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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-07">
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 day="13" month="July" year="2009"/>
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.06"/>.
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><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><artwork type="abnf2616"><![CDATA[
285  Last-Modified  = <Last-Modified, defined in [Part4], Section 6.6>
286]]></artwork></figure>
287<figure><artwork type="abnf2616"><![CDATA[
288  Content-Range  = <Content-Range, defined in [Part5], Section 5.2>
289]]></artwork></figure>
290<figure><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>
322  <t>
323    Note: This use of the term "character set" is more commonly
324    referred to as a "character encoding." However, since HTTP and
325    MIME share the same registry, it is important that the terminology
326    also be shared.
327  </t>
328</list></t>
329<t anchor="rule.charset">
330 
331   HTTP character sets are identified by case-insensitive tokens. The
332   complete set of tokens is defined by the IANA Character Set registry
333   (<eref target="http://www.iana.org/assignments/character-sets"/>).
334</t>
335<figure><iref primary="true" item="Grammar" subitem="charset"/><artwork type="abnf2616"><![CDATA[
336  charset = token
337]]></artwork></figure>
338<t>
339   Although HTTP allows an arbitrary token to be used as a charset
340   value, any token that has a predefined value within the IANA
341   Character Set registry MUST represent the character set defined
342   by that registry. Applications SHOULD limit their use of character
343   sets to those defined by the IANA registry.
344</t>
345<t>
346   HTTP uses charset in two contexts: within an Accept-Charset request
347   header (in which the charset value is an unquoted token) and as the
348   value of a parameter in a Content-Type header (within a request or
349   response), in which case the parameter value of the charset parameter
350   may be quoted.
351</t>
352<t>
353   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
354   <xref target="RFC2277"/>.
355</t>
356
357<section title="Missing Charset" anchor="missing.charset">
358<t>
359   Some HTTP/1.0 software has interpreted a Content-Type header without
360   charset parameter incorrectly to mean "recipient should guess."
361   Senders wishing to defeat this behavior MAY include a charset
362   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and SHOULD do so when
363   it is known that it will not confuse the recipient.
364</t>
365<t>
366   Unfortunately, some older HTTP/1.0 clients did not deal properly with
367   an explicit charset parameter. HTTP/1.1 recipients MUST respect the
368   charset label provided by the sender; and those user agents that have
369   a provision to "guess" a charset MUST use the charset from the
370   content-type field if they support that charset, rather than the
371   recipient's preference, when initially displaying a document. See
372   <xref target="canonicalization.and.text.defaults"/>.
373</t>
374</section>
375</section>
376
377<section title="Content Codings" anchor="content.codings">
378 
379<t>
380   Content coding values indicate an encoding transformation that has
381   been or can be applied to an entity. Content codings are primarily
382   used to allow a document to be compressed or otherwise usefully
383   transformed without losing the identity of its underlying media type
384   and without loss of information. Frequently, the entity is stored in
385   coded form, transmitted directly, and only decoded by the recipient.
386</t>
387<figure><iref primary="true" item="Grammar" subitem="content-coding"/><artwork type="abnf2616"><![CDATA[
388  content-coding   = token
389]]></artwork></figure>
390<t>
391   All content-coding values are case-insensitive. HTTP/1.1 uses
392   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
393   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
394   describes the content-coding, what is more important is that it
395   indicates what decoding mechanism will be required to remove the
396   encoding.
397</t>
398<t>
399   The Internet Assigned Numbers Authority (IANA) acts as a registry for
400   content-coding value tokens. Initially, the registry contains the
401   following tokens:
402</t>
403<t>
404   gzip<iref item="gzip"/>
405  <list>
406    <t>
407        An encoding format produced by the file compression program
408        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
409        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
410    </t>
411  </list>
412</t>
413<t>
414   compress<iref item="compress"/>
415  <list><t>
416        The encoding format produced by the common UNIX file compression
417        program "compress". This format is an adaptive Lempel-Ziv-Welch
418        coding (LZW).
419</t><t>
420        Use of program names for the identification of encoding formats
421        is not desirable and is discouraged for future encodings. Their
422        use here is representative of historical practice, not good
423        design. For compatibility with previous implementations of HTTP,
424        applications SHOULD consider "x-gzip" and "x-compress" to be
425        equivalent to "gzip" and "compress" respectively.
426  </t></list>
427</t>
428<t>
429   deflate<iref item="deflate"/>
430  <list><t>
431        The "zlib" format defined in <xref target="RFC1950"/> in combination with
432        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
433  </t></list>
434</t>
435<t>
436   identity<iref item="identity"/>
437  <list><t>
438        The default (identity) encoding; the use of no transformation
439        whatsoever. This content-coding is used only in the Accept-Encoding
440        header, and SHOULD NOT  be used in the Content-Encoding
441        header.
442  </t></list>
443</t>
444<t>
445   New content-coding value tokens SHOULD be registered; to allow
446   interoperability between clients and servers, specifications of the
447   content coding algorithms needed to implement a new value SHOULD be
448   publicly available and adequate for independent implementation, and
449   conform to the purpose of content coding defined in this section.
450</t>
451</section>
452
453<section title="Media Types" anchor="media.types">
454 
455 
456 
457<t>
458   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
459   and Accept (<xref target="header.accept"/>) header fields in order to provide
460   open and extensible data typing and type negotiation.
461</t>
462<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[
463  media-type = type "/" subtype *( OWS ";" OWS parameter )
464  type       = token
465  subtype    = token
466]]></artwork></figure>
467<t anchor="rule.parameter">
468 
469 
470 
471   Parameters MAY follow the type/subtype in the form of attribute/value
472   pairs.
473</t>
474<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[
475  parameter      = attribute "=" value
476  attribute      = token
477  value          = token / quoted-string
478]]></artwork></figure>
479<t>
480   The type, subtype, and parameter attribute names are case-insensitive.
481   Parameter values might or might not be case-sensitive, depending on the
482   semantics of the parameter name.  The presence or absence of a parameter might
483   be significant to the processing of a media-type, depending on its
484   definition within the media type registry.
485</t>
486<t>
487   A parameter value that matches the <xref target="core.rules" format="none">token</xref> production may be
488   transmitted as either a token or within a quoted-string. The quoted and
489   unquoted values are equivalent.
490</t>
491<t>
492   Note that some older HTTP applications do not recognize media type
493   parameters. When sending data to older HTTP applications,
494   implementations SHOULD only use media type parameters when they are
495   required by that type/subtype definition.
496</t>
497<t>
498   Media-type values are registered with the Internet Assigned Number
499   Authority (IANA). The media type registration process is
500   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
501   discouraged.
502</t>
503
504<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
505<t>
506   Internet media types are registered with a canonical form. An
507   entity-body transferred via HTTP messages MUST be represented in the
508   appropriate canonical form prior to its transmission except for
509   "text" types, as defined in the next paragraph.
510</t>
511<t>
512   When in canonical form, media subtypes of the "text" type use CRLF as
513   the text line break. HTTP relaxes this requirement and allows the
514   transport of text media with plain CR or LF alone representing a line
515   break when it is done consistently for an entire entity-body. HTTP
516   applications MUST accept CRLF, bare CR, and bare LF as being
517   representative of a line break in text media received via HTTP. In
518   addition, if the text is represented in a character set that does not
519   use octets 13 and 10 for CR and LF respectively, as is the case for
520   some multi-byte character sets, HTTP allows the use of whatever octet
521   sequences are defined by that character set to represent the
522   equivalent of CR and LF for line breaks. This flexibility regarding
523   line breaks applies only to text media in the entity-body; a bare CR
524   or LF MUST NOT be substituted for CRLF within any of the HTTP control
525   structures (such as header fields and multipart boundaries).
526</t>
527<t>
528   If an entity-body is encoded with a content-coding, the underlying
529   data MUST be in a form defined above prior to being encoded.
