unwilling or unable to provide a varying response using server-driven
961   negotiation.
962</t>
963</section>
964</section>
965
966<section title="Header Field Definitions" anchor="header.fields">
967<t>
968   This section defines the syntax and semantics of HTTP/1.1 header fields
969   related to the payload of messages.
970</t>
971
972<section title="Accept" anchor="header.accept">
973  <iref primary="true" item="Accept header" x:for-anchor=""/>
974  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
975  <x:anchor-alias value="Accept"/>
976  <x:anchor-alias value="Accept-v"/>
977  <x:anchor-alias value="accept-ext"/>
978  <x:anchor-alias value="accept-params"/>
979  <x:anchor-alias value="media-range"/>
980<t>
981   The "Accept" request-header field can be used by user agents to specify
982   response media types that are acceptable. Accept header fields can be used to
983   indicate that the request is specifically limited to a small set of desired
984   types, as in the case of a request for an in-line image.
985</t>
986<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
987  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
988  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
989 
990  <x:ref>media-range</x:ref>    = ( "*/*"
991                   / ( <x:ref>type</x:ref> "/" "*" )
992                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
993                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
994  <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
995  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
996</artwork></figure>
997<t>
998   The asterisk "*" character is used to group media types into ranges,
999   with "*/*" indicating all media types and "type/*" indicating all
1000   subtypes of that type. The media-range &MAY; include media type
1001   parameters that are applicable to that range.
1002</t>
1003<t>
1004   Each media-range &MAY; be followed by one or more accept-params,
1005   beginning with the "q" parameter for indicating a relative quality
1006   factor. The first "q" parameter (if any) separates the media-range
1007   parameter(s) from the accept-params. Quality factors allow the user
1008   or user agent to indicate the relative degree of preference for that
1009   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1010   default value is q=1.
1011</t>
1012<x:note>
1013  <t>
1014    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1015    parameters from Accept extension parameters is due to historical
1016    practice. Although this prevents any media type parameter named
1017    "q" from being used with a media range, such an event is believed
1018    to be unlikely given the lack of any "q" parameters in the IANA
1019    media type registry and the rare usage of any media type
1020    parameters in Accept. Future media types are discouraged from
1021    registering any parameter named "q".
1022  </t>
1023</x:note>
1024<t>
1025   The example
1026</t>
1027<figure><artwork type="example">
1028  Accept: audio/*; q=0.2, audio/basic
1029</artwork></figure>
1030<t>
1031   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1032   type if it is the best available after an 80% mark-down in quality".
1033</t>
1034<t>
1035   If no Accept header field is present, then it is assumed that the
1036   client accepts all media types. If an Accept header field is present,
1037   and if the server cannot send a response which is acceptable
1038   according to the combined Accept field value, then the server &SHOULD;
1039   send a 406 (Not Acceptable) response.
1040</t>
1041<t>
1042   A more elaborate example is
1043</t>
1044<figure><artwork type="example">
1045  Accept: text/plain; q=0.5, text/html,
1046          text/x-dvi; q=0.8, text/x-c
1047</artwork></figure>
1048<t>
1049   Verbally, this would be interpreted as "text/html and text/x-c are
1050   the preferred media types, but if they do not exist, then send the
1051   text/x-dvi representation, and if that does not exist, send the text/plain
1052   representation".
1053</t>
1054<t>
1055   Media ranges can be overridden by more specific media ranges or
1056   specific media types. If more than one media range applies to a given
1057   type, the most specific reference has precedence. For example,
1058</t>
1059<figure><artwork type="example">
1060  Accept: text/*, text/html, text/html;level=1, */*
1061</artwork></figure>
1062<t>
1063   have the following precedence:
1064   <list style="numbers">
1065    <t>text/html;level=1</t>
1066    <t>text/html</t>
1067    <t>text/*</t>
1068    <t>*/*</t>
1069   </list>
1070</t>
1071<t>
1072   The media type quality factor associated with a given type is
1073   determined by finding the media range with the highest precedence
1074   which matches that type. For example,
1075</t>
1076<figure><artwork type="example">
1077  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1078          text/html;level=2;q=0.4, */*;q=0.5
1079</artwork></figure>
1080<t>
1081   would cause the following values to be associated:
1082</t>
1083<texttable align="left">
1084  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1085  <c>text/html;level=1</c>    <c>1</c>
1086  <c>text/html</c>            <c>0.7</c>
1087  <c>text/plain</c>           <c>0.3</c>
1088  <c>image/jpeg</c>           <c>0.5</c>
1089  <c>text/html;level=2</c>    <c>0.4</c>
1090  <c>text/html;level=3</c>    <c>0.7</c>
1091</texttable>
1092<t>
1093      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1094      values for certain media ranges. However, unless the user agent is
1095      a closed system which cannot interact with other rendering agents,
1096      this default set ought to be configurable by the user.
1097</t>
1098</section>
1099
1100<section title="Accept-Charset" anchor="header.accept-charset">
1101  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1102  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1103  <x:anchor-alias value="Accept-Charset"/>
1104  <x:anchor-alias value="Accept-Charset-v"/>
1105<t>
1106   The "Accept-Charset" request-header field can be used by user agents to
1107   indicate what response character sets are acceptable. This field allows
1108   clients capable of understanding more comprehensive or special-purpose
1109   character sets to signal that capability to a server which is capable of
1110   representing documents in those character sets.
1111</t>
1112<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1113  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1114          <x:ref>Accept-Charset-v</x:ref>
1115  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1116                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1117</artwork></figure>
1118<t>
1119   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1120   be given an associated quality value which represents the user's
1121   preference for that charset. The default value is q=1. An example is
1122</t>
1123<figure><artwork type="example">
1124  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1125</artwork></figure>
1126<t>
1127   The special value "*", if present in the Accept-Charset field,
1128   matches every character set (including ISO-8859-1) which is not
1129   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1130   in an Accept-Charset field, then all character sets not explicitly
1131   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1132   a quality value of 1 if not explicitly mentioned.
1133</t>
1134<t>
1135   If no Accept-Charset header field is present, the default is that any
1136   character set is acceptable. If an Accept-Charset header field is present,
1137   and if the server cannot send a response which is acceptable
1138   according to the Accept-Charset header field, then the server &SHOULD; send
1139   an error response with the 406 (Not Acceptable) status code, though
1140   the sending of an unacceptable response is also allowed.
1141</t>
1142</section>
1143
1144<section title="Accept-Encoding" anchor="header.accept-encoding">
1145  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1146  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1147  <x:anchor-alias value="Accept-Encoding"/>
1148  <x:anchor-alias value="Accept-Encoding-v"/>
1149  <x:anchor-alias value="codings"/>
1150<t>
1151   The "Accept-Encoding" request-header field can be used by user agents to
1152   indicate what response content-codings (<xref target="content.codings"/>)
1153   are acceptable in the response.
1154</t>
1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1156  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1157                     <x:ref>Accept-Encoding-v</x:ref>
1158  <x:ref>Accept-Encoding-v</x:ref>  =
1159                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1160  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1161</artwork></figure>
1162<t>
1163   Each codings value &MAY; be given an associated quality value which
1164   represents the preference for that encoding. The default value is q=1.
1165</t>
1166<t>
1167   Examples of its use are:
1168</t>
1169<figure><artwork type="example">
1170  Accept-Encoding: compress, gzip
1171  Accept-Encoding:
1172  Accept-Encoding: *
1173  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1174  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1175</artwork></figure>
1176<t>
1177   A server tests whether a content-coding is acceptable, according to
1178   an Accept-Encoding field, using these rules:
1179  <list style="numbers">
1180      <t>If the content-coding is one of the content-codings listed in
1181         the Accept-Encoding field, then it is acceptable, unless it is
1182         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1183         qvalue of 0 means "not acceptable".)</t>
1184
1185      <t>The special "*" symbol in an Accept-Encoding field matches any
1186         available content-coding not explicitly listed in the header
1187         field.</t>
1188
1189      <t>If multiple content-codings are acceptable, then the acceptable
1190         content-coding with the highest non-zero qvalue is preferred.</t>
1191
1192      <t>The "identity" content-coding is always acceptable, unless
1193         specifically refused because the Accept-Encoding field includes
1194         "identity;q=0", or because the field includes "*;q=0" and does
1195         not explicitly include the "identity" content-coding. If the
1196         Accept-Encoding field-value is empty, then only the "identity"
1197         encoding is acceptable.</t>
1198  </list>
1199</t>
1200<t>
1201   If an Accept-Encoding field is present in a request, and if the
1202   server cannot send a response which is acceptable according to the
1203   Accept-Encoding header field, then the server &SHOULD; send an error response
1204   with the 406 (Not Acceptable) status code.
