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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<!DOCTYPE rfc
17  PUBLIC "" "rfc2629.dtd">
18<rfc obsoletes="2616" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-09">
19<front>
20
21  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
22
23  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
24    <organization abbrev="Day Software">Day Software</organization>
25    <address>
26      <postal>
27        <street>23 Corporate Plaza DR, Suite 280</street>
28        <city>Newport Beach</city>
29        <region>CA</region>
30        <code>92660</code>
31        <country>USA</country>
32      </postal>
33      <phone>+1-949-706-5300</phone>
34      <facsimile>+1-949-706-5305</facsimile>
35      <email>fielding@gbiv.com</email>
36      <uri>http://roy.gbiv.com/</uri>
37    </address>
38  </author>
39
40  <author initials="J." surname="Gettys" fullname="Jim Gettys">
41    <organization>One Laptop per Child</organization>
42    <address>
43      <postal>
44        <street>21 Oak Knoll Road</street>
45        <city>Carlisle</city>
46        <region>MA</region>
47        <code>01741</code>
48        <country>USA</country>
49      </postal>
50      <email>jg@laptop.org</email>
51      <uri>http://www.laptop.org/</uri>
52    </address>
53  </author>
54 
55  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
56    <organization abbrev="HP">Hewlett-Packard Company</organization>
57    <address>
58      <postal>
59        <street>HP Labs, Large Scale Systems Group</street>
60        <street>1501 Page Mill Road, MS 1177</street>
61        <city>Palo Alto</city>
62        <region>CA</region>
63        <code>94304</code>
64        <country>USA</country>
65      </postal>
66      <email>JeffMogul@acm.org</email>
67    </address>
68  </author>
69
70  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
71    <organization abbrev="Microsoft">Microsoft Corporation</organization>
72    <address>
73      <postal>
74        <street>1 Microsoft Way</street>
75        <city>Redmond</city>
76        <region>WA</region>
77        <code>98052</code>
78        <country>USA</country>
79      </postal>
80      <email>henrikn@microsoft.com</email>
81    </address>
82  </author>
83
84  <author initials="L." surname="Masinter" fullname="Larry Masinter">
85    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
86    <address>
87      <postal>
88        <street>345 Park Ave</street>
89        <city>San Jose</city>
90        <region>CA</region>
91        <code>95110</code>
92        <country>USA</country>
93      </postal>
94      <email>LMM@acm.org</email>
95      <uri>http://larry.masinter.net/</uri>
96    </address>
97  </author>
98 
99  <author initials="P." surname="Leach" fullname="Paul J. Leach">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107      </postal>
108      <email>paulle@microsoft.com</email>
109    </address>
110  </author>
111   
112  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
113    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
114    <address>
115      <postal>
116        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
117        <street>The Stata Center, Building 32</street>
118        <street>32 Vassar Street</street>
119        <city>Cambridge</city>
120        <region>MA</region>
121        <code>02139</code>
122        <country>USA</country>
123      </postal>
124      <email>timbl@w3.org</email>
125      <uri>http://www.w3.org/People/Berners-Lee/</uri>
126    </address>
127  </author>
128
129  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
130    <organization abbrev="W3C">World Wide Web Consortium</organization>
131    <address>
132      <postal>
133        <street>W3C / ERCIM</street>
134        <street>2004, rte des Lucioles</street>
135        <city>Sophia-Antipolis</city>
136        <region>AM</region>
137        <code>06902</code>
138        <country>France</country>
139      </postal>
140      <email>ylafon@w3.org</email>
141      <uri>http://www.raubacapeu.net/people/yves/</uri>
142    </address>
143  </author>
144
145  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
146    <organization abbrev="greenbytes">greenbytes GmbH</organization>
147    <address>
148      <postal>
149        <street>Hafenweg 16</street>
150        <city>Muenster</city><region>NW</region><code>48155</code>
151        <country>Germany</country>
152      </postal>
153      <phone>+49 251 2807760</phone>
154      <facsimile>+49 251 2807761</facsimile>
155      <email>julian.reschke@greenbytes.de</email>
156      <uri>http://greenbytes.de/tech/webdav/</uri>
157    </address>
158  </author>
159
160  <date month="March" year="2010" day="8"/>
161  <workgroup>HTTPbis Working Group</workgroup>
162
163<abstract>
164<t>
165   The Hypertext Transfer Protocol (HTTP) is an application-level
166   protocol for distributed, collaborative, hypermedia information
167   systems. HTTP has been in use by the World Wide Web global information
168   initiative since 1990. This document is Part 3 of the seven-part specification
169   that defines the protocol referred to as "HTTP/1.1" and, taken together,
170   obsoletes RFC 2616.  Part 3 defines HTTP message content,
171   metadata, and content negotiation.
172</t>
173</abstract>
174
175<note title="Editorial Note (To be removed by RFC Editor)">
176  <t>
177    Discussion of this draft should take place on the HTTPBIS working group
178    mailing list (ietf-http-wg@w3.org). The current issues list is
179    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
180    and related documents (including fancy diffs) can be found at
181    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
182  </t>
183  <t>
184    The changes in this draft are summarized in <xref target="changes.since.08"/>.
185  </t>
186</note>
187</front>
188<middle>
189<section title="Introduction" anchor="introduction">
190<t>
191   This document defines HTTP/1.1 message payloads (a.k.a., content), the
192   associated metadata header fields that define how the payload is intended
193   to be interpreted by a recipient, the request header fields that
194   may influence content selection, and the various selection algorithms
195   that are collectively referred to as HTTP content negotiation.
196</t>
197<t>
198   This document is currently disorganized in order to minimize the changes
199   between drafts and enable reviewers to see the smaller errata changes.
200   The next draft will reorganize the sections to better reflect the content.
201   In particular, the sections on entities will be renamed payload and moved
202   to the first half of the document, while the sections on content negotiation
203   and associated request header fields will be moved to the second half.  The
204   current mess reflects how widely dispersed these topics and associated
205   requirements had become in <xref target="RFC2616"/>.
206</t>
207
208<section title="Terminology" anchor="terminology">
209<t>
210   This specification uses a number of terms to refer to the roles
211   played by participants in, and objects of, the HTTP communication.
212</t>
213<t>
214  <iref item="content negotiation"/>
215  <?rfc needLines="4"?>content negotiation
216  <list>
217    <t>
218      The mechanism for selecting the appropriate representation when
219      servicing a request. The representation of entities in any response
220      can be negotiated (including error responses).
221    </t>
222  </list>
223</t>
224<t>
225  <iref item="entity"/>
226  <?rfc needLines="4"?>entity
227  <list>
228    <t>
229      The information transferred as the payload of a request or
230      response. An entity consists of metadata in the form of
231      entity-header fields and content in the form of an entity-body.
232    </t>
233  </list>
234</t>
235<t>
236  <iref item="representation"/>
237  <?rfc needLines="4"?>representation
238  <list>
239    <t>
240      An entity included with a response that is subject to content
241      negotiation. There may exist multiple
242      representations associated with a particular response status.
243    </t>
244  </list>
245</t>
246<t>
247  <iref item="variant"/>
248  <?rfc needLines="4"?>variant
249  <list>
250    <t>
251      A resource may have one, or more than one, representation(s)
252      associated with it at any given instant. Each of these
253      representations is termed a "variant".  Use of the term "variant"
254      does not necessarily imply that the resource is subject to content
255      negotiation.
256    </t>
257  </list>
258</t>
259</section>
260
261<section title="Requirements" anchor="intro.requirements">
262<t>
263   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
264   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
265   document are to be interpreted as described in <xref target="RFC2119"/>.
266</t>
267<t>
268   An implementation is not compliant if it fails to satisfy one or more
269   of the MUST or REQUIRED level requirements for the protocols it
270   implements. An implementation that satisfies all the MUST or REQUIRED
271   level and all the SHOULD level requirements for its protocols is said
272   to be "unconditionally compliant"; one that satisfies all the MUST
273   level requirements but not all the SHOULD level requirements for its
274   protocols is said to be "conditionally compliant."
275</t>
276</section>
277
278<section title="Syntax Notation" anchor="notation">
279 
280 
281 
282 
283 
284 
285 
286<t>
287  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
288  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
289  <xref target="collected.abnf"/> shows the collected ABNF, with the list
290  rule expanded.
291</t>
292<t>
293  The following core rules are included by
294  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
295  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
296  DIGIT (decimal 0-9), DQUOTE (double quote),
297  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
298  OCTET (any 8-bit sequence of data), SP (space),
299  VCHAR (any visible USASCII character),
300  and WSP (whitespace).
301</t>
302
303<section title="Core Rules" anchor="core.rules">
304 
305 
306 
307<t>
308  The core rules below are defined in Section 1.2.2 of <xref target="Part1"/>:
309</t>
310<figure><artwork type="abnf2616"><![CDATA[
311  quoted-string  = <quoted-string, defined in [Part1], Section 1.2.2>
312  token          = <token, defined in [Part1], Section 1.2.2>
313  OWS            = <OWS, defined in [Part1], Section 1.2.2>
314]]></artwork></figure>
315</section>
316
317<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
318 
319 
320 
321 
322 
323 
324 
325 
326 
327<t>
328  The ABNF rules below are defined in other parts:
329</t>
330<figure><artwork type="abnf2616"><![CDATA[
331  absolute-URI   = <absolute-URI, defined in [Part1], Section 2.6>
332  Content-Length = <Content-Length, defined in [Part1], Section 9.2>
333  header-field   = <header-field, defined in [Part1], Section 3.2>
334  partial-URI    = <partial-URI, defined in [Part1], Section 2.6>
335  qvalue         = <qvalue, defined in [Part1], Section 6.4>
336]]></artwork></figure>
337<figure><artwork type="abnf2616"><![CDATA[
338  Last-Modified  = <Last-Modified, defined in [Part4], Section 6.6>
339]]></artwork></figure>
340<figure><artwork type="abnf2616"><![CDATA[
341  Content-Range  = <Content-Range, defined in [Part5], Section 5.2>
342]]></artwork></figure>
343<figure><artwork type="abnf2616"><![CDATA[
344  Expires        = <Expires, defined in [Part6], Section 3.3>
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 may
364   be available in a given character set and a character set may 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<t><list>
375  <t>
376    Note: 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</list></t>
382<t anchor="rule.charset">
383 
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><iref primary="true" item="Grammar" subitem="charset"/><artwork type="abnf2616"><![CDATA[
389  charset = token
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 (in which the charset value is an unquoted token) and as the
401   value of a parameter in a Content-Type header (within a request or
402   response), in which case the parameter value of the charset parameter
403   may be quoted.
404</t>
405<t>
406   Implementors should 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 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 
432<t>
433   Content coding values indicate an encoding transformation that has
434   been or can be applied to an entity. Content codings are primarily
435   used to allow a document 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 entity is stored in
438   coded form, transmitted directly, and only decoded by the recipient.
439</t>
440<figure><iref primary="true" item="Grammar" subitem="content-coding"/><artwork type="abnf2616"><![CDATA[
441  content-coding   = token
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 Section 6.2.2.1 of <xref target="Part1"/>.
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 Section 6.2.2.2 of <xref target="Part1"/>.
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 Section 6.2.2.3 of <xref target="Part1"/>.
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, and SHOULD NOT  be used in the Content-Encoding
481        header.
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   Values to be added to this name space require expert review and a specification
500   (see "Expert Review" and "Specification Required" in
501   Section 4.1 of <xref target="RFC5226"/>), and MUST
502   conform to the purpose of content coding defined in this section.
503</t>
504<t>
505   The registry itself is maintained at
506   <eref target="http://www.iana.org/assignments/http-parameters"/>.
507</t>
508</section>
509
510</section>
511
512<section title="Media Types" anchor="media.types">
513 
514 
515 
516<t>
517   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
518   and Accept (<xref target="header.accept"/>) header fields in order to provide
519   open and extensible data typing and type negotiation.
520</t>
521<figure><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/><artwork type="abnf2616"><![CDATA[
522  media-type = type "/" subtype *( OWS ";" OWS parameter )
523  type       = token
524  subtype    = token
525]]></artwork></figure>
526<t anchor="rule.parameter">
527 
528 
529 
530   Parameters MAY follow the type/subtype in the form of attribute/value
531   pairs.