530</t>
531<t>
532   The "charset" parameter is used with some media types to define the
533   character set (<xref target="character.sets"/>) of the data. When no explicit charset
534   parameter is provided by the sender, media subtypes of the "text"
535   type are defined to have a default charset value of "ISO-8859-1" when
536   received via HTTP. Data in character sets other than "ISO-8859-1" or
537   its subsets MUST be labeled with an appropriate charset value. See
538   <xref target="missing.charset"/> for compatibility problems.
539</t>
540</section>
541
542<section title="Multipart Types" anchor="multipart.types">
543<t>
544   MIME provides for a number of "multipart" types -- encapsulations of
545   one or more entities within a single message-body. All multipart
546   types share a common syntax, as defined in Section 5.1.1 of <xref target="RFC2046"/>,
547   and MUST include a boundary parameter as part of the media type
548   value. The message body is itself a protocol element and MUST
549   therefore use only CRLF to represent line breaks between body-parts.
550   Unlike in RFC 2046, the epilogue of any multipart message MUST be
551   empty; HTTP applications MUST NOT transmit the epilogue (even if the
552   original multipart contains an epilogue). These restrictions exist in
553   order to preserve the self-delimiting nature of a multipart message-body,
554   wherein the "end" of the message-body is indicated by the
555   ending multipart boundary.
556</t>
557<t>
558   In general, HTTP treats a multipart message-body no differently than
559   any other media type: strictly as payload. The one exception is the
560   "multipart/byteranges" type (Appendix A of <xref target="Part5"/>) when it appears in a 206
561   (Partial Content) response.
562   <!-- jre: re-insert removed text pointing to caching? -->
563   In all
564   other cases, an HTTP user agent SHOULD follow the same or similar
565   behavior as a MIME user agent would upon receipt of a multipart type.
566   The MIME header fields within each body-part of a multipart message-body
567   do not have any significance to HTTP beyond that defined by
568   their MIME semantics.
569</t>
570<t>
571   In general, an HTTP user agent SHOULD follow the same or similar
572   behavior as a MIME user agent would upon receipt of a multipart type.
573   If an application receives an unrecognized multipart subtype, the
574   application MUST treat it as being equivalent to "multipart/mixed".
575</t>
576<t><list>
577  <t>
578    Note: The "multipart/form-data" type has been specifically defined
579    for carrying form data suitable for processing via the POST
580    request method, as described in <xref target="RFC2388"/>.
581  </t>
582</list></t>
583</section>
584</section>
585
586<section title="Language Tags" anchor="language.tags">
587 
588 
589 
590<t>
591   A language tag identifies a natural language spoken, written, or
592   otherwise conveyed by human beings for communication of information
593   to other human beings. Computer languages are explicitly excluded.
594   HTTP uses language tags within the Accept-Language and Content-Language
595   fields.
596</t>
597<t>
598   The syntax and registry of HTTP language tags is the same as that
599   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
600   or more parts: A primary language tag and a possibly empty series of
601   subtags:
602</t>
603<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[
604  language-tag  = primary-tag *( "-" subtag )
605  primary-tag   = 1*8ALPHA
606  subtag        = 1*8ALPHA
607]]></artwork></figure>
608<t>
609   White space is not allowed within the tag and all tags are case-insensitive.
610   The name space of language tags is administered by the
611   IANA. Example tags include:
612</t>
613<figure><artwork type="example"><![CDATA[
614  en, en-US, en-cockney, i-cherokee, x-pig-latin
615]]></artwork></figure>
616<t>
617   where any two-letter primary-tag is an ISO-639 language abbreviation
618   and any two-letter initial subtag is an ISO-3166 country code. (The
619   last three tags above are not registered tags; all but the last are
620   examples of tags which could be registered in future.)
621</t>
622</section>
623</section>
624
625<section title="Entity" anchor="entity">
626<t>
627   Request and Response messages MAY transfer an entity if not otherwise
628   restricted by the request method or response status code. An entity
629   consists of entity-header fields and an entity-body, although some
630   responses will only include the entity-headers.
631</t>
632<t>
633   In this section, both sender and recipient refer to either the client
634   or the server, depending on who sends and who receives the entity.
635</t>
636
637<section title="Entity Header Fields" anchor="entity.header.fields">
638 
639 
640<t>
641   Entity-header fields define metainformation about the entity-body or,
642   if no body is present, about the resource identified by the request.
643</t>
644<figure><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/><artwork type="abnf2616"><![CDATA[
645  entity-header  = Content-Encoding         ; Section 5.5
646                 / Content-Language         ; Section 5.6
647                 / Content-Length           ; [Part1], Section 8.2
648                 / Content-Location         ; Section 5.7
649                 / Content-MD5              ; Section 5.8
650                 / Content-Range            ; [Part5], Section 5.2
651                 / Content-Type             ; Section 5.9
652                 / Expires                  ; [Part6], Section 3.3
653                 / Last-Modified            ; [Part4], Section 6.6
654                 / extension-header
655 
656  extension-header = message-header
657]]></artwork></figure>
658<t>
659   The extension-header mechanism allows additional entity-header fields
660   to be defined without changing the protocol, but these fields cannot
661   be assumed to be recognizable by the recipient. Unrecognized header
662   fields SHOULD be ignored by the recipient and MUST be forwarded by
663   transparent proxies.
664</t>
665</section>
666
667<section title="Entity Body" anchor="entity.body">
668 
669<t>
670   The entity-body (if any) sent with an HTTP request or response is in
671   a format and encoding defined by the entity-header fields.
672</t>
673<figure><iref primary="true" item="Grammar" subitem="entity-body"/><artwork type="abnf2616"><![CDATA[
674  entity-body    = *OCTET
675]]></artwork></figure>
676<t>
677   An entity-body is only present in a message when a message-body is
678   present, as described in Section 4.3 of <xref target="Part1"/>. The entity-body is obtained
679   from the message-body by decoding any Transfer-Encoding that might
680   have been applied to ensure safe and proper transfer of the message.
681</t>
682
683<section title="Type" anchor="type">
684<t>
685   When an entity-body is included with a message, the data type of that
686   body is determined via the header fields Content-Type and Content-Encoding.
687   These define a two-layer, ordered encoding model:
688</t>
689<figure><artwork type="example"><![CDATA[
690  entity-body := Content-Encoding( Content-Type( data ) )
691]]></artwork></figure>
692<t>
693   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
694   message containing an entity-body SHOULD include a Content-Type header
695   field defining the media type of that body, unless that information is
696   unknown.  If the Content-Type header field is not present, it indicates that
697   the sender does not know the media type of the data; recipients MAY
698   either assume that it is "application/octet-stream" (<xref target="RFC2046"/>, Section 4.5.1)
699   or examine the content to determine its type.
700</t>
701<t>
702   Content-Encoding may be used to indicate any additional content
703   codings applied to the data, usually for the purpose of data
704   compression, that are a property of the requested resource.  There is
705   no default encoding.
706</t>
707<t>
708   Note that neither the interpretation of the data type of a message nor
709   the behaviors caused by it are defined by HTTP; this
710   potentially includes examination of the content to override any
711   indicated type ("sniffing")<iref item="Content Type Sniffing"/>.
712</t>
713</section>
714   
715<section title="Entity Length" anchor="entity.length">
716<t>
717   The entity-length of a message is the length of the message-body
718   before any transfer-codings have been applied. Section 4.4 of <xref target="Part1"/> defines
719   how the transfer-length of a message-body is determined.
720</t>
721</section>
722</section>
723</section>
724
725<section title="Content Negotiation" anchor="content.negotiation">
726<t>
727   Most HTTP responses include an entity which contains information for
728   interpretation by a human user. Naturally, it is desirable to supply
729   the user with the "best available" entity corresponding to the
730   request. Unfortunately for servers and caches, not all users have the
731   same preferences for what is "best," and not all user agents are
732   equally capable of rendering all entity types. For that reason, HTTP
733   has provisions for several mechanisms for "content negotiation" --
734   the process of selecting the best representation for a given response
735   when there are multiple representations available.
736</t>
737<t><list>
738  <t>
739    Note: This is not called "format negotiation" because the
740    alternate representations may be of the same media type, but use
741    different capabilities of that type, be in different languages,
742    etc.