1205</t>
1206<t>
1207   If no Accept-Encoding field is present in a request, the server &MAY;
1208   assume that the client will accept any content coding. In this case,
1209   if "identity" is one of the available content-codings, then the
1210   server &SHOULD; use the "identity" content-coding, unless it has
1211   additional information that a different content-coding is meaningful
1212   to the client.
1213</t>
1214<x:note>
1215  <t>
1216    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1217    and if the "identity" content-coding is unavailable, then
1218    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1219    "gzip" and "compress") are preferred; some older clients
1220    improperly display messages sent with other content-codings.  The
1221    server might also make this decision based on information about
1222    the particular user-agent or client.
1223  </t>
1224</x:note>
1225<x:note>
1226  <t>
1227    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1228    associated with content-codings. This means that qvalues will not
1229    work and are not permitted with x-gzip or x-compress.
1230  </t>
1231</x:note>
1232</section>
1233
1234<section title="Accept-Language" anchor="header.accept-language">
1235  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1236  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1237  <x:anchor-alias value="Accept-Language"/>
1238  <x:anchor-alias value="Accept-Language-v"/>
1239  <x:anchor-alias value="language-range"/>
1240<t>
1241   The "Accept-Language" request-header field can be used by user agents to
1242   indicate the set of natural languages that are preferred in the response.
1243   Language tags are defined in <xref target="language.tags"/>.
1244</t>
1245<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1246  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1247                    <x:ref>Accept-Language-v</x:ref>
1248  <x:ref>Accept-Language-v</x:ref> =
1249                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1250  <x:ref>language-range</x:ref>    =
1251            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1252</artwork></figure>
1253<t>
1254   Each language-range can be given an associated quality value which
1255   represents an estimate of the user's preference for the languages
1256   specified by that range. The quality value defaults to "q=1". For
1257   example,
1258</t>
1259<figure><artwork type="example">
1260  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1261</artwork></figure>
1262<t>
1263   would mean: "I prefer Danish, but will accept British English and
1264   other types of English".
1265   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1266</t>
1267<t>
1268   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1269   several matching schemes. Implementations can offer the most appropriate
1270   matching scheme for their requirements.
1271</t>
1272<x:note>
1273  <t>
1274    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1275    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1276    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1277  </t>
1278</x:note>
1279<t>
1280   It might be contrary to the privacy expectations of the user to send
1281   an Accept-Language header field with the complete linguistic preferences of
1282   the user in every request. For a discussion of this issue, see
1283   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1284</t>
1285<t>
1286   As intelligibility is highly dependent on the individual user, it is
1287   recommended that client applications make the choice of linguistic
1288   preference available to the user. If the choice is not made
1289   available, then the Accept-Language header field &MUST-NOT; be given in
1290   the request.
1291</t>
1292<x:note>
1293  <t>
1294    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1295    the user, we remind implementors of  the fact that users are not
1296    familiar with the details of language matching as described above,
1297    and ought to be provided appropriate guidance. As an example, users
1298    might assume that on selecting "en-gb", they will be served any
1299    kind of English document if British English is not available. A
1300    user agent might suggest in such a case to add "en" to get the
1301    best matching behavior.
1302  </t>
1303</x:note>
1304</section>
1305
1306<section title="Content-Encoding" anchor="header.content-encoding">
1307  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1308  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1309  <x:anchor-alias value="Content-Encoding"/>
1310  <x:anchor-alias value="Content-Encoding-v"/>
1311<t>
1312   The "Content-Encoding" header field indicates what content-codings
1313   have been applied to the representation, and thus what decoding mechanisms
1314   must be applied in order to obtain the media-type referenced by the
1315   Content-Type header field. Content-Encoding is primarily used to allow a
1316   representation to be compressed without losing the identity of its underlying
1317   media type.
1318</t>
1319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1320  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1321  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1322</artwork></figure>
1323<t>
1324   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1325</t>
1326<figure><artwork type="example">
1327  Content-Encoding: gzip
1328</artwork></figure>
1329<t>
1330   The content-coding is a characteristic of the representation.
1331   Typically, the representation body is stored with this
1332   encoding and is only decoded before rendering or analogous usage.
1333   However, a non-transparent proxy &MAY; modify the content-coding if the
1334   new coding is known to be acceptable to the recipient, unless the
1335   "no-transform" cache-control directive is present in the message.
1336</t>
1337<t>
1338   If the content-coding of a representation is not "identity", then the
1339   representation metadata &MUST; include a Content-Encoding header
1340   field (<xref target="header.content-encoding"/>)
1341   that lists the non-identity content-coding(s) used.
1342</t>
1343<t>
1344   If the content-coding of a representation in a request message is not
1345   acceptable to the origin server, the server &SHOULD; respond with a
1346   status code of 415 (Unsupported Media Type).
1347</t>
1348<t>
1349   If multiple encodings have been applied to a representation, the content
1350   codings &MUST; be listed in the order in which they were applied.
1351   Additional information about the encoding parameters &MAY; be provided
1352   by other header fields not defined by this specification.
1353</t>
1354</section>
1355
1356<section title="Content-Language" anchor="header.content-language">
1357  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1358  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1359  <x:anchor-alias value="Content-Language"/>
1360  <x:anchor-alias value="Content-Language-v"/>
1361<t>
1362   The "Content-Language" header field describes the natural
1363   language(s) of the intended audience for the representation. Note that this might
1364   not be equivalent to all the languages used within the representation.
1365</t>
1366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1367  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1368  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1369</artwork></figure>
1370<t>
1371   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1372   Content-Language is to allow a user to identify and differentiate
1373   representations according to the user's own preferred language. Thus, if the
1374   body content is intended only for a Danish-literate audience, the
1375   appropriate field is
1376</t>
1377<figure><artwork type="example">
1378  Content-Language: da
1379</artwork></figure>
1380<t>
1381   If no Content-Language is specified, the default is that the content
1382   is intended for all language audiences. This might mean that the
1383   sender does not consider it to be specific to any natural language,
1384   or that the sender does not know for which language it is intended.
1385</t>
1386<t>
1387   Multiple languages &MAY; be listed for content that is intended for
1388   multiple audiences. For example, a rendition of the "Treaty of
1389   Waitangi", presented simultaneously in the original Maori and English
1390   versions, would call for
1391</t>
1392<figure><artwork type="example">
1393  Content-Language: mi, en
1394</artwork></figure>
1395<t>
1396   However, just because multiple languages are present within a representation
1397   does not mean that it is intended for multiple linguistic audiences.
1398   An example would be a beginner's language primer, such as "A First
1399   Lesson in Latin", which is clearly intended to be used by an
1400   English-literate audience. In this case, the Content-Language would
1401   properly only include "en".
1402</t>
1403<t>
1404   Content-Language &MAY; be applied to any media type &mdash; it is not
1405   limited to textual documents.
1406</t>
1407</section>
1408
1409<section title="Content-Location" anchor="header.content-location">
1410  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1411  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1412  <x:anchor-alias value="Content-Location"/>
1413  <x:anchor-alias value="Content-Location-v"/>
1414<t>
1415   The "Content-Location" header field supplies a URI that can be used
1416   as a specific identifier for the representation in this message.
1417   In other words, if one were to perform a GET on this URI at the time
1418   of this message's generation, then a 200 response would contain the
1419   same representation that is enclosed as payload in this message.
1420</t>
1421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1422  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1423                    <x:ref>Content-Location-v</x:ref>
1424  <x:ref>Content-Location-v</x:ref> =
1425                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1426</artwork></figure>
1427<t>
1428   The Content-Location value is not a replacement for the effective
1429   Request URI (&effective-request-uri;).  It is representation metadata.
1430   It has the same syntax and semantics as the header field of the same name
1431   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1432   However, its appearance in an HTTP message has some special implications
1433   for HTTP recipients.
1434</t>
1435<t>
1436   If Content-Location is included in a response message and its value
1437   is the same as the effective request URI, then the response payload
1438   &SHOULD; be considered the current representation of that resource.
