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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-06">
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="2009" day="9"/>
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.05"/>.
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="Requirements" anchor="intro.requirements">
209<t>
210   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
211   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
212   document are to be interpreted as described in <xref target="RFC2119"/>.
213</t>
214<t>
215   An implementation is not compliant if it fails to satisfy one or more
216   of the MUST or REQUIRED level requirements for the protocols it
217   implements. An implementation that satisfies all the MUST or REQUIRED
218   level and all the SHOULD level requirements for its protocols is said
219   to be "unconditionally compliant"; one that satisfies all the MUST
220   level requirements but not all the SHOULD level requirements for its
221   protocols is said to be "conditionally compliant."
222</t>
223</section>
224
225<section title="Syntax Notation" anchor="notation">
226 
227 
228 
229 
230 
231 
232 
233<t>
234  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
235  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
236  <xref target="collected.abnf"/> shows the collected ABNF, with the list
237  rule expanded.
238</t>
239<t>
240  The following core rules are included by
241  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
242  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
243  DIGIT (decimal 0-9), DQUOTE (double quote),
244  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
245  OCTET (any 8-bit sequence of data), SP (space),
246  VCHAR (any visible USASCII character),
247  and WSP (whitespace).
248</t>
249
250<section title="Core Rules" anchor="core.rules">
251 
252 
253 
254<t>
255  The core rules below are defined in Section 1.2.2 of <xref target="Part1"/>:
256</t>
257<figure><artwork type="abnf2616"><![CDATA[
258  quoted-string  = <quoted-string, defined in [Part1], Section 1.2.2>
259  token          = <token, defined in [Part1], Section 1.2.2>
260  OWS            = <OWS, defined in [Part1], Section 1.2.2>
261]]></artwork></figure>
262</section>
263
264<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
265 
266 
267 
268 
269 
270 
271 
272 
273 
274<t>
275  The ABNF rules below are defined in other parts:
276</t>
277<figure><!--Part1--><artwork type="abnf2616"><![CDATA[
278  absolute-URI   = <absolute-URI, defined in [Part1], Section 2.1>
279  Content-Length = <Content-Length, defined in [Part1], Section 8.2>
280  message-header = <message-header, defined in [Part1], Section 4.2>
281  partial-URI    = <partial-URI, defined in [Part1], Section 2.1>
282  qvalue         = <qvalue, defined in [Part1], Section 3.5>
283]]></artwork></figure>
284<figure><!--Part4--><artwork type="abnf2616"><![CDATA[
285  Last-Modified  = <Last-Modified, defined in [Part4], Section 6.6>
286]]></artwork></figure>
287<figure><!--Part5--><artwork type="abnf2616"><![CDATA[
288  Content-Range  = <Content-Range, defined in [Part5], Section 5.2>
289]]></artwork></figure>
290<figure><!--Part6--><artwork type="abnf2616"><![CDATA[
291  Expires        = <Expires, defined in [Part6], Section 3.3>
292]]></artwork></figure>
293</section>
294
295</section>
296
297</section>
298
299<section title="Protocol Parameters" anchor="protocol.parameters">
300
301<section title="Character Sets" anchor="character.sets">
302<t>
303   HTTP uses the same definition of the term "character set" as that
304   described for MIME:
305</t>
306<t>
307   The term "character set" is used in this document to refer to a
308   method used with one or more tables to convert a sequence of octets
309   into a sequence of characters. Note that unconditional conversion in
310   the other direction is not required, in that not all characters may
311   be available in a given character set and a character set may provide
312   more than one sequence of octets to represent a particular character.
313   This definition is intended to allow various kinds of character
314   encoding, from simple single-table mappings such as US-ASCII to
315   complex table switching methods such as those that use ISO-2022's
316   techniques. However, the definition associated with a MIME character
317   set name MUST fully specify the mapping to be performed from octets
318   to characters. In particular, use of external profiling information
319   to determine the exact mapping is not permitted.
320</t>
321<t><list><t>
322      Note: This use of the term "character set" is more commonly
323      referred to as a "character encoding." However, since HTTP and
324      MIME share the same registry, it is important that the terminology
325      also be shared.
326</t></list></t>
327<t anchor="rule.charset">
328 
329   HTTP character sets are identified by case-insensitive tokens. The
330   complete set of tokens is defined by the IANA Character Set registry
331   (<eref target="http://www.iana.org/assignments/character-sets"/>).
332</t>
333<figure><iref primary="true" item="Grammar" subitem="charset"/><artwork type="abnf2616"><![CDATA[
334  charset = token
335]]></artwork></figure>
336<t>
337   Although HTTP allows an arbitrary token to be used as a charset
338   value, any token that has a predefined value within the IANA
339   Character Set registry MUST represent the character set defined
340   by that registry. Applications SHOULD limit their use of character
341   sets to those defined by the IANA registry.
342</t>
343<t>
344   HTTP uses charset in two contexts: within an Accept-Charset request
345   header (in which the charset value is an unquoted token) and as the
346   value of a parameter in a Content-Type header (within a request or
347   response), in which case the parameter value of the charset parameter
348   may be quoted.
349</t>
350<t>
351   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
352   <xref target="RFC2277"/>.
353</t>
354
355<section title="Missing Charset" anchor="missing.charset">
356<t>
357   Some HTTP/1.0 software has interpreted a Content-Type header without
358   charset parameter incorrectly to mean "recipient should guess."
359   Senders wishing to defeat this behavior MAY include a charset
360   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and SHOULD do so when
361   it is known that it will not confuse the recipient.
362</t>
363<t>
364   Unfortunately, some older HTTP/1.0 clients did not deal properly with
365   an explicit charset parameter. HTTP/1.1 recipients MUST respect the
366   charset label provided by the sender; and those user agents that have
367   a provision to "guess" a charset MUST use the charset from the
368   content-type field if they support that charset, rather than the
369   recipient's preference, when initially displaying a document. See
370   <xref target="canonicalization.and.text.defaults"/>.
371</t>
372</section>
373</section>
374
375<section title="Content Codings" anchor="content.codings">
376 
377<t>
378   Content coding values indicate an encoding transformation that has
379   been or can be applied to an entity. Content codings are primarily
380   used to allow a document to be compressed or otherwise usefully
381   transformed without losing the identity of its underlying media type
382   and without loss of information. Frequently, the entity is stored in
383   coded form, transmitted directly, and only decoded by the recipient.
384</t>
385<figure><iref primary="true" item="Grammar" subitem="content-coding"/><artwork type="abnf2616"><![CDATA[
386  content-coding   = token
387]]></artwork></figure>
388<t>
389   All content-coding values are case-insensitive. HTTP/1.1 uses
390   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
391   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
392   describes the content-coding, what is more important is that it
393   indicates what decoding mechanism will be required to remove the
394   encoding.
395</t>
396<t>
397   The Internet Assigned Numbers Authority (IANA) acts as a registry for
398   content-coding value tokens. Initially, the registry contains the
399   following tokens:
400</t>
401<t>
402   gzip<iref item="gzip"/>
403  <list>
404    <t>
405        An encoding format produced by the file compression program
406        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
407        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
408    </t>
409  </list>
410</t>
411<t>
412   compress<iref item="compress"/>
413  <list><t>
414        The encoding format produced by the common UNIX file compression
415        program "compress". This format is an adaptive Lempel-Ziv-Welch
416        coding (LZW).
417</t><t>
418        Use of program names for the identification of encoding formats
419        is not desirable and is discouraged for future encodings. Their
420        use here is representative of historical practice, not good
421        design. For compatibility with previous implementations of HTTP,
422        applications SHOULD consider "x-gzip" and "x-compress" to be
423        equivalent to "gzip" and "compress" respectively.
424  </t></list>
425</t>
426<t>
427   deflate<iref item="deflate"/>
428  <list><t>
429        The "zlib" format defined in <xref target="RFC1950"/> in combination with
430        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
431  </t></list>
432</t>
433<t>
434   identity<iref item="identity"/>
435  <list><t>
436        The default (identity) encoding; the use of no transformation
437        whatsoever. This content-coding is used only in the Accept-Encoding
438        header, and SHOULD NOT  be used in the Content-Encoding
439        header.
440  </t></list>
441</t>
442<t>
443   New content-coding value tokens SHOULD be registered; to allow
444   interoperability between clients and servers, specifications of the
445   content coding algorithms needed to implement a new value SHOULD be
446   publicly available and adequate for independent implementation, and
447   conform to the purpose of content coding defined in this section.
448</t>
449</section>
450
451<section title="Media Types" anchor="media.types">
452 
453 
454 
455<t>
456   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
457   and Accept (<xref target="header.accept"/>) header fields in order to provide
458   open and extensible data typing and type negotiation.
459</t>
460<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[
461  media-type = type "/" subtype *( OWS ";" OWS parameter )
462  type       = token
463  subtype    = token
464]]></artwork></figure>
465<t anchor="rule.parameter">
466 
467 
468 
469   Parameters MAY follow the type/subtype in the form of attribute/value
470   pairs.
471</t>
472<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[
473  parameter      = attribute "=" value
474  attribute      = token
475  value          = token / quoted-string
476]]></artwork></figure>
477<t>
478   The type, subtype, and parameter attribute names are case-insensitive.
479   Parameter values might or might not be case-sensitive, depending on the
480   semantics of the parameter name.  The presence or absence of a parameter might
481   be significant to the processing of a media-type, depending on its
482   definition within the media type registry.
483</t>
484<t>
485   A parameter value that matches the <xref target="core.rules" format="none">token</xref> production may be
486   transmitted as either a token or within a quoted-string. The quoted and
487   unquoted values are equivalent.
488</t>
489<t>
490   Note that some older HTTP applications do not recognize media type
491   parameters. When sending data to older HTTP applications,
492   implementations SHOULD only use media type parameters when they are
493   required by that type/subtype definition.
494</t>
495<t>
496   Media-type values are registered with the Internet Assigned Number
497   Authority (IANA). The media type registration process is
498   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
499   discouraged.
500</t>
501
502<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
503<t>
504   Internet media types are registered with a canonical form. An
505   entity-body transferred via HTTP messages MUST be represented in the
506   appropriate canonical form prior to its transmission except for
507   "text" types, as defined in the next paragraph.
508</t>
509<t>
510   When in canonical form, media subtypes of the "text" type use CRLF as
511   the text line break. HTTP relaxes this requirement and allows the
512   transport of text media with plain CR or LF alone representing a line
513   break when it is done consistently for an entire entity-body. HTTP
514   applications MUST accept CRLF, bare CR, and bare LF as being
515   representative of a line break in text media received via HTTP. In
516   addition, if the text is represented in a character set that does not
517   use octets 13 and 10 for CR and LF respectively, as is the case for
518   some multi-byte character sets, HTTP allows the use of whatever octet
519   sequences are defined by that character set to represent the
520   equivalent of CR and LF for line breaks. This flexibility regarding
521   line breaks applies only to text media in the entity-body; a bare CR
522   or LF MUST NOT be substituted for CRLF within any of the HTTP control
523   structures (such as header fields and multipart boundaries).
524</t>
525<t>
526   If an entity-body is encoded with a content-coding, the underlying
527   data MUST be in a form defined above prior to being encoded.
528</t>
529<t>
530   The "charset" parameter is used with some media types to define the
531   character set (<xref target="character.sets"/>) of the data. When no explicit charset
532   parameter is provided by the sender, media subtypes of the "text"
533   type are defined to have a default charset value of "ISO-8859-1" when
534   received via HTTP. Data in character sets other than "ISO-8859-1" or
535   its subsets MUST be labeled with an appropriate charset value. See
536   <xref target="missing.charset"/> for compatibility problems.