532</t>
533<figure><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><artwork type="abnf2616"><![CDATA[
534  parameter      = attribute "=" value
535  attribute      = token
536  value          = token / quoted-string
537]]></artwork></figure>
538<t>
539   The type, subtype, and parameter attribute names are case-insensitive.
540   Parameter values might or might not be case-sensitive, depending on the
541   semantics of the parameter name.  The presence or absence of a parameter might
542   be significant to the processing of a media-type, depending on its
543   definition within the media type registry.
544</t>
545<t>
546   A parameter value that matches the <xref target="core.rules" format="none">token</xref> production may be
547   transmitted as either a token or within a quoted-string. The quoted and
548   unquoted values are equivalent.
549</t>
550<t>
551   Note that some older HTTP applications do not recognize media type
552   parameters. When sending data to older HTTP applications,
553   implementations SHOULD only use media type parameters when they are
554   required by that type/subtype definition.
555</t>
556<t>
557   Media-type values are registered with the Internet Assigned Number
558   Authority (IANA). The media type registration process is
559   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
560   discouraged.
561</t>
562
563<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
564<t>
565   Internet media types are registered with a canonical form. An
566   entity-body transferred via HTTP messages MUST be represented in the
567   appropriate canonical form prior to its transmission except for
568   "text" types, as defined in the next paragraph.
569</t>
570<t>
571   When in canonical form, media subtypes of the "text" type use CRLF as
572   the text line break. HTTP relaxes this requirement and allows the
573   transport of text media with plain CR or LF alone representing a line
574   break when it is done consistently for an entire entity-body. HTTP
575   applications MUST accept CRLF, bare CR, and bare LF as being
576   representative of a line break in text media received via HTTP. In
577   addition, if the text is represented in a character set that does not
578   use octets 13 and 10 for CR and LF respectively, as is the case for
579   some multi-byte character sets, HTTP allows the use of whatever octet
580   sequences are defined by that character set to represent the
581   equivalent of CR and LF for line breaks. This flexibility regarding
582   line breaks applies only to text media in the entity-body; a bare CR
583   or LF MUST NOT be substituted for CRLF within any of the HTTP control
584   structures (such as header fields and multipart boundaries).
585</t>
586<t>
587   If an entity-body is encoded with a content-coding, the underlying
588   data MUST be in a form defined above prior to being encoded.
589</t>
590<t>
591   The "charset" parameter is used with some media types to define the
592   character set (<xref target="character.sets"/>) of the data. When no explicit charset
593   parameter is provided by the sender, media subtypes of the "text"
594   type are defined to have a default charset value of "ISO-8859-1" when
595   received via HTTP. Data in character sets other than "ISO-8859-1" or
596   its subsets MUST be labeled with an appropriate charset value. See
597   <xref target="missing.charset"/> for compatibility problems.
598</t>
599</section>
600
601<section title="Multipart Types" anchor="multipart.types">
602<t>
603   MIME provides for a number of "multipart" types -- encapsulations of
604   one or more entities within a single message-body. All multipart
605   types share a common syntax, as defined in Section 5.1.1 of <xref target="RFC2046"/>,
606   and MUST include a boundary parameter as part of the media type
607   value. The message body is itself a protocol element and MUST
608   therefore use only CRLF to represent line breaks between body-parts.
609   Unlike in RFC 2046, the epilogue of any multipart message MUST be
610   empty; HTTP applications MUST NOT transmit the epilogue (even if the
611   original multipart contains an epilogue). These restrictions exist in
612   order to preserve the self-delimiting nature of a multipart message-body,
613   wherein the "end" of the message-body is indicated by the
614   ending multipart boundary.
615</t>
616<t>
617   In general, HTTP treats a multipart message-body no differently than
618   any other media type: strictly as payload. The one exception is the
619   "multipart/byteranges" type (Appendix A of <xref target="Part5"/>) when it appears in a 206
620   (Partial Content) response.
621   <!-- jre: re-insert removed text pointing to caching? -->
622   In all
623   other cases, an HTTP user agent SHOULD follow the same or similar
624   behavior as a MIME user agent would upon receipt of a multipart type.
625   The MIME header fields within each body-part of a multipart message-body
626   do not have any significance to HTTP beyond that defined by
627   their MIME semantics.
628</t>
629<t>
630   In general, an HTTP user agent SHOULD follow the same or similar
631   behavior as a MIME user agent would upon receipt of a multipart type.
632   If an application receives an unrecognized multipart subtype, the
633   application MUST treat it as being equivalent to "multipart/mixed".
634</t>
635<t><list>
636  <t>
637    Note: The "multipart/form-data" type has been specifically defined
638    for carrying form data suitable for processing via the POST
639    request method, as described in <xref target="RFC2388"/>.
640  </t>
641</list></t>
642</section>
643</section>
644
645<section title="Language Tags" anchor="language.tags">
646 
647<t>
648   A language tag, as defined in <xref target="RFC5646"/>, identifies a
649   natural language spoken, written, or otherwise conveyed by human beings for
650   communication of information to other human beings. Computer languages are
651   explicitly excluded. HTTP uses language tags within the Accept-Language and
652   Content-Language fields.
653</t>
654<t>
655   In summary, a language tag is composed of one or more parts: A primary
656   language subtag followed by a possibly empty series of subtags:
657</t>
658<figure><iref primary="true" item="Grammar" subitem="language-tag"/><artwork type="abnf2616"><![CDATA[
659  language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
660]]></artwork></figure>
661<t>
662   White space is not allowed within the tag and all tags are case-insensitive.
663   The name space of language subtags is administered by the IANA (see
664   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
665</t>
666<figure>
667  <preamble>Example tags include:</preamble>
668<artwork type="example"><![CDATA[
669  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
670]]></artwork>
671</figure>
672<t>
673   See <xref target="RFC5646"/> for further information.
674</t>
675</section>
676</section>
677
678<section title="Entity" anchor="entity">
679<t>
680   Request and Response messages MAY transfer an entity if not otherwise
681   restricted by the request method or response status code. An entity
682   consists of entity-header fields and an entity-body, although some
683   responses will only include the entity-headers.
684</t>
685<t>
686   In this section, both sender and recipient refer to either the client
687   or the server, depending on who sends and who receives the entity.
688</t>
689
690<section title="Entity Header Fields" anchor="entity.header.fields">
691 
692 
693<t>
694   Entity-header fields define metainformation about the entity-body or,
695   if no body is present, about the resource identified by the request.
696</t>
697<figure><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/><artwork type="abnf2616"><![CDATA[
698  entity-header  = Content-Encoding         ; Section 5.5
699                 / Content-Language         ; Section 5.6
700                 / Content-Length           ; [Part1], Section 9.2
701                 / Content-Location         ; Section 5.7
702                 / Content-MD5              ; Section 5.8
703                 / Content-Range            ; [Part5], Section 5.2
704                 / Content-Type             ; Section 5.9
705                 / Expires                  ; [Part6], Section 3.3
706                 / Last-Modified            ; [Part4], Section 6.6
707                 / extension-header
708 
709  extension-header = header-field
710]]></artwork></figure>
711<t>
712   The extension-header mechanism allows additional entity-header fields
713   to be defined without changing the protocol, but these fields cannot
714   be assumed to be recognizable by the recipient. Unrecognized header
715   fields SHOULD be ignored by the recipient and MUST be forwarded by
716   transparent proxies.
717</t>
718</section>
719
720<section title="Entity Body" anchor="entity.body">
721 
722<t>
723   The entity-body (if any) sent with an HTTP request or response is in
724   a format and encoding defined by the entity-header fields.
725</t>
726<figure><iref primary="true" item="Grammar" subitem="entity-body"/><artwork type="abnf2616"><![CDATA[
727  entity-body    = *OCTET
728]]></artwork></figure>
729<t>
730   An entity-body is only present in a message when a message-body is
731   present, as described in Section 3.3 of <xref target="Part1"/>. The entity-body is obtained
732   from the message-body by decoding any Transfer-Encoding that might
733   have been applied to ensure safe and proper transfer of the message.
734</t>
735
736<section title="Type" anchor="type">
737<t>
738   When an entity-body is included with a message, the data type of that
739   body is determined via the header fields Content-Type and Content-Encoding.
740   These define a two-layer, ordered encoding model:
741</t>
742<figure><artwork type="example"><![CDATA[
743  entity-body := Content-Encoding( Content-Type( data ) )
744]]></artwork></figure>
745<t>
746   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
747   message containing an entity-body SHOULD include a Content-Type header
748   field defining the media type of that body, unless that information is
749   unknown.  If the Content-Type header field is not present, it indicates that
750   the sender does not know the media type of the data; recipients MAY
751   either assume that it is "application/octet-stream" (<xref target="RFC2046"/>, Section 4.5.1)
752   or examine the content to determine its type.
753</t>
754<t>
755   Content-Encoding may be used to indicate any additional content
756   codings applied to the data, usually for the purpose of data
757   compression, that are a property of the requested resource.  There is
758   no default encoding.
759</t>
760</section>
761   
762<section title="Entity Length" anchor="entity.length">
763<t>
764   The entity-length of a message is the length of the message-body
765   before any transfer-codings have been applied. Section 3.4 of <xref target="Part1"/> defines
766   how the transfer-length of a message-body is determined.
767</t>
768</section>
769</section>
770</section>
771
772<section title="Content Negotiation" anchor="content.negotiation">
773<t>
774   HTTP responses include a representation which contains information for
775   interpretation, whether by a human user or for further processing.
776   Often, the server has different ways of representing the
777   same information; for example, in different formats, languages,
778   or using different character encodings.
779</t>
780<t>
781   HTTP clients and their users might have different or variable
782   capabilities, characteristics or preferences which would influence
783   which representation, among those available from the server,
784   would be best for the server to deliver. For this reason, HTTP
785   provides mechanisms for "content negotiation" -- a process of
786   allowing selection of a representation of a given resource,
787   when more than one is available.
788</t>
789<t>
790   This specification defines two patterns of content negotiation;
791   "server-driven", where the server selects the representation based
792   upon the client's stated preferences, and "agent-driven" negotiation,
793   where the server provides a list of representations for the client to
794   choose from, based upon their metadata. In addition,  there are
795   other patterns: some applications use an "active content" pattern,
796   where the server returns active content which runs on the client
797   and, based on client available parameters, selects additional
798   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
799   has also been proposed.
800</t>
801<t>
802   These patterns are all widely used, and have trade-offs in applicability
803   and practicality. In particular, when the number of preferences or
804   capabilities to be expressed by a client are large (such as when many
805   different formats are supported by a user-agent), server-driven
806   negotiation becomes unwieldy, and may not be appropriate. Conversely,
807   when the number of representations to choose from is very large,
808   agent-driven negotiation may not be appropriate.
809</t>
810<t>
811   Note that in all cases, the supplier of representations has the
812   responsibility for determining which representations might be
813   considered to be the "same information".
814</t>
815
816<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
817<t>
818   If the selection of the best representation for a response is made by
819   an algorithm located at the server, it is called server-driven
820   negotiation. Selection is based on the available representations of
821   the response (the dimensions over which it can vary; e.g., language,
822   content-coding, etc.) and the contents of particular header fields in
823   the request message or on other information pertaining to the request
824   (such as the network address of the client).
825</t>
826<t>
827   Server-driven negotiation is advantageous when the algorithm for
828   selecting from among the available representations is difficult to
829   describe to the user agent, or when the server desires to send its
830   "best guess" to the client along with the first response (hoping to
831   avoid the round-trip delay of a subsequent request if the "best
832   guess" is good enough for the user). In order to improve the server's
833   guess, the user agent MAY include request header fields (Accept,
834   Accept-Language, Accept-Encoding, etc.) which describe its
835   preferences for such a response.
836</t>
837<t>
838   Server-driven negotiation has disadvantages:
839  <list style="numbers">
840    <t>
841         It is impossible for the server to accurately determine what
842         might be "best" for any given user, since that would require
843         complete knowledge of both the capabilities of the user agent
844         and the intended use for the response (e.g., does the user want
845         to view it on screen or print it on paper?).
846    </t>
847    <t>
848         Having the user agent describe its capabilities in every
849         request can be both very inefficient (given that only a small
850         percentage of responses have multiple representations) and a
851         potential violation of the user's privacy.
852    </t>
853    <t>
854         It complicates the implementation of an origin server and the
855         algorithms for generating responses to a request.
856    </t>
857    <t>
858         It may limit a public cache's ability to use the same response
859         for multiple user's requests.