1439   For a GET or HEAD request, this is the same as the default semantics
1440   when no Content-Location is provided by the server.  For a state-changing
1441   method like PUT or POST, it implies that the server's response contains
1442   the new representation of that resource, thereby distinguishing it from
1443   representations that might only report about the action (e.g., "It worked!").
1444   This allows authoring applications to update their local copies without
1445   the need for a subsequent GET request.
1446</t>
1447<t>
1448   If Content-Location is included in a response message and its value
1449   differs from the effective request URI, then the origin server is
1450   informing recipients that this representation has its own, presumably
1451   more specific, identifier.  For a GET or HEAD request, this is an
1452   indication that the effective request URI identifies a resource that
1453   is subject to content negotiation and the representation selected for
1454   this response can also be found at the identified URI.  For other
1455   methods, such a Content-Location indicates that this representation
1456   contains a report on the action's status and the same report is
1457   available (for future access with GET) at the given URI.  For
1458   example, a purchase transaction made via the POST method might
1459   include a receipt document as the payload of the 200 response;
1460   the Content-Location value provides an identifier for retrieving
1461   a copy of that same receipt in the future.
1462</t>
1463<t>
1464   If Content-Location is included in a request message, then it &MAY;
1465   be interpreted by the origin server as an indication of where the
1466   user agent originally obtained the content of the enclosed
1467   representation (prior to any subsequent modification of the content
1468   by that user agent).  In other words, the user agent is providing
1469   the same representation metadata that it received with the original
1470   representation.  However, such interpretation &MUST-NOT; be used to
1471   alter the semantics of the method requested by the client.  For
1472   example, if a client makes a PUT request on a negotiated resource
1473   and the origin server accepts that PUT (without redirection), then the
1474   new set of values for that resource is expected to be consistent with
1475   the one representation supplied in that PUT; the Content-Location
1476   cannot be used as a form of reverse content selection that
1477   identifies only one of the negotiated representations to be updated.
1478   If the user agent had wanted the latter semantics, it would have applied
1479   the PUT directly to the Content-Location URI.
1480</t>
1481<t>
1482   A Content-Location field received in a request message is transitory
1483   information that &SHOULD-NOT; be saved with other representation
1484   metadata for use in later responses.  The Content-Location's value
1485   might be saved for use in other contexts, such as within source links
1486   or other metadata.
1487</t>
1488<t>
1489   A cache cannot assume that a representation with a Content-Location
1490   different from the URI used to retrieve it can be used to respond to
1491   later requests on that Content-Location URI.
1492</t>
1493<t>
1494   If the Content-Location value is a partial URI, the partial URI is
1495   interpreted relative to the effective request URI.
1496</t>
1497</section>
1498
1499<section title="Content-MD5" anchor="header.content-md5">
1500  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1501  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1502  <x:anchor-alias value="Content-MD5"/>
1503  <x:anchor-alias value="Content-MD5-v"/>
1504<t>
1505   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
1506   an MD5 digest of the payload body that provides an end-to-end message
1507   integrity check (MIC) of the payload body (the message-body after any
1508   transfer-coding is decoded). Note that a MIC is good for
1509   detecting accidental modification of the payload body in transit, but is not
1510   proof against malicious attacks.
1511</t>
1512<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1513  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1514  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1515</artwork></figure>
1516<t>
1517   The Content-MD5 header field &MAY; be generated by an origin server or
1518   client to function as an integrity check of the payload body. Only
1519   origin servers or user agents &MAY; generate the Content-MD5 header field;
1520   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1521   value as an end-to-end integrity check. Any recipient &MAY; check that
1522   the digest value in this header field matches a corresponding digest
1523   calculated on payload body as received.
1524</t>
1525<t>
1526   The MD5 digest is computed based on the content of the payload body,
1527   including any content-coding, but not including any transfer-coding
1528   applied to the message-body because such transfer-codings might be
1529   applied or removed anywhere along the request/response chain.
1530   If the message is received with a transfer-coding, that encoding &MUST;
1531   be decoded prior to checking the Content-MD5 value against the received
1532   payload.
1533</t>
1534<t>
1535   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1536   composite media-types (e.g., multipart/* and message/rfc822), but
1537   this does not change how the digest is computed as defined in the
1538   preceding paragraph.
1539</t>
1540<t>
1541   There are several consequences of this. The payload for composite
1542   types &MAY; contain many body-parts, each with its own MIME and HTTP
1543   header fields (including Content-MD5, Content-Transfer-Encoding, and
1544   Content-Encoding header fields). If a body-part has a Content-Transfer-Encoding
1545   or Content-Encoding header field, it is assumed that the content
1546   of the body-part has had the encoding applied, and the body-part is
1547   included in the Content-MD5 digest as is &mdash; i.e., after the
1548   application. The Transfer-Encoding header field is not allowed within
1549   body-parts.
1550</t>
1551<t>
1552   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1553   computing or checking the digest: the line break convention used in
1554   the text actually transmitted &MUST; be left unaltered when computing
1555   the digest.
1556</t>
1557<x:note>
1558  <t>
1559    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1560    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1561    in which the application of Content-MD5 to HTTP entity-bodies
1562    differs from its application to MIME entity-bodies. One is that
1563    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1564    does use Transfer-Encoding and Content-Encoding. Another is that
1565    HTTP more frequently uses binary content types than MIME, so it is
1566    worth noting that, in such cases, the byte order used to compute
1567    the digest is the transmission byte order defined for the type.
1568    Lastly, HTTP allows transmission of text types with any of several
1569    line break conventions and not just the canonical form using CRLF.
1570  </t>
1571</x:note>
1572</section>
1573
1574<section title="Content-Type" anchor="header.content-type">
1575  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1576  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1577  <x:anchor-alias value="Content-Type"/>
1578  <x:anchor-alias value="Content-Type-v"/>
1579<t>
1580   The "Content-Type" header field indicates the media type of the
1581   representation. In the case of responses to the HEAD method, the media type is
1582   that which would have been sent had the request been a GET.
1583</t>
1584<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1585  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1586  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1587</artwork></figure>
1588<t>
1589   Media types are defined in <xref target="media.types"/>. An example of the field is
1590</t>
1591<figure><artwork type="example">
1592  Content-Type: text/html; charset=ISO-8859-4
1593</artwork></figure>
1594<t>
1595   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1596</t>
1597</section>
1598
1599</section>
1600
1601<section title="IANA Considerations" anchor="IANA.considerations">
1602<section title="Header Field Registration" anchor="header.field.registration">
1603<t>
1604   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1605   with the permanent registrations below (see <xref target="RFC3864"/>):
1606</t>
1607<?BEGININC p3-payload.iana-headers ?>
1608<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1609<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1610   <ttcol>Header Field Name</ttcol>
1611   <ttcol>Protocol</ttcol>
1612   <ttcol>Status</ttcol>
1613   <ttcol>Reference</ttcol>
1614
1615   <c>Accept</c>
1616   <c>http</c>
1617   <c>standard</c>
1618   <c>
1619      <xref target="header.accept"/>
1620   </c>
1621   <c>Accept-Charset</c>
1622   <c>http</c>
1623   <c>standard</c>
1624   <c>
1625      <xref target="header.accept-charset"/>
1626   </c>
1627   <c>Accept-Encoding</c>
1628   <c>http</c>
1629   <c>standard</c>
1630   <c>
1631      <xref target="header.accept-encoding"/>
1632   </c>
1633   <c>Accept-Language</c>
1634   <c>http</c>
1635   <c>standard</c>
1636   <c>
1637      <xref target="header.accept-language"/>
1638   </c>
1639   <c>Content-Encoding</c>
1640   <c>http</c>
1641   <c>standard</c>
1642   <c>
1643      <xref target="header.content-encoding"/>
1644   </c>
1645   <c>Content-Language</c>
1646   <c>http</c>
1647   <c>standard</c>
1648   <c>
1649      <xref target="header.content-language"/>
1650   </c>
1651   <c>Content-Location</c>
1652   <c>http</c>
1653   <c>standard</c>
1654   <c>
1655      <xref target="header.content-location"/>
1656   </c>
1657   <c>Content-MD5</c>
1658   <c>http</c>
1659   <c>standard</c>
1660   <c>
1661      <xref target="header.content-md5"/>
1662   </c>
1663   <c>Content-Type</c>
1664   <c>http</c>
1665   <c>standard</c>
1666   <c>
1667      <xref target="header.content-type"/>
1668   </c>
1669   <c>MIME-Version</c>
1670   <c>http</c>
1671   <c>standard</c>
1672   <c>
1673      <xref target="mime-version"/>
1674   </c>
1675</texttable>
1676<!--(END)-->
1677<?ENDINC p3-payload.iana-headers ?>
1678<t>
1679   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1680</t>
1681</section>
1682
1683<section title="Content Coding Registry" anchor="content.coding.registration">
1684<t>
1685   The registration procedure for HTTP Content Codings is now defined
1686   by <xref target="content.coding.registry"/> of this document.