537</t>
538</section>
539
540<section title="Multipart Types" anchor="multipart.types">
541<t>
542   MIME provides for a number of "multipart" types -- encapsulations of
543   one or more entities within a single message-body. All multipart
544   types share a common syntax, as defined in Section 5.1.1 of <xref target="RFC2046"/>,
545   and MUST include a boundary parameter as part of the media type
546   value. The message body is itself a protocol element and MUST
547   therefore use only CRLF to represent line breaks between body-parts.
548   Unlike in RFC 2046, the epilogue of any multipart message MUST be
549   empty; HTTP applications MUST NOT transmit the epilogue (even if the
550   original multipart contains an epilogue). These restrictions exist in
551   order to preserve the self-delimiting nature of a multipart message-body,
552   wherein the "end" of the message-body is indicated by the
553   ending multipart boundary.
554</t>
555<t>
556   In general, HTTP treats a multipart message-body no differently than
557   any other media type: strictly as payload. The one exception is the
558   "multipart/byteranges" type (Appendix A of <xref target="Part5"/>) when it appears in a 206
559   (Partial Content) response.
560   <!-- jre: re-insert removed text pointing to caching? -->
561   In all
562   other cases, an HTTP user agent SHOULD follow the same or similar
563   behavior as a MIME user agent would upon receipt of a multipart type.
564   The MIME header fields within each body-part of a multipart message-body
565   do not have any significance to HTTP beyond that defined by
566   their MIME semantics.
567</t>
568<t>
569   In general, an HTTP user agent SHOULD follow the same or similar
570   behavior as a MIME user agent would upon receipt of a multipart type.
571   If an application receives an unrecognized multipart subtype, the
572   application MUST treat it as being equivalent to "multipart/mixed".
573</t>
574<t><list><t>
575      Note: The "multipart/form-data" type has been specifically defined
576      for carrying form data suitable for processing via the POST
577      request method, as described in <xref target="RFC2388"/>.
578</t></list></t>
579</section>
580</section>
581
582<section title="Language Tags" anchor="language.tags">
583 
584 
585 
586<t>
587   A language tag identifies a natural language spoken, written, or
588   otherwise conveyed by human beings for communication of information
589   to other human beings. Computer languages are explicitly excluded.
590   HTTP uses language tags within the Accept-Language and Content-Language
591   fields.
592</t>
593<t>
594   The syntax and registry of HTTP language tags is the same as that
595   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
596   or more parts: A primary language tag and a possibly empty series of
597   subtags:
598</t>
599<figure><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/><artwork type="abnf2616"><![CDATA[
600  language-tag  = primary-tag *( "-" subtag )
601  primary-tag   = 1*8ALPHA
602  subtag        = 1*8ALPHA
603]]></artwork></figure>
604<t>
605   White space is not allowed within the tag and all tags are case-insensitive.
606   The name space of language tags is administered by the
607   IANA. Example tags include:
608</t>
609<figure><artwork type="example"><![CDATA[
610  en, en-US, en-cockney, i-cherokee, x-pig-latin
611]]></artwork></figure>
612<t>
613   where any two-letter primary-tag is an ISO-639 language abbreviation
614   and any two-letter initial subtag is an ISO-3166 country code. (The
615   last three tags above are not registered tags; all but the last are
616   examples of tags which could be registered in future.)
617</t>
618</section>
619</section>
620
621<section title="Entity" anchor="entity">
622<t>
623   Request and Response messages MAY transfer an entity if not otherwise
624   restricted by the request method or response status code. An entity
625   consists of entity-header fields and an entity-body, although some
626   responses will only include the entity-headers.
627</t>
628<t>
629   In this section, both sender and recipient refer to either the client
630   or the server, depending on who sends and who receives the entity.
631</t>
632
633<section title="Entity Header Fields" anchor="entity.header.fields">
634 
635 
636<t>
637   Entity-header fields define metainformation about the entity-body or,
638   if no body is present, about the resource identified by the request.
639</t>
640<figure><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/><artwork type="abnf2616"><![CDATA[
641  entity-header  = Content-Encoding         ; Section 5.5
642                 / Content-Language         ; Section 5.6
643                 / Content-Length           ; [Part1], Section 8.2
644                 / Content-Location         ; Section 5.7
645                 / Content-MD5              ; Section 5.8
646                 / Content-Range            ; [Part5], Section 5.2
647                 / Content-Type             ; Section 5.9
648                 / Expires                  ; [Part6], Section 3.3
649                 / Last-Modified            ; [Part4], Section 6.6
650                 / extension-header
651 
652  extension-header = message-header
653]]></artwork></figure>
654<t>
655   The extension-header mechanism allows additional entity-header fields
656   to be defined without changing the protocol, but these fields cannot
657   be assumed to be recognizable by the recipient. Unrecognized header
658   fields SHOULD be ignored by the recipient and MUST be forwarded by
659   transparent proxies.
660</t>
661</section>
662
663<section title="Entity Body" anchor="entity.body">
664 
665<t>
666   The entity-body (if any) sent with an HTTP request or response is in
667   a format and encoding defined by the entity-header fields.
668</t>
669<figure><iref primary="true" item="Grammar" subitem="entity-body"/><artwork type="abnf2616"><![CDATA[
670  entity-body    = *OCTET
671]]></artwork></figure>
672<t>
673   An entity-body is only present in a message when a message-body is
674   present, as described in Section 4.3 of <xref target="Part1"/>. The entity-body is obtained
675   from the message-body by decoding any Transfer-Encoding that might
676   have been applied to ensure safe and proper transfer of the message.
677</t>
678
679<section title="Type" anchor="type">
680<t>
681   When an entity-body is included with a message, the data type of that
682   body is determined via the header fields Content-Type and Content-Encoding.
683   These define a two-layer, ordered encoding model:
684</t>
685<figure><artwork type="example"><![CDATA[
686  entity-body := Content-Encoding( Content-Type( data ) )
687]]></artwork></figure>
688<t>
689   Content-Type specifies the media type of the underlying data.
690   Content-Encoding may be used to indicate any additional content
691   codings applied to the data, usually for the purpose of data
692   compression, that are a property of the requested resource. There is
693   no default encoding.
694</t>
695<t>
696   Any HTTP/1.1 message containing an entity-body SHOULD include a
697   Content-Type header field defining the media type of that body. If
698   and only if the media type is not given by a Content-Type field, the
699   recipient MAY attempt to guess the media type via inspection of its
700   content and/or the name extension(s) of the URI used to identify the
701   resource. If the media type remains unknown, the recipient SHOULD
702   treat it as type "application/octet-stream".
703</t>
704</section>
705   
706<section title="Entity Length" anchor="entity.length">
707<t>
708   The entity-length of a message is the length of the message-body
709   before any transfer-codings have been applied. Section 4.4 of <xref target="Part1"/> defines
710   how the transfer-length of a message-body is determined.
711</t>
712</section>
713</section>
714</section>
715
716<section title="Content Negotiation" anchor="content.negotiation">
717<t>
718   Most HTTP responses include an entity which contains information for
719   interpretation by a human user. Naturally, it is desirable to supply
720   the user with the "best available" entity corresponding to the
721   request. Unfortunately for servers and caches, not all users have the
722   same preferences for what is "best," and not all user agents are
723   equally capable of rendering all entity types. For that reason, HTTP
724   has provisions for several mechanisms for "content negotiation" --
725   the process of selecting the best representation for a given response
726   when there are multiple representations available.
727  <list><t>
728      Note: This is not called "format negotiation" because the
729      alternate representations may be of the same media type, but use
730      different capabilities of that type, be in different languages,
731      etc.
732  </t></list>
733</t>
734<t>
735   Any response containing an entity-body MAY be subject to negotiation,
736   including error responses.
737</t>
738<t>
739   There are two kinds of content negotiation which are possible in
740   HTTP: server-driven and agent-driven negotiation. These two kinds of
741   negotiation are orthogonal and thus may be used separately or in
742   combination. One method of combination, referred to as transparent
743   negotiation, occurs when a cache uses the agent-driven negotiation
744   information provided by the origin server in order to provide
745   server-driven negotiation for subsequent requests.
746</t>
747
748<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
749<t>
750   If the selection of the best representation for a response is made by
751   an algorithm located at the server, it is called server-driven
752   negotiation. Selection is based on the available representations of
753   the response (the dimensions over which it can vary; e.g. language,
754   content-coding, etc.) and the contents of particular header fields in
755   the request message or on other information pertaining to the request
756   (such as the network address of the client).
757</t>
758<t>
759   Server-driven negotiation is advantageous when the algorithm for
760   selecting from among the available representations is difficult to
761   describe to the user agent, or when the server desires to send its
762   "best guess" to the client along with the first response (hoping to
763   avoid the round-trip delay of a subsequent request if the "best
764   guess" is good enough for the user). In order to improve the server's
765   guess, the user agent MAY include request header fields (Accept,
766   Accept-Language, Accept-Encoding, etc.) which describe its
767   preferences for such a response.
768</t>
769<t>
770   Server-driven negotiation has disadvantages:
771  <list style="numbers">
772    <t>
773         It is impossible for the server to accurately determine what
774         might be "best" for any given user, since that would require
775         complete knowledge of both the capabilities of the user agent
776         and the intended use for the response (e.g., does the user want
777         to view it on screen or print it on paper?).
778    </t>
779    <t>
780         Having the user agent describe its capabilities in every
781         request can be both very inefficient (given that only a small
782         percentage of responses have multiple representations) and a
783         potential violation of the user's privacy.
784    </t>
785    <t>
786         It complicates the implementation of an origin server and the
787         algorithms for generating responses to a request.
788    </t>
789    <t>
790         It may limit a public cache's ability to use the same response
791         for multiple user's requests.
792    </t>
793  </list>
794</t>
795<t>
796   HTTP/1.1 includes the following request-header fields for enabling
797   server-driven negotiation through description of user agent
798   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
799   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
800   (<xref target="header.accept-language"/>), and User-Agent (Section 9.9 of <xref target="Part2"/>). However, an
801   origin server is not limited to these dimensions and MAY vary the
802   response based on any aspect of the request, including information
803   outside the request-header fields or within extension header fields
804   not defined by this specification.
805</t>
806<t>
807   The Vary header field (Section 3.5 of <xref target="Part6"/>) can be used to express the parameters the
808   server uses to select a representation that is subject to server-driven
809   negotiation.
810</t>
811</section>
812
813<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
814<t>
815   With agent-driven negotiation, selection of the best representation
816   for a response is performed by the user agent after receiving an
817   initial response from the origin server. Selection is based on a list
818   of the available representations of the response included within the
819   header fields or entity-body of the initial response, with each
820   representation identified by its own URI. Selection from among the
821   representations may be performed automatically (if the user agent is
822   capable of doing so) or manually by the user selecting from a
823   generated (possibly hypertext) menu.
824</t>
825<t>
826   Agent-driven negotiation is advantageous when the response would vary
827   over commonly-used dimensions (such as type, language, or encoding),
828   when the origin server is unable to determine a user agent's
829   capabilities from examining the request, and generally when public
830   caches are used to distribute server load and reduce network usage.
831</t>
832<t>
833   Agent-driven negotiation suffers from the disadvantage of needing a
834   second request to obtain the best alternate representation. This
835   second request is only efficient when caching is used. In addition,
836   this specification does not define any mechanism for supporting
837   automatic selection, though it also does not prevent any such
838   mechanism from being developed as an extension and used within
839   HTTP/1.1.
840</t>
841<t>
842   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
843   status codes for enabling agent-driven negotiation when the server is
844   unwilling or unable to provide a varying response using server-driven
845   negotiation.