860    </t>
861  </list>
862</t>
863<t>
864   HTTP/1.1 includes the following request-header fields for enabling
865   server-driven negotiation through description of user agent
866   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
867   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
868   (<xref target="header.accept-language"/>), and User-Agent (Section 9.9 of <xref target="Part2"/>).
869   However, an origin server is not limited to these dimensions and MAY vary
870   the response based on any aspect of the request, including information
871   outside the request-header fields or within extension header fields
872   not defined by this specification.
873</t>
874<t><list>
875  <t>
876    Note: In practice, User-Agent based negotiation is fragile,
877    because new clients might not be recognized.
878  </t>
879</list></t>
880<t>
881   The Vary header field (Section 3.5 of <xref target="Part6"/>) can be used to express the parameters the
882   server uses to select a representation that is subject to server-driven
883   negotiation.
884</t>
885</section>
886
887<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
888<t>
889   With agent-driven negotiation, selection of the best representation
890   for a response is performed by the user agent after receiving an
891   initial response from the origin server. Selection is based on a list
892   of the available representations of the response included within the
893   header fields or entity-body of the initial response, with each
894   representation identified by its own URI. Selection from among the
895   representations may be performed automatically (if the user agent is
896   capable of doing so) or manually by the user selecting from a
897   generated (possibly hypertext) menu.
898</t>
899<t>
900   Agent-driven negotiation is advantageous when the response would vary
901   over commonly-used dimensions (such as type, language, or encoding),
902   when the origin server is unable to determine a user agent's
903   capabilities from examining the request, and generally when public
904   caches are used to distribute server load and reduce network usage.
905</t>
906<t>
907   Agent-driven negotiation suffers from the disadvantage of needing a
908   second request to obtain the best alternate representation. This
909   second request is only efficient when caching is used. In addition,
910   this specification does not define any mechanism for supporting
911   automatic selection, though it also does not prevent any such
912   mechanism from being developed as an extension and used within
913   HTTP/1.1.
914</t>
915<t>
916   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
917   status codes for enabling agent-driven negotiation when the server is
918   unwilling or unable to provide a varying response using server-driven
919   negotiation.
920</t>
921</section>
922</section>
923
924<section title="Header Field Definitions" anchor="header.fields">
925<t>
926   This section defines the syntax and semantics of HTTP/1.1 header fields
927   related to the payload of messages.
928</t>
929<t>
930   For entity-header fields, both sender and recipient refer to either the
931   client or the server, depending on who sends and who receives the entity.
932</t>
933
934<section title="Accept" anchor="header.accept">
935  <iref primary="true" item="Accept header"/>
936  <iref primary="true" item="Headers" subitem="Accept"/>
937 
938 
939 
940 
941 
942<t>
943   The "Accept" request-header field can be used by user agents to specify
944   response media types that are acceptable. Accept headers can be used to
945   indicate that the request is specifically limited to a small set of desired
946   types, as in the case of a request for an in-line image.
947</t>
948<figure><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"/><artwork type="abnf2616"><![CDATA[
949  Accept   = "Accept" ":" OWS Accept-v
950  Accept-v = #( media-range [ accept-params ] )
951 
952  media-range    = ( "*/*"
953                   / ( type "/" "*" )
954                   / ( type "/" subtype )
955                   ) *( OWS ";" OWS parameter )
956  accept-params  = OWS ";" OWS "q=" qvalue *( accept-ext )
957  accept-ext     = OWS ";" OWS token
958                   [ "=" ( token / quoted-string ) ]
959]]></artwork></figure>
960<t>
961   The asterisk "*" character is used to group media types into ranges,
962   with "*/*" indicating all media types and "type/*" indicating all
963   subtypes of that type. The media-range MAY include media type
964   parameters that are applicable to that range.
965</t>
966<t>
967   Each media-range MAY be followed by one or more accept-params,
968   beginning with the "q" parameter for indicating a relative quality
969   factor. The first "q" parameter (if any) separates the media-range
970   parameter(s) from the accept-params. Quality factors allow the user
971   or user agent to indicate the relative degree of preference for that
972   media-range, using the qvalue scale from 0 to 1 (Section 6.4 of <xref target="Part1"/>). The
973   default value is q=1.
974</t>
975<t><list>
976  <t>
977    Note: Use of the "q" parameter name to separate media type
978    parameters from Accept extension parameters is due to historical
979    practice. Although this prevents any media type parameter named
980    "q" from being used with a media range, such an event is believed
981    to be unlikely given the lack of any "q" parameters in the IANA
982    media type registry and the rare usage of any media type
983    parameters in Accept. Future media types are discouraged from
984    registering any parameter named "q".
985  </t>
986</list></t>
987<t>
988   The example
989</t>
990<figure><artwork type="example"><![CDATA[
991  Accept: audio/*; q=0.2, audio/basic
992]]></artwork></figure>
993<t>
994   SHOULD be interpreted as "I prefer audio/basic, but send me any audio
995   type if it is the best available after an 80% mark-down in quality."
996</t>
997<t>
998   If no Accept header field is present, then it is assumed that the
999   client accepts all media types. If an Accept header field is present,
1000   and if the server cannot send a response which is acceptable
1001   according to the combined Accept field value, then the server SHOULD
1002   send a 406 (Not Acceptable) response.
1003</t>
1004<t>
1005   A more elaborate example is
1006</t>
1007<figure><artwork type="example"><![CDATA[
1008  Accept: text/plain; q=0.5, text/html,
1009          text/x-dvi; q=0.8, text/x-c
1010]]></artwork></figure>
1011<t>
1012   Verbally, this would be interpreted as "text/html and text/x-c are
1013   the preferred media types, but if they do not exist, then send the
1014   text/x-dvi entity, and if that does not exist, send the text/plain
1015   entity."
1016</t>
1017<t>
1018   Media ranges can be overridden by more specific media ranges or
1019   specific media types. If more than one media range applies to a given
1020   type, the most specific reference has precedence. For example,
1021</t>
1022<figure><artwork type="example"><![CDATA[
1023  Accept: text/*, text/html, text/html;level=1, */*
1024]]></artwork></figure>
1025<t>
1026   have the following precedence:
1027   <list style="numbers">
1028    <t>text/html;level=1</t>
1029    <t>text/html</t>
1030    <t>text/*</t>
1031    <t>*/*</t>
1032   </list>
1033</t>
1034<t>
1035   The media type quality factor associated with a given type is
1036   determined by finding the media range with the highest precedence
1037   which matches that type. For example,
1038</t>
1039<figure><artwork type="example"><![CDATA[
1040  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1041          text/html;level=2;q=0.4, */*;q=0.5
1042]]></artwork></figure>
1043<t>
1044   would cause the following values to be associated:
1045</t>
1046<texttable align="left">
1047  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1048  <c>text/html;level=1</c>    <c>1</c>
1049  <c>text/html</c>            <c>0.7</c>
1050  <c>text/plain</c>           <c>0.3</c>
1051  <c>image/jpeg</c>           <c>0.5</c>
1052  <c>text/html;level=2</c>    <c>0.4</c>
1053  <c>text/html;level=3</c>    <c>0.7</c>
1054</texttable>
1055<t>
1056      Note: A user agent might be provided with a default set of quality
1057      values for certain media ranges. However, unless the user agent is
1058      a closed system which cannot interact with other rendering agents,
1059      this default set ought to be configurable by the user.
1060</t>
1061</section>
1062
1063<section title="Accept-Charset" anchor="header.accept-charset">
1064  <iref primary="true" item="Accept-Charset header"/>
1065  <iref primary="true" item="Headers" subitem="Accept-Charset"/>
1066 
1067 
1068<t>
1069   The "Accept-Charset" request-header field can be used by user agents to
1070   indicate what response character sets are acceptable. This field allows
1071   clients capable of understanding more comprehensive or special-purpose
1072   character sets to signal that capability to a server which is capable of
1073   representing documents in those character sets.
1074</t>
1075<figure><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/><artwork type="abnf2616"><![CDATA[
1076  Accept-Charset   = "Accept-Charset" ":" OWS
1077          Accept-Charset-v
1078  Accept-Charset-v = 1#( ( charset / "*" )
1079                         [ OWS ";" OWS "q=" qvalue ] )
1080]]></artwork></figure>
1081<t>
1082   Character set values are described in <xref target="character.sets"/>. Each charset MAY
1083   be given an associated quality value which represents the user's
1084   preference for that charset. The default value is q=1. An example is
1085</t>
1086<figure><artwork type="example"><![CDATA[
1087  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1088]]></artwork></figure>
1089<t>
1090   The special value "*", if present in the Accept-Charset field,
1091   matches every character set (including ISO-8859-1) which is not
1092   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1093   in an Accept-Charset field, then all character sets not explicitly
1094   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1095   a quality value of 1 if not explicitly mentioned.
1096</t>
1097<t>
1098   If no Accept-Charset header is present, the default is that any
1099   character set is acceptable. If an Accept-Charset header is present,
1100   and if the server cannot send a response which is acceptable
1101   according to the Accept-Charset header, then the server SHOULD send
1102   an error response with the 406 (Not Acceptable) status code, though
1103   the sending of an unacceptable response is also allowed.
1104</t>
1105</section>
1106
1107<section title="Accept-Encoding" anchor="header.accept-encoding">
1108  <iref primary="true" item="Accept-Encoding header"/>
1109  <iref primary="true" item="Headers" subitem="Accept-Encoding"/>
1110 
1111 
1112 
1113<t>
1114   The "Accept-Encoding" request-header field can be used by user agents to
1115   indicate what response content-codings (<xref target="content.codings"/>)
1116   are acceptable in the response.
1117</t>
1118<figure><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/><artwork type="abnf2616"><![CDATA[
1119  Accept-Encoding    = "Accept-Encoding" ":" OWS
1120                     Accept-Encoding-v
1121  Accept-Encoding-v  =
1122                     #( codings [ OWS ";" OWS "q=" qvalue ] )
1123  codings            = ( content-coding / "*" )
1124]]></artwork></figure>
1125<t>
1126   Each codings value MAY be given an associated quality value which
1127   represents the preference for that encoding. The default value is q=1.
1128</t>
1129<t>
1130   Examples of its use are:
1131</t>
1132<figure><artwork type="example"><![CDATA[
1133  Accept-Encoding: compress, gzip
1134  Accept-Encoding:
1135  Accept-Encoding: *
1136  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1137  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1138]]></artwork></figure>
1139<t>
1140   A server tests whether a content-coding is acceptable, according to
1141   an Accept-Encoding field, using these rules:
1142  <list style="numbers">
1143      <t>If the content-coding is one of the content-codings listed in
1144         the Accept-Encoding field, then it is acceptable, unless it is
1145         accompanied by a qvalue of 0. (As defined in Section 6.4 of <xref target="Part1"/>, a
1146         qvalue of 0 means "not acceptable.")</t>
1147
1148      <t>The special "*" symbol in an Accept-Encoding field matches any
1149         available content-coding not explicitly listed in the header
1150         field.</t>
1151
1152      <t>If multiple content-codings are acceptable, then the acceptable
1153         content-coding with the highest non-zero qvalue is preferred.</t>
1154
1155      <t>The "identity" content-coding is always acceptable, unless
1156         specifically refused because the Accept-Encoding field includes
1157         "identity;q=0", or because the field includes "*;q=0" and does
1158         not explicitly include the "identity" content-coding. If the
1159         Accept-Encoding field-value is empty, then only the "identity"
1160         encoding is acceptable.</t>
1161  </list>
1162</t>
1163<t>
1164   If an Accept-Encoding field is present in a request, and if the
1165   server cannot send a response which is acceptable according to the
1166   Accept-Encoding header, then the server SHOULD send an error response
1167   with the 406 (Not Acceptable) status code.
1168</t>
1169<t>
1170   If no Accept-Encoding field is present in a request, the server MAY
1171   assume that the client will accept any content coding. In this case,
1172   if "identity" is one of the available content-codings, then the
1173   server SHOULD use the "identity" content-coding, unless it has
1174   additional information that a different content-coding is meaningful
1175   to the client.
1176</t>
1177<t><list>
1178  <t>
1179    Note: If the request does not include an Accept-Encoding field,
1180    and if the "identity" content-coding is unavailable, then
1181    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1182    "gzip" and "compress") are preferred; some older clients
1183    improperly display messages sent with other content-codings.  The
1184    server might also make this decision based on information about
1185    the particular user-agent or client.
1186  </t>
1187</list></t>
1188<t><list>
1189  <t>
1190    Note: Most HTTP/1.0 applications do not recognize or obey qvalues
1191    associated with content-codings. This means that qvalues will not
1192    work and are not permitted with x-gzip or x-compress.