1687</t>
1688<t>
1689   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1690   shall be updated with the registration below:
1691</t>
1692<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1693   <ttcol>Name</ttcol>
1694   <ttcol>Description</ttcol>
1695   <ttcol>Reference</ttcol>
1696   <c>compress</c>
1697   <c>UNIX "compress" program method</c>
1698   <c>
1699      &compress-coding;
1700   </c>
1701   <c>deflate</c>
1702   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1703   the "zlib" data format (<xref target="RFC1950"/>)
1704   </c>
1705   <c>
1706      &deflate-coding;
1707   </c>
1708   <c>gzip</c>
1709   <c>Same as GNU zip <xref target="RFC1952"/></c>
1710   <c>
1711      &gzip-coding;
1712   </c>
1713   <c>identity</c>
1714   <c>No transformation</c>
1715   <c>
1716      <xref target="content.codings"/>
1717   </c>
1718</texttable>
1719</section>
1720
1721</section>
1722
1723<section title="Security Considerations" anchor="security.considerations">
1724<t>
1725   This section is meant to inform application developers, information
1726   providers, and users of the security limitations in HTTP/1.1 as
1727   described by this document. The discussion does not include
1728   definitive solutions to the problems revealed, though it does make
1729   some suggestions for reducing security risks.
1730</t>
1731
1732<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1733<t>
1734   Accept request-headers fields can reveal information about the user to all
1735   servers which are accessed. The Accept-Language header field in particular
1736   can reveal information the user would consider to be of a private
1737   nature, because the understanding of particular languages is often
1738   strongly correlated to the membership of a particular ethnic group.
1739   User agents which offer the option to configure the contents of an
1740   Accept-Language header field to be sent in every request are strongly
1741   encouraged to let the configuration process include a message which
1742   makes the user aware of the loss of privacy involved.
1743</t>
1744<t>
1745   An approach that limits the loss of privacy would be for a user agent
1746   to omit the sending of Accept-Language header fields by default, and to ask
1747   the user whether or not to start sending Accept-Language header fields to a
1748   server if it detects, by looking for any Vary response-header fields
1749   generated by the server, that such sending could improve the quality
1750   of service.
1751</t>
1752<t>
1753   Elaborate user-customized accept header fields sent in every request,
1754   in particular if these include quality values, can be used by servers
1755   as relatively reliable and long-lived user identifiers. Such user
1756   identifiers would allow content providers to do click-trail tracking,
1757   and would allow collaborating content providers to match cross-server
1758   click-trails or form submissions of individual users. Note that for
1759   many users not behind a proxy, the network address of the host
1760   running the user agent will also serve as a long-lived user
1761   identifier. In environments where proxies are used to enhance
1762   privacy, user agents ought to be conservative in offering accept
1763   header configuration options to end users. As an extreme privacy
1764   measure, proxies could filter the accept header fields in relayed requests.
1765   General purpose user agents which provide a high degree of header
1766   configurability &SHOULD; warn users about the loss of privacy which can
1767   be involved.
1768</t>
1769</section>
1770
1771</section>
1772
1773<section title="Acknowledgments" anchor="ack">
1774</section>
1775</middle>
1776<back>
1777
1778<references title="Normative References">
1779
1780<reference anchor="ISO-8859-1">
1781  <front>
1782    <title>
1783     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1784    </title>
1785    <author>
1786      <organization>International Organization for Standardization</organization>
1787    </author>
1788    <date year="1998"/>
1789  </front>
1790  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1791</reference>
1792
1793<reference anchor="Part1">
1794  <front>
1795    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1796    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1797      <organization abbrev="Day Software">Day Software</organization>
1798      <address><email>fielding@gbiv.com</email></address>
1799    </author>
1800    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1801      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1802      <address><email>jg@freedesktop.org</email></address>
1803    </author>
1804    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1805      <organization abbrev="HP">Hewlett-Packard Company</organization>
1806      <address><email>JeffMogul@acm.org</email></address>
1807    </author>
1808    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1809      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1810      <address><email>henrikn@microsoft.com</email></address>
1811    </author>
1812    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1813      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1814      <address><email>LMM@acm.org</email></address>
1815    </author>
1816    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1817      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1818      <address><email>paulle@microsoft.com</email></address>
1819    </author>
1820    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1821      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1822      <address><email>timbl@w3.org</email></address>
1823    </author>
1824    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1825      <organization abbrev="W3C">World Wide Web Consortium</organization>
1826      <address><email>ylafon@w3.org</email></address>
1827    </author>
1828    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1829      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1830      <address><email>julian.reschke@greenbytes.de</email></address>
1831    </author>
1832    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1833  </front>
1834  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1835  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1836</reference>
1837
1838<reference anchor="Part2">
1839  <front>
1840    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1841    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1842      <organization abbrev="Day Software">Day Software</organization>
1843      <address><email>fielding@gbiv.com</email></address>
1844    </author>
1845    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1846      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1847      <address><email>jg@freedesktop.org</email></address>
1848    </author>
1849    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1850      <organization abbrev="HP">Hewlett-Packard Company</organization>
1851      <address><email>JeffMogul@acm.org</email></address>
1852    </author>
1853    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1854      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1855      <address><email>henrikn@microsoft.com</email></address>
1856    </author>
1857    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1858      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1859      <address><email>LMM@acm.org</email></address>
1860    </author>
1861    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1862      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1863      <address><email>paulle@microsoft.com</email></address>
1864    </author>
1865    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1866      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1867      <address><email>timbl@w3.org</email></address>
1868    </author>
1869    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1870      <organization abbrev="W3C">World Wide Web Consortium</organization>
1871      <address><email>ylafon@w3.org</email></address>
1872    </author>
1873    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1874      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1875      <address><email>julian.reschke@greenbytes.de</email></address>
1876    </author>
1877    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1878  </front>
1879  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1880  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1881</reference>
1882
1883<reference anchor="Part4">
1884  <front>
1885    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1886    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1887      <organization abbrev="Day Software">Day Software</organization>
1888      <address><email>fielding@gbiv.com</email></address>
1889    </author>
1890    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1891      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1892      <address><email>jg@freedesktop.org</email></address>
1893    </author>
1894    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1895      <organization abbrev="HP">Hewlett-Packard Company</organization>
1896      <address><email>JeffMogul@acm.org</email></address>
1897    </author>
1898    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1899      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1900      <address><email>henrikn@microsoft.com</email></address>
1901    </author>
1902    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1903      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1904      <address><email>LMM@acm.org</email></address>
1905    </author>
1906    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1907      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1908      <address><email>paulle@microsoft.com</email></address>
1909    </author>
1910    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1911      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1912      <address><email>timbl@w3.org</email></address>
1913    </author>
1914    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1915      <organization abbrev="W3C">World Wide Web Consortium</organization>
1916      <address><email>ylafon@w3.org</email></address>
1917    </author>
1918    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1919      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1920      <address><email>julian.reschke@greenbytes.de</email></address>
1921    </author>
1922    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1923  </front>
1924  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1925  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1926</reference>
1927
1928<reference anchor="Part5">
1929  <front>
1930    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1931    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1932      <organization abbrev="Day Software">Day Software</organization>
1933      <address><email>fielding@gbiv.com</email></address>
1934    </author>
1935    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1936      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1937      <address><email>jg@freedesktop.org</email></address>
1938    </author>
1939    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1940      <organization abbrev="HP">Hewlett-Packard Company</organization>
1941      <address><email>JeffMogul@acm.org</email></address>
1942    </author>
