source: draft-ietf-httpbis/latest/p3-payload.xml @ 1052

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prepare publication of -12 drafts on 2010-10-25

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