846</t>
847</section>
848
849<section title="Transparent Negotiation" anchor="transparent.negotiation">
850<t>
851   Transparent negotiation is a combination of both server-driven and
852   agent-driven negotiation. When a cache is supplied with a form of the
853   list of available representations of the response (as in agent-driven
854   negotiation) and the dimensions of variance are completely understood
855   by the cache, then the cache becomes capable of performing server-driven
856   negotiation on behalf of the origin server for subsequent
857   requests on that resource.
858</t>
859<t>
860   Transparent negotiation has the advantage of distributing the
861   negotiation work that would otherwise be required of the origin
862   server and also removing the second request delay of agent-driven
863   negotiation when the cache is able to correctly guess the right
864   response.
865</t>
866<t>
867   This specification does not define any mechanism for transparent
868   negotiation, though it also does not prevent any such mechanism from
869   being developed as an extension that could be used within HTTP/1.1.
870</t>
871</section>
872</section>
873
874<section title="Header Field Definitions" anchor="header.fields">
875<t>
876   This section defines the syntax and semantics of HTTP/1.1 header fields
877   related to the payload of messages.
878</t>
879<t>
880   For entity-header fields, both sender and recipient refer to either the
881   client or the server, depending on who sends and who receives the entity.
882</t>
883
884<section title="Accept" anchor="header.accept">
885  <iref primary="true" item="Accept header"/>
886  <iref primary="true" item="Headers" subitem="Accept"/>
887 
888 
889 
890 
891 
892<t>
893   The request-header field "Accept" can be used to specify certain media
894   types which are acceptable for the response. Accept headers can be
895   used to indicate that the request is specifically limited to a small
896   set of desired types, as in the case of a request for an in-line
897   image.
898</t>
899<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[
900  Accept   = "Accept" ":" OWS Accept-v
901  Accept-v = #( media-range [ accept-params ] )
902 
903  media-range    = ( "*/*"
904                   / ( type "/" "*" )
905                   / ( type "/" subtype )
906                   ) *( OWS ";" OWS parameter )
907  accept-params  = OWS ";" OWS "q=" qvalue *( accept-ext )
908  accept-ext     = OWS ";" OWS token
909                   [ "=" ( token / quoted-string ) ]
910]]></artwork></figure>
911<t>
912   The asterisk "*" character is used to group media types into ranges,
913   with "*/*" indicating all media types and "type/*" indicating all
914   subtypes of that type. The media-range MAY include media type
915   parameters that are applicable to that range.
916</t>
917<t>
918   Each media-range MAY be followed by one or more accept-params,
919   beginning with the "q" parameter for indicating a relative quality
920   factor. The first "q" parameter (if any) separates the media-range
921   parameter(s) from the accept-params. Quality factors allow the user
922   or user agent to indicate the relative degree of preference for that
923   media-range, using the qvalue scale from 0 to 1 (Section 3.5 of <xref target="Part1"/>). The
924   default value is q=1.
925  <list><t>
926      Note: Use of the "q" parameter name to separate media type
927      parameters from Accept extension parameters is due to historical
928      practice. Although this prevents any media type parameter named
929      "q" from being used with a media range, such an event is believed
930      to be unlikely given the lack of any "q" parameters in the IANA
931      media type registry and the rare usage of any media type
932      parameters in Accept. Future media types are discouraged from
933      registering any parameter named "q".
934  </t></list>
935</t>
936<t>
937   The example
938</t>
939<figure><artwork type="example"><![CDATA[
940  Accept: audio/*; q=0.2, audio/basic
941]]></artwork></figure>
942<t>
943   SHOULD be interpreted as "I prefer audio/basic, but send me any audio
944   type if it is the best available after an 80% mark-down in quality."
945</t>
946<t>
947   If no Accept header field is present, then it is assumed that the
948   client accepts all media types. If an Accept header field is present,
949   and if the server cannot send a response which is acceptable
950   according to the combined Accept field value, then the server SHOULD
951   send a 406 (Not Acceptable) response.
952</t>
953<t>
954   A more elaborate example is
955</t>
956<figure><artwork type="example"><![CDATA[
957  Accept: text/plain; q=0.5, text/html,
958          text/x-dvi; q=0.8, text/x-c
959]]></artwork></figure>
960<t>
961   Verbally, this would be interpreted as "text/html and text/x-c are
962   the preferred media types, but if they do not exist, then send the
963   text/x-dvi entity, and if that does not exist, send the text/plain
964   entity."
965</t>
966<t>
967   Media ranges can be overridden by more specific media ranges or
968   specific media types. If more than one media range applies to a given
969   type, the most specific reference has precedence. For example,
970</t>
971<figure><artwork type="example"><![CDATA[
972  Accept: text/*, text/html, text/html;level=1, */*
973]]></artwork></figure>
974<t>
975   have the following precedence:
976   <list style="numbers">
977    <t>text/html;level=1</t>
978    <t>text/html</t>
979    <t>text/*</t>
980    <t>*/*</t>
981   </list>
982</t>
983<t>
984   The media type quality factor associated with a given type is
985   determined by finding the media range with the highest precedence
986   which matches that type. For example,
987</t>
988<figure><artwork type="example"><![CDATA[
989  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
990          text/html;level=2;q=0.4, */*;q=0.5
991]]></artwork></figure>
992<t>
993   would cause the following values to be associated:
994</t>
995<texttable align="left">
996  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
997  <c>text/html;level=1</c>    <c>1</c>
998  <c>text/html</c>            <c>0.7</c>
999  <c>text/plain</c>           <c>0.3</c>
1000  <c>image/jpeg</c>           <c>0.5</c>
1001  <c>text/html;level=2</c>    <c>0.4</c>
1002  <c>text/html;level=3</c>    <c>0.7</c>
1003</texttable>
1004<t>
1005      Note: A user agent might be provided with a default set of quality
1006      values for certain media ranges. However, unless the user agent is
1007      a closed system which cannot interact with other rendering agents,
1008      this default set ought to be configurable by the user.
1009</t>
1010</section>
1011
1012<section title="Accept-Charset" anchor="header.accept-charset">
1013  <iref primary="true" item="Accept-Charset header"/>
1014  <iref primary="true" item="Headers" subitem="Accept-Charset"/>
1015 
1016 
1017<t>
1018   The request-header field "Accept-Charset" can be used to indicate what
1019   character sets are acceptable for the response. This field allows
1020   clients capable of understanding more comprehensive or special-purpose
1021   character sets to signal that capability to a server which is
1022   capable of representing documents in those character sets.
1023</t>
1024<figure><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/><artwork type="abnf2616"><![CDATA[
1025  Accept-Charset   = "Accept-Charset" ":" OWS
1026          Accept-Charset-v
1027  Accept-Charset-v = 1#( ( charset / "*" )
1028                         [ OWS ";" OWS "q=" qvalue ] )
1029]]></artwork></figure>
1030<t>
1031   Character set values are described in <xref target="character.sets"/>. Each charset MAY
1032   be given an associated quality value which represents the user's
1033   preference for that charset. The default value is q=1. An example is
1034</t>
1035<figure><artwork type="example"><![CDATA[
1036  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1037]]></artwork></figure>
1038<t>
1039   The special value "*", if present in the Accept-Charset field,
1040   matches every character set (including ISO-8859-1) which is not
1041   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1042   in an Accept-Charset field, then all character sets not explicitly
1043   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1044   a quality value of 1 if not explicitly mentioned.
1045</t>
1046<t>
1047   If no Accept-Charset header is present, the default is that any
1048   character set is acceptable. If an Accept-Charset header is present,
1049   and if the server cannot send a response which is acceptable
1050   according to the Accept-Charset header, then the server SHOULD send
1051   an error response with the 406 (Not Acceptable) status code, though
1052   the sending of an unacceptable response is also allowed.
1053</t>
1054</section>
1055
1056<section title="Accept-Encoding" anchor="header.accept-encoding">
1057  <iref primary="true" item="Accept-Encoding header"/>
1058  <iref primary="true" item="Headers" subitem="Accept-Encoding"/>
1059 
1060 
1061 
1062<t>
1063   The request-header field "Accept-Encoding" is similar to Accept, but
1064   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1065   the response.
1066</t>
1067<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[
1068  Accept-Encoding    = "Accept-Encoding" ":" OWS
1069                     Accept-Encoding-v
1070  Accept-Encoding-v  =
1071                     #( codings [ OWS ";" OWS "q=" qvalue ] )
1072  codings            = ( content-coding / "*" )
1073]]></artwork></figure>
1074<t>
1075   Each codings value MAY be given an associated quality value which
1076   represents the preference for that encoding. The default value is q=1.
1077</t>
1078<t>
1079   Examples of its use are:
1080</t>
1081<figure><artwork type="example"><![CDATA[
1082  Accept-Encoding: compress, gzip
1083  Accept-Encoding:
1084  Accept-Encoding: *
1085  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1086  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1087]]></artwork></figure>
1088<t>
1089   A server tests whether a content-coding is acceptable, according to
1090   an Accept-Encoding field, using these rules:
1091  <list style="numbers">
1092      <t>If the content-coding is one of the content-codings listed in
1093         the Accept-Encoding field, then it is acceptable, unless it is
1094         accompanied by a qvalue of 0. (As defined in Section 3.5 of <xref target="Part1"/>, a
1095         qvalue of 0 means "not acceptable.")</t>
1096
1097      <t>The special "*" symbol in an Accept-Encoding field matches any
1098         available content-coding not explicitly listed in the header
1099         field.</t>
1100
1101      <t>If multiple content-codings are acceptable, then the acceptable
1102         content-coding with the highest non-zero qvalue is preferred.</t>
1103
1104      <t>The "identity" content-coding is always acceptable, unless
1105         specifically refused because the Accept-Encoding field includes
1106         "identity;q=0", or because the field includes "*;q=0" and does
1107         not explicitly include the "identity" content-coding. If the
1108         Accept-Encoding field-value is empty, then only the "identity"
1109         encoding is acceptable.</t>
1110  </list>
1111</t>
1112<t>
1113   If an Accept-Encoding field is present in a request, and if the
1114   server cannot send a response which is acceptable according to the
1115   Accept-Encoding header, then the server SHOULD send an error response
1116   with the 406 (Not Acceptable) status code.
1117</t>
1118<t>
1119   If no Accept-Encoding field is present in a request, the server MAY
1120   assume that the client will accept any content coding. In this case,
1121   if "identity" is one of the available content-codings, then the
1122   server SHOULD use the "identity" content-coding, unless it has
1123   additional information that a different content-coding is meaningful
1124   to the client.
1125  <list><t>
1126      Note: If the request does not include an Accept-Encoding field,
1127      and if the "identity" content-coding is unavailable, then
1128      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1129      "gzip" and "compress") are preferred; some older clients
1130      improperly display messages sent with other content-codings.  The
1131      server might also make this decision based on information about
1132      the particular user-agent or client.
1133    </t><t>
1134      Note: Most HTTP/1.0 applications do not recognize or obey qvalues
1135      associated with content-codings. This means that qvalues will not
1136      work and are not permitted with x-gzip or x-compress.
1137    </t></list>
1138</t>
1139</section>
1140
1141<section title="Accept-Language" anchor="header.accept-language">
1142  <iref primary="true" item="Accept-Language header"/>
1143  <iref primary="true" item="Headers" subitem="Accept-Language"/>
1144 
1145 
1146 
1147<t>
1148   The request-header field "Accept-Language" is similar to Accept, but
1149   restricts the set of natural languages that are preferred as a
1150   response to the request. Language tags are defined in <xref target="language.tags"/>.