1943    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1944      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1945      <address><email>henrikn@microsoft.com</email></address>
1946    </author>
1947    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1948      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1949      <address><email>LMM@acm.org</email></address>
1950    </author>
1951    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1952      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1953      <address><email>paulle@microsoft.com</email></address>
1954    </author>
1955    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1956      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1957      <address><email>timbl@w3.org</email></address>
1958    </author>
1959    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1960      <organization abbrev="W3C">World Wide Web Consortium</organization>
1961      <address><email>ylafon@w3.org</email></address>
1962    </author>
1963    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1964      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1965      <address><email>julian.reschke@greenbytes.de</email></address>
1966    </author>
1967    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1968  </front>
1969  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1970  <x:source href="p5-range.xml" basename="p5-range"/>
1971</reference>
1972
1973<reference anchor="Part6">
1974  <front>
1975    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1976    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1977      <organization abbrev="Day Software">Day Software</organization>
1978      <address><email>fielding@gbiv.com</email></address>
1979    </author>
1980    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1981      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1982      <address><email>jg@freedesktop.org</email></address>
1983    </author>
1984    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1985      <organization abbrev="HP">Hewlett-Packard Company</organization>
1986      <address><email>JeffMogul@acm.org</email></address>
1987    </author>
1988    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1989      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1990      <address><email>henrikn@microsoft.com</email></address>
1991    </author>
1992    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1993      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1994      <address><email>LMM@acm.org</email></address>
1995    </author>
1996    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1997      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1998      <address><email>paulle@microsoft.com</email></address>
1999    </author>
2000    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2001      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2002      <address><email>timbl@w3.org</email></address>
2003    </author>
2004    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2005      <organization abbrev="W3C">World Wide Web Consortium</organization>
2006      <address><email>ylafon@w3.org</email></address>
2007    </author>
2008    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2009      <address><email>mnot@mnot.net</email></address>
2010    </author>
2011    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2012      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2013      <address><email>julian.reschke@greenbytes.de</email></address>
2014    </author>
2015    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2016  </front>
2017  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2018  <x:source href="p6-cache.xml" basename="p6-cache"/>
2019</reference>
2020
2021<reference anchor="RFC1864">
2022  <front>
2023    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2024    <author initials="J." surname="Myers" fullname="John G. Myers">
2025      <organization>Carnegie Mellon University</organization>
2026      <address><email>jgm+@cmu.edu</email></address>
2027    </author>
2028    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2029      <organization>Dover Beach Consulting, Inc.</organization>
2030      <address><email>mrose@dbc.mtview.ca.us</email></address>
2031    </author>
2032    <date month="October" year="1995"/>
2033  </front>
2034  <seriesInfo name="RFC" value="1864"/>
2035</reference>
2036
2037<reference anchor="RFC1950">
2038  <front>
2039    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2040    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2041      <organization>Aladdin Enterprises</organization>
2042      <address><email>ghost@aladdin.com</email></address>
2043    </author>
2044    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2045    <date month="May" year="1996"/>
2046  </front>
2047  <seriesInfo name="RFC" value="1950"/>
2048  <annotation>
2049    RFC 1950 is an Informational RFC, thus it might be less stable than
2050    this specification. On the other hand, this downward reference was
2051    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2052    therefore it is unlikely to cause problems in practice. See also
2053    <xref target="BCP97"/>.
2054  </annotation>
2055</reference>
2056
2057<reference anchor="RFC1951">
2058  <front>
2059    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2060    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2061      <organization>Aladdin Enterprises</organization>
2062      <address><email>ghost@aladdin.com</email></address>
2063    </author>
2064    <date month="May" year="1996"/>
2065  </front>
2066  <seriesInfo name="RFC" value="1951"/>
2067  <annotation>
2068    RFC 1951 is an Informational RFC, thus it might be less stable than
2069    this specification. On the other hand, this downward reference was
2070    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2071    therefore it is unlikely to cause problems in practice. See also
2072    <xref target="BCP97"/>.
2073  </annotation>
2074</reference>
2075
2076<reference anchor="RFC1952">
2077  <front>
2078    <title>GZIP file format specification version 4.3</title>
2079    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2080      <organization>Aladdin Enterprises</organization>
2081      <address><email>ghost@aladdin.com</email></address>
2082    </author>
2083    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2084      <address><email>gzip@prep.ai.mit.edu</email></address>
2085    </author>
2086    <author initials="M." surname="Adler" fullname="Mark Adler">
2087      <address><email>madler@alumni.caltech.edu</email></address>
2088    </author>
2089    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2090      <address><email>ghost@aladdin.com</email></address>
2091    </author>
2092    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2093      <address><email>randeg@alumni.rpi.edu</email></address>
2094    </author>
2095    <date month="May" year="1996"/>
2096  </front>
2097  <seriesInfo name="RFC" value="1952"/>
2098  <annotation>
2099    RFC 1952 is an Informational RFC, thus it might be less stable than
2100    this specification. On the other hand, this downward reference was
2101    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2102    therefore it is unlikely to cause problems in practice. See also
2103    <xref target="BCP97"/>.
2104  </annotation>
2105</reference>
2106
2107<reference anchor="RFC2045">
2108  <front>
2109    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2110    <author initials="N." surname="Freed" fullname="Ned Freed">
2111      <organization>Innosoft International, Inc.</organization>
2112      <address><email>ned@innosoft.com</email></address>
2113    </author>
2114    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2115      <organization>First Virtual Holdings</organization>
2116      <address><email>nsb@nsb.fv.com</email></address>
2117    </author>
2118    <date month="November" year="1996"/>
2119  </front>
2120  <seriesInfo name="RFC" value="2045"/>
2121</reference>
2122
2123<reference anchor="RFC2046">
2124  <front>
2125    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2126    <author initials="N." surname="Freed" fullname="Ned Freed">
2127      <organization>Innosoft International, Inc.</organization>
2128      <address><email>ned@innosoft.com</email></address>
2129    </author>
2130    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2131      <organization>First Virtual Holdings</organization>
2132      <address><email>nsb@nsb.fv.com</email></address>
2133    </author>
2134    <date month="November" year="1996"/>
2135  </front>
2136  <seriesInfo name="RFC" value="2046"/>
2137</reference>
2138
2139<reference anchor="RFC2119">
2140  <front>
2141    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2142    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2143      <organization>Harvard University</organization>
2144      <address><email>sob@harvard.edu</email></address>
2145    </author>
2146    <date month="March" year="1997"/>
2147  </front>
2148  <seriesInfo name="BCP" value="14"/>
2149  <seriesInfo name="RFC" value="2119"/>
2150</reference>
2151
2152<reference anchor='RFC4647'>
2153  <front>
2154    <title>Matching of Language Tags</title>
2155    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2156      <organization>Yahoo! Inc.</organization>
2157      <address><email>addison@inter-locale.com</email></address>
2158    </author>
2159    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2160      <organization>Google</organization>
2161      <address><email>mark.davis@macchiato.com</email></address>
2162    </author>
2163    <date year='2006' month='September' />
2164  </front>
2165  <seriesInfo name='BCP' value='47' />
2166  <seriesInfo name='RFC' value='4647' />
2167</reference>
2168
2169<reference anchor="RFC5234">
2170  <front>
2171    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2172    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2173      <organization>Brandenburg InternetWorking</organization>
2174      <address>
2175        <email>dcrocker@bbiw.net</email>
2176      </address> 
2177    </author>
2178    <author initials="P." surname="Overell" fullname="Paul Overell">
2179      <organization>THUS plc.</organization>
2180      <address>
2181        <email>paul.overell@thus.net</email>
2182      </address>
2183    </author>
2184    <date month="January" year="2008"/>
2185  </front>
2186  <seriesInfo name="STD" value="68"/>
2187  <seriesInfo name="RFC" value="5234"/>
2188</reference>
2189
2190<reference anchor='RFC5646'>
2191  <front>
2192    <title>Tags for Identifying Languages</title>
2193    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2194      <organization>Lab126</organization>
2195      <address><email>addison@inter-locale.com</email></address>
2196    </author>
2197    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2198      <organization>Google</organization>
2199      <address><email>mark.davis@google.com</email></address>
2200    </author>
2201    <date month='September' year='2009' />
2202  </front>
2203  <seriesInfo name='BCP' value='47' />
2204  <seriesInfo name='RFC' value='5646' />
2205</reference>
2206
2207</references>
2208
2209<references title="Informative References">
2210
2211<reference anchor="RFC1945">
2212  <front>
2213    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2214    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2215      <organization>MIT, Laboratory for Computer Science</organization>
2216      <address><email>timbl@w3.org</email></address>
2217    </author>