1193  </t>
1194</list></t>
1195</section>
1196
1197<section title="Accept-Language" anchor="header.accept-language">
1198  <iref primary="true" item="Accept-Language header"/>
1199  <iref primary="true" item="Headers" subitem="Accept-Language"/>
1200 
1201 
1202 
1203<t>
1204   The "Accept-Language" request-header field can be used by user agents to
1205   indicate the set of natural languages that are preferred in the response.
1206   Language tags are defined in <xref target="language.tags"/>.
1207</t>
1208<figure><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"/><artwork type="abnf2616"><![CDATA[
1209  Accept-Language   = "Accept-Language" ":" OWS
1210                    Accept-Language-v
1211  Accept-Language-v =
1212                    1#( language-range [ OWS ";" OWS "q=" qvalue ] )
1213  language-range    =
1214            <language-range, defined in [RFC4647], Section 2.1>
1215]]></artwork></figure>
1216<t>
1217   Each language-range can be given an associated quality value which
1218   represents an estimate of the user's preference for the languages
1219   specified by that range. The quality value defaults to "q=1". For
1220   example,
1221</t>
1222<figure><artwork type="example"><![CDATA[
1223  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1224]]></artwork></figure>
1225<t>
1226   would mean: "I prefer Danish, but will accept British English and
1227   other types of English."
1228   (see also Section 2.3 of <xref target="RFC4647"/>)
1229</t>
1230<t>
1231   For matching, Section 3 of <xref target="RFC4647"/> defines
1232   several matching schemes. Implementations can offer the most appropriate
1233   matching scheme for their requirements.
1234</t>
1235<t><list>
1236  <t>
1237    Note: The "Basic Filtering" scheme (<xref target="RFC4647"/>, Section 3.3.1) is identical to the matching scheme that was
1238    previously defined in Section 14.4 of <xref target="RFC2616"/>.
1239  </t>
1240</list></t>
1241<t>
1242   It might be contrary to the privacy expectations of the user to send
1243   an Accept-Language header with the complete linguistic preferences of
1244   the user in every request. For a discussion of this issue, see
1245   <xref target="privacy.issues.connected.to.accept.headers"/>.
1246</t>
1247<t>
1248   As intelligibility is highly dependent on the individual user, it is
1249   recommended that client applications make the choice of linguistic
1250   preference available to the user. If the choice is not made
1251   available, then the Accept-Language header field MUST NOT be given in
1252   the request.
1253</t>
1254<t><list>
1255  <t>
1256    Note: When making the choice of linguistic preference available to
1257    the user, we remind implementors of  the fact that users are not
1258    familiar with the details of language matching as described above,
1259    and should provide appropriate guidance. As an example, users
1260    might assume that on selecting "en-gb", they will be served any
1261    kind of English document if British English is not available. A
1262    user agent might suggest in such a case to add "en" to get the
1263    best matching behavior.
1264  </t>
1265</list></t>
1266</section>
1267
1268<section title="Content-Encoding" anchor="header.content-encoding">
1269  <iref primary="true" item="Content-Encoding header"/>
1270  <iref primary="true" item="Headers" subitem="Content-Encoding"/>
1271 
1272 
1273<t>
1274   The "Content-Encoding" entity-header field indicates what content-codings
1275   have been applied to the entity-body, and thus what decoding mechanisms
1276   must be applied in order to obtain the media-type referenced by the
1277   Content-Type header field. Content-Encoding is primarily used to allow a
1278   document to be compressed without losing the identity of its underlying
1279   media type.
1280</t>
1281<figure><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/><artwork type="abnf2616"><![CDATA[
1282  Content-Encoding   = "Content-Encoding" ":" OWS Content-Encoding-v
1283  Content-Encoding-v = 1#content-coding
1284]]></artwork></figure>
1285<t>
1286   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1287</t>
1288<figure><artwork type="example"><![CDATA[
1289  Content-Encoding: gzip
1290]]></artwork></figure>
1291<t>
1292   The content-coding is a characteristic of the entity identified by
1293   the request-target. Typically, the entity-body is stored with this
1294   encoding and is only decoded before rendering or analogous usage.
1295   However, a non-transparent proxy MAY modify the content-coding if the
1296   new coding is known to be acceptable to the recipient, unless the
1297   "no-transform" cache-control directive is present in the message.
1298</t>
1299<t>
1300   If the content-coding of an entity is not "identity", then the
1301   response MUST include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1302   that lists the non-identity content-coding(s) used.
1303</t>
1304<t>
1305   If the content-coding of an entity in a request message is not
1306   acceptable to the origin server, the server SHOULD respond with a
1307   status code of 415 (Unsupported Media Type).
1308</t>
1309<t>
1310   If multiple encodings have been applied to an entity, the content
1311   codings MUST be listed in the order in which they were applied.
1312   Additional information about the encoding parameters MAY be provided
1313   by other entity-header fields not defined by this specification.
1314</t>
1315</section>
1316
1317<section title="Content-Language" anchor="header.content-language">
1318  <iref primary="true" item="Content-Language header"/>
1319  <iref primary="true" item="Headers" subitem="Content-Language"/>
1320 
1321 
1322<t>
1323   The "Content-Language" entity-header field describes the natural
1324   language(s) of the intended audience for the entity. Note that this might
1325   not be equivalent to all the languages used within the entity-body.
1326</t>
1327<figure><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/><artwork type="abnf2616"><![CDATA[
1328  Content-Language   = "Content-Language" ":" OWS Content-Language-v
1329  Content-Language-v = 1#language-tag
1330]]></artwork></figure>
1331<t>
1332   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1333   Content-Language is to allow a user to identify and differentiate
1334   entities according to the user's own preferred language. Thus, if the
1335   body content is intended only for a Danish-literate audience, the
1336   appropriate field is
1337</t>
1338<figure><artwork type="example"><![CDATA[
1339  Content-Language: da
1340]]></artwork></figure>
1341<t>
1342   If no Content-Language is specified, the default is that the content
1343   is intended for all language audiences. This might mean that the
1344   sender does not consider it to be specific to any natural language,
1345   or that the sender does not know for which language it is intended.
1346</t>
1347<t>
1348   Multiple languages MAY be listed for content that is intended for
1349   multiple audiences. For example, a rendition of the "Treaty of
1350   Waitangi," presented simultaneously in the original Maori and English
1351   versions, would call for
1352</t>
1353<figure><artwork type="example"><![CDATA[
1354  Content-Language: mi, en
1355]]></artwork></figure>
1356<t>
1357   However, just because multiple languages are present within an entity
1358   does not mean that it is intended for multiple linguistic audiences.
1359   An example would be a beginner's language primer, such as "A First
1360   Lesson in Latin," which is clearly intended to be used by an
1361   English-literate audience. In this case, the Content-Language would
1362   properly only include "en".
1363</t>
1364<t>
1365   Content-Language MAY be applied to any media type -- it is not
1366   limited to textual documents.
1367</t>
1368</section>
1369
1370<section title="Content-Location" anchor="header.content-location">
1371  <iref primary="true" item="Content-Location header"/>
1372  <iref primary="true" item="Headers" subitem="Content-Location"/>
1373 
1374 
1375<t>
1376   The "Content-Location" entity-header field is used to supply a URI for the
1377   entity in the message when it is accessible from a location separate from
1378   the requested resource's URI.
1379</t>
1380<t>
1381   A server SHOULD provide a Content-Location for the variant corresponding
1382   to the response entity, especially in the case where a resource has multiple
1383   entities associated with it, and those entities actually have separate
1384   locations by which they might be individually accessed, the server SHOULD
1385   provide a Content-Location for the particular variant which is returned.
1386</t>
1387<figure><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/><artwork type="abnf2616"><![CDATA[
1388  Content-Location   = "Content-Location" ":" OWS
1389                    Content-Location-v
1390  Content-Location-v =
1391                    absolute-URI / partial-URI
1392]]></artwork></figure>
1393<t>
1394   The Content-Location value is not a replacement for the original
1395   requested URI; it is only a statement of the location of the resource
1396   corresponding to this particular entity at the time of the request.
1397   Future requests MAY specify the Content-Location URI as the request-target
1398   if the desire is to identify the source of that particular
1399   entity.
1400</t>
1401<t>
1402   Section 6.1 of <xref target="Part2"/> describes how clients may process the Content-Location header field.
1403</t>
1404<t>
1405   A cache cannot assume that an entity with a Content-Location
1406   different from the URI used to retrieve it can be used to respond to
1407   later requests on that Content-Location URI. However, the Content-Location
1408   can be used to differentiate between multiple entities
1409   retrieved from a single requested resource, as described in Section 2.6 of <xref target="Part6"/>.
1410</t>
1411<t>
1412   If the Content-Location is a relative URI, the relative URI is
1413   interpreted relative to the request-target.
1414</t>
1415<t>
1416   The meaning of the Content-Location header in requests is
1417   undefined; servers are free to ignore it in those cases.
1418</t>
1419</section>
1420
1421<section title="Content-MD5" anchor="header.content-md5">
1422  <iref primary="true" item="Content-MD5 header"/>
1423  <iref primary="true" item="Headers" subitem="Content-MD5"/>
1424 
1425 
1426<t>
1427   The "Content-MD5" entity-header field, as defined in <xref target="RFC1864"/>, is
1428   an MD5 digest of the entity-body that provides an end-to-end message
1429   integrity check (MIC) of the entity-body. Note that a MIC is good for
1430   detecting accidental modification of the entity-body in transit, but is not
1431   proof against malicious attacks.
1432</t>
1433<figure><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/><artwork type="abnf2616"><![CDATA[
1434  Content-MD5   = "Content-MD5" ":" OWS Content-MD5-v
1435  Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]>
1436]]></artwork></figure>
1437<t>
1438   The Content-MD5 header field MAY be generated by an origin server or
1439   client to function as an integrity check of the entity-body. Only
1440   origin servers or clients MAY generate the Content-MD5 header field;
1441   proxies and gateways MUST NOT generate it, as this would defeat its
1442   value as an end-to-end integrity check. Any recipient of the entity-body,
1443   including gateways and proxies, MAY check that the digest value
1444   in this header field matches that of the entity-body as received.
1445</t>
1446<t>
1447   The MD5 digest is computed based on the content of the entity-body,
1448   including any content-coding that has been applied, but not including
1449   any transfer-encoding applied to the message-body. If the message is
1450   received with a transfer-encoding, that encoding MUST be removed
1451   prior to checking the Content-MD5 value against the received entity.
1452</t>
1453<t>
1454   This has the result that the digest is computed on the octets of the
1455   entity-body exactly as, and in the order that, they would be sent if
1456   no transfer-encoding were being applied.
1457</t>
1458<t>
1459   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1460   composite media-types (e.g., multipart/* and message/rfc822), but
1461   this does not change how the digest is computed as defined in the
1462   preceding paragraph.
1463</t>
1464<t>
1465   There are several consequences of this. The entity-body for composite
1466   types MAY contain many body-parts, each with its own MIME and HTTP
1467   headers (including Content-MD5, Content-Transfer-Encoding, and
1468   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1469   or Content-Encoding header, it is assumed that the content
1470   of the body-part has had the encoding applied, and the body-part is
1471   included in the Content-MD5 digest as is -- i.e., after the
1472   application. The Transfer-Encoding header field is not allowed within
1473   body-parts.
1474</t>
1475<t>
1476   Conversion of all line breaks to CRLF MUST NOT be done before
1477   computing or checking the digest: the line break convention used in
1478   the text actually transmitted MUST be left unaltered when computing
1479   the digest.
1480</t>
1481<t><list>
1482  <t>
1483    Note: While the definition of Content-MD5 is exactly the same for
1484    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1485    in which the application of Content-MD5 to HTTP entity-bodies
1486    differs from its application to MIME entity-bodies. One is that
1487    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1488    does use Transfer-Encoding and Content-Encoding. Another is that
1489    HTTP more frequently uses binary content types than MIME, so it is
1490    worth noting that, in such cases, the byte order used to compute
1491    the digest is the transmission byte order defined for the type.
1492    Lastly, HTTP allows transmission of text types with any of several
1493    line break conventions and not just the canonical form using CRLF.