743  </t>
744</list></t>
745<t>
746   Any response containing an entity-body MAY be subject to negotiation,
747   including error responses.
748</t>
749<t>
750   There are two kinds of content negotiation which are possible in
751   HTTP: server-driven and agent-driven negotiation. These two kinds of
752   negotiation are orthogonal and thus may be used separately or in
753   combination. One method of combination, referred to as transparent
754   negotiation, occurs when a cache uses the agent-driven negotiation
755   information provided by the origin server in order to provide
756   server-driven negotiation for subsequent requests.
757</t>
758
759<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
760<t>
761   If the selection of the best representation for a response is made by
762   an algorithm located at the server, it is called server-driven
763   negotiation. Selection is based on the available representations of
764   the response (the dimensions over which it can vary; e.g. language,
765   content-coding, etc.) and the contents of particular header fields in
766   the request message or on other information pertaining to the request
767   (such as the network address of the client).
768</t>
769<t>
770   Server-driven negotiation is advantageous when the algorithm for
771   selecting from among the available representations is difficult to
772   describe to the user agent, or when the server desires to send its
773   "best guess" to the client along with the first response (hoping to
774   avoid the round-trip delay of a subsequent request if the "best
775   guess" is good enough for the user). In order to improve the server's
776   guess, the user agent MAY include request header fields (Accept,
777   Accept-Language, Accept-Encoding, etc.) which describe its
778   preferences for such a response.
779</t>
780<t>
781   Server-driven negotiation has disadvantages:
782  <list style="numbers">
783    <t>
784         It is impossible for the server to accurately determine what
785         might be "best" for any given user, since that would require
786         complete knowledge of both the capabilities of the user agent
787         and the intended use for the response (e.g., does the user want
788         to view it on screen or print it on paper?).
789    </t>
790    <t>
791         Having the user agent describe its capabilities in every
792         request can be both very inefficient (given that only a small
793         percentage of responses have multiple representations) and a
794         potential violation of the user's privacy.
795    </t>
796    <t>
797         It complicates the implementation of an origin server and the
798         algorithms for generating responses to a request.
799    </t>
800    <t>
801         It may limit a public cache's ability to use the same response
802         for multiple user's requests.
803    </t>
804  </list>
805</t>
806<t>
807   HTTP/1.1 includes the following request-header fields for enabling
808   server-driven negotiation through description of user agent
809   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
810   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
811   (<xref target="header.accept-language"/>), and User-Agent (Section 9.9 of <xref target="Part2"/>). However, an
812   origin server is not limited to these dimensions and MAY vary the
813   response based on any aspect of the request, including information
814   outside the request-header fields or within extension header fields
815   not defined by this specification.
816</t>
817<t>
818   The Vary header field (Section 3.5 of <xref target="Part6"/>) can be used to express the parameters the
819   server uses to select a representation that is subject to server-driven
820   negotiation.
821</t>
822</section>
823
824<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
825<t>
826   With agent-driven negotiation, selection of the best representation
827   for a response is performed by the user agent after receiving an
828   initial response from the origin server. Selection is based on a list
829   of the available representations of the response included within the
830   header fields or entity-body of the initial response, with each
831   representation identified by its own URI. Selection from among the
832   representations may be performed automatically (if the user agent is
833   capable of doing so) or manually by the user selecting from a
834   generated (possibly hypertext) menu.
835</t>
836<t>
837   Agent-driven negotiation is advantageous when the response would vary
838   over commonly-used dimensions (such as type, language, or encoding),
839   when the origin server is unable to determine a user agent's
840   capabilities from examining the request, and generally when public
841   caches are used to distribute server load and reduce network usage.
842</t>
843<t>
844   Agent-driven negotiation suffers from the disadvantage of needing a
845   second request to obtain the best alternate representation. This
846   second request is only efficient when caching is used. In addition,
847   this specification does not define any mechanism for supporting
848   automatic selection, though it also does not prevent any such
849   mechanism from being developed as an extension and used within
850   HTTP/1.1.
851</t>
852<t>
853   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
854   status codes for enabling agent-driven negotiation when the server is
855   unwilling or unable to provide a varying response using server-driven
856   negotiation.
857</t>
858</section>
859
860<section title="Transparent Negotiation" anchor="transparent.negotiation">
861<t>
862   Transparent negotiation is a combination of both server-driven and
863   agent-driven negotiation. When a cache is supplied with a form of the
864   list of available representations of the response (as in agent-driven
865   negotiation) and the dimensions of variance are completely understood
866   by the cache, then the cache becomes capable of performing server-driven
867   negotiation on behalf of the origin server for subsequent
868   requests on that resource.
869</t>
870<t>
871   Transparent negotiation has the advantage of distributing the
872   negotiation work that would otherwise be required of the origin
873   server and also removing the second request delay of agent-driven
874   negotiation when the cache is able to correctly guess the right
875   response.
876</t>
877<t>
878   This specification does not define any mechanism for transparent
879   negotiation, though it also does not prevent any such mechanism from
880   being developed as an extension that could be used within HTTP/1.1.
881</t>
882</section>
883</section>
884
885<section title="Header Field Definitions" anchor="header.fields">
886<t>
887   This section defines the syntax and semantics of HTTP/1.1 header fields
888   related to the payload of messages.
889</t>
890<t>
891   For entity-header fields, both sender and recipient refer to either the
892   client or the server, depending on who sends and who receives the entity.
893</t>
894
895<section title="Accept" anchor="header.accept">
896  <iref primary="true" item="Accept header"/>
897  <iref primary="true" item="Headers" subitem="Accept"/>
898 
899 
900 
901 
902 
903<t>
904   The request-header field "Accept" can be used to specify certain media
905   types which are acceptable for the response. Accept headers can be
906   used to indicate that the request is specifically limited to a small
907   set of desired types, as in the case of a request for an in-line
908   image.
909</t>
910<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[
911  Accept   = "Accept" ":" OWS Accept-v
912  Accept-v = #( media-range [ accept-params ] )
913 
914  media-range    = ( "*/*"
915                   / ( type "/" "*" )
916                   / ( type "/" subtype )
917                   ) *( OWS ";" OWS parameter )
918  accept-params  = OWS ";" OWS "q=" qvalue *( accept-ext )
919  accept-ext     = OWS ";" OWS token
920                   [ "=" ( token / quoted-string ) ]
921]]></artwork></figure>
922<t>
923   The asterisk "*" character is used to group media types into ranges,
924   with "*/*" indicating all media types and "type/*" indicating all
925   subtypes of that type. The media-range MAY include media type
926   parameters that are applicable to that range.
927</t>
928<t>
929   Each media-range MAY be followed by one or more accept-params,
930   beginning with the "q" parameter for indicating a relative quality
931   factor. The first "q" parameter (if any) separates the media-range
932   parameter(s) from the accept-params. Quality factors allow the user
933   or user agent to indicate the relative degree of preference for that
934   media-range, using the qvalue scale from 0 to 1 (Section 3.5 of <xref target="Part1"/>). The
935   default value is q=1.
936</t>
937<t><list>
938  <t>
939    Note: Use of the "q" parameter name to separate media type
940    parameters from Accept extension parameters is due to historical
941    practice. Although this prevents any media type parameter named
942    "q" from being used with a media range, such an event is believed
943    to be unlikely given the lack of any "q" parameters in the IANA
944    media type registry and the rare usage of any media type
945    parameters in Accept. Future media types are discouraged from
946    registering any parameter named "q".
947  </t>
948</list></t>
949<t>
950   The example
951</t>
952<figure><artwork type="example"><![CDATA[
953  Accept: audio/*; q=0.2, audio/basic
954]]></artwork></figure>
955<t>
956   SHOULD be interpreted as "I prefer audio/basic, but send me any audio
957   type if it is the best available after an 80% mark-down in quality."
958</t>
959<t>
960   If no Accept header field is present, then it is assumed that the
961   client accepts all media types. If an Accept header field is present,
962   and if the server cannot send a response which is acceptable
963   according to the combined Accept field value, then the server SHOULD
964   send a 406 (Not Acceptable) response.