2218    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2219      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2220      <address><email>fielding@ics.uci.edu</email></address>
2221    </author>
2222    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2223      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2224      <address><email>frystyk@w3.org</email></address>
2225    </author>
2226    <date month="May" year="1996"/>
2227  </front>
2228  <seriesInfo name="RFC" value="1945"/>
2229</reference>
2230
2231<reference anchor="RFC2049">
2232  <front>
2233    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2234    <author initials="N." surname="Freed" fullname="Ned Freed">
2235      <organization>Innosoft International, Inc.</organization>
2236      <address><email>ned@innosoft.com</email></address>
2237    </author>
2238    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2239      <organization>First Virtual Holdings</organization>
2240      <address><email>nsb@nsb.fv.com</email></address>
2241    </author>
2242    <date month="November" year="1996"/>
2243  </front>
2244  <seriesInfo name="RFC" value="2049"/>
2245</reference>
2246
2247<reference anchor="RFC2068">
2248  <front>
2249    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2250    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2251      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2252      <address><email>fielding@ics.uci.edu</email></address>
2253    </author>
2254    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2255      <organization>MIT Laboratory for Computer Science</organization>
2256      <address><email>jg@w3.org</email></address>
2257    </author>
2258    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2259      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2260      <address><email>mogul@wrl.dec.com</email></address>
2261    </author>
2262    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2263      <organization>MIT Laboratory for Computer Science</organization>
2264      <address><email>frystyk@w3.org</email></address>
2265    </author>
2266    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2267      <organization>MIT Laboratory for Computer Science</organization>
2268      <address><email>timbl@w3.org</email></address>
2269    </author>
2270    <date month="January" year="1997"/>
2271  </front>
2272  <seriesInfo name="RFC" value="2068"/>
2273</reference>
2274
2275<reference anchor="RFC2076">
2276  <front>
2277    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2278    <author initials="J." surname="Palme" fullname="Jacob Palme">
2279      <organization>Stockholm University/KTH</organization>
2280      <address><email>jpalme@dsv.su.se</email></address>
2281    </author>
2282    <date month="February" year="1997"/>
2283  </front>
2284  <seriesInfo name="RFC" value="2076"/>
2285</reference>
2286
2287<reference anchor="RFC2277">
2288  <front>
2289    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2290    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2291      <organization>UNINETT</organization>
2292      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2293    </author>
2294    <date month="January" year="1998"/>
2295  </front>
2296  <seriesInfo name="BCP" value="18"/>
2297  <seriesInfo name="RFC" value="2277"/>
2298</reference>
2299
2300<reference anchor='RFC2295'>
2301  <front>
2302    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2303    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2304      <organization>Technische Universiteit Eindhoven</organization>
2305      <address>
2306        <email>koen@win.tue.nl</email>
2307      </address>
2308    </author>
2309    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2310      <organization>Hewlett-Packard Company</organization>
2311      <address>
2312        <email>mutz@hpl.hp.com</email>
2313      </address>
2314    </author>
2315    <date year='1998' month='March'/>
2316  </front>
2317  <seriesInfo name='RFC' value='2295'/>
2318</reference>
2319
2320<reference anchor="RFC2388">
2321  <front>
2322    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2323    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2324      <organization>Xerox Palo Alto Research Center</organization>
2325      <address><email>masinter@parc.xerox.com</email></address>
2326    </author>
2327    <date year="1998" month="August"/>
2328  </front>
2329  <seriesInfo name="RFC" value="2388"/>
2330</reference>
2331
2332<reference anchor="RFC2557">
2333  <front>
2334    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2335    <author initials="F." surname="Palme" fullname="Jacob Palme">
2336      <organization>Stockholm University and KTH</organization>
2337      <address><email>jpalme@dsv.su.se</email></address>
2338    </author>
2339    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2340      <organization>Microsoft Corporation</organization>
2341      <address><email>alexhop@microsoft.com</email></address>
2342    </author>
2343    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2344      <organization>Lotus Development Corporation</organization>
2345      <address><email>Shelness@lotus.com</email></address>
2346    </author>
2347    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2348      <address><email>stef@nma.com</email></address>
2349    </author>
2350    <date year="1999" month="March"/>
2351  </front>
2352  <seriesInfo name="RFC" value="2557"/>
2353</reference>
2354
2355<reference anchor="RFC2616">
2356  <front>
2357    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2358    <author initials="R." surname="Fielding" fullname="R. Fielding">
2359      <organization>University of California, Irvine</organization>
2360      <address><email>fielding@ics.uci.edu</email></address>
2361    </author>
2362    <author initials="J." surname="Gettys" fullname="J. Gettys">
2363      <organization>W3C</organization>
2364      <address><email>jg@w3.org</email></address>
2365    </author>
2366    <author initials="J." surname="Mogul" fullname="J. Mogul">
2367      <organization>Compaq Computer Corporation</organization>
2368      <address><email>mogul@wrl.dec.com</email></address>
2369    </author>
2370    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2371      <organization>MIT Laboratory for Computer Science</organization>
2372      <address><email>frystyk@w3.org</email></address>
2373    </author>
2374    <author initials="L." surname="Masinter" fullname="L. Masinter">
2375      <organization>Xerox Corporation</organization>
2376      <address><email>masinter@parc.xerox.com</email></address>
2377    </author>
2378    <author initials="P." surname="Leach" fullname="P. Leach">
2379      <organization>Microsoft Corporation</organization>
2380      <address><email>paulle@microsoft.com</email></address>
2381    </author>
2382    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2383      <organization>W3C</organization>
2384      <address><email>timbl@w3.org</email></address>
2385    </author>
2386    <date month="June" year="1999"/>
2387  </front>
2388  <seriesInfo name="RFC" value="2616"/>
2389</reference>
2390
2391<reference anchor="RFC3629">
2392  <front>
2393    <title>UTF-8, a transformation format of ISO 10646</title>
2394    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2395      <organization>Alis Technologies</organization>
2396      <address><email>fyergeau@alis.com</email></address>
2397    </author>
2398    <date month="November" year="2003"/>
2399  </front>
2400  <seriesInfo name="STD" value="63"/>
2401  <seriesInfo name="RFC" value="3629"/>
2402</reference>
2403
2404<reference anchor='RFC3864'>
2405  <front>
2406    <title>Registration Procedures for Message Header Fields</title>
2407    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2408      <organization>Nine by Nine</organization>
2409      <address><email>GK-IETF@ninebynine.org</email></address>
2410    </author>
2411    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2412      <organization>BEA Systems</organization>
2413      <address><email>mnot@pobox.com</email></address>
2414    </author>
2415    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2416      <organization>HP Labs</organization>
2417      <address><email>JeffMogul@acm.org</email></address>
2418    </author>
2419    <date year='2004' month='September' />
2420  </front>
2421  <seriesInfo name='BCP' value='90' />
2422  <seriesInfo name='RFC' value='3864' />
2423</reference>
2424
2425<reference anchor="RFC4288">
2426  <front>
2427    <title>Media Type Specifications and Registration Procedures</title>
2428    <author initials="N." surname="Freed" fullname="N. Freed">
2429      <organization>Sun Microsystems</organization>
2430      <address>
2431        <email>ned.freed@mrochek.com</email>
2432      </address>
2433    </author>
2434    <author initials="J." surname="Klensin" fullname="J. Klensin">
2435      <address>
2436        <email>klensin+ietf@jck.com</email>
2437      </address>
2438    </author>
2439    <date year="2005" month="December"/>
2440  </front>
2441  <seriesInfo name="BCP" value="13"/>
2442  <seriesInfo name="RFC" value="4288"/>
2443</reference>
2444
2445<reference anchor='RFC5226'>
2446  <front>
2447    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2448    <author initials='T.' surname='Narten' fullname='T. Narten'>
2449      <organization>IBM</organization>
2450      <address><email>narten@us.ibm.com</email></address>
2451    </author>
2452    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2453      <organization>Google</organization>
2454      <address><email>Harald@Alvestrand.no</email></address>
2455    </author>
2456    <date year='2008' month='May' />
2457  </front>
2458  <seriesInfo name='BCP' value='26' />
2459  <seriesInfo name='RFC' value='5226' />
2460</reference>
2461
2462<reference anchor="RFC5322">
2463  <front>
2464    <title>Internet Message Format</title>
2465    <author initials="P." surname="Resnick" fullname="P. Resnick">
2466      <organization>Qualcomm Incorporated</organization>
2467    </author>
2468    <date year="2008" month="October"/>
2469  </front> 
2470  <seriesInfo name="RFC" value="5322"/>
2471</reference>
2472
2473<reference anchor='BCP97'>
2474  <front>
2475    <title>Handling Normative References to Standards-Track Documents</title>
2476    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2477      <address>
2478        <email>klensin+ietf@jck.com</email>
2479      </address>
2480    </author>
2481    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2482      <organization>MIT</organization>
2483      <address>
2484        <email>hartmans-ietf@mit.edu</email>
2485      </address>
2486    </author>
2487    <date year='2007' month='June' />
2488  </front>
2489  <seriesInfo name='BCP' value='97' />
2490  <seriesInfo name='RFC' value='4897' />
2491</reference>
2492
2493
2494</references>
2495
2496<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2497<t>
2498   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
2499   allow a message-body to be transmitted in an open variety of
2500   representations and with extensible mechanisms. However, RFC 2045
2501   discusses mail, and HTTP has a few features that are different from
2502   those described in MIME. These differences were carefully chosen
2503   to optimize performance over binary connections, to allow greater
2504   freedom in the use of new media types, to make date comparisons
2505   easier, and to acknowledge the practice of some early HTTP servers
2506   and clients.