1151</t>
1152<figure><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/><artwork type="abnf2616"><![CDATA[
1153  Accept-Language   = "Accept-Language" ":" OWS
1154                    Accept-Language-v
1155  Accept-Language-v =
1156                    1#( language-range [ OWS ";" OWS "q=" qvalue ] )
1157  language-range    =
1158            <language-range, defined in [RFC4647], Section 2.1>
1159]]></artwork></figure>
1160<t>
1161   Each language-range can be given an associated quality value which
1162   represents an estimate of the user's preference for the languages
1163   specified by that range. The quality value defaults to "q=1". For
1164   example,
1165</t>
1166<figure><artwork type="example"><![CDATA[
1167  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1168]]></artwork></figure>
1169<t>
1170   would mean: "I prefer Danish, but will accept British English and
1171   other types of English."
1172</t>
1173<t>
1174   For matching, the "Basic Filtering" matching scheme, defined in
1175   Section 3.3.1 of <xref target="RFC4647"/>, is used:
1176</t>
1177<t><list>
1178  <t>
1179     A language range matches a
1180     particular language tag if, in a case-insensitive comparison, it
1181     exactly equals the tag, or if it exactly equals a prefix of the tag
1182     such that the first character following the prefix is "-".
1183  </t>
1184</list></t> 
1185<t>
1186   The special range "*", if present in the Accept-Language field,
1187   matches every tag not matched by any other range present in the
1188   Accept-Language field.
1189  <list><t>
1190      Note: This use of a prefix matching rule does not imply that
1191      language tags are assigned to languages in such a way that it is
1192      always true that if a user understands a language with a certain
1193      tag, then this user will also understand all languages with tags
1194      for which this tag is a prefix. The prefix rule simply allows the
1195      use of prefix tags if this is the case.
1196  </t></list>
1197</t>
1198<t>
1199   The language quality factor assigned to a language-tag by the
1200   Accept-Language field is the quality value of the longest language-range
1201   in the field that matches the language-tag. If no language-range
1202   in the field matches the tag, the language quality factor
1203   assigned is 0. If no Accept-Language header is present in the
1204   request, the server
1205   SHOULD assume that all languages are equally acceptable. If an
1206   Accept-Language header is present, then all languages which are
1207   assigned a quality factor greater than 0 are acceptable.
1208</t>
1209<t>
1210   It might be contrary to the privacy expectations of the user to send
1211   an Accept-Language header with the complete linguistic preferences of
1212   the user in every request. For a discussion of this issue, see
1213   <xref target="privacy.issues.connected.to.accept.headers"/>.
1214</t>
1215<t>
1216   As intelligibility is highly dependent on the individual user, it is
1217   recommended that client applications make the choice of linguistic
1218   preference available to the user. If the choice is not made
1219   available, then the Accept-Language header field MUST NOT be given in
1220   the request.
1221  <list><t>
1222      Note: When making the choice of linguistic preference available to
1223      the user, we remind implementors of  the fact that users are not
1224      familiar with the details of language matching as described above,
1225      and should provide appropriate guidance. As an example, users
1226      might assume that on selecting "en-gb", they will be served any
1227      kind of English document if British English is not available. A
1228      user agent might suggest in such a case to add "en" to get the
1229      best matching behavior.
1230  </t></list>
1231</t>
1232</section>
1233
1234<section title="Content-Encoding" anchor="header.content-encoding">
1235  <iref primary="true" item="Content-Encoding header"/>
1236  <iref primary="true" item="Headers" subitem="Content-Encoding"/>
1237 
1238 
1239<t>
1240   The entity-header field "Content-Encoding" is used as a modifier to the
1241   media-type. When present, its value indicates what additional content
1242   codings have been applied to the entity-body, and thus what decoding
1243   mechanisms must be applied in order to obtain the media-type
1244   referenced by the Content-Type header field. Content-Encoding is
1245   primarily used to allow a document to be compressed without losing
1246   the identity of its underlying media type.
1247</t>
1248<figure><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/><artwork type="abnf2616"><![CDATA[
1249  Content-Encoding   = "Content-Encoding" ":" OWS Content-Encoding-v
1250  Content-Encoding-v = 1#content-coding
1251]]></artwork></figure>
1252<t>
1253   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1254</t>
1255<figure><artwork type="example"><![CDATA[
1256  Content-Encoding: gzip
1257]]></artwork></figure>
1258<t>
1259   The content-coding is a characteristic of the entity identified by
1260   the request-target. Typically, the entity-body is stored with this
1261   encoding and is only decoded before rendering or analogous usage.
1262   However, a non-transparent proxy MAY modify the content-coding if the
1263   new coding is known to be acceptable to the recipient, unless the
1264   "no-transform" cache-control directive is present in the message.
1265</t>
1266<t>
1267   If the content-coding of an entity is not "identity", then the
1268   response MUST include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1269   that lists the non-identity content-coding(s) used.
1270</t>
1271<t>
1272   If the content-coding of an entity in a request message is not
1273   acceptable to the origin server, the server SHOULD respond with a
1274   status code of 415 (Unsupported Media Type).
1275</t>
1276<t>
1277   If multiple encodings have been applied to an entity, the content
1278   codings MUST be listed in the order in which they were applied.
1279   Additional information about the encoding parameters MAY be provided
1280   by other entity-header fields not defined by this specification.
1281</t>
1282</section>
1283
1284<section title="Content-Language" anchor="header.content-language">
1285  <iref primary="true" item="Content-Language header"/>
1286  <iref primary="true" item="Headers" subitem="Content-Language"/>
1287 
1288 
1289<t>
1290   The entity-header field "Content-Language" describes the natural
1291   language(s) of the intended audience for the enclosed entity. Note
1292   that this might not be equivalent to all the languages used within
1293   the entity-body.
1294</t>
1295<figure><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/><artwork type="abnf2616"><![CDATA[
1296  Content-Language   = "Content-Language" ":" OWS Content-Language-v
1297  Content-Language-v = 1#language-tag
1298]]></artwork></figure>
1299<t>
1300   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1301   Content-Language is to allow a user to identify and differentiate
1302   entities according to the user's own preferred language. Thus, if the
1303   body content is intended only for a Danish-literate audience, the
1304   appropriate field is
1305</t>
1306<figure><artwork type="example"><![CDATA[
1307  Content-Language: da
1308]]></artwork></figure>
1309<t>
1310   If no Content-Language is specified, the default is that the content
1311   is intended for all language audiences. This might mean that the
1312   sender does not consider it to be specific to any natural language,
1313   or that the sender does not know for which language it is intended.
1314</t>
1315<t>
1316   Multiple languages MAY be listed for content that is intended for
1317   multiple audiences. For example, a rendition of the "Treaty of
1318   Waitangi," presented simultaneously in the original Maori and English
1319   versions, would call for
1320</t>
1321<figure><artwork type="example"><![CDATA[
1322  Content-Language: mi, en
1323]]></artwork></figure>
1324<t>
1325   However, just because multiple languages are present within an entity
1326   does not mean that it is intended for multiple linguistic audiences.
1327   An example would be a beginner's language primer, such as "A First
1328   Lesson in Latin," which is clearly intended to be used by an
1329   English-literate audience. In this case, the Content-Language would
1330   properly only include "en".
1331</t>
1332<t>
1333   Content-Language MAY be applied to any media type -- it is not
1334   limited to textual documents.
1335</t>
1336</section>
1337
1338<section title="Content-Location" anchor="header.content-location">
1339  <iref primary="true" item="Content-Location header"/>
1340  <iref primary="true" item="Headers" subitem="Content-Location"/>
1341 
1342 
1343<t>
1344   The entity-header field "Content-Location" MAY be used to supply the
1345   resource location for the entity enclosed in the message when that
1346   entity is accessible from a location separate from the requested
1347   resource's URI. A server SHOULD provide a Content-Location for the
1348   variant corresponding to the response entity; especially in the case
1349   where a resource has multiple entities associated with it, and those
1350   entities actually have separate locations by which they might be
1351   individually accessed, the server SHOULD provide a Content-Location
1352   for the particular variant which is returned.
1353</t>
1354<figure><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/><artwork type="abnf2616"><![CDATA[
1355  Content-Location   = "Content-Location" ":" OWS
1356                    Content-Location-v
1357  Content-Location-v =
1358                    absolute-URI / partial-URI
1359]]></artwork></figure>
1360<t>
1361   The value of Content-Location also defines the base URI for the
1362   entity.
1363</t>
1364<t>
1365   The Content-Location value is not a replacement for the original
1366   requested URI; it is only a statement of the location of the resource
1367   corresponding to this particular entity at the time of the request.
1368   Future requests MAY specify the Content-Location URI as the request-target
1369   if the desire is to identify the source of that particular
1370   entity.
1371</t>
1372<t>
1373   A cache cannot assume that an entity with a Content-Location
1374   different from the URI used to retrieve it can be used to respond to
1375   later requests on that Content-Location URI. However, the Content-Location
1376   can be used to differentiate between multiple entities
1377   retrieved from a single requested resource, as described in Section 2.6 of <xref target="Part6"/>.
1378</t>
1379<t>
1380   If the Content-Location is a relative URI, the relative URI is
1381   interpreted relative to the request-target.
1382</t>
1383<t>
1384   The meaning of the Content-Location header in PUT or POST requests is
1385   undefined; servers are free to ignore it in those cases.
1386</t>
1387</section>
1388
1389<section title="Content-MD5" anchor="header.content-md5">
1390  <iref primary="true" item="Content-MD5 header"/>
1391  <iref primary="true" item="Headers" subitem="Content-MD5"/>
1392 
1393 
1394<t>
1395   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1396   an MD5 digest of the entity-body for the purpose of providing an
1397   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1398   MIC is good for detecting accidental modification of the entity-body
1399   in transit, but is not proof against malicious attacks.)
1400</t>
1401<figure><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/><artwork type="abnf2616"><![CDATA[
1402  Content-MD5   = "Content-MD5" ":" OWS Content-MD5-v
1403  Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]>
1404]]></artwork></figure>
1405<t>
1406   The Content-MD5 header field MAY be generated by an origin server or
1407   client to function as an integrity check of the entity-body. Only
1408   origin servers or clients MAY generate the Content-MD5 header field;
1409   proxies and gateways MUST NOT generate it, as this would defeat its
1410   value as an end-to-end integrity check. Any recipient of the entity-body,
1411   including gateways and proxies, MAY check that the digest value
1412   in this header field matches that of the entity-body as received.
1413</t>
1414<t>
1415   The MD5 digest is computed based on the content of the entity-body,
1416   including any content-coding that has been applied, but not including
1417   any transfer-encoding applied to the message-body. If the message is
1418   received with a transfer-encoding, that encoding MUST be removed
1419   prior to checking the Content-MD5 value against the received entity.
1420</t>
1421<t>
1422   This has the result that the digest is computed on the octets of the
1423   entity-body exactly as, and in the order that, they would be sent if
1424   no transfer-encoding were being applied.
1425</t>
1426<t>
1427   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1428   composite media-types (e.g., multipart/* and message/rfc822), but
1429   this does not change how the digest is computed as defined in the
1430   preceding paragraph.
1431</t>
1432<t>
1433   There are several consequences of this. The entity-body for composite
1434   types MAY contain many body-parts, each with its own MIME and HTTP
1435   headers (including Content-MD5, Content-Transfer-Encoding, and
1436   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1437   or Content-Encoding header, it is assumed that the content
1438   of the body-part has had the encoding applied, and the body-part is
1439   included in the Content-MD5 digest as is -- i.e., after the
1440   application. The Transfer-Encoding header field is not allowed within
1441   body-parts.