965</t>
966<t>
967   A more elaborate example is
968</t>
969<figure><artwork type="example"><![CDATA[
970  Accept: text/plain; q=0.5, text/html,
971          text/x-dvi; q=0.8, text/x-c
972]]></artwork></figure>
973<t>
974   Verbally, this would be interpreted as "text/html and text/x-c are
975   the preferred media types, but if they do not exist, then send the
976   text/x-dvi entity, and if that does not exist, send the text/plain
977   entity."
978</t>
979<t>
980   Media ranges can be overridden by more specific media ranges or
981   specific media types. If more than one media range applies to a given
982   type, the most specific reference has precedence. For example,
983</t>
984<figure><artwork type="example"><![CDATA[
985  Accept: text/*, text/html, text/html;level=1, */*
986]]></artwork></figure>
987<t>
988   have the following precedence:
989   <list style="numbers">
990    <t>text/html;level=1</t>
991    <t>text/html</t>
992    <t>text/*</t>
993    <t>*/*</t>
994   </list>
995</t>
996<t>
997   The media type quality factor associated with a given type is
998   determined by finding the media range with the highest precedence
999   which matches that type. For example,
1000</t>
1001<figure><artwork type="example"><![CDATA[
1002  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1003          text/html;level=2;q=0.4, */*;q=0.5
1004]]></artwork></figure>
1005<t>
1006   would cause the following values to be associated:
1007</t>
1008<texttable align="left">
1009  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1010  <c>text/html;level=1</c>    <c>1</c>
1011  <c>text/html</c>            <c>0.7</c>
1012  <c>text/plain</c>           <c>0.3</c>
1013  <c>image/jpeg</c>           <c>0.5</c>
1014  <c>text/html;level=2</c>    <c>0.4</c>
1015  <c>text/html;level=3</c>    <c>0.7</c>
1016</texttable>
1017<t>
1018      Note: A user agent might be provided with a default set of quality
1019      values for certain media ranges. However, unless the user agent is
1020      a closed system which cannot interact with other rendering agents,
1021      this default set ought to be configurable by the user.
1022</t>
1023</section>
1024
1025<section title="Accept-Charset" anchor="header.accept-charset">
1026  <iref primary="true" item="Accept-Charset header"/>
1027  <iref primary="true" item="Headers" subitem="Accept-Charset"/>
1028 
1029 
1030<t>
1031   The request-header field "Accept-Charset" can be used to indicate what
1032   character sets are acceptable for the response. This field allows
1033   clients capable of understanding more comprehensive or special-purpose
1034   character sets to signal that capability to a server which is
1035   capable of representing documents in those character sets.
1036</t>
1037<figure><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/><artwork type="abnf2616"><![CDATA[
1038  Accept-Charset   = "Accept-Charset" ":" OWS
1039          Accept-Charset-v
1040  Accept-Charset-v = 1#( ( charset / "*" )
1041                         [ OWS ";" OWS "q=" qvalue ] )
1042]]></artwork></figure>
1043<t>
1044   Character set values are described in <xref target="character.sets"/>. Each charset MAY
1045   be given an associated quality value which represents the user's
1046   preference for that charset. The default value is q=1. An example is
1047</t>
1048<figure><artwork type="example"><![CDATA[
1049  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1050]]></artwork></figure>
1051<t>
1052   The special value "*", if present in the Accept-Charset field,
1053   matches every character set (including ISO-8859-1) which is not
1054   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1055   in an Accept-Charset field, then all character sets not explicitly
1056   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1057   a quality value of 1 if not explicitly mentioned.
1058</t>
1059<t>
1060   If no Accept-Charset header is present, the default is that any
1061   character set is acceptable. If an Accept-Charset header is present,
1062   and if the server cannot send a response which is acceptable
1063   according to the Accept-Charset header, then the server SHOULD send
1064   an error response with the 406 (Not Acceptable) status code, though
1065   the sending of an unacceptable response is also allowed.
1066</t>
1067</section>
1068
1069<section title="Accept-Encoding" anchor="header.accept-encoding">
1070  <iref primary="true" item="Accept-Encoding header"/>
1071  <iref primary="true" item="Headers" subitem="Accept-Encoding"/>
1072 
1073 
1074 
1075<t>
1076   The request-header field "Accept-Encoding" is similar to Accept, but
1077   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1078   the response.
1079</t>
1080<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[
1081  Accept-Encoding    = "Accept-Encoding" ":" OWS
1082                     Accept-Encoding-v
1083  Accept-Encoding-v  =
1084                     #( codings [ OWS ";" OWS "q=" qvalue ] )
1085  codings            = ( content-coding / "*" )
1086]]></artwork></figure>
1087<t>
1088   Each codings value MAY be given an associated quality value which
1089   represents the preference for that encoding. The default value is q=1.
1090</t>
1091<t>
1092   Examples of its use are:
1093</t>
1094<figure><artwork type="example"><![CDATA[
1095  Accept-Encoding: compress, gzip
1096  Accept-Encoding:
1097  Accept-Encoding: *
1098  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1099  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1100]]></artwork></figure>
1101<t>
1102   A server tests whether a content-coding is acceptable, according to
1103   an Accept-Encoding field, using these rules:
1104  <list style="numbers">
1105      <t>If the content-coding is one of the content-codings listed in
1106         the Accept-Encoding field, then it is acceptable, unless it is
1107         accompanied by a qvalue of 0. (As defined in Section 3.5 of <xref target="Part1"/>, a
1108         qvalue of 0 means "not acceptable.")</t>
1109
1110      <t>The special "*" symbol in an Accept-Encoding field matches any
1111         available content-coding not explicitly listed in the header
1112         field.</t>
1113
1114      <t>If multiple content-codings are acceptable, then the acceptable
1115         content-coding with the highest non-zero qvalue is preferred.</t>
1116
1117      <t>The "identity" content-coding is always acceptable, unless
1118         specifically refused because the Accept-Encoding field includes
1119         "identity;q=0", or because the field includes "*;q=0" and does
1120         not explicitly include the "identity" content-coding. If the
1121         Accept-Encoding field-value is empty, then only the "identity"
1122         encoding is acceptable.</t>
1123  </list>
1124</t>
1125<t>
1126   If an Accept-Encoding field is present in a request, and if the
1127   server cannot send a response which is acceptable according to the
1128   Accept-Encoding header, then the server SHOULD send an error response
1129   with the 406 (Not Acceptable) status code.
1130</t>
1131<t>
1132   If no Accept-Encoding field is present in a request, the server MAY
1133   assume that the client will accept any content coding. In this case,
1134   if "identity" is one of the available content-codings, then the
1135   server SHOULD use the "identity" content-coding, unless it has
1136   additional information that a different content-coding is meaningful
1137   to the client.
1138</t>
1139<t><list>
1140  <t>
1141    Note: If the request does not include an Accept-Encoding field,
1142    and if the "identity" content-coding is unavailable, then
1143    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1144    "gzip" and "compress") are preferred; some older clients
1145    improperly display messages sent with other content-codings.  The
1146    server might also make this decision based on information about
1147    the particular user-agent or client.
1148  </t>
1149</list></t>
1150<t><list>
1151  <t>
1152    Note: Most HTTP/1.0 applications do not recognize or obey qvalues
1153    associated with content-codings. This means that qvalues will not
1154    work and are not permitted with x-gzip or x-compress.
1155  </t>
1156</list></t>
1157</section>
1158
1159<section title="Accept-Language" anchor="header.accept-language">
1160  <iref primary="true" item="Accept-Language header"/>
1161  <iref primary="true" item="Headers" subitem="Accept-Language"/>
1162 
1163 
1164 
1165<t>
1166   The request-header field "Accept-Language" is similar to Accept, but
1167   restricts the set of natural languages that are preferred as a
1168   response to the request. Language tags are defined in <xref target="language.tags"/>.