2507</t>
2508<t>
2509   This appendix describes specific areas where HTTP differs from MIME.
2510   Proxies and gateways to strict MIME environments &SHOULD; be
2511   aware of these differences and provide the appropriate conversions
2512   where necessary. Proxies and gateways from MIME environments to HTTP
2513   also need to be aware of the differences because some conversions
2514   might be required.
2515</t>
2516
2517<section title="MIME-Version" anchor="mime-version">
2518  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2519  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2520  <x:anchor-alias value="MIME-Version"/>
2521  <x:anchor-alias value="MIME-Version-v"/>
2522<t>
2523   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2524   include a single MIME-Version general-header field to indicate what
2525   version of the MIME protocol was used to construct the message. Use
2526   of the MIME-Version header field indicates that the message is in
2527   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2528   Proxies/gateways are responsible for ensuring full compliance (where
2529   possible) when exporting HTTP messages to strict MIME environments.
2530</t>
2531<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2532  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2533  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2534</artwork></figure>
2535<t>
2536   MIME version "1.0" is the default for use in HTTP/1.1. However,
2537   HTTP/1.1 message parsing and semantics are defined by this document
2538   and not the MIME specification.
2539</t>
2540</section>
2541
2542<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2543<t>
2544   MIME requires that an Internet mail body-part be converted to
2545   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2546   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2547   allowed for subtypes of the "text" media type when transmitted over
2548   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2549   line breaks as CRLF and forbids the use of CR or LF outside of line
2550   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2551   line break within text content when a message is transmitted over
2552   HTTP.
2553</t>
2554<t>
2555   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2556   environment &SHOULD; translate all line breaks within the text media
2557   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2558   canonical form of CRLF. Note, however, that this might be complicated
2559   by the presence of a Content-Encoding and by the fact that HTTP
2560   allows the use of some character sets which do not use octets 13 and
2561   10 to represent CR and LF, as is the case for some multi-byte
2562   character sets.
2563</t>
2564<t>
2565   Conversion will break any cryptographic
2566   checksums applied to the original content unless the original content
2567   is already in canonical form. Therefore, the canonical form is
2568   recommended for any content that uses such checksums in HTTP.
2569</t>
2570</section>
2571
2572
2573<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2574<t>
2575   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2576   simplify the process of date comparison. Proxies and gateways from
2577   other protocols &SHOULD; ensure that any Date header field present in a
2578   message conforms to one of the HTTP/1.1 formats and rewrite the date
2579   if necessary.
2580</t>
2581</section>
2582
2583<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2584<t>
2585   MIME does not include any concept equivalent to HTTP/1.1's
2586   Content-Encoding header field. Since this acts as a modifier on the
2587   media type, proxies and gateways from HTTP to MIME-compliant
2588   protocols &MUST; either change the value of the Content-Type header
2589   field or decode the representation before forwarding the message. (Some
2590   experimental applications of Content-Type for Internet mail have used
2591   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2592   a function equivalent to Content-Encoding. However, this parameter is
2593   not part of the MIME standards).
2594</t>
2595</section>
2596
2597<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2598<t>
2599   HTTP does not use the Content-Transfer-Encoding field of MIME.
2600   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2601   remove any Content-Transfer-Encoding
2602   prior to delivering the response message to an HTTP client.
2603</t>
2604<t>
2605   Proxies and gateways from HTTP to MIME-compliant protocols are
2606   responsible for ensuring that the message is in the correct format
2607   and encoding for safe transport on that protocol, where "safe
2608   transport" is defined by the limitations of the protocol being used.
2609   Such a proxy or gateway &SHOULD; label the data with an appropriate
2610   Content-Transfer-Encoding if doing so will improve the likelihood of
2611   safe transport over the destination protocol.
2612</t>
2613</section>
2614
2615<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2616<t>
2617   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2618   Proxies/gateways &MUST; remove any transfer-coding prior to
2619   forwarding a message via a MIME-compliant protocol.
2620</t>
2621</section>
2622
2623<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2624<t>
2625   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2626   need to be aware of MIME line length limitations. Since HTTP does not
2627   have this limitation, HTTP does not fold long lines. MHTML messages
2628   being transported by HTTP follow all conventions of MHTML, including
2629   line length limitations and folding, canonicalization, etc., since
2630   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2631   does not interpret the content or any MIME header lines that might be
2632   contained therein.
2633</t>
2634</section>
2635</section>
2636
2637<section title="Additional Features" anchor="additional.features">
2638<t>
2639   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2640   existing HTTP implementations, but not consistently and correctly
2641   across most HTTP/1.1 applications. Implementors are advised to be
2642   aware of these features, but cannot rely upon their presence in, or
2643   interoperability with, other HTTP/1.1 applications. Some of these
2644   describe proposed experimental features, and some describe features
2645   that experimental deployment found lacking that are now addressed in
2646   the base HTTP/1.1 specification.
2647</t>
2648<t>
2649   A number of other header fields, such as Content-Disposition and Title,
2650   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2651</t>
2652</section>
2653
2654<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2655<t>
2656  Clarify contexts that charset is used in.
2657  (<xref target="character.sets"/>)
2658</t>
2659<t>
2660  Remove base URI setting semantics for Content-Location due to poor
2661  implementation support, which was caused by too many broken servers emitting
2662  bogus Content-Location header fields, and also the potentially undesirable effect
2663  of potentially breaking relative links in content-negotiated resources.
2664  (<xref target="header.content-location"/>)
2665</t>
2666<t>
2667  Remove reference to non-existant identity transfer-coding value tokens.
2668  (<xref target="no.content-transfer-encoding"/>)
2669</t>
2670</section>
2671
2672<?BEGININC p3-payload.abnf-appendix ?>
2673<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2674<figure>
2675<artwork type="abnf" name="p3-payload.parsed-abnf">
2676<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2677<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2678<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2679 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2680 qvalue ] ] )
2681<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2682<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2683 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2684<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2685<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2686 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2687 ] )
2688<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2689 OWS media-range [ accept-params ] ] ) ]
2690
2691<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2692<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2693 content-coding ] )
2694<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2695<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2696 language-tag ] )
2697<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2698<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2699<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2700<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2701<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2702<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2703<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2704<x:ref>Content-Type-v</x:ref> = media-type
2705
2706<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2707
2708<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2709
2710<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2711<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2712
2713<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2714
2715<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2716<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2717<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2718<x:ref>attribute</x:ref> = token
2719
2720<x:ref>charset</x:ref> = token
2721<x:ref>codings</x:ref> = ( content-coding / "*" )
2722<x:ref>content-coding</x:ref> = token
2723
2724<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2725<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2726
2727<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2728 ";" OWS parameter )
2729<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2730
2731<x:ref>parameter</x:ref> = attribute "=" value
2732<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2733
2734<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2735
2736<x:ref>subtype</x:ref> = token
2737
2738<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2739<x:ref>type</x:ref> = token
2740
2741<x:ref>value</x:ref> = word
2742
2743<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2744</artwork>
2745</figure>
2746<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2747; Accept defined but not used