1442</t>
1443<t>
1444   Conversion of all line breaks to CRLF MUST NOT be done before
1445   computing or checking the digest: the line break convention used in
1446   the text actually transmitted MUST be left unaltered when computing
1447   the digest.
1448  <list><t>
1449      Note: while the definition of Content-MD5 is exactly the same for
1450      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1451      in which the application of Content-MD5 to HTTP entity-bodies
1452      differs from its application to MIME entity-bodies. One is that
1453      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1454      does use Transfer-Encoding and Content-Encoding. Another is that
1455      HTTP more frequently uses binary content types than MIME, so it is
1456      worth noting that, in such cases, the byte order used to compute
1457      the digest is the transmission byte order defined for the type.
1458      Lastly, HTTP allows transmission of text types with any of several
1459      line break conventions and not just the canonical form using CRLF.
1460  </t></list>
1461</t>
1462</section>
1463
1464<section title="Content-Type" anchor="header.content-type">
1465  <iref primary="true" item="Content-Type header"/>
1466  <iref primary="true" item="Headers" subitem="Content-Type"/>
1467 
1468 
1469<t>
1470   The entity-header field "Content-Type" indicates the media type of the
1471   entity-body sent to the recipient or, in the case of the HEAD method,
1472   the media type that would have been sent had the request been a GET.
1473</t>
1474<figure><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/><artwork type="abnf2616"><![CDATA[
1475  Content-Type   = "Content-Type" ":" OWS Content-Type-v
1476  Content-Type-v = media-type
1477]]></artwork></figure>
1478<t>
1479   Media types are defined in <xref target="media.types"/>. An example of the field is
1480</t>
1481<figure><artwork type="example"><![CDATA[
1482  Content-Type: text/html; charset=ISO-8859-4
1483]]></artwork></figure>
1484<t>
1485   Further discussion of methods for identifying the media type of an
1486   entity is provided in <xref target="type"/>.
1487</t>
1488</section>
1489
1490</section>
1491
1492<section title="IANA Considerations" anchor="IANA.considerations">
1493<section title="Message Header Registration" anchor="message.header.registration">
1494<t>
1495   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1496   with the permanent registrations below (see <xref target="RFC3864"/>):
1497</t>
1498<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1499<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1500   <ttcol>Header Field Name</ttcol>
1501   <ttcol>Protocol</ttcol>
1502   <ttcol>Status</ttcol>
1503   <ttcol>Reference</ttcol>
1504
1505   <c>Accept</c>
1506   <c>http</c>
1507   <c>standard</c>
1508   <c>
1509      <xref target="header.accept"/>
1510   </c>
1511   <c>Accept-Charset</c>
1512   <c>http</c>
1513   <c>standard</c>
1514   <c>
1515      <xref target="header.accept-charset"/>
1516   </c>
1517   <c>Accept-Encoding</c>
1518   <c>http</c>
1519   <c>standard</c>
1520   <c>
1521      <xref target="header.accept-encoding"/>
1522   </c>
1523   <c>Accept-Language</c>
1524   <c>http</c>
1525   <c>standard</c>
1526   <c>
1527      <xref target="header.accept-language"/>
1528   </c>
1529   <c>Content-Disposition</c>
1530   <c>http</c>
1531   <c/>
1532   <c>
1533      <xref target="content-disposition"/>
1534   </c>
1535   <c>Content-Encoding</c>
1536   <c>http</c>
1537   <c>standard</c>
1538   <c>
1539      <xref target="header.content-encoding"/>
1540   </c>
1541   <c>Content-Language</c>
1542   <c>http</c>
1543   <c>standard</c>
1544   <c>
1545      <xref target="header.content-language"/>
1546   </c>
1547   <c>Content-Location</c>
1548   <c>http</c>
1549   <c>standard</c>
1550   <c>
1551      <xref target="header.content-location"/>
1552   </c>
1553   <c>Content-MD5</c>
1554   <c>http</c>
1555   <c>standard</c>
1556   <c>
1557      <xref target="header.content-md5"/>
1558   </c>
1559   <c>Content-Type</c>
1560   <c>http</c>
1561   <c>standard</c>
1562   <c>
1563      <xref target="header.content-type"/>
1564   </c>
1565   <c>MIME-Version</c>
1566   <c>http</c>
1567   <c/>
1568   <c>
1569      <xref target="mime-version"/>
1570   </c>
1571</texttable>
1572<!--(END)-->
1573<t>
1574   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1575</t>
1576</section>
1577</section>
1578
1579<section title="Security Considerations" anchor="security.considerations">
1580<t>
1581   This section is meant to inform application developers, information
1582   providers, and users of the security limitations in HTTP/1.1 as
1583   described by this document. The discussion does not include
1584   definitive solutions to the problems revealed, though it does make
1585   some suggestions for reducing security risks.
1586</t>
1587
1588<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1589<t>
1590   Accept request-headers can reveal information about the user to all
1591   servers which are accessed. The Accept-Language header in particular
1592   can reveal information the user would consider to be of a private
1593   nature, because the understanding of particular languages is often
1594   strongly correlated to the membership of a particular ethnic group.
1595   User agents which offer the option to configure the contents of an
1596   Accept-Language header to be sent in every request are strongly
1597   encouraged to let the configuration process include a message which
1598   makes the user aware of the loss of privacy involved.
1599</t>
1600<t>
1601   An approach that limits the loss of privacy would be for a user agent
1602   to omit the sending of Accept-Language headers by default, and to ask
1603   the user whether or not to start sending Accept-Language headers to a
1604   server if it detects, by looking for any Vary response-header fields
1605   generated by the server, that such sending could improve the quality
1606   of service.
1607</t>
1608<t>
1609   Elaborate user-customized accept header fields sent in every request,
1610   in particular if these include quality values, can be used by servers
1611   as relatively reliable and long-lived user identifiers. Such user
1612   identifiers would allow content providers to do click-trail tracking,
1613   and would allow collaborating content providers to match cross-server
1614   click-trails or form submissions of individual users. Note that for
1615   many users not behind a proxy, the network address of the host
1616   running the user agent will also serve as a long-lived user
1617   identifier. In environments where proxies are used to enhance
1618   privacy, user agents ought to be conservative in offering accept
1619   header configuration options to end users. As an extreme privacy
1620   measure, proxies could filter the accept headers in relayed requests.
1621   General purpose user agents which provide a high degree of header
1622   configurability SHOULD warn users about the loss of privacy which can
1623   be involved.
1624</t>
1625</section>
1626
1627<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1628<t>
1629   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1630   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1631   serious security considerations. Content-Disposition is not part of
1632   the HTTP standard, but since it is widely implemented, we are
1633   documenting its use and risks for implementors. See Section 5 of <xref target="RFC2183"/>
1634   for details.
1635</t>
1636</section>
1637
1638</section>
1639
1640<section title="Acknowledgments" anchor="ack">
1641</section>
1642</middle>
1643<back>
1644
1645<references title="Normative References">
1646
1647<reference anchor="ISO-8859-1">
1648  <front>
1649    <title>
1650     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1651    </title>
1652    <author>
1653      <organization>International Organization for Standardization</organization>
1654    </author>
1655    <date year="1998"/>
1656  </front>
1657  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1658</reference>
1659
1660<reference anchor="Part1">
1661  <front>
1662    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1663    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1664      <organization abbrev="Day Software">Day Software</organization>
1665      <address><email>fielding@gbiv.com</email></address>
1666    </author>
1667    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1668      <organization>One Laptop per Child</organization>
1669      <address><email>jg@laptop.org</email></address>
1670    </author>
1671    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1672      <organization abbrev="HP">Hewlett-Packard Company</organization>
1673      <address><email>JeffMogul@acm.org</email></address>
1674    </author>
1675    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1676      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1677      <address><email>henrikn@microsoft.com</email></address>
1678    </author>
1679    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1680      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1681      <address><email>LMM@acm.org</email></address>
1682    </author>
1683    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1684      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1685      <address><email>paulle@microsoft.com</email></address>
1686    </author>
1687    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1688      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1689      <address><email>timbl@w3.org</email></address>
1690    </author>
1691    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1692      <organization abbrev="W3C">World Wide Web Consortium</organization>
1693      <address><email>ylafon@w3.org</email></address>
1694    </author>
1695    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1696      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1697      <address><email>julian.reschke@greenbytes.de</email></address>
1698    </author>
1699    <date month="March" year="2009"/>
1700  </front>
1701  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-06"/>
1702 
1703</reference>
1704
1705<reference anchor="Part2">
1706  <front>
1707    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1708    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1709      <organization abbrev="Day Software">Day Software</organization>
1710      <address><email>fielding@gbiv.com</email></address>
1711    </author>
1712    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1713      <organization>One Laptop per Child</organization>
1714      <address><email>jg@laptop.org</email></address>
1715    </author>
1716    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1717      <organization abbrev="HP">Hewlett-Packard Company</organization>
1718      <address><email>JeffMogul@acm.org</email></address>
1719    </author>
1720    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1721      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1722      <address><email>henrikn@microsoft.com</email></address>
1723    </author>
1724    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1725      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1726      <address><email>LMM@acm.org</email></address>
1727    </author>
1728    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1729      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1730      <address><email>paulle@microsoft.com</email></address>
1731    </author>
1732    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1733      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1734      <address><email>timbl@w3.org</email></address>
1735    </author>
1736    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1737      <organization abbrev="W3C">World Wide Web Consortium</organization>
1738      <address><email>ylafon@w3.org</email></address>
1739    </author>
1740    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1741      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1742      <address><email>julian.reschke@greenbytes.de</email></address>
1743    </author>
1744    <date month="March" year="2009"/>
1745  </front>
1746  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-06"/>
1747 
1748</reference>
1749
1750<reference anchor="Part4">
1751  <front>
1752    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1753    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1754      <organization abbrev="Day Software">Day Software</organization>
1755      <address><email>fielding@gbiv.com</email></address>
1756    </author>
1757    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1758      <organization>One Laptop per Child</organization>
1759      <address><email>jg@laptop.org</email></address>
1760    </author>
1761    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1762      <organization abbrev="HP">Hewlett-Packard Company</organization>
1763      <address><email>JeffMogul@acm.org</email></address>
1764    </author>
1765    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1766      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1767      <address><email>henrikn@microsoft.com</email></address>
1768    </author>
1769    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1770      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1771      <address><email>LMM@acm.org</email></address>
1772    </author>
1773    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1774      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1775      <address><email>paulle@microsoft.com</email></address>
1776    </author>
1777    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1778      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1779      <address><email>timbl@w3.org</email></address>
1780    </author>
1781    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1782      <organization abbrev="W3C">World Wide Web Consortium</organization>
1783      <address><email>ylafon@w3.org</email></address>
1784    </author>
1785    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1786      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1787      <address><email>julian.reschke@greenbytes.de</email></address>
1788    </author>
1789    <date month="March" year="2009"/>
1790  </front>
1791  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-06"/>
1792 
1793</reference>
1794
1795<reference anchor="Part5">
1796  <front>
1797    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1798    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1799      <organization abbrev="Day Software">Day Software</organization>
1800      <address><email>fielding@gbiv.com</email></address>
1801    </author>
1802    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1803      <organization>One Laptop per Child</organization>
1804      <address><email>jg@laptop.org</email></address>
1805    </author>
1806    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1807      <organization abbrev="HP">Hewlett-Packard Company</organization>
1808      <address><email>JeffMogul@acm.org</email></address>
1809    </author>
1810    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1811      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1812      <address><email>henrikn@microsoft.com</email></address>
1813    </author>
1814    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1815      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1816      <address><email>LMM@acm.org</email></address>
1817    </author>
1818    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1819      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1820      <address><email>paulle@microsoft.com</email></address>
1821    </author>
1822    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1823      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1824      <address><email>timbl@w3.org</email></address>
1825    </author>
1826    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1827      <organization abbrev="W3C">World Wide Web Consortium</organization>
1828      <address><email>ylafon@w3.org</email></address>
1829    </author>
1830    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1831      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1832      <address><email>julian.reschke@greenbytes.de</email></address>
1833    </author>
1834    <date month="March" year="2009"/>
1835  </front>
1836  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-06"/>
1837 
1838</reference>
1839
1840<reference anchor="Part6">
1841  <front>
1842    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1843    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1844      <organization abbrev="Day Software">Day Software</organization>
1845      <address><email>fielding@gbiv.com</email></address>
1846    </author>
1847    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1848      <organization>One Laptop per Child</organization>
1849      <address><email>jg@laptop.org</email></address>
1850    </author>
1851    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1852      <organization abbrev="HP">Hewlett-Packard Company</organization>
1853      <address><email>JeffMogul@acm.org</email></address>
1854    </author>
1855    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1856      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1857      <address><email>henrikn@microsoft.com</email></address>
1858    </author>
1859    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1860      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1861      <address><email>LMM@acm.org</email></address>
1862    </author>
1863    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1864      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1865      <address><email>paulle@microsoft.com</email></address>
1866    </author>
1867    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1868      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1869      <address><email>timbl@w3.org</email></address>
1870    </author>
1871    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1872      <organization abbrev="W3C">World Wide Web Consortium</organization>
1873      <address><email>ylafon@w3.org</email></address>
1874    </author>
1875    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1876      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1877      <address><email>julian.reschke@greenbytes.de</email></address>
1878    </author>
1879    <date month="March" year="2009"/>
1880  </front>
1881  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-06"/>
1882 
1883</reference>
1884
1885<reference anchor="RFC1766">
1886  <front>
1887    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1888    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1889      <organization>UNINETT</organization>
1890      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1891    </author>
1892    <date month="March" year="1995"/>
1893  </front>
1894  <seriesInfo name="RFC" value="1766"/>
1895</reference>
1896
1897<reference anchor="RFC1864">
1898  <front>
1899    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1900    <author initials="J." surname="Myers" fullname="John G. Myers">
1901      <organization>Carnegie Mellon University</organization>
1902      <address><email>jgm+@cmu.edu</email></address>
1903    </author>
1904    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1905      <organization>Dover Beach Consulting, Inc.</organization>
1906      <address><email>mrose@dbc.mtview.ca.us</email></address>
1907    </author>
1908    <date month="October" year="1995"/>
1909  </front>
1910  <seriesInfo name="RFC" value="1864"/>
1911</reference>
1912
1913<reference anchor="RFC1950">
1914  <front>
1915    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1916    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1917      <organization>Aladdin Enterprises</organization>
1918      <address><email>ghost@aladdin.com</email></address>
1919    </author>
1920    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1921      <organization/>
1922    </author>
1923    <date month="May" year="1996"/>
1924  </front>
1925  <seriesInfo name="RFC" value="1950"/>
1926  <annotation>
1927    RFC 1950 is an Informational RFC, thus it may be less stable than
1928    this specification. On the other hand, this downward reference was
1929    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1930    therefore it is unlikely to cause problems in practice. See also
1931    <xref target="BCP97"/>.