1169</t>
1170<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[
1171  Accept-Language   = "Accept-Language" ":" OWS
1172                    Accept-Language-v
1173  Accept-Language-v =
1174                    1#( language-range [ OWS ";" OWS "q=" qvalue ] )
1175  language-range    =
1176            <language-range, defined in [RFC4647], Section 2.1>
1177]]></artwork></figure>
1178<t>
1179   Each language-range can be given an associated quality value which
1180   represents an estimate of the user's preference for the languages
1181   specified by that range. The quality value defaults to "q=1". For
1182   example,
1183</t>
1184<figure><artwork type="example"><![CDATA[
1185  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1186]]></artwork></figure>
1187<t>
1188   would mean: "I prefer Danish, but will accept British English and
1189   other types of English."
1190</t>
1191<t>
1192   For matching, the "Basic Filtering" matching scheme, defined in
1193   Section 3.3.1 of <xref target="RFC4647"/>, is used:
1194</t>
1195<t><list>
1196  <t>
1197     A language range matches a
1198     particular language tag if, in a case-insensitive comparison, it
1199     exactly equals the tag, or if it exactly equals a prefix of the tag
1200     such that the first character following the prefix is "-".
1201  </t>
1202</list></t> 
1203<t>
1204   The special range "*", if present in the Accept-Language field,
1205   matches every tag not matched by any other range present in the
1206   Accept-Language field.
1207</t>
1208<t><list>
1209  <t>
1210    Note: This use of a prefix matching rule does not imply that
1211    language tags are assigned to languages in such a way that it is
1212    always true that if a user understands a language with a certain
1213    tag, then this user will also understand all languages with tags
1214    for which this tag is a prefix. The prefix rule simply allows the
1215    use of prefix tags if this is the case.
1216  </t>
1217</list></t>
1218<t>
1219   The language quality factor assigned to a language-tag by the
1220   Accept-Language field is the quality value of the longest language-range
1221   in the field that matches the language-tag. If no language-range
1222   in the field matches the tag, the language quality factor
1223   assigned is 0. If no Accept-Language header is present in the
1224   request, the server
1225   SHOULD assume that all languages are equally acceptable. If an
1226   Accept-Language header is present, then all languages which are
1227   assigned a quality factor greater than 0 are acceptable.
1228</t>
1229<t>
1230   It might be contrary to the privacy expectations of the user to send
1231   an Accept-Language header with the complete linguistic preferences of
1232   the user in every request. For a discussion of this issue, see
1233   <xref target="privacy.issues.connected.to.accept.headers"/>.
1234</t>
1235<t>
1236   As intelligibility is highly dependent on the individual user, it is
1237   recommended that client applications make the choice of linguistic
1238   preference available to the user. If the choice is not made
1239   available, then the Accept-Language header field MUST NOT be given in
1240   the request.
1241</t>
1242<t><list>
1243  <t>
1244    Note: When making the choice of linguistic preference available to
1245    the user, we remind implementors of  the fact that users are not
1246    familiar with the details of language matching as described above,
1247    and should provide appropriate guidance. As an example, users
1248    might assume that on selecting "en-gb", they will be served any
1249    kind of English document if British English is not available. A
1250    user agent might suggest in such a case to add "en" to get the
1251    best matching behavior.
1252  </t>
1253</list></t>
1254</section>
1255
1256<section title="Content-Encoding" anchor="header.content-encoding">
1257  <iref primary="true" item="Content-Encoding header"/>
1258  <iref primary="true" item="Headers" subitem="Content-Encoding"/>
1259 
1260 
1261<t>
1262   The entity-header field "Content-Encoding" is used as a modifier to the
1263   media-type. When present, its value indicates what additional content
1264   codings have been applied to the entity-body, and thus what decoding
1265   mechanisms must be applied in order to obtain the media-type
1266   referenced by the Content-Type header field. Content-Encoding is
1267   primarily used to allow a document to be compressed without losing
1268   the identity of its underlying media type.
1269</t>
1270<figure><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/><artwork type="abnf2616"><![CDATA[
1271  Content-Encoding   = "Content-Encoding" ":" OWS Content-Encoding-v
1272  Content-Encoding-v = 1#content-coding
1273]]></artwork></figure>
1274<t>
1275   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1276</t>
1277<figure><artwork type="example"><![CDATA[
1278  Content-Encoding: gzip
1279]]></artwork></figure>
1280<t>
1281   The content-coding is a characteristic of the entity identified by
1282   the request-target. Typically, the entity-body is stored with this
1283   encoding and is only decoded before rendering or analogous usage.
1284   However, a non-transparent proxy MAY modify the content-coding if the
1285   new coding is known to be acceptable to the recipient, unless the
1286   "no-transform" cache-control directive is present in the message.
1287</t>
1288<t>
1289   If the content-coding of an entity is not "identity", then the
1290   response MUST include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1291   that lists the non-identity content-coding(s) used.
1292</t>
1293<t>
1294   If the content-coding of an entity in a request message is not
1295   acceptable to the origin server, the server SHOULD respond with a
1296   status code of 415 (Unsupported Media Type).
1297</t>
1298<t>
1299   If multiple encodings have been applied to an entity, the content
1300   codings MUST be listed in the order in which they were applied.
1301   Additional information about the encoding parameters MAY be provided
1302   by other entity-header fields not defined by this specification.
1303</t>
1304</section>
1305
1306<section title="Content-Language" anchor="header.content-language">
1307  <iref primary="true" item="Content-Language header"/>
1308  <iref primary="true" item="Headers" subitem="Content-Language"/>
1309 
1310 
1311<t>
1312   The entity-header field "Content-Language" describes the natural
1313   language(s) of the intended audience for the enclosed entity. Note
1314   that this might not be equivalent to all the languages used within
1315   the entity-body.
1316</t>
1317<figure><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/><artwork type="abnf2616"><![CDATA[
1318  Content-Language   = "Content-Language" ":" OWS Content-Language-v
1319  Content-Language-v = 1#language-tag
1320]]></artwork></figure>
1321<t>
1322   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1323   Content-Language is to allow a user to identify and differentiate
1324   entities according to the user's own preferred language. Thus, if the
1325   body content is intended only for a Danish-literate audience, the
1326   appropriate field is
1327</t>
1328<figure><artwork type="example"><![CDATA[
1329  Content-Language: da
1330]]></artwork></figure>
1331<t>
1332   If no Content-Language is specified, the default is that the content
1333   is intended for all language audiences. This might mean that the
1334   sender does not consider it to be specific to any natural language,
1335   or that the sender does not know for which language it is intended.
1336</t>
1337<t>
1338   Multiple languages MAY be listed for content that is intended for
1339   multiple audiences. For example, a rendition of the "Treaty of
1340   Waitangi," presented simultaneously in the original Maori and English
1341   versions, would call for
1342</t>
1343<figure><artwork type="example"><![CDATA[
1344  Content-Language: mi, en
1345]]></artwork></figure>
1346<t>
1347   However, just because multiple languages are present within an entity
1348   does not mean that it is intended for multiple linguistic audiences.
1349   An example would be a beginner's language primer, such as "A First
1350   Lesson in Latin," which is clearly intended to be used by an
1351   English-literate audience. In this case, the Content-Language would
1352   properly only include "en".
1353</t>
1354<t>
1355   Content-Language MAY be applied to any media type -- it is not
1356   limited to textual documents.
1357</t>
1358</section>
1359
1360<section title="Content-Location" anchor="header.content-location">
1361  <iref primary="true" item="Content-Location header"/>
1362  <iref primary="true" item="Headers" subitem="Content-Location"/>
1363 
1364 
1365<t>
1366   The entity-header field "Content-Location" MAY be used to supply the
1367   resource location for the entity enclosed in the message when that
1368   entity is accessible from a location separate from the requested
1369   resource's URI. A server SHOULD provide a Content-Location for the
1370   variant corresponding to the response entity; especially in the case
1371   where a resource has multiple entities associated with it, and those
1372   entities actually have separate locations by which they might be
1373   individually accessed, the server SHOULD provide a Content-Location
1374   for the particular variant which is returned.