1494  </t>
1495</list></t>
1496</section>
1497
1498<section title="Content-Type" anchor="header.content-type">
1499  <iref primary="true" item="Content-Type header"/>
1500  <iref primary="true" item="Headers" subitem="Content-Type"/>
1501 
1502 
1503<t>
1504   The "Content-Type" entity-header field indicates the media type of the
1505   entity-body. In the case of responses to the HEAD method, the media type is
1506   that which would have been sent had the request been a GET.
1507</t>
1508<figure><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/><artwork type="abnf2616"><![CDATA[
1509  Content-Type   = "Content-Type" ":" OWS Content-Type-v
1510  Content-Type-v = media-type
1511]]></artwork></figure>
1512<t>
1513   Media types are defined in <xref target="media.types"/>. An example of the field is
1514</t>
1515<figure><artwork type="example"><![CDATA[
1516  Content-Type: text/html; charset=ISO-8859-4
1517]]></artwork></figure>
1518<t>
1519   Further discussion of methods for identifying the media type of an
1520   entity is provided in <xref target="type"/>.
1521</t>
1522</section>
1523
1524</section>
1525
1526<section title="IANA Considerations" anchor="IANA.considerations">
1527<section title="Message Header Registration" anchor="message.header.registration">
1528<t>
1529   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1530   with the permanent registrations below (see <xref target="RFC3864"/>):
1531</t>
1532
1533<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1534<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1535   <ttcol>Header Field Name</ttcol>
1536   <ttcol>Protocol</ttcol>
1537   <ttcol>Status</ttcol>
1538   <ttcol>Reference</ttcol>
1539
1540   <c>Accept</c>
1541   <c>http</c>
1542   <c>standard</c>
1543   <c>
1544      <xref target="header.accept"/>
1545   </c>
1546   <c>Accept-Charset</c>
1547   <c>http</c>
1548   <c>standard</c>
1549   <c>
1550      <xref target="header.accept-charset"/>
1551   </c>
1552   <c>Accept-Encoding</c>
1553   <c>http</c>
1554   <c>standard</c>
1555   <c>
1556      <xref target="header.accept-encoding"/>
1557   </c>
1558   <c>Accept-Language</c>
1559   <c>http</c>
1560   <c>standard</c>
1561   <c>
1562      <xref target="header.accept-language"/>
1563   </c>
1564   <c>Content-Disposition</c>
1565   <c>http</c>
1566   <c/>
1567   <c>
1568      <xref target="content-disposition"/>
1569   </c>
1570   <c>Content-Encoding</c>
1571   <c>http</c>
1572   <c>standard</c>
1573   <c>
1574      <xref target="header.content-encoding"/>
1575   </c>
1576   <c>Content-Language</c>
1577   <c>http</c>
1578   <c>standard</c>
1579   <c>
1580      <xref target="header.content-language"/>
1581   </c>
1582   <c>Content-Location</c>
1583   <c>http</c>
1584   <c>standard</c>
1585   <c>
1586      <xref target="header.content-location"/>
1587   </c>
1588   <c>Content-MD5</c>
1589   <c>http</c>
1590   <c>standard</c>
1591   <c>
1592      <xref target="header.content-md5"/>
1593   </c>
1594   <c>Content-Type</c>
1595   <c>http</c>
1596   <c>standard</c>
1597   <c>
1598      <xref target="header.content-type"/>
1599   </c>
1600   <c>MIME-Version</c>
1601   <c>http</c>
1602   <c/>
1603   <c>
1604      <xref target="mime-version"/>
1605   </c>
1606</texttable>
1607<!--(END)-->
1608
1609<t>
1610   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1611</t>
1612</section>
1613
1614<section title="Content Coding Registry" anchor="content.coding.registration">
1615<t>
1616   The registration procedure for HTTP Content Codings is now defined
1617   by <xref target="content.coding.registry"/> of this document.
1618</t>
1619<t>
1620   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1621   should be updated with the registration below:
1622</t>
1623<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1624   <ttcol>Name</ttcol>
1625   <ttcol>Description</ttcol>
1626   <ttcol>Reference</ttcol>
1627   <c>compress</c>
1628   <c>UNIX "compress" program method</c>
1629   <c>
1630      Section 6.2.2.1 of <xref target="Part1"/>
1631   </c>
1632   <c>deflate</c>
1633   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
1634   <c>
1635      Section 6.2.2.2 of <xref target="Part1"/>
1636   </c>
1637   <c>gzip</c>
1638   <c>Same as GNU zip <xref target="RFC1952"/></c>
1639   <c>
1640      Section 6.2.2.3 of <xref target="Part1"/>
1641   </c>
1642   <c>identity</c>
1643   <c>No transformation</c>
1644   <c>
1645      <xref target="content.codings"/>
1646   </c>
1647</texttable>
1648</section>
1649
1650</section>
1651
1652<section title="Security Considerations" anchor="security.considerations">
1653<t>
1654   This section is meant to inform application developers, information
1655   providers, and users of the security limitations in HTTP/1.1 as
1656   described by this document. The discussion does not include
1657   definitive solutions to the problems revealed, though it does make
1658   some suggestions for reducing security risks.
1659</t>
1660
1661<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1662<t>
1663   Accept request-headers can reveal information about the user to all
1664   servers which are accessed. The Accept-Language header in particular
1665   can reveal information the user would consider to be of a private
1666   nature, because the understanding of particular languages is often
1667   strongly correlated to the membership of a particular ethnic group.
1668   User agents which offer the option to configure the contents of an
1669   Accept-Language header to be sent in every request are strongly
1670   encouraged to let the configuration process include a message which
1671   makes the user aware of the loss of privacy involved.
1672</t>
1673<t>
1674   An approach that limits the loss of privacy would be for a user agent
1675   to omit the sending of Accept-Language headers by default, and to ask
1676   the user whether or not to start sending Accept-Language headers to a
1677   server if it detects, by looking for any Vary response-header fields
1678   generated by the server, that such sending could improve the quality
1679   of service.
1680</t>
1681<t>
1682   Elaborate user-customized accept header fields sent in every request,
1683   in particular if these include quality values, can be used by servers
1684   as relatively reliable and long-lived user identifiers. Such user
1685   identifiers would allow content providers to do click-trail tracking,
1686   and would allow collaborating content providers to match cross-server
1687   click-trails or form submissions of individual users. Note that for
1688   many users not behind a proxy, the network address of the host
1689   running the user agent will also serve as a long-lived user
1690   identifier. In environments where proxies are used to enhance
1691   privacy, user agents ought to be conservative in offering accept
1692   header configuration options to end users. As an extreme privacy
1693   measure, proxies could filter the accept headers in relayed requests.
1694   General purpose user agents which provide a high degree of header
1695   configurability SHOULD warn users about the loss of privacy which can
1696   be involved.
1697</t>
1698</section>
1699
1700<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1701<t>
1702   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1703   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1704   serious security considerations. Content-Disposition is not part of
1705   the HTTP standard, but since it is widely implemented, we are
1706   documenting its use and risks for implementors. See Section 5 of <xref target="RFC2183"/>
1707   for details.
1708</t>
1709</section>
1710
1711</section>
1712
1713<section title="Acknowledgments" anchor="ack">
1714</section>
1715</middle>
1716<back>
1717
1718<references title="Normative References">
1719
1720<reference anchor="ISO-8859-1">
1721  <front>
1722    <title>
1723     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1724    </title>
1725    <author>
1726      <organization>International Organization for Standardization</organization>
1727    </author>
1728    <date year="1998"/>
1729  </front>
1730  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1731</reference>
1732
1733<reference anchor="Part1">
1734  <front>
1735    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1736    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1737      <organization abbrev="Day Software">Day Software</organization>
1738      <address><email>fielding@gbiv.com</email></address>
1739    </author>
1740    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1741      <organization>One Laptop per Child</organization>
1742      <address><email>jg@laptop.org</email></address>
1743    </author>
1744    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1745      <organization abbrev="HP">Hewlett-Packard Company</organization>
1746      <address><email>JeffMogul@acm.org</email></address>
1747    </author>
1748    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1749      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1750      <address><email>henrikn@microsoft.com</email></address>
1751    </author>
1752    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1753      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1754      <address><email>LMM@acm.org</email></address>
1755    </author>
1756    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1757      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1758      <address><email>paulle@microsoft.com</email></address>
1759    </author>
1760    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1761      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1762      <address><email>timbl@w3.org</email></address>
1763    </author>
1764    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1765      <organization abbrev="W3C">World Wide Web Consortium</organization>
1766      <address><email>ylafon@w3.org</email></address>
1767    </author>
1768    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1769      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1770      <address><email>julian.reschke@greenbytes.de</email></address>
1771    </author>
1772    <date month="March" year="2010"/>
1773  </front>
1774  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-09"/>
1775 
1776</reference>
1777
1778<reference anchor="Part2">
1779  <front>
1780    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1781    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1782      <organization abbrev="Day Software">Day Software</organization>
1783      <address><email>fielding@gbiv.com</email></address>
1784    </author>
1785    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1786      <organization>One Laptop per Child</organization>
1787      <address><email>jg@laptop.org</email></address>
1788    </author>
1789    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1790      <organization abbrev="HP">Hewlett-Packard Company</organization>
1791      <address><email>JeffMogul@acm.org</email></address>
1792    </author>
1793    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1794      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1795      <address><email>henrikn@microsoft.com</email></address>
1796    </author>
1797    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1798      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1799      <address><email>LMM@acm.org</email></address>
1800    </author>
1801    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1802      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1803      <address><email>paulle@microsoft.com</email></address>
1804    </author>
1805    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1806      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1807      <address><email>timbl@w3.org</email></address>
1808    </author>
1809    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1810      <organization abbrev="W3C">World Wide Web Consortium</organization>
1811      <address><email>ylafon@w3.org</email></address>
1812    </author>
1813    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1814      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1815      <address><email>julian.reschke@greenbytes.de</email></address>
1816    </author>
1817    <date month="March" year="2010"/>
1818  </front>
1819  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-09"/>
1820 
1821</reference>
1822
1823<reference anchor="Part4">
1824  <front>
1825    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1826    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1827      <organization abbrev="Day Software">Day Software</organization>
1828      <address><email>fielding@gbiv.com</email></address>
1829    </author>
1830    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1831      <organization>One Laptop per Child</organization>
1832      <address><email>jg@laptop.org</email></address>
1833    </author>
1834    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1835      <organization abbrev="HP">Hewlett-Packard Company</organization>
1836      <address><email>JeffMogul@acm.org</email></address>
1837    </author>
1838    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1839      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1840      <address><email>henrikn@microsoft.com</email></address>
1841    </author>
1842    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1843      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1844      <address><email>LMM@acm.org</email></address>
1845    </author>
1846    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1847      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1848      <address><email>paulle@microsoft.com</email></address>
1849    </author>
1850    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1851      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1852      <address><email>timbl@w3.org</email></address>
1853    </author>
1854    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1855      <organization abbrev="W3C">World Wide Web Consortium</organization>
1856      <address><email>ylafon@w3.org</email></address>
1857    </author>
1858    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1859      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1860      <address><email>julian.reschke@greenbytes.de</email></address>
1861    </author>
1862    <date month="March" year="2010"/>
1863  </front>
1864  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-09"/>
1865 
1866</reference>
1867
1868<reference anchor="Part5">
1869  <front>
1870    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1871    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1872      <organization abbrev="Day Software">Day Software</organization>
1873      <address><email>fielding@gbiv.com</email></address>
1874    </author>
1875    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1876      <organization>One Laptop per Child</organization>
1877      <address><email>jg@laptop.org</email></address>
1878    </author>
1879    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1880      <organization abbrev="HP">Hewlett-Packard Company</organization>
1881      <address><email>JeffMogul@acm.org</email></address>
1882    </author>
1883    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1884      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1885      <address><email>henrikn@microsoft.com</email></address>
1886    </author>
1887    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1888      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1889      <address><email>LMM@acm.org</email></address>
1890    </author>
1891    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1892      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1893      <address><email>paulle@microsoft.com</email></address>
1894    </author>
1895    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1896      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1897      <address><email>timbl@w3.org</email></address>
1898    </author>
1899    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1900      <organization abbrev="W3C">World Wide Web Consortium</organization>
1901      <address><email>ylafon@w3.org</email></address>
1902    </author>
1903    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1904      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1905      <address><email>julian.reschke@greenbytes.de</email></address>
1906    </author>
1907    <date month="March" year="2010"/>
1908  </front>
1909  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-09"/>
1910 
1911</reference>
1912
1913<reference anchor="Part6">
1914  <front>
1915    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1916    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1917      <organization abbrev="Day Software">Day Software</organization>
1918      <address><email>fielding@gbiv.com</email></address>
1919    </author>
1920    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1921      <organization>One Laptop per Child</organization>
1922      <address><email>jg@laptop.org</email></address>
1923    </author>
1924    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1925      <organization abbrev="HP">Hewlett-Packard Company</organization>
1926      <address><email>JeffMogul@acm.org</email></address>
1927    </author>
1928    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1929      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1930      <address><email>henrikn@microsoft.com</email></address>
1931    </author>
1932    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1933      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1934      <address><email>LMM@acm.org</email></address>
1935    </author>
1936    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1937      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1938      <address><email>paulle@microsoft.com</email></address>
1939    </author>
1940    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1941      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1942      <address><email>timbl@w3.org</email></address>
1943    </author>
1944    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1945      <organization abbrev="W3C">World Wide Web Consortium</organization>
1946      <address><email>ylafon@w3.org</email></address>
1947    </author>
1948    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1949      <address><email>mnot@mnot.net</email></address>
1950    </author>
1951    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1952      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1953      <address><email>julian.reschke@greenbytes.de</email></address>
1954    </author>
1955    <date month="March" year="2010"/>
1956  </front>
1957  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-09"/>
1958 
1959</reference>
1960
1961<reference anchor="RFC1864">
1962  <front>
1963    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1964    <author initials="J." surname="Myers" fullname="John G. Myers">
1965      <organization>Carnegie Mellon University</organization>
1966      <address><email>jgm+@cmu.edu</email></address>
1967    </author>
1968    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1969      <organization>Dover Beach Consulting, Inc.</organization>
1970      <address><email>mrose@dbc.mtview.ca.us</email></address>
1971    </author>
1972    <date month="October" year="1995"/>
1973  </front>
1974  <seriesInfo name="RFC" value="1864"/>
1975</reference>
1976
1977<reference anchor="RFC1950">
1978  <front>
1979    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1980    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1981      <organization>Aladdin Enterprises</organization>
1982      <address><email>ghost@aladdin.com</email></address>
1983    </author>
1984    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1985    <date month="May" year="1996"/>
1986  </front>
1987  <seriesInfo name="RFC" value="1950"/>
1988  <annotation>
1989    RFC 1950 is an Informational RFC, thus it may be less stable than
1990    this specification. On the other hand, this downward reference was
1991    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1992    therefore it is unlikely to cause problems in practice. See also
1993    <xref target="BCP97"/>.