1932  </annotation>
1933</reference>
1934
1935<reference anchor="RFC1951">
1936  <front>
1937    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1938    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1939      <organization>Aladdin Enterprises</organization>
1940      <address><email>ghost@aladdin.com</email></address>
1941    </author>
1942    <date month="May" year="1996"/>
1943  </front>
1944  <seriesInfo name="RFC" value="1951"/>
1945  <annotation>
1946    RFC 1951 is an Informational RFC, thus it may be less stable than
1947    this specification. On the other hand, this downward reference was
1948    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1949    therefore it is unlikely to cause problems in practice. See also
1950    <xref target="BCP97"/>.
1951  </annotation>
1952</reference>
1953
1954<reference anchor="RFC1952">
1955  <front>
1956    <title>GZIP file format specification version 4.3</title>
1957    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1958      <organization>Aladdin Enterprises</organization>
1959      <address><email>ghost@aladdin.com</email></address>
1960    </author>
1961    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1962      <organization/>
1963      <address><email>gzip@prep.ai.mit.edu</email></address>
1964    </author>
1965    <author initials="M." surname="Adler" fullname="Mark Adler">
1966      <organization/>
1967      <address><email>madler@alumni.caltech.edu</email></address>
1968    </author>
1969    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1970      <organization/>
1971      <address><email>ghost@aladdin.com</email></address>
1972    </author>
1973    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1974      <organization/>
1975      <address><email>randeg@alumni.rpi.edu</email></address>
1976    </author>
1977    <date month="May" year="1996"/>
1978  </front>
1979  <seriesInfo name="RFC" value="1952"/>
1980  <annotation>
1981    RFC 1952 is an Informational RFC, thus it may be less stable than
1982    this specification. On the other hand, this downward reference was
1983    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1984    therefore it is unlikely to cause problems in practice. See also
1985    <xref target="BCP97"/>.
1986  </annotation>
1987</reference>
1988
1989<reference anchor="RFC2045">
1990  <front>
1991    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1992    <author initials="N." surname="Freed" fullname="Ned Freed">
1993      <organization>Innosoft International, Inc.</organization>
1994      <address><email>ned@innosoft.com</email></address>
1995    </author>
1996    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1997      <organization>First Virtual Holdings</organization>
1998      <address><email>nsb@nsb.fv.com</email></address>
1999    </author>
2000    <date month="November" year="1996"/>
2001  </front>
2002  <seriesInfo name="RFC" value="2045"/>
2003</reference>
2004
2005<reference anchor="RFC2046">
2006  <front>
2007    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2008    <author initials="N." surname="Freed" fullname="Ned Freed">
2009      <organization>Innosoft International, Inc.</organization>
2010      <address><email>ned@innosoft.com</email></address>
2011    </author>
2012    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2013      <organization>First Virtual Holdings</organization>
2014      <address><email>nsb@nsb.fv.com</email></address>
2015    </author>
2016    <date month="November" year="1996"/>
2017  </front>
2018  <seriesInfo name="RFC" value="2046"/>
2019</reference>
2020
2021<reference anchor="RFC2119">
2022  <front>
2023    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2024    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2025      <organization>Harvard University</organization>
2026      <address><email>sob@harvard.edu</email></address>
2027    </author>
2028    <date month="March" year="1997"/>
2029  </front>
2030  <seriesInfo name="BCP" value="14"/>
2031  <seriesInfo name="RFC" value="2119"/>
2032</reference>
2033
2034<reference anchor="RFC4647">
2035  <front>
2036    <title>Matching of Language Tags</title>
2037    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
2038      <organization>Yahoo! Inc.</organization>
2039      <address><email>addison@inter-locale.com</email></address>
2040    </author>
2041    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
2042      <organization>Google</organization>
2043      <address><email>mark.davis@macchiato.com</email></address>
2044    </author>
2045    <date year="2006" month="September"/>
2046  </front>
2047  <seriesInfo name="BCP" value="47"/>
2048  <seriesInfo name="RFC" value="4647"/>
2049</reference>
2050
2051<reference anchor="RFC5234">
2052  <front>
2053    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2054    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2055      <organization>Brandenburg InternetWorking</organization>
2056      <address>
2057      <postal>
2058      <street>675 Spruce Dr.</street>
2059      <city>Sunnyvale</city>
2060      <region>CA</region>
2061      <code>94086</code>
2062      <country>US</country></postal>
2063      <phone>+1.408.246.8253</phone>
2064      <email>dcrocker@bbiw.net</email></address> 
2065    </author>
2066    <author initials="P." surname="Overell" fullname="Paul Overell">
2067      <organization>THUS plc.</organization>
2068      <address>
2069      <postal>
2070      <street>1/2 Berkeley Square</street>
2071      <street>99 Berkely Street</street>
2072      <city>Glasgow</city>
2073      <code>G3 7HR</code>
2074      <country>UK</country></postal>
2075      <email>paul.overell@thus.net</email></address>
2076    </author>
2077    <date month="January" year="2008"/>
2078  </front>
2079  <seriesInfo name="STD" value="68"/>
2080  <seriesInfo name="RFC" value="5234"/>
2081</reference>
2082
2083</references>
2084
2085<references title="Informative References">
2086
2087<reference anchor="RFC1945">
2088  <front>
2089    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2090    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2091      <organization>MIT, Laboratory for Computer Science</organization>
2092      <address><email>timbl@w3.org</email></address>
2093    </author>
2094    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2095      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2096      <address><email>fielding@ics.uci.edu</email></address>
2097    </author>
2098    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2099      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2100      <address><email>frystyk@w3.org</email></address>
2101    </author>
2102    <date month="May" year="1996"/>
2103  </front>
2104  <seriesInfo name="RFC" value="1945"/>
2105</reference>
2106
2107<reference anchor="RFC2049">
2108  <front>
2109    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2110    <author initials="N." surname="Freed" fullname="Ned Freed">
2111      <organization>Innosoft International, Inc.</organization>
2112      <address><email>ned@innosoft.com</email></address>
2113    </author>
2114    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2115      <organization>First Virtual Holdings</organization>
2116      <address><email>nsb@nsb.fv.com</email></address>
2117    </author>
2118    <date month="November" year="1996"/>
2119  </front>
2120  <seriesInfo name="RFC" value="2049"/>
2121</reference>
2122
2123<reference anchor="RFC2068">
2124  <front>
2125    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2126    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2127      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2128      <address><email>fielding@ics.uci.edu</email></address>
2129    </author>
2130    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2131      <organization>MIT Laboratory for Computer Science</organization>
2132      <address><email>jg@w3.org</email></address>
2133    </author>
2134    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2135      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2136      <address><email>mogul@wrl.dec.com</email></address>
2137    </author>
2138    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2139      <organization>MIT Laboratory for Computer Science</organization>
2140      <address><email>frystyk@w3.org</email></address>
2141    </author>
2142    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2143      <organization>MIT Laboratory for Computer Science</organization>
2144      <address><email>timbl@w3.org</email></address>
2145    </author>
2146    <date month="January" year="1997"/>
2147  </front>
2148  <seriesInfo name="RFC" value="2068"/>
2149</reference>
2150
2151<reference anchor="RFC2076">
2152  <front>
2153    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2154    <author initials="J." surname="Palme" fullname="Jacob Palme">
2155      <organization>Stockholm University/KTH</organization>
2156      <address><email>jpalme@dsv.su.se</email></address>
2157    </author>
2158    <date month="February" year="1997"/>
2159  </front>
2160  <seriesInfo name="RFC" value="2076"/>
2161</reference>
2162
2163<reference anchor="RFC2183">
2164  <front>
2165    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2166    <author initials="R." surname="Troost" fullname="Rens Troost">
2167      <organization>New Century Systems</organization>
2168      <address><email>rens@century.com</email></address>
2169    </author>
2170    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2171      <organization>QUALCOMM Incorporated</organization>
2172      <address><email>sdorner@qualcomm.com</email></address>
2173    </author>
2174    <author initials="K." surname="Moore" fullname="Keith Moore">
2175      <organization>Department of Computer Science</organization>
2176      <address><email>moore@cs.utk.edu</email></address>
2177    </author>
2178    <date month="August" year="1997"/>
2179  </front>
2180  <seriesInfo name="RFC" value="2183"/>
2181</reference>
2182
2183<reference anchor="RFC2277">
2184  <front>
2185    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2186    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2187      <organization>UNINETT</organization>
2188      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2189    </author>
2190    <date month="January" year="1998"/>
2191  </front>
2192  <seriesInfo name="BCP" value="18"/>
2193  <seriesInfo name="RFC" value="2277"/>
2194</reference>
2195
2196<reference anchor="RFC2388">
2197  <front>
2198    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2199    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2200      <organization>Xerox Palo Alto Research Center</organization>
2201      <address><email>masinter@parc.xerox.com</email></address>
2202    </author>
2203    <date year="1998" month="August"/>
2204  </front>
2205  <seriesInfo name="RFC" value="2388"/>
2206</reference>
2207
2208<reference anchor="RFC2557">
2209  <front>
2210    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2211    <author initials="F." surname="Palme" fullname="Jacob Palme">
2212      <organization>Stockholm University and KTH</organization>
2213      <address><email>jpalme@dsv.su.se</email></address>
2214    </author>
2215    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2216      <organization>Microsoft Corporation</organization>
2217      <address><email>alexhop@microsoft.com</email></address>
2218    </author>
2219    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2220      <organization>Lotus Development Corporation</organization>
2221      <address><email>Shelness@lotus.com</email></address>
2222    </author>
2223    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2224      <organization/>