1375</t>
1376<figure><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/><artwork type="abnf2616"><![CDATA[
1377  Content-Location   = "Content-Location" ":" OWS
1378                    Content-Location-v
1379  Content-Location-v =
1380                    absolute-URI / partial-URI
1381]]></artwork></figure>
1382<t>
1383   The value of Content-Location also defines the base URI for the
1384   entity.
1385</t>
1386<t>
1387   The Content-Location value is not a replacement for the original
1388   requested URI; it is only a statement of the location of the resource
1389   corresponding to this particular entity at the time of the request.
1390   Future requests MAY specify the Content-Location URI as the request-target
1391   if the desire is to identify the source of that particular
1392   entity.
1393</t>
1394<t>
1395   A cache cannot assume that an entity with a Content-Location
1396   different from the URI used to retrieve it can be used to respond to
1397   later requests on that Content-Location URI. However, the Content-Location
1398   can be used to differentiate between multiple entities
1399   retrieved from a single requested resource, as described in Section 2.6 of <xref target="Part6"/>.
1400</t>
1401<t>
1402   If the Content-Location is a relative URI, the relative URI is
1403   interpreted relative to the request-target.
1404</t>
1405<t>
1406   The meaning of the Content-Location header in requests is
1407   undefined; servers are free to ignore it in those cases.
1408</t>
1409</section>
1410
1411<section title="Content-MD5" anchor="header.content-md5">
1412  <iref primary="true" item="Content-MD5 header"/>
1413  <iref primary="true" item="Headers" subitem="Content-MD5"/>
1414 
1415 
1416<t>
1417   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1418   an MD5 digest of the entity-body for the purpose of providing an
1419   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1420   MIC is good for detecting accidental modification of the entity-body
1421   in transit, but is not proof against malicious attacks.)
1422</t>
1423<figure><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/><artwork type="abnf2616"><![CDATA[
1424  Content-MD5   = "Content-MD5" ":" OWS Content-MD5-v
1425  Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]>
1426]]></artwork></figure>
1427<t>
1428   The Content-MD5 header field MAY be generated by an origin server or
1429   client to function as an integrity check of the entity-body. Only
1430   origin servers or clients MAY generate the Content-MD5 header field;
1431   proxies and gateways MUST NOT generate it, as this would defeat its
1432   value as an end-to-end integrity check. Any recipient of the entity-body,
1433   including gateways and proxies, MAY check that the digest value
1434   in this header field matches that of the entity-body as received.
1435</t>
1436<t>
1437   The MD5 digest is computed based on the content of the entity-body,
1438   including any content-coding that has been applied, but not including
1439   any transfer-encoding applied to the message-body. If the message is
1440   received with a transfer-encoding, that encoding MUST be removed
1441   prior to checking the Content-MD5 value against the received entity.
1442</t>
1443<t>
1444   This has the result that the digest is computed on the octets of the
1445   entity-body exactly as, and in the order that, they would be sent if
1446   no transfer-encoding were being applied.
1447</t>
1448<t>
1449   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1450   composite media-types (e.g., multipart/* and message/rfc822), but
1451   this does not change how the digest is computed as defined in the
1452   preceding paragraph.
1453</t>
1454<t>
1455   There are several consequences of this. The entity-body for composite
1456   types MAY contain many body-parts, each with its own MIME and HTTP
1457   headers (including Content-MD5, Content-Transfer-Encoding, and
1458   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1459   or Content-Encoding header, it is assumed that the content
1460   of the body-part has had the encoding applied, and the body-part is
1461   included in the Content-MD5 digest as is -- i.e., after the
1462   application. The Transfer-Encoding header field is not allowed within
1463   body-parts.
1464</t>
1465<t>
1466   Conversion of all line breaks to CRLF MUST NOT be done before
1467   computing or checking the digest: the line break convention used in
1468   the text actually transmitted MUST be left unaltered when computing
1469   the digest.
1470</t>
1471<t><list>
1472  <t>
1473    Note: while the definition of Content-MD5 is exactly the same for
1474    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1475    in which the application of Content-MD5 to HTTP entity-bodies
1476    differs from its application to MIME entity-bodies. One is that
1477    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1478    does use Transfer-Encoding and Content-Encoding. Another is that
1479    HTTP more frequently uses binary content types than MIME, so it is
1480    worth noting that, in such cases, the byte order used to compute
1481    the digest is the transmission byte order defined for the type.
1482    Lastly, HTTP allows transmission of text types with any of several
1483    line break conventions and not just the canonical form using CRLF.
1484  </t>
1485</list></t>
1486</section>
1487
1488<section title="Content-Type" anchor="header.content-type">
1489  <iref primary="true" item="Content-Type header"/>
1490  <iref primary="true" item="Headers" subitem="Content-Type"/>
1491 
1492 
1493<t>
1494   The entity-header field "Content-Type" indicates the media type of the
1495   entity-body sent to the recipient or, in the case of the HEAD method,
1496   the media type that would have been sent had the request been a GET.
1497</t>
1498<figure><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/><artwork type="abnf2616"><![CDATA[
1499  Content-Type   = "Content-Type" ":" OWS Content-Type-v
1500  Content-Type-v = media-type
1501]]></artwork></figure>
1502<t>
1503   Media types are defined in <xref target="media.types"/>. An example of the field is
1504</t>
1505<figure><artwork type="example"><![CDATA[
1506  Content-Type: text/html; charset=ISO-8859-4
1507]]></artwork></figure>
1508<t>
1509   Further discussion of methods for identifying the media type of an
1510   entity is provided in <xref target="type"/>.
1511</t>
1512</section>
1513
1514</section>
1515
1516<section title="IANA Considerations" anchor="IANA.considerations">
1517<section title="Message Header Registration" anchor="message.header.registration">
1518<t>
1519   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1520   with the permanent registrations below (see <xref target="RFC3864"/>):
1521</t>
1522<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1523<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1524   <ttcol>Header Field Name</ttcol>
1525   <ttcol>Protocol</ttcol>
1526   <ttcol>Status</ttcol>
1527   <ttcol>Reference</ttcol>
1528
1529   <c>Accept</c>
1530   <c>http</c>
1531   <c>standard</c>
1532   <c>
1533      <xref target="header.accept"/>
1534   </c>
1535   <c>Accept-Charset</c>
1536   <c>http</c>
1537   <c>standard</c>
1538   <c>
1539      <xref target="header.accept-charset"/>
1540   </c>
1541   <c>Accept-Encoding</c>
1542   <c>http</c>
1543   <c>standard</c>
1544   <c>
1545      <xref target="header.accept-encoding"/>
1546   </c>
1547   <c>Accept-Language</c>
1548   <c>http</c>
1549   <c>standard</c>
1550   <c>
1551      <xref target="header.accept-language"/>
1552   </c>
1553   <c>Content-Disposition</c>
1554   <c>http</c>
1555   <c/>
1556   <c>
1557      <xref target="content-disposition"/>
1558   </c>
1559   <c>Content-Encoding</c>
1560   <c>http</c>
1561   <c>standard</c>
1562   <c>
1563      <xref target="header.content-encoding"/>
1564   </c>
1565   <c>Content-Language</c>
1566   <c>http</c>
1567   <c>standard</c>
1568   <c>
1569      <xref target="header.content-language"/>
1570   </c>
1571   <c>Content-Location</c>
1572   <c>http</c>
1573   <c>standard</c>
1574   <c>
1575      <xref target="header.content-location"/>
1576   </c>
1577   <c>Content-MD5</c>
1578   <c>http</c>
1579   <c>standard</c>
1580   <c>
1581      <xref target="header.content-md5"/>
1582   </c>
1583   <c>Content-Type</c>
1584   <c>http</c>
1585   <c>standard</c>
1586   <c>
1587      <xref target="header.content-type"/>
1588   </c>
1589   <c>MIME-Version</c>
1590   <c>http</c>
1591   <c/>
1592   <c>
1593      <xref target="mime-version"/>
1594   </c>
1595</texttable>
1596<!--(END)-->
1597<t>
1598   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1599</t>
1600</section>
1601</section>
1602
1603<section title="Security Considerations" anchor="security.considerations">
1604<t>
1605   This section is meant to inform application developers, information
1606   providers, and users of the security limitations in HTTP/1.1 as
1607   described by this document. The discussion does not include
1608   definitive solutions to the problems revealed, though it does make
1609   some suggestions for reducing security risks.