1994  </annotation>
1995</reference>
1996
1997<reference anchor="RFC1952">
1998  <front>
1999    <title>GZIP file format specification version 4.3</title>
2000    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2001      <organization>Aladdin Enterprises</organization>
2002      <address><email>ghost@aladdin.com</email></address>
2003    </author>
2004    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2005      <address><email>gzip@prep.ai.mit.edu</email></address>
2006    </author>
2007    <author initials="M." surname="Adler" fullname="Mark Adler">
2008      <address><email>madler@alumni.caltech.edu</email></address>
2009    </author>
2010    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2011      <address><email>ghost@aladdin.com</email></address>
2012    </author>
2013    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2014      <address><email>randeg@alumni.rpi.edu</email></address>
2015    </author>
2016    <date month="May" year="1996"/>
2017  </front>
2018  <seriesInfo name="RFC" value="1952"/>
2019  <annotation>
2020    RFC 1952 is an Informational RFC, thus it may be less stable than
2021    this specification. On the other hand, this downward reference was
2022    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2023    therefore it is unlikely to cause problems in practice. See also
2024    <xref target="BCP97"/>.
2025  </annotation>
2026</reference>
2027
2028<reference anchor="RFC2045">
2029  <front>
2030    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2031    <author initials="N." surname="Freed" fullname="Ned Freed">
2032      <organization>Innosoft International, Inc.</organization>
2033      <address><email>ned@innosoft.com</email></address>
2034    </author>
2035    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2036      <organization>First Virtual Holdings</organization>
2037      <address><email>nsb@nsb.fv.com</email></address>
2038    </author>
2039    <date month="November" year="1996"/>
2040  </front>
2041  <seriesInfo name="RFC" value="2045"/>
2042</reference>
2043
2044<reference anchor="RFC2046">
2045  <front>
2046    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2047    <author initials="N." surname="Freed" fullname="Ned Freed">
2048      <organization>Innosoft International, Inc.</organization>
2049      <address><email>ned@innosoft.com</email></address>
2050    </author>
2051    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2052      <organization>First Virtual Holdings</organization>
2053      <address><email>nsb@nsb.fv.com</email></address>
2054    </author>
2055    <date month="November" year="1996"/>
2056  </front>
2057  <seriesInfo name="RFC" value="2046"/>
2058</reference>
2059
2060<reference anchor="RFC2119">
2061  <front>
2062    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2063    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2064      <organization>Harvard University</organization>
2065      <address><email>sob@harvard.edu</email></address>
2066    </author>
2067    <date month="March" year="1997"/>
2068  </front>
2069  <seriesInfo name="BCP" value="14"/>
2070  <seriesInfo name="RFC" value="2119"/>
2071</reference>
2072
2073<reference anchor="RFC4647">
2074  <front>
2075    <title>Matching of Language Tags</title>
2076    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
2077      <organization>Yahoo! Inc.</organization>
2078      <address><email>addison@inter-locale.com</email></address>
2079    </author>
2080    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
2081      <organization>Google</organization>
2082      <address><email>mark.davis@macchiato.com</email></address>
2083    </author>
2084    <date year="2006" month="September"/>
2085  </front>
2086  <seriesInfo name="BCP" value="47"/>
2087  <seriesInfo name="RFC" value="4647"/>
2088</reference>
2089
2090<reference anchor="RFC5234">
2091  <front>
2092    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2093    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2094      <organization>Brandenburg InternetWorking</organization>
2095      <address>
2096        <email>dcrocker@bbiw.net</email>
2097      </address> 
2098    </author>
2099    <author initials="P." surname="Overell" fullname="Paul Overell">
2100      <organization>THUS plc.</organization>
2101      <address>
2102        <email>paul.overell@thus.net</email>
2103      </address>
2104    </author>
2105    <date month="January" year="2008"/>
2106  </front>
2107  <seriesInfo name="STD" value="68"/>
2108  <seriesInfo name="RFC" value="5234"/>
2109</reference>
2110
2111<reference anchor="RFC5646">
2112  <front>
2113    <title>Tags for Identifying Languages</title>
2114    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
2115      <organization>Lab126</organization>
2116      <address><email>addison@inter-locale.com</email></address>
2117    </author>
2118    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
2119      <organization>Google</organization>
2120      <address><email>mark.davis@google.com</email></address>
2121    </author>
2122    <date month="September" year="2009"/>
2123  </front>
2124  <seriesInfo name="BCP" value="47"/>
2125  <seriesInfo name="RFC" value="5646"/>
2126</reference>
2127
2128</references>
2129
2130<references title="Informative References">
2131
2132<reference anchor="RFC1945">
2133  <front>
2134    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2135    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2136      <organization>MIT, Laboratory for Computer Science</organization>
2137      <address><email>timbl@w3.org</email></address>
2138    </author>
2139    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2140      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2141      <address><email>fielding@ics.uci.edu</email></address>
2142    </author>
2143    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2144      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2145      <address><email>frystyk@w3.org</email></address>
2146    </author>
2147    <date month="May" year="1996"/>
2148  </front>
2149  <seriesInfo name="RFC" value="1945"/>
2150</reference>
2151
2152<reference anchor="RFC2049">
2153  <front>
2154    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2155    <author initials="N." surname="Freed" fullname="Ned Freed">
2156      <organization>Innosoft International, Inc.</organization>
2157      <address><email>ned@innosoft.com</email></address>
2158    </author>
2159    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2160      <organization>First Virtual Holdings</organization>
2161      <address><email>nsb@nsb.fv.com</email></address>
2162    </author>
2163    <date month="November" year="1996"/>
2164  </front>
2165  <seriesInfo name="RFC" value="2049"/>
2166</reference>
2167
2168<reference anchor="RFC2068">
2169  <front>
2170    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2171    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2172      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2173      <address><email>fielding@ics.uci.edu</email></address>
2174    </author>
2175    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2176      <organization>MIT Laboratory for Computer Science</organization>
2177      <address><email>jg@w3.org</email></address>
2178    </author>
2179    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2180      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2181      <address><email>mogul@wrl.dec.com</email></address>
2182    </author>
2183    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2184      <organization>MIT Laboratory for Computer Science</organization>
2185      <address><email>frystyk@w3.org</email></address>
2186    </author>
2187    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2188      <organization>MIT Laboratory for Computer Science</organization>
2189      <address><email>timbl@w3.org</email></address>
2190    </author>
2191    <date month="January" year="1997"/>
2192  </front>
2193  <seriesInfo name="RFC" value="2068"/>
2194</reference>
2195
2196<reference anchor="RFC2076">
2197  <front>
2198    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2199    <author initials="J." surname="Palme" fullname="Jacob Palme">
2200      <organization>Stockholm University/KTH</organization>
2201      <address><email>jpalme@dsv.su.se</email></address>
2202    </author>
2203    <date month="February" year="1997"/>
2204  </front>
2205  <seriesInfo name="RFC" value="2076"/>
2206</reference>
2207
2208<reference anchor="RFC2183">
2209  <front>
2210    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2211    <author initials="R." surname="Troost" fullname="Rens Troost">
2212      <organization>New Century Systems</organization>
2213      <address><email>rens@century.com</email></address>
2214    </author>
2215    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2216      <organization>QUALCOMM Incorporated</organization>
2217      <address><email>sdorner@qualcomm.com</email></address>
2218    </author>
2219    <author initials="K." surname="Moore" fullname="Keith Moore">
2220      <organization>Department of Computer Science</organization>
2221      <address><email>moore@cs.utk.edu</email></address>
2222    </author>
2223    <date month="August" year="1997"/>
2224  </front>
2225  <seriesInfo name="RFC" value="2183"/>
2226</reference>
2227
2228<reference anchor="RFC2277">
2229  <front>
2230    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2231    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2232      <organization>UNINETT</organization>
2233      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2234    </author>
2235    <date month="January" year="1998"/>
2236  </front>
2237  <seriesInfo name="BCP" value="18"/>
2238  <seriesInfo name="RFC" value="2277"/>
2239</reference>
2240
2241<reference anchor="RFC2295">
2242  <front>
2243    <title abbrev="HTTP Content Negotiation">Transparent Content Negotiation in HTTP</title>
2244    <author initials="K." surname="Holtman" fullname="Koen Holtman">
2245      <organization>Technische Universiteit Eindhoven</organization>
2246      <address>
2247        <email>koen@win.tue.nl</email>
2248      </address>
2249    </author>
2250    <author initials="A.H." surname="Mutz" fullname="Andrew H. Mutz">
2251      <organization>Hewlett-Packard Company</organization>
2252      <address>
2253        <email>mutz@hpl.hp.com</email>
2254      </address>
2255    </author>
2256    <date year="1998" month="March"/>
2257  </front>
2258  <seriesInfo name="RFC" value="2295"/>
2259</reference>
2260
2261<reference anchor="RFC2388">
2262  <front>
2263    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2264    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2265      <organization>Xerox Palo Alto Research Center</organization>
2266      <address><email>masinter@parc.xerox.com</email></address>
2267    </author>
2268    <date year="1998" month="August"/>
2269  </front>
2270  <seriesInfo name="RFC" value="2388"/>
2271</reference>
2272
2273<reference anchor="RFC2557">
2274  <front>
2275    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2276    <author initials="F." surname="Palme" fullname="Jacob Palme">
2277      <organization>Stockholm University and KTH</organization>
2278      <address><email>jpalme@dsv.su.se</email></address>
2279    </author>
2280    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2281      <organization>Microsoft Corporation</organization>
2282      <address><email>alexhop@microsoft.com</email></address>
2283    </author>
2284    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2285      <organization>Lotus Development Corporation</organization>
2286      <address><email>Shelness@lotus.com</email></address>
2287    </author>
2288    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2289      <address><email>stef@nma.com</email></address>
2290    </author>
2291    <date year="1999" month="March"/>
2292  </front>
2293  <seriesInfo name="RFC" value="2557"/>
2294</reference>
2295
2296<reference anchor="RFC2616">
2297  <front>
2298    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2299    <author initials="R." surname="Fielding" fullname="R. Fielding">
2300      <organization>University of California, Irvine</organization>
2301      <address><email>fielding@ics.uci.edu</email></address>
2302    </author>
2303    <author initials="J." surname="Gettys" fullname="J. Gettys">
2304      <organization>W3C</organization>
2305      <address><email>jg@w3.org</email></address>
2306    </author>
2307    <author initials="J." surname="Mogul" fullname="J. Mogul">
2308      <organization>Compaq Computer Corporation</organization>
2309      <address><email>mogul@wrl.dec.com</email></address>
2310    </author>
2311    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2312      <organization>MIT Laboratory for Computer Science</organization>
2313      <address><email>frystyk@w3.org</email></address>
2314    </author>
2315    <author initials="L." surname="Masinter" fullname="L. Masinter">
2316      <organization>Xerox Corporation</organization>
2317      <address><email>masinter@parc.xerox.com</email></address>
2318    </author>
2319    <author initials="P." surname="Leach" fullname="P. Leach">
2320      <organization>Microsoft Corporation</organization>