2225      <address><email>stef@nma.com</email></address>
2226    </author>
2227    <date year="1999" month="March"/>
2228  </front>
2229  <seriesInfo name="RFC" value="2557"/>
2230</reference>
2231
2232<reference anchor="RFC2616">
2233  <front>
2234    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2235    <author initials="R." surname="Fielding" fullname="R. Fielding">
2236      <organization>University of California, Irvine</organization>
2237      <address><email>fielding@ics.uci.edu</email></address>
2238    </author>
2239    <author initials="J." surname="Gettys" fullname="J. Gettys">
2240      <organization>W3C</organization>
2241      <address><email>jg@w3.org</email></address>
2242    </author>
2243    <author initials="J." surname="Mogul" fullname="J. Mogul">
2244      <organization>Compaq Computer Corporation</organization>
2245      <address><email>mogul@wrl.dec.com</email></address>
2246    </author>
2247    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2248      <organization>MIT Laboratory for Computer Science</organization>
2249      <address><email>frystyk@w3.org</email></address>
2250    </author>
2251    <author initials="L." surname="Masinter" fullname="L. Masinter">
2252      <organization>Xerox Corporation</organization>
2253      <address><email>masinter@parc.xerox.com</email></address>
2254    </author>
2255    <author initials="P." surname="Leach" fullname="P. Leach">
2256      <organization>Microsoft Corporation</organization>
2257      <address><email>paulle@microsoft.com</email></address>
2258    </author>
2259    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2260      <organization>W3C</organization>
2261      <address><email>timbl@w3.org</email></address>
2262    </author>
2263    <date month="June" year="1999"/>
2264  </front>
2265  <seriesInfo name="RFC" value="2616"/>
2266</reference>
2267
2268<reference anchor="RFC3629">
2269  <front>
2270    <title>UTF-8, a transformation format of ISO 10646</title>
2271    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2272      <organization>Alis Technologies</organization>
2273      <address><email>fyergeau@alis.com</email></address>
2274    </author>
2275    <date month="November" year="2003"/>
2276  </front>
2277  <seriesInfo name="RFC" value="3629"/>
2278  <seriesInfo name="STD" value="63"/>
2279</reference>
2280
2281<reference anchor="RFC3864">
2282  <front>
2283    <title>Registration Procedures for Message Header Fields</title>
2284    <author initials="G." surname="Klyne" fullname="G. Klyne">
2285      <organization>Nine by Nine</organization>
2286      <address><email>GK-IETF@ninebynine.org</email></address>
2287    </author>
2288    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
2289      <organization>BEA Systems</organization>
2290      <address><email>mnot@pobox.com</email></address>
2291    </author>
2292    <author initials="J." surname="Mogul" fullname="J. Mogul">
2293      <organization>HP Labs</organization>
2294      <address><email>JeffMogul@acm.org</email></address>
2295    </author>
2296    <date year="2004" month="September"/>
2297  </front>
2298  <seriesInfo name="BCP" value="90"/>
2299  <seriesInfo name="RFC" value="3864"/>
2300</reference>
2301
2302<reference anchor="RFC4288">
2303  <front>
2304    <title>Media Type Specifications and Registration Procedures</title>
2305    <author initials="N." surname="Freed" fullname="N. Freed">
2306      <organization>Sun Microsystems</organization>
2307      <address>
2308        <email>ned.freed@mrochek.com</email>
2309      </address>
2310    </author>
2311    <author initials="J." surname="Klensin" fullname="J. Klensin">
2312      <organization/>
2313      <address>
2314        <email>klensin+ietf@jck.com</email>
2315      </address>
2316    </author>
2317    <date year="2005" month="December"/>
2318  </front>
2319  <seriesInfo name="BCP" value="13"/>
2320  <seriesInfo name="RFC" value="4288"/>
2321</reference>
2322
2323<reference anchor="RFC5322">
2324  <front>
2325    <title>Internet Message Format</title>
2326    <author initials="P." surname="Resnick" fullname="P. Resnick">
2327      <organization>Qualcomm Incorporated</organization>
2328    </author>
2329    <date year="2008" month="October"/>
2330  </front> 
2331  <seriesInfo name="RFC" value="5322"/>
2332</reference>
2333
2334<reference anchor="BCP97">
2335  <front>
2336    <title>Handling Normative References to Standards-Track Documents</title>
2337    <author initials="J." surname="Klensin" fullname="J. Klensin">
2338      <organization/>
2339      <address>
2340        <email>klensin+ietf@jck.com</email>
2341      </address>
2342    </author>
2343    <author initials="S." surname="Hartman" fullname="S. Hartman">
2344      <organization>MIT</organization>
2345      <address>
2346        <email>hartmans-ietf@mit.edu</email>
2347      </address>
2348    </author>
2349    <date year="2007" month="June"/>
2350  </front>
2351  <seriesInfo name="BCP" value="97"/>
2352  <seriesInfo name="RFC" value="4897"/>
2353</reference>
2354
2355
2356</references>
2357
2358<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2359<t>
2360   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
2361   allow entities to be transmitted in an open variety of
2362   representations and with extensible mechanisms. However, RFC 2045
2363   discusses mail, and HTTP has a few features that are different from
2364   those described in RFC 2045. These differences were carefully chosen
2365   to optimize performance over binary connections, to allow greater
2366   freedom in the use of new media types, to make date comparisons
2367   easier, and to acknowledge the practice of some early HTTP servers
2368   and clients.
2369</t>
2370<t>
2371   This appendix describes specific areas where HTTP differs from RFC
2372   2045. Proxies and gateways to strict MIME environments SHOULD be
2373   aware of these differences and provide the appropriate conversions
2374   where necessary. Proxies and gateways from MIME environments to HTTP
2375   also need to be aware of the differences because some conversions
2376   might be required.
2377</t>
2378
2379<section title="MIME-Version" anchor="mime-version">
2380  <iref primary="true" item="MIME-Version header"/>
2381  <iref primary="true" item="Headers" subitem="MIME-Version"/>
2382 
2383 
2384<t>
2385   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages MAY
2386   include a single MIME-Version general-header field to indicate what
2387   version of the MIME protocol was used to construct the message. Use
2388   of the MIME-Version header field indicates that the message is in
2389   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2390   Proxies/gateways are responsible for ensuring full compliance (where
2391   possible) when exporting HTTP messages to strict MIME environments.
2392</t>
2393<figure><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/><artwork type="abnf2616"><![CDATA[
2394  MIME-Version   = "MIME-Version" ":" OWS MIME-Version-v
2395  MIME-Version-v = 1*DIGIT "." 1*DIGIT
2396]]></artwork></figure>
2397<t>
2398   MIME version "1.0" is the default for use in HTTP/1.1. However,
2399   HTTP/1.1 message parsing and semantics are defined by this document
2400   and not the MIME specification.
2401</t>
2402</section>
2403
2404<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2405<t>
2406   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2407   canonical form prior to being transferred, as described in Section 4 of <xref target="RFC2049"/>.
2408   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2409   allowed for subtypes of the "text" media type when transmitted over
2410   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2411   line breaks as CRLF and forbids the use of CR or LF outside of line
2412   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2413   line break within text content when a message is transmitted over
2414   HTTP.
2415</t>
2416<t>
2417   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2418   environment SHOULD translate all line breaks within the text media
2419   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2420   canonical form of CRLF. Note, however, that this might be complicated
2421   by the presence of a Content-Encoding and by the fact that HTTP
2422   allows the use of some character sets which do not use octets 13 and
2423   10 to represent CR and LF, as is the case for some multi-byte
2424   character sets.
2425</t>
2426<t>
2427   Implementors should note that conversion will break any cryptographic
2428   checksums applied to the original content unless the original content
2429   is already in canonical form. Therefore, the canonical form is
2430   recommended for any content that uses such checksums in HTTP.
2431</t>
2432</section>
2433
2434
2435<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2436<t>
2437   HTTP/1.1 uses a restricted set of date formats (Section 3.2.1 of <xref target="Part1"/>) to
2438   simplify the process of date comparison. Proxies and gateways from
2439   other protocols SHOULD ensure that any Date header field present in a
2440   message conforms to one of the HTTP/1.1 formats and rewrite the date
2441   if necessary.
2442</t>
2443</section>
2444
2445<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2446<t>
2447   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2448   Content-Encoding header field. Since this acts as a modifier on the
2449   media type, proxies and gateways from HTTP to MIME-compliant
2450   protocols MUST either change the value of the Content-Type header
2451   field or decode the entity-body before forwarding the message. (Some
2452   experimental applications of Content-Type for Internet mail have used
2453   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2454   a function equivalent to Content-Encoding. However, this parameter is
2455   not part of RFC 2045).
2456</t>
2457</section>
2458
2459<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2460<t>
2461   HTTP does not use the Content-Transfer-Encoding field of RFC
2462   2045. Proxies and gateways from MIME-compliant protocols to HTTP MUST
2463   remove any Content-Transfer-Encoding
2464   prior to delivering the response message to an HTTP client.
2465</t>
2466<t>
2467   Proxies and gateways from HTTP to MIME-compliant protocols are
2468   responsible for ensuring that the message is in the correct format
2469   and encoding for safe transport on that protocol, where "safe
2470   transport" is defined by the limitations of the protocol being used.
2471   Such a proxy or gateway SHOULD label the data with an appropriate
2472   Content-Transfer-Encoding if doing so will improve the likelihood of
2473   safe transport over the destination protocol.
2474</t>
2475</section>
2476
2477<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2478<t>
2479   HTTP/1.1 introduces the Transfer-Encoding header field (Section 8.7 of <xref target="Part1"/>).
2480   Proxies/gateways MUST remove any transfer-coding prior to
2481   forwarding a message via a MIME-compliant protocol.
2482</t>
2483</section>
2484
2485<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2486<t>
2487   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2488   need to be aware of MIME line length limitations. Since HTTP does not
2489   have this limitation, HTTP does not fold long lines. MHTML messages
2490   being transported by HTTP follow all conventions of MHTML, including
2491   line length limitations and folding, canonicalization, etc., since
2492   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2493   does not interpret the content or any MIME header lines that might be
2494   contained therein.