1610</t>
1611
1612<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1613<t>
1614   Accept request-headers can reveal information about the user to all
1615   servers which are accessed. The Accept-Language header in particular
1616   can reveal information the user would consider to be of a private
1617   nature, because the understanding of particular languages is often
1618   strongly correlated to the membership of a particular ethnic group.
1619   User agents which offer the option to configure the contents of an
1620   Accept-Language header to be sent in every request are strongly
1621   encouraged to let the configuration process include a message which
1622   makes the user aware of the loss of privacy involved.
1623</t>
1624<t>
1625   An approach that limits the loss of privacy would be for a user agent
1626   to omit the sending of Accept-Language headers by default, and to ask
1627   the user whether or not to start sending Accept-Language headers to a
1628   server if it detects, by looking for any Vary response-header fields
1629   generated by the server, that such sending could improve the quality
1630   of service.
1631</t>
1632<t>
1633   Elaborate user-customized accept header fields sent in every request,
1634   in particular if these include quality values, can be used by servers
1635   as relatively reliable and long-lived user identifiers. Such user
1636   identifiers would allow content providers to do click-trail tracking,
1637   and would allow collaborating content providers to match cross-server
1638   click-trails or form submissions of individual users. Note that for
1639   many users not behind a proxy, the network address of the host
1640   running the user agent will also serve as a long-lived user
1641   identifier. In environments where proxies are used to enhance
1642   privacy, user agents ought to be conservative in offering accept
1643   header configuration options to end users. As an extreme privacy
1644   measure, proxies could filter the accept headers in relayed requests.
1645   General purpose user agents which provide a high degree of header
1646   configurability SHOULD warn users about the loss of privacy which can
1647   be involved.
1648</t>
1649</section>
1650
1651<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1652<t>
1653   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1654   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1655   serious security considerations. Content-Disposition is not part of
1656   the HTTP standard, but since it is widely implemented, we are
1657   documenting its use and risks for implementors. See Section 5 of <xref target="RFC2183"/>
1658   for details.
1659</t>
1660</section>
1661
1662</section>
1663
1664<section title="Acknowledgments" anchor="ack">
1665</section>
1666</middle>
1667<back>
1668
1669<references title="Normative References">
1670
1671<reference anchor="ISO-8859-1">
1672  <front>
1673    <title>
1674     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1675    </title>
1676    <author>
1677      <organization>International Organization for Standardization</organization>
1678    </author>
1679    <date year="1998"/>
1680  </front>
1681  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1682</reference>
1683
1684<reference anchor="Part1">
1685  <front>
1686    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1687    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1688      <organization abbrev="Day Software">Day Software</organization>
1689      <address><email>fielding@gbiv.com</email></address>
1690    </author>
1691    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1692      <organization>One Laptop per Child</organization>
1693      <address><email>jg@laptop.org</email></address>
1694    </author>
1695    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1696      <organization abbrev="HP">Hewlett-Packard Company</organization>
1697      <address><email>JeffMogul@acm.org</email></address>
1698    </author>
1699    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1700      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1701      <address><email>henrikn@microsoft.com</email></address>
1702    </author>
1703    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1704      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1705      <address><email>LMM@acm.org</email></address>
1706    </author>
1707    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1708      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1709      <address><email>paulle@microsoft.com</email></address>
1710    </author>
1711    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1712      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1713      <address><email>timbl@w3.org</email></address>
1714    </author>
1715    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1716      <organization abbrev="W3C">World Wide Web Consortium</organization>
1717      <address><email>ylafon@w3.org</email></address>
1718    </author>
1719    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1720      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1721      <address><email>julian.reschke@greenbytes.de</email></address>
1722    </author>
1723    <date month="July" year="2009"/>
1724  </front>
1725  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-07"/>
1726 
1727</reference>
1728
1729<reference anchor="Part2">
1730  <front>
1731    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1732    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1733      <organization abbrev="Day Software">Day Software</organization>
1734      <address><email>fielding@gbiv.com</email></address>
1735    </author>
1736    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1737      <organization>One Laptop per Child</organization>
1738      <address><email>jg@laptop.org</email></address>
1739    </author>
1740    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1741      <organization abbrev="HP">Hewlett-Packard Company</organization>
1742      <address><email>JeffMogul@acm.org</email></address>
1743    </author>
1744    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1745      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1746      <address><email>henrikn@microsoft.com</email></address>
1747    </author>
1748    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1749      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1750      <address><email>LMM@acm.org</email></address>
1751    </author>
1752    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1753      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1754      <address><email>paulle@microsoft.com</email></address>
1755    </author>
1756    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1757      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1758      <address><email>timbl@w3.org</email></address>
1759    </author>
1760    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1761      <organization abbrev="W3C">World Wide Web Consortium</organization>
1762      <address><email>ylafon@w3.org</email></address>
1763    </author>
1764    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1765      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1766      <address><email>julian.reschke@greenbytes.de</email></address>
1767    </author>
1768    <date month="July" year="2009"/>
1769  </front>
1770  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-07"/>
1771 
1772</reference>
1773
1774<reference anchor="Part4">
1775  <front>
1776    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1777    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1778      <organization abbrev="Day Software">Day Software</organization>
1779      <address><email>fielding@gbiv.com</email></address>
1780    </author>
1781    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1782      <organization>One Laptop per Child</organization>
1783      <address><email>jg@laptop.org</email></address>
1784    </author>
1785    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1786      <organization abbrev="HP">Hewlett-Packard Company</organization>
1787      <address><email>JeffMogul@acm.org</email></address>
1788    </author>
1789    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1790      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1791      <address><email>henrikn@microsoft.com</email></address>
1792    </author>
1793    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1794      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1795      <address><email>LMM@acm.org</email></address>
1796    </author>
1797    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1798      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1799      <address><email>paulle@microsoft.com</email></address>
1800    </author>
1801    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1802      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1803      <address><email>timbl@w3.org</email></address>
1804    </author>
1805    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1806      <organization abbrev="W3C">World Wide Web Consortium</organization>
1807      <address><email>ylafon@w3.org</email></address>
1808    </author>
1809    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1810      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1811      <address><email>julian.reschke@greenbytes.de</email></address>
1812    </author>
1813    <date month="July" year="2009"/>
1814  </front>
1815  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-07"/>
1816 
1817</reference>
1818
1819<reference anchor="Part5">
1820  <front>
1821    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1822    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1823      <organization abbrev="Day Software">Day Software</organization>
1824      <address><email>fielding@gbiv.com</email></address>
1825    </author>
1826    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1827      <organization>One Laptop per Child</organization>
1828      <address><email>jg@laptop.org</email></address>
1829    </author>
1830    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1831      <organization abbrev="HP">Hewlett-Packard Company</organization>
1832      <address><email>JeffMogul@acm.org</email></address>
1833    </author>
1834    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1835      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1836      <address><email>henrikn@microsoft.com</email></address>
1837    </author>
1838    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1839      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1840      <address><email>LMM@acm.org</email></address>
1841    </author>
1842    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1843      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1844      <address><email>paulle@microsoft.com</email></address>
1845    </author>