2321      <address><email>paulle@microsoft.com</email></address>
2322    </author>
2323    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2324      <organization>W3C</organization>
2325      <address><email>timbl@w3.org</email></address>
2326    </author>
2327    <date month="June" year="1999"/>
2328  </front>
2329  <seriesInfo name="RFC" value="2616"/>
2330</reference>
2331
2332<reference anchor="RFC3629">
2333  <front>
2334    <title>UTF-8, a transformation format of ISO 10646</title>
2335    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2336      <organization>Alis Technologies</organization>
2337      <address><email>fyergeau@alis.com</email></address>
2338    </author>
2339    <date month="November" year="2003"/>
2340  </front>
2341  <seriesInfo name="RFC" value="3629"/>
2342  <seriesInfo name="STD" value="63"/>
2343</reference>
2344
2345<reference anchor="RFC3864">
2346  <front>
2347    <title>Registration Procedures for Message Header Fields</title>
2348    <author initials="G." surname="Klyne" fullname="G. Klyne">
2349      <organization>Nine by Nine</organization>
2350      <address><email>GK-IETF@ninebynine.org</email></address>
2351    </author>
2352    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
2353      <organization>BEA Systems</organization>
2354      <address><email>mnot@pobox.com</email></address>
2355    </author>
2356    <author initials="J." surname="Mogul" fullname="J. Mogul">
2357      <organization>HP Labs</organization>
2358      <address><email>JeffMogul@acm.org</email></address>
2359    </author>
2360    <date year="2004" month="September"/>
2361  </front>
2362  <seriesInfo name="BCP" value="90"/>
2363  <seriesInfo name="RFC" value="3864"/>
2364</reference>
2365
2366<reference anchor="RFC4288">
2367  <front>
2368    <title>Media Type Specifications and Registration Procedures</title>
2369    <author initials="N." surname="Freed" fullname="N. Freed">
2370      <organization>Sun Microsystems</organization>
2371      <address>
2372        <email>ned.freed@mrochek.com</email>
2373      </address>
2374    </author>
2375    <author initials="J." surname="Klensin" fullname="J. Klensin">
2376      <address>
2377        <email>klensin+ietf@jck.com</email>
2378      </address>
2379    </author>
2380    <date year="2005" month="December"/>
2381  </front>
2382  <seriesInfo name="BCP" value="13"/>
2383  <seriesInfo name="RFC" value="4288"/>
2384</reference>
2385
2386<reference anchor="RFC5226">
2387  <front>
2388    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2389    <author initials="T." surname="Narten" fullname="T. Narten">
2390      <organization>IBM</organization>
2391      <address><email>narten@us.ibm.com</email></address>
2392    </author>
2393    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
2394      <organization>Google</organization>
2395      <address><email>Harald@Alvestrand.no</email></address>
2396    </author>
2397    <date year="2008" month="May"/>
2398  </front>
2399  <seriesInfo name="BCP" value="26"/>
2400  <seriesInfo name="RFC" value="5226"/>
2401</reference>
2402
2403<reference anchor="RFC5322">
2404  <front>
2405    <title>Internet Message Format</title>
2406    <author initials="P." surname="Resnick" fullname="P. Resnick">
2407      <organization>Qualcomm Incorporated</organization>
2408    </author>
2409    <date year="2008" month="October"/>
2410  </front> 
2411  <seriesInfo name="RFC" value="5322"/>
2412</reference>
2413
2414<reference anchor="BCP97">
2415  <front>
2416    <title>Handling Normative References to Standards-Track Documents</title>
2417    <author initials="J." surname="Klensin" fullname="J. Klensin">
2418      <address>
2419        <email>klensin+ietf@jck.com</email>
2420      </address>
2421    </author>
2422    <author initials="S." surname="Hartman" fullname="S. Hartman">
2423      <organization>MIT</organization>
2424      <address>
2425        <email>hartmans-ietf@mit.edu</email>
2426      </address>
2427    </author>
2428    <date year="2007" month="June"/>
2429  </front>
2430  <seriesInfo name="BCP" value="97"/>
2431  <seriesInfo name="RFC" value="4897"/>
2432</reference>
2433
2434
2435</references>
2436
2437<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2438<t>
2439   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
2440   allow entities to be transmitted in an open variety of
2441   representations and with extensible mechanisms. However, RFC 2045
2442   discusses mail, and HTTP has a few features that are different from
2443   those described in RFC 2045. These differences were carefully chosen
2444   to optimize performance over binary connections, to allow greater
2445   freedom in the use of new media types, to make date comparisons
2446   easier, and to acknowledge the practice of some early HTTP servers
2447   and clients.
2448</t>
2449<t>
2450   This appendix describes specific areas where HTTP differs from RFC
2451   2045. Proxies and gateways to strict MIME environments SHOULD be
2452   aware of these differences and provide the appropriate conversions
2453   where necessary. Proxies and gateways from MIME environments to HTTP
2454   also need to be aware of the differences because some conversions
2455   might be required.
2456</t>
2457
2458<section title="MIME-Version" anchor="mime-version">
2459  <iref primary="true" item="MIME-Version header"/>
2460  <iref primary="true" item="Headers" subitem="MIME-Version"/>
2461 
2462 
2463<t>
2464   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages MAY
2465   include a single MIME-Version general-header field to indicate what
2466   version of the MIME protocol was used to construct the message. Use
2467   of the MIME-Version header field indicates that the message is in
2468   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2469   Proxies/gateways are responsible for ensuring full compliance (where
2470   possible) when exporting HTTP messages to strict MIME environments.
2471</t>
2472<figure><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/><artwork type="abnf2616"><![CDATA[
2473  MIME-Version   = "MIME-Version" ":" OWS MIME-Version-v
2474  MIME-Version-v = 1*DIGIT "." 1*DIGIT
2475]]></artwork></figure>
2476<t>
2477   MIME version "1.0" is the default for use in HTTP/1.1. However,
2478   HTTP/1.1 message parsing and semantics are defined by this document
2479   and not the MIME specification.
2480</t>
2481</section>
2482
2483<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2484<t>
2485   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2486   canonical form prior to being transferred, as described in Section 4 of <xref target="RFC2049"/>.
2487   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2488   allowed for subtypes of the "text" media type when transmitted over
2489   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2490   line breaks as CRLF and forbids the use of CR or LF outside of line
2491   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2492   line break within text content when a message is transmitted over
2493   HTTP.
2494</t>
2495<t>
2496   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2497   environment SHOULD translate all line breaks within the text media
2498   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2499   canonical form of CRLF. Note, however, that this might be complicated
2500   by the presence of a Content-Encoding and by the fact that HTTP
2501   allows the use of some character sets which do not use octets 13 and
2502   10 to represent CR and LF, as is the case for some multi-byte
2503   character sets.
2504</t>
2505<t>
2506   Implementors should note that conversion will break any cryptographic
2507   checksums applied to the original content unless the original content
2508   is already in canonical form. Therefore, the canonical form is
2509   recommended for any content that uses such checksums in HTTP.
2510</t>
2511</section>
2512
2513
2514<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2515<t>
2516   HTTP/1.1 uses a restricted set of date formats (Section 6.1 of <xref target="Part1"/>) to
2517   simplify the process of date comparison. Proxies and gateways from
2518   other protocols SHOULD ensure that any Date header field present in a
2519   message conforms to one of the HTTP/1.1 formats and rewrite the date
2520   if necessary.
2521</t>
2522</section>
2523
2524<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2525<t>
2526   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2527   Content-Encoding header field. Since this acts as a modifier on the
2528   media type, proxies and gateways from HTTP to MIME-compliant
2529   protocols MUST either change the value of the Content-Type header
2530   field or decode the entity-body before forwarding the message. (Some
2531   experimental applications of Content-Type for Internet mail have used
2532   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2533   a function equivalent to Content-Encoding. However, this parameter is
2534   not part of RFC 2045).
2535</t>
2536</section>
2537
2538<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2539<t>
2540   HTTP does not use the Content-Transfer-Encoding field of RFC
2541   2045. Proxies and gateways from MIME-compliant protocols to HTTP MUST
2542   remove any Content-Transfer-Encoding
2543   prior to delivering the response message to an HTTP client.
2544</t>
2545<t>
2546   Proxies and gateways from HTTP to MIME-compliant protocols are
2547   responsible for ensuring that the message is in the correct format
2548   and encoding for safe transport on that protocol, where "safe
2549   transport" is defined by the limitations of the protocol being used.
2550   Such a proxy or gateway SHOULD label the data with an appropriate
2551   Content-Transfer-Encoding if doing so will improve the likelihood of
2552   safe transport over the destination protocol.
2553</t>
2554</section>
2555
2556<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2557<t>
2558   HTTP/1.1 introduces the Transfer-Encoding header field (Section 9.7 of <xref target="Part1"/>).
2559   Proxies/gateways MUST remove any transfer-coding prior to
2560   forwarding a message via a MIME-compliant protocol.
2561</t>
2562</section>
2563
2564<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2565<t>
2566   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2567   need to be aware of MIME line length limitations. Since HTTP does not
2568   have this limitation, HTTP does not fold long lines. MHTML messages
2569   being transported by HTTP follow all conventions of MHTML, including
2570   line length limitations and folding, canonicalization, etc., since
2571   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2572   does not interpret the content or any MIME header lines that might be
2573   contained therein.
2574</t>
2575</section>
2576</section>
2577
2578<section title="Additional Features" anchor="additional.features">
2579<t>
2580   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2581   existing HTTP implementations, but not consistently and correctly
2582   across most HTTP/1.1 applications. Implementors are advised to be
2583   aware of these features, but cannot rely upon their presence in, or
2584   interoperability with, other HTTP/1.1 applications. Some of these
2585   describe proposed experimental features, and some describe features
2586   that experimental deployment found lacking that are now addressed in
2587   the base HTTP/1.1 specification.
2588</t>
2589<t>
2590   A number of other headers, such as Content-Disposition and Title,
2591   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2592</t>
2593
2594<section title="Content-Disposition" anchor="content-disposition">
2595<iref item="Headers" subitem="Content-Disposition" primary="true"/>
2596<iref item="Content-Disposition header" primary="true"/>
2597 
2598 
2599 
2600 
2601 
2602 
2603 
2604<t>
2605   The "Content-Disposition" response-header field has been proposed as a
2606   means for the origin server to suggest a default filename if the user
2607   requests that the content is saved to a file. This usage is derived
2608   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2609</t>
2610<figure><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/><artwork type="abnf2616"><![CDATA[
2611  content-disposition = "Content-Disposition" ":" OWS
2612                        content-disposition-v
2613  content-disposition-v = disposition-type
2614                          *( OWS ";" OWS disposition-parm )
2615  disposition-type = "attachment" / disp-extension-token
2616  disposition-parm = filename-parm / disp-extension-parm
2617  filename-parm = "filename" "=" quoted-string
2618  disp-extension-token = token
2619  disp-extension-parm = token "=" ( token / quoted-string )
2620]]></artwork></figure>
2621<t>
2622   An example is
2623</t>
2624<figure><artwork type="example"><![CDATA[
2625  Content-Disposition: attachment; filename="fname.ext"
2626]]></artwork></figure>
2627<t>
2628   The receiving user agent SHOULD NOT  respect any directory path
2629   information present in the filename-parm parameter, which is the only
2630   parameter believed to apply to HTTP implementations at this time. The
2631   filename SHOULD be treated as a terminal component only.