2748; Accept-Charset defined but not used
2749; Accept-Encoding defined but not used
2750; Accept-Language defined but not used
2751; Content-Encoding defined but not used
2752; Content-Language defined but not used
2753; Content-Length defined but not used
2754; Content-Location defined but not used
2755; Content-MD5 defined but not used
2756; Content-Range defined but not used
2757; Content-Type defined but not used
2758; Expires defined but not used
2759; Last-Modified defined but not used
2760; MIME-Version defined but not used
2761</artwork></figure></section>
2762<?ENDINC p3-payload.abnf-appendix ?>
2763
2764<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2765
2766<section title="Since RFC 2616">
2767<t>
2768  Extracted relevant partitions from <xref target="RFC2616"/>.
2769</t>
2770</section>
2771
2772<section title="Since draft-ietf-httpbis-p3-payload-00">
2773<t>
2774  Closed issues:
2775  <list style="symbols"> 
2776    <t>
2777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2778      "Media Type Registrations"
2779      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2780    </t>
2781    <t>
2782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2783      "Clarification regarding quoting of charset values"
2784      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2785    </t>
2786    <t>
2787      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2788      "Remove 'identity' token references"
2789      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2790    </t>
2791    <t>
2792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2793      "Accept-Encoding BNF"
2794    </t>
2795    <t>
2796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2797      "Normative and Informative references"
2798    </t>
2799    <t>
2800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2801      "RFC1700 references"
2802    </t>
2803    <t>
2804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2805      "Updating to RFC4288"
2806    </t>
2807    <t>
2808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2809      "Informative references"
2810    </t>
2811    <t>
2812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2813      "ISO-8859-1 Reference"
2814    </t>
2815    <t>
2816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2817      "Encoding References Normative"
2818    </t>
2819    <t>
2820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2821      "Normative up-to-date references"
2822    </t>
2823  </list>
2824</t>
2825</section>
2826
2827<section title="Since draft-ietf-httpbis-p3-payload-01">
2828<t>
2829  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2830  <list style="symbols"> 
2831    <t>
2832      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2833    </t>
2834  </list>
2835</t>
2836</section>
2837
2838<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2839<t>
2840  Closed issues:
2841  <list style="symbols"> 
2842    <t>
2843      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2844      "Quoting Charsets"
2845    </t>
2846    <t>
2847      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2848      "Classification for Allow header"
2849    </t>
2850    <t>
2851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2852      "missing default for qvalue in description of Accept-Encoding"
2853    </t>
2854  </list>
2855</t>
2856<t>
2857  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2858  <list style="symbols"> 
2859    <t>
2860      Reference RFC 3984, and update header field registrations for headers defined
2861      in this document.
2862    </t>
2863  </list>
2864</t>
2865</section>
2866
2867<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2868<t>
2869  Closed issues:
2870  <list style="symbols"> 
2871    <t>
2872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2873      "Quoting Charsets"
2874    </t>
2875    <t>
2876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2877      "language tag matching (Accept-Language) vs RFC4647"
2878    </t>
2879    <t>
2880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2881      "RFC 1806 has been replaced by RFC2183"
2882    </t>
2883  </list>
2884</t>
2885<t>
2886  Other changes:
2887  <list style="symbols"> 
2888    <t>
2889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2890      "Encoding References Normative" &mdash; rephrase the annotation and reference
2891      <xref target="BCP97"/>.
2892    </t>
2893  </list>
2894</t>
2895 </section>
2896
2897<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2898<t>
2899  Closed issues:
2900  <list style="symbols"> 
2901    <t>
2902      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2903      "RFC 2822 is updated by RFC 5322"
2904    </t>
2905  </list>
2906</t>
2907<t>
2908  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2909  <list style="symbols"> 
2910    <t>
2911      Use "/" instead of "|" for alternatives.
2912    </t>
2913    <t>
2914      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2915      whitespace ("OWS") and required whitespace ("RWS").
2916    </t>
2917    <t>
2918      Rewrite ABNFs to spell out whitespace rules, factor out
2919      header field value format definitions.
2920    </t>
2921  </list>
2922</t>
2923</section>
2924
2925<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2926<t>
2927  Closed issues:
2928  <list style="symbols"> 
2929    <t>
2930      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2931      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2932    </t>
2933  </list>
2934</t>
2935<t>
2936  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2937  <list style="symbols"> 
2938    <t>
2939      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2940    </t>
2941  </list>
2942</t>
2943<t>
2944  Other changes:
2945  <list style="symbols"> 
2946    <t>
2947      Move definition of quality values into Part 1.
2948    </t>
2949  </list>
2950</t>
2951</section>
2952
2953<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2954<t>
2955  Closed issues:
2956  <list style="symbols"> 
2957    <t>
2958      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2959      "Content-Location isn't special"
2960    </t>
2961    <t>
2962      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2963      "Content Sniffing"
2964    </t>
2965  </list>
2966</t>
2967</section>
2968
2969<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2970<t>
2971  Closed issues:
2972  <list style="symbols"> 
2973    <t>
2974      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2975      "Updated reference for language tags"
2976    </t>
2977    <t>
2978      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2979      "Clarify rules for determining what entities a response carries"
2980    </t>
2981    <t>
2982      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2983      "Content-Location base-setting problems"
2984    </t>
2985    <t>
2986      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2987      "Content Sniffing"
2988    </t>
2989    <t>
2990      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2991      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2992    </t>
2993    <t>
2994      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2995      "move definitions of gzip/deflate/compress to part 1"
2996    </t>
2997  </list>
2998</t>
2999<t>
3000  Partly resolved issues:
3001  <list style="symbols"> 
3002    <t>
3003      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3004      "update IANA requirements wrt Transfer-Coding values" (add the
3005      IANA Considerations subsection)
3006    </t>
3007    <t>
3008      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3009      "update IANA requirements wrt Content-Coding values" (add the
3010      IANA Considerations subsection)
3011    </t>
3012  </list>
3013</t>
3014</section>
3015
3016<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3017<t>
3018  Closed issues:
3019  <list style="symbols"> 
3020    <t>
3021      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3022      "Content Negotiation for media types"
3023    </t>
3024    <t>
3025      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3026      "Accept-Language: which RFC4647 filtering?"
3027    </t>
3028  </list>
3029</t>
3030</section>
3031
3032<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3033<t>
3034  Closed issues:
3035  <list style="symbols"> 
3036    <t>
3037      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
3038      "MIME-Version not listed in P1, general header fields"
3039    </t>
3040    <t>
3041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
3042      "IANA registry for content/transfer encodings"
3043    </t>
3044    <t>
3045      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3046      "Content Sniffing"
3047    </t>
3048    <t>
3049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
3050      "use of term "word" when talking about header structure"
3051    </t>
3052  </list>
3053</t>
3054<t>
3055  Partly resolved issues:
3056  <list style="symbols"> 
3057    <t>
3058      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
3059      "Term for the requested resource's URI"
3060    </t>
3061  </list>
3062</t>
3063</section>
3064
3065<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
3066<t>
3067  Closed issues:
3068  <list style="symbols"> 
3069    <t>
3070      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
3071      "Clarify 'Requested Variant'"
3072    </t>
3073    <t>
3074      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3075      "Content-Location isn't special"
3076    </t>
3077    <t>
3078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
3079      "Delimiting messages with multipart/byteranges"
3080    </t>
3081    <t>
3082      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
3083      "Clarify entity / representation / variant terminology"
3084    </t>
3085    <t>
3086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
3087      "confusing req. language for Content-Location"
3088    </t>
3089    <t>
3090      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
3091      "Content-Location on 304 responses"
3092    </t>
3093    <t>
3094      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
3095      "'requested resource' in content-encoding definition"
3096    </t>
3097    <t>
3098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
3099      "consider removing the 'changes from 2068' sections"
3100    </t>
3101  </list>
3102</t>
3103<t>
3104  Partly resolved issues:
3105  <list style="symbols"> 
3106    <t>
3107      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
3108      "Content-MD5 and partial responses"
3109    </t>
3110  </list>
3111</t>
3112</section>
3113
3114<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
3115<t>
3116  Closed issues:
3117  <list style="symbols"> 
3118    <t>
3119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
3120      "Factor out Content-Disposition"
3121    </t>
3122  </list>
3123</t>
3124</section>
3125
3126<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
3127<t>
3128  None yet.
3129</t>
3130</section>
3131
3132</section>
3133
3134</back>
3135</rfc>
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