2495</t>
2496</section>
2497</section>
2498
2499<section title="Additional Features" anchor="additional.features">
2500<t>
2501   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2502   existing HTTP implementations, but not consistently and correctly
2503   across most HTTP/1.1 applications. Implementors are advised to be
2504   aware of these features, but cannot rely upon their presence in, or
2505   interoperability with, other HTTP/1.1 applications. Some of these
2506   describe proposed experimental features, and some describe features
2507   that experimental deployment found lacking that are now addressed in
2508   the base HTTP/1.1 specification.
2509</t>
2510<t>
2511   A number of other headers, such as Content-Disposition and Title,
2512   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2513</t>
2514
2515<section title="Content-Disposition" anchor="content-disposition">
2516<iref item="Headers" subitem="Content-Disposition" primary="true"/>
2517<iref item="Content-Disposition header" primary="true"/>
2518 
2519 
2520 
2521 
2522 
2523 
2524 
2525<t>
2526   The Content-Disposition response-header field has been proposed as a
2527   means for the origin server to suggest a default filename if the user
2528   requests that the content is saved to a file. This usage is derived
2529   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2530</t>
2531<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[
2532  content-disposition = "Content-Disposition" ":" OWS
2533                        content-disposition-v
2534  content-disposition-v = disposition-type
2535                          *( OWS ";" OWS disposition-parm )
2536  disposition-type = "attachment" / disp-extension-token
2537  disposition-parm = filename-parm / disp-extension-parm
2538  filename-parm = "filename" "=" quoted-string
2539  disp-extension-token = token
2540  disp-extension-parm = token "=" ( token / quoted-string )
2541]]></artwork></figure>
2542<t>
2543   An example is
2544</t>
2545<figure><artwork type="example"><![CDATA[
2546  Content-Disposition: attachment; filename="fname.ext"
2547]]></artwork></figure>
2548<t>
2549   The receiving user agent SHOULD NOT  respect any directory path
2550   information present in the filename-parm parameter, which is the only
2551   parameter believed to apply to HTTP implementations at this time. The
2552   filename SHOULD be treated as a terminal component only.
2553</t>
2554<t>
2555   If this header is used in a response with the application/octet-stream
2556   content-type, the implied suggestion is that the user agent
2557   should not display the response, but directly enter a `save response
2558   as...' dialog.
2559</t>
2560<t>
2561   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2562</t>
2563</section>
2564</section>
2565
2566<section title="Compatibility with Previous Versions" anchor="compatibility">
2567<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2568<t>
2569   Transfer-coding and message lengths all interact in ways that
2570   required fixing exactly when chunked encoding is used (to allow for
2571   transfer encoding that may not be self delimiting); it was important
2572   to straighten out exactly how message lengths are computed.
2573   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2574   <xref target="Part5"/> and <xref target="Part6"/>).
2575</t>
2576<t>
2577   Charset wildcarding is introduced to avoid explosion of character set
2578   names in accept headers. (<xref target="header.accept-charset"/>)
2579</t>
2580<t>
2581   Content-Base was deleted from the specification: it was not
2582   implemented widely, and there is no simple, safe way to introduce it
2583   without a robust extension mechanism. In addition, it is used in a
2584   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2585</t>
2586<t>
2587   A content-coding of "identity" was introduced, to solve problems
2588   discovered in caching. (<xref target="content.codings"/>)
2589</t>
2590<t>
2591   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
2592   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
2593   specification, but not commonly implemented. See Section 19.6.2 of <xref target="RFC2068"/>.
2594</t>
2595</section>
2596
2597<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2598<t>
2599  Clarify contexts that charset is used in.
2600  (<xref target="character.sets"/>)
2601</t>
2602<t>
2603  Remove reference to non-existant identity transfer-coding value tokens.
2604  (<xref target="no.content-transfer-encoding"/>)
2605</t>
2606</section>
2607
2608</section>
2609
2610<section title="Collected ABNF" anchor="collected.abnf">
2611<figure>
2612<artwork type="abnf" name="p3-payload.parsed-abnf"><![CDATA[
2613Accept = "Accept:" OWS Accept-v
2614Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v
2615Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2616 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2617 qvalue ] ] )
2618Accept-Encoding = "Accept-Encoding:" OWS Accept-Encoding-v
2619Accept-Encoding-v = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2620 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2621Accept-Language = "Accept-Language:" OWS Accept-Language-v
2622Accept-Language-v = *( "," OWS ) language-range [ OWS ";" OWS "q="
2623 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2624 ] )
2625Accept-v = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2626 OWS media-range [ accept-params ] ] ) ]
2627
2628Content-Encoding = "Content-Encoding:" OWS Content-Encoding-v
2629Content-Encoding-v = *( "," OWS ) content-coding *( OWS "," [ OWS
2630 content-coding ] )
2631Content-Language = "Content-Language:" OWS Content-Language-v
2632Content-Language-v = *( "," OWS ) language-tag *( OWS "," [ OWS
2633 language-tag ] )
2634Content-Length = <Content-Length, defined in [Part1], Section 8.2>
2635Content-Location = "Content-Location:" OWS Content-Location-v
2636Content-Location-v = absolute-URI / partial-URI
2637Content-MD5 = "Content-MD5:" OWS Content-MD5-v
2638Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]>
2639Content-Range = <Content-Range, defined in [Part5], Section 5.2>
2640Content-Type = "Content-Type:" OWS Content-Type-v
2641Content-Type-v = media-type
2642
2643Expires = <Expires, defined in [Part6], Section 3.3>
2644
2645Last-Modified = <Last-Modified, defined in [Part4], Section 6.6>
2646
2647MIME-Version = "MIME-Version:" OWS MIME-Version-v
2648MIME-Version-v = 1*DIGIT "." 1*DIGIT
2649
2650OWS = <OWS, defined in [Part1], Section 1.2.2>
2651
2652absolute-URI = <absolute-URI, defined in [Part1], Section 2.1>
2653accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2654accept-params = OWS ";" OWS "q=" qvalue *accept-ext
2655attribute = token
2656
2657charset = token
2658codings = ( content-coding / "*" )
2659content-coding = token
2660content-disposition = "Content-Disposition:" OWS
2661 content-disposition-v
2662content-disposition-v = disposition-type *( OWS ";" OWS
2663 disposition-parm )
2664
2665disp-extension-parm = token "=" ( token / quoted-string )
2666disp-extension-token = token
2667disposition-parm = filename-parm / disp-extension-parm
2668disposition-type = "attachment" / disp-extension-token
2669
2670entity-body = *OCTET
2671entity-header = Content-Encoding / Content-Language / Content-Length
2672 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2673 Expires / Last-Modified / extension-header
2674extension-header = message-header
2675
2676filename-parm = "filename=" quoted-string
2677
2678language-range = <language-range, defined in [RFC4647], Section 2.1>
2679language-tag = primary-tag *( "-" subtag )
2680
2681media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2682 ";" OWS parameter )
2683media-type = type "/" subtype *( OWS ";" OWS parameter )
2684message-header = <message-header, defined in [Part1], Section 4.2>
2685
2686parameter = attribute "=" value
2687partial-URI = <partial-URI, defined in [Part1], Section 2.1>
2688primary-tag = 1*8ALPHA
2689
2690quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
2691qvalue = <qvalue, defined in [Part1], Section 3.5>
2692
2693subtag = 1*8ALPHA
2694subtype = token
2695
2696token = <token, defined in [Part1], Section 1.2.2>
2697type = token
2698
2699value = token / quoted-string
2700
2701
2702]]></artwork>
2703</figure>
2704<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
2705; Accept defined but not used
2706; Accept-Charset defined but not used
2707; Accept-Encoding defined but not used
2708; Accept-Language defined but not used
2709; MIME-Version defined but not used
2710; content-disposition defined but not used
2711; entity-body defined but not used
2712; entity-header defined but not used
2713]]></artwork></figure></section>
2714
2715<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2716
2717<section title="Since RFC2616">
2718<t>
2719  Extracted relevant partitions from <xref target="RFC2616"/>.
2720</t>
2721</section>
2722
2723<section title="Since draft-ietf-httpbis-p3-payload-00">
2724<t>
2725  Closed issues:
2726  <list style="symbols"> 
2727    <t>
2728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2729      "Media Type Registrations"
2730      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2731    </t>
2732    <t>
2733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2734      "Clarification regarding quoting of charset values"
2735      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2736    </t>
2737    <t>
2738      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2739      "Remove 'identity' token references"
2740      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2741    </t>
2742    <t>
2743      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2744      "Accept-Encoding BNF"
2745    </t>
2746    <t>
2747      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2748      "Normative and Informative references"
2749    </t>
2750    <t>
2751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2752      "RFC1700 references"
2753    </t>
2754    <t>
2755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2756      "Updating to RFC4288"
2757    </t>
2758    <t>
2759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2760      "Informative references"
2761    </t>
2762    <t>
2763      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2764      "ISO-8859-1 Reference"
2765    </t>
2766    <t>
2767      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2768      "Encoding References Normative"
2769    </t>
2770    <t>
2771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2772      "Normative up-to-date references"
2773    </t>
2774  </list>
2775</t>
2776</section>
2777
2778<section title="Since draft-ietf-httpbis-p3-payload-01">
2779<t>
2780  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2781  <list style="symbols"> 
2782    <t>
2783      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2784    </t>
2785  </list>
2786</t>
2787</section>
2788
2789<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2790<t>
2791  Closed issues:
2792  <list style="symbols"> 
2793    <t>
2794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2795      "Quoting Charsets"
2796    </t>
2797    <t>
2798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2799      "Classification for Allow header"
2800    </t>
2801    <t>
2802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2803      "missing default for qvalue in description of Accept-Encoding"
2804    </t>
2805  </list>
2806</t>
2807<t>
2808  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2809  <list style="symbols"> 
2810    <t>
2811      Reference RFC 3984, and update header registrations for headers defined
2812      in this document.
2813    </t>
2814  </list>
2815</t>
2816</section>
2817
2818<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2819<t>
2820  Closed issues:
2821  <list style="symbols"> 
2822    <t>
2823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2824      "Quoting Charsets"
2825    </t>
2826    <t>
2827      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2828      "language tag matching (Accept-Language) vs RFC4647"
2829    </t>
2830    <t>
2831      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2832      "RFC 1806 has been replaced by RFC2183"
2833    </t>
2834  </list>
2835</t>
2836<t>
2837  Other changes:
2838  <list style="symbols"> 
2839    <t>
2840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2841      "Encoding References Normative" -- rephrase the annotation and reference
2842      <xref target="BCP97"/>.
2843    </t>
2844  </list>
2845</t>
2846 </section>
2847
2848<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2849<t>
2850  Closed issues:
2851  <list style="symbols"> 
2852    <t>
2853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2854      "RFC 2822 is updated by RFC 5322"
2855    </t>
2856  </list>
2857</t>
2858<t>
2859  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2860  <list style="symbols"> 
2861    <t>
2862      Use "/" instead of "|" for alternatives.
2863    </t>
2864    <t>
2865      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2866      whitespace ("OWS") and required whitespace ("RWS").
2867    </t>
2868    <t>
2869      Rewrite ABNFs to spell out whitespace rules, factor out
2870      header value format definitions.
2871    </t>
2872  </list>
2873</t>
2874</section>
2875
2876<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2877<t>
2878  Closed issues:
2879  <list style="symbols"> 
2880    <t>
2881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2882      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2883    </t>
2884  </list>
2885</t>
2886<t>
2887  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2888  <list style="symbols"> 
2889    <t>
2890      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2891    </t>
2892  </list>
2893</t>
2894<t>
2895  Other changes:
2896  <list style="symbols"> 
2897    <t>
2898      Move definition of quality values into Part 1.
2899    </t>
2900  </list>
2901</t>
2902</section>
2903
2904</section>
2905
2906</back>
2907</rfc>
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