2632</t>
2633<t>
2634   If this header is used in a response with the application/octet-stream
2635   content-type, the implied suggestion is that the user agent
2636   should not display the response, but directly enter a "save response
2637   as..." dialog.
2638</t>
2639<t>
2640   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2641</t>
2642</section>
2643</section>
2644
2645<section title="Compatibility with Previous Versions" anchor="compatibility">
2646<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2647<t>
2648   Transfer-coding and message lengths all interact in ways that
2649   required fixing exactly when chunked encoding is used (to allow for
2650   transfer encoding that may not be self delimiting); it was important
2651   to straighten out exactly how message lengths are computed.
2652   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2653   <xref target="Part5"/> and <xref target="Part6"/>).
2654</t>
2655<t>
2656   Charset wildcarding is introduced to avoid explosion of character set
2657   names in accept headers. (<xref target="header.accept-charset"/>)
2658</t>
2659<t>
2660   Content-Base was deleted from the specification: it was not
2661   implemented widely, and there is no simple, safe way to introduce it
2662   without a robust extension mechanism. In addition, it is used in a
2663   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2664</t>
2665<t>
2666   A content-coding of "identity" was introduced, to solve problems
2667   discovered in caching. (<xref target="content.codings"/>)
2668</t>
2669<t>
2670   The Alternates<iref item="Alternates header" primary="true"/><iref item="Headers" subitem="Alternate" primary="true"/>, Content-Version<iref item="Content-Version header" primary="true"/><iref item="Headers" subitem="Content-Version" primary="true"/>, Derived-From<iref item="Derived-From header" primary="true"/><iref item="Headers" subitem="Derived-From" primary="true"/>, Link<iref item="Link header" primary="true"/><iref item="Headers" subitem="Link" primary="true"/>, URI<iref item="URI header" primary="true"/><iref item="Headers" subitem="URI" primary="true"/>, Public<iref item="Public header" primary="true"/><iref item="Headers" subitem="Public" primary="true"/> and
2671   Content-Base<iref item="Content-Base header" primary="true"/><iref item="Headers" subitem="Content-Base" primary="true"/> header fields were defined in previous versions of this
2672   specification, but not commonly implemented. See Section 19.6.2 of <xref target="RFC2068"/>.
2673</t>
2674</section>
2675
2676<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2677<t>
2678  Clarify contexts that charset is used in.
2679  (<xref target="character.sets"/>)
2680</t>
2681<t>
2682  Remove base URI setting semantics for Content-Location due to poor
2683  implementation support, which was caused by too many broken servers emitting
2684  bogus Content-Location headers, and also the potentially undesirable effect
2685  of potentially breaking relative links in content-negotiated resources.
2686  (<xref target="header.content-location"/>)
2687</t>
2688<t>
2689  Remove reference to non-existant identity transfer-coding value tokens.
2690  (<xref target="no.content-transfer-encoding"/>)
2691</t>
2692</section>
2693
2694</section>
2695
2696
2697<section title="Collected ABNF" anchor="collected.abnf">
2698<figure>
2699<artwork type="abnf" name="p3-payload.parsed-abnf"><![CDATA[
2700Accept = "Accept:" OWS Accept-v
2701Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v
2702Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2703 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2704 qvalue ] ] )
2705Accept-Encoding = "Accept-Encoding:" OWS Accept-Encoding-v
2706Accept-Encoding-v = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2707 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2708Accept-Language = "Accept-Language:" OWS Accept-Language-v
2709Accept-Language-v = *( "," OWS ) language-range [ OWS ";" OWS "q="
2710 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2711 ] )
2712Accept-v = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2713 OWS media-range [ accept-params ] ] ) ]
2714
2715Content-Encoding = "Content-Encoding:" OWS Content-Encoding-v
2716Content-Encoding-v = *( "," OWS ) content-coding *( OWS "," [ OWS
2717 content-coding ] )
2718Content-Language = "Content-Language:" OWS Content-Language-v
2719Content-Language-v = *( "," OWS ) language-tag *( OWS "," [ OWS
2720 language-tag ] )
2721Content-Length = <Content-Length, defined in [Part1], Section 9.2>
2722Content-Location = "Content-Location:" OWS Content-Location-v
2723Content-Location-v = absolute-URI / partial-URI
2724Content-MD5 = "Content-MD5:" OWS Content-MD5-v
2725Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]>
2726Content-Range = <Content-Range, defined in [Part5], Section 5.2>
2727Content-Type = "Content-Type:" OWS Content-Type-v
2728Content-Type-v = media-type
2729
2730Expires = <Expires, defined in [Part6], Section 3.3>
2731
2732Last-Modified = <Last-Modified, defined in [Part4], Section 6.6>
2733
2734MIME-Version = "MIME-Version:" OWS MIME-Version-v
2735MIME-Version-v = 1*DIGIT "." 1*DIGIT
2736
2737OWS = <OWS, defined in [Part1], Section 1.2.2>
2738
2739absolute-URI = <absolute-URI, defined in [Part1], Section 2.6>
2740accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2741accept-params = OWS ";" OWS "q=" qvalue *accept-ext
2742attribute = token
2743
2744charset = token
2745codings = ( content-coding / "*" )
2746content-coding = token
2747content-disposition = "Content-Disposition:" OWS
2748 content-disposition-v
2749content-disposition-v = disposition-type *( OWS ";" OWS
2750 disposition-parm )
2751
2752disp-extension-parm = token "=" ( token / quoted-string )
2753disp-extension-token = token
2754disposition-parm = filename-parm / disp-extension-parm
2755disposition-type = "attachment" / disp-extension-token
2756
2757entity-body = *OCTET
2758entity-header = Content-Encoding / Content-Language / Content-Length
2759 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2760 Expires / Last-Modified / extension-header
2761extension-header = header-field
2762
2763filename-parm = "filename=" quoted-string
2764
2765header-field = <header-field, defined in [Part1], Section 3.2>
2766
2767language-range = <language-range, defined in [RFC4647], Section 2.1>
2768language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
2769
2770media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2771 ";" OWS parameter )
2772media-type = type "/" subtype *( OWS ";" OWS parameter )
2773
2774parameter = attribute "=" value
2775partial-URI = <partial-URI, defined in [Part1], Section 2.6>
2776
2777quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
2778qvalue = <qvalue, defined in [Part1], Section 6.4>
2779
2780subtype = token
2781
2782token = <token, defined in [Part1], Section 1.2.2>
2783type = token
2784
2785value = token / quoted-string
2786]]></artwork>
2787</figure>
2788<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
2789; Accept defined but not used
2790; Accept-Charset defined but not used
2791; Accept-Encoding defined but not used
2792; Accept-Language defined but not used
2793; MIME-Version defined but not used
2794; content-disposition defined but not used
2795; entity-body defined but not used
2796; entity-header defined but not used
2797]]></artwork></figure></section>
2798
2799
2800<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2801
2802<section title="Since RFC2616">
2803<t>
2804  Extracted relevant partitions from <xref target="RFC2616"/>.
2805</t>
2806</section>
2807
2808<section title="Since draft-ietf-httpbis-p3-payload-00">
2809<t>
2810  Closed issues:
2811  <list style="symbols"> 
2812    <t>
2813      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2814      "Media Type Registrations"
2815      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2816    </t>
2817    <t>
2818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2819      "Clarification regarding quoting of charset values"
2820      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2821    </t>
2822    <t>
2823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2824      "Remove 'identity' token references"
2825      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2826    </t>
2827    <t>
2828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2829      "Accept-Encoding BNF"
2830    </t>
2831    <t>
2832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2833      "Normative and Informative references"
2834    </t>
2835    <t>
2836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2837      "RFC1700 references"
2838    </t>
2839    <t>
2840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2841      "Updating to RFC4288"
2842    </t>
2843    <t>
2844      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2845      "Informative references"
2846    </t>
2847    <t>
2848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2849      "ISO-8859-1 Reference"
2850    </t>
2851    <t>
2852      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2853      "Encoding References Normative"
2854    </t>
2855    <t>
2856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2857      "Normative up-to-date references"
2858    </t>
2859  </list>
2860</t>
2861</section>
2862
2863<section title="Since draft-ietf-httpbis-p3-payload-01">
2864<t>
2865  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2866  <list style="symbols"> 
2867    <t>
2868      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2869    </t>
2870  </list>
2871</t>
2872</section>
2873
2874<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2875<t>
2876  Closed issues:
2877  <list style="symbols"> 
2878    <t>
2879      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2880      "Quoting Charsets"
2881    </t>
2882    <t>
2883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2884      "Classification for Allow header"
2885    </t>
2886    <t>
2887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2888      "missing default for qvalue in description of Accept-Encoding"
2889    </t>
2890  </list>
2891</t>
2892<t>
2893  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2894  <list style="symbols"> 
2895    <t>
2896      Reference RFC 3984, and update header registrations for headers defined
2897      in this document.
2898    </t>
2899  </list>
2900</t>
2901</section>
2902
2903<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2904<t>
2905  Closed issues:
2906  <list style="symbols"> 
2907    <t>
2908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2909      "Quoting Charsets"
2910    </t>
2911    <t>
2912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2913      "language tag matching (Accept-Language) vs RFC4647"
2914    </t>
2915    <t>
2916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2917      "RFC 1806 has been replaced by RFC2183"
2918    </t>
2919  </list>
2920</t>
2921<t>
2922  Other changes:
2923  <list style="symbols"> 
2924    <t>
2925      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2926      "Encoding References Normative" -- rephrase the annotation and reference
2927      <xref target="BCP97"/>.
2928    </t>
2929  </list>
2930</t>
2931 </section>
2932
2933<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2934<t>
2935  Closed issues:
2936  <list style="symbols"> 
2937    <t>
2938      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2939      "RFC 2822 is updated by RFC 5322"
2940    </t>
2941  </list>
2942</t>
2943<t>
2944  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2945  <list style="symbols"> 
2946    <t>
2947      Use "/" instead of "|" for alternatives.
2948    </t>
2949    <t>
2950      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2951      whitespace ("OWS") and required whitespace ("RWS").
2952    </t>
2953    <t>
2954      Rewrite ABNFs to spell out whitespace rules, factor out
2955      header value format definitions.
2956    </t>
2957  </list>
2958</t>
2959</section>
2960
2961<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2962<t>
2963  Closed issues:
2964  <list style="symbols"> 
2965    <t>
2966      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2967      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2968    </t>
2969  </list>
2970</t>
2971<t>
2972  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2973  <list style="symbols"> 
2974    <t>
2975      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2976    </t>
2977  </list>
2978</t>
2979<t>
2980  Other changes:
2981  <list style="symbols"> 
2982    <t>
2983      Move definition of quality values into Part 1.
2984    </t>
2985  </list>
2986</t>
2987</section>
2988
2989<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2990<t>
2991  Closed issues:
2992  <list style="symbols"> 
2993    <t>
2994      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2995      "Content-Location isn't special"
2996    </t>
2997    <t>
2998      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2999      "Content Sniffing"
3000    </t>
3001  </list>
3002</t>
3003</section>
3004
3005<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3006<t>
3007  Closed issues:
3008  <list style="symbols"> 
3009    <t>
3010      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3011      "Updated reference for language tags"
3012    </t>
3013    <t>
3014      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3015      "Clarify rules for determining what entities a response carries"
3016    </t>
3017    <t>
3018      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
3019      "Content-Location base-setting problems"
3020    </t>
3021    <t>
3022      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3023      "Content Sniffing"
3024    </t>
3025    <t>
3026      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3027      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3028    </t>
3029    <t>
3030      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
3031      "move definitions of gzip/deflate/compress to part 1"
3032    </t>
3033  </list>
3034</t>
3035<t>
3036  Partly resolved issues:
3037  <list style="symbols"> 
3038    <t>
3039      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3040      "update IANA requirements wrt Transfer-Coding values" (add the
3041      IANA Considerations subsection)
3042    </t>
3043    <t>
3044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3045      "update IANA requirements wrt Content-Coding values" (add the
3046      IANA Considerations subsection)
3047    </t>
3048  </list>
3049</t>
3050</section>
3051
3052<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3053<t>
3054  Closed issues:
3055  <list style="symbols"> 
3056    <t>
3057      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3058      "Content Negotiation for media types"
3059    </t>
3060    <t>
3061      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3062      "Accept-Language: which RFC4647 filtering?"
3063    </t>
3064  </list>
3065</t>
3066</section>
3067
3068</section>
3069
3070</back>
3071</rfc>
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