1846    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1847      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1848      <address><email>timbl@w3.org</email></address>
1849    </author>
1850    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1851      <organization abbrev="W3C">World Wide Web Consortium</organization>
1852      <address><email>ylafon@w3.org</email></address>
1853    </author>
1854    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1855      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1856      <address><email>julian.reschke@greenbytes.de</email></address>
1857    </author>
1858    <date month="July" year="2009"/>
1859  </front>
1860  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-07"/>
1861 
1862</reference>
1863
1864<reference anchor="Part6">
1865  <front>
1866    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1867    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1868      <organization abbrev="Day Software">Day Software</organization>
1869      <address><email>fielding@gbiv.com</email></address>
1870    </author>
1871    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1872      <organization>One Laptop per Child</organization>
1873      <address><email>jg@laptop.org</email></address>
1874    </author>
1875    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1876      <organization abbrev="HP">Hewlett-Packard Company</organization>
1877      <address><email>JeffMogul@acm.org</email></address>
1878    </author>
1879    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1880      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1881      <address><email>henrikn@microsoft.com</email></address>
1882    </author>
1883    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1884      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1885      <address><email>LMM@acm.org</email></address>
1886    </author>
1887    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1888      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1889      <address><email>paulle@microsoft.com</email></address>
1890    </author>
1891    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1892      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1893      <address><email>timbl@w3.org</email></address>
1894    </author>
1895    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1896      <organization abbrev="W3C">World Wide Web Consortium</organization>
1897      <address><email>ylafon@w3.org</email></address>
1898    </author>
1899    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1900      <organization/>
1901      <address><email>mnot@mnot.net</email></address>
1902    </author>
1903    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1904      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1905      <address><email>julian.reschke@greenbytes.de</email></address>
1906    </author>
1907    <date month="July" year="2009"/>
1908  </front>
1909  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-07"/>
1910 
1911</reference>
1912
1913<reference anchor="RFC1766">
1914  <front>
1915    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1916    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1917      <organization>UNINETT</organization>
1918      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1919    </author>
1920    <date month="March" year="1995"/>
1921  </front>
1922  <seriesInfo name="RFC" value="1766"/>
1923</reference>
1924
1925<reference anchor="RFC1864">
1926  <front>
1927    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1928    <author initials="J." surname="Myers" fullname="John G. Myers">
1929      <organization>Carnegie Mellon University</organization>
1930      <address><email>jgm+@cmu.edu</email></address>
1931    </author>
1932    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1933      <organization>Dover Beach Consulting, Inc.</organization>
1934      <address><email>mrose@dbc.mtview.ca.us</email></address>
1935    </author>
1936    <date month="October" year="1995"/>
1937  </front>
1938  <seriesInfo name="RFC" value="1864"/>
1939</reference>
1940
1941<reference anchor="RFC1950">
1942  <front>
1943    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1944    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1945      <organization>Aladdin Enterprises</organization>
1946      <address><email>ghost@aladdin.com</email></address>
1947    </author>
1948    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1949      <organization/>
1950    </author>
1951    <date month="May" year="1996"/>
1952  </front>
1953  <seriesInfo name="RFC" value="1950"/>
1954  <annotation>
1955    RFC 1950 is an Informational RFC, thus it may be less stable than
1956    this specification. On the other hand, this downward reference was
1957    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1958    therefore it is unlikely to cause problems in practice. See also
1959    <xref target="BCP97"/>.
1960  </annotation>
1961</reference>
1962
1963<reference anchor="RFC1951">
1964  <front>
1965    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1966    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1967      <organization>Aladdin Enterprises</organization>
1968      <address><email>ghost@aladdin.com</email></address>
1969    </author>
1970    <date month="May" year="1996"/>
1971  </front>
1972  <seriesInfo name="RFC" value="1951"/>
1973  <annotation>
1974    RFC 1951 is an Informational RFC, thus it may be less stable than
1975    this specification. On the other hand, this downward reference was
1976    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1977    therefore it is unlikely to cause problems in practice. See also
1978    <xref target="BCP97"/>.
1979  </annotation>
1980</reference>
1981
1982<reference anchor="RFC1952">
1983  <front>
1984    <title>GZIP file format specification version 4.3</title>
1985    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1986      <organization>Aladdin Enterprises</organization>
1987      <address><email>ghost@aladdin.com</email></address>
1988    </author>
1989    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1990      <organization/>
1991      <address><email>gzip@prep.ai.mit.edu</email></address>
1992    </author>
1993    <author initials="M." surname="Adler" fullname="Mark Adler">
1994      <organization/>
1995      <address><email>madler@alumni.caltech.edu</email></address>
1996    </author>
1997    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1998      <organization/>
1999      <address><email>ghost@aladdin.com</email></address>
2000    </author>
2001    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2002      <organization/>
2003      <address><email>randeg@alumni.rpi.edu</email></address>
2004    </author>
2005    <date month="May" year="1996"/>
2006  </front>
2007  <seriesInfo name="RFC" value="1952"/>
2008  <annotation>
2009    RFC 1952 is an Informational RFC, thus it may be less stable than
2010    this specification. On the other hand, this downward reference was
2011    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2012    therefore it is unlikely to cause problems in practice. See also
2013    <xref target="BCP97"/>.
2014  </annotation>
2015</reference>
2016
2017<reference anchor="RFC2045">
2018  <front>
2019    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2020    <author initials="N." surname="Freed" fullname="Ned Freed">
2021      <organization>Innosoft International, Inc.</organization>
2022      <address><email>ned@innosoft.com</email></address>
2023    </author>
2024    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2025      <organization>First Virtual Holdings</organization>
2026      <address><email>nsb@nsb.fv.com</email></address>
2027    </author>
2028    <date month="November" year="1996"/>
2029  </front>
2030  <seriesInfo name="RFC" value="2045"/>
2031</reference>
2032
2033<reference anchor="RFC2046">
2034  <front>
2035    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2036    <author initials="N." surname="Freed" fullname="Ned Freed">
2037      <organization>Innosoft International, Inc.</organization>
2038      <address><email>ned@innosoft.com</email></address>
2039    </author>
2040    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2041      <organization>First Virtual Holdings</organization>
2042      <address><email>nsb@nsb.fv.com</email></address>
2043    </author>
2044    <date month="November" year="1996"/>
2045  </front>
2046  <seriesInfo name="RFC" value="2046"/>
2047</reference>
2048
2049<reference anchor="RFC2119">
2050  <front>
2051    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2052    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2053      <organization>Harvard University</organization>
2054      <address><email>sob@harvard.edu</email></address>
2055    </author>
2056    <date month="March" year="1997"/>
2057  </front>
2058  <seriesInfo name="BCP" value="14"/>
2059  <seriesInfo name="RFC" value="2119"/>
2060</reference>
2061
2062<reference anchor="RFC4647">
2063  <front>
2064    <title>Matching of Language Tags</title>
2065    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
2066      <organization>Yahoo! Inc.</organization>
2067      <address><email>addison@inter-locale.com</email></address>
2068    </author>
2069    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
2070      <organization>Google</organization>
2071      <address><email>mark.davis@macchiato.com</email></address>
2072    </author>
2073    <date year="2006" month="September"/>
2074  </front>
2075  <seriesInfo name="BCP" value="47"/>
2076  <seriesInfo name="RFC" value="4647"/>
2077</reference>
2078
2079<reference anchor="RFC5234">
2080  <front>
2081    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2082    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2083      <organization>Brandenburg InternetWorking</organization>
2084      <address>
2085      <postal>
2086      <street>675 Spruce Dr.</street>
2087      <city>Sunnyvale</city>
2088      <region>CA</region>
2089      <code>94086</code>
2090      <country>US</country></postal>
2091      <phone>+1.408.246.8253</phone>
2092      <email>dcrocker@bbiw.net</email></address> 
2093    </author>
2094    <author initials="P." surname="Overell" fullname="Paul Overell">
2095      <organization>THUS plc.</organization>
2096      <address>
2097      <postal>
2098      <street>1/2 Berkeley Square</street>
2099      <street>99 Berkely Street</street>
2100      <city>Glasgow</city>
2101      <code>G3 7HR</code>
2102      <country>UK</country></postal>
2103      <email>paul.overell@thus.net</email></address>
2104    </author>
2105    <date month="January" year="2008"/>
2106  </front>
2107  <seriesInfo name="STD" value="68"/>
2108  <seriesInfo name="RFC" value="5234"/>
2109</reference>
2110
2111</references>
2112
2113<references title="Informative References">
2114
2115<reference anchor="RFC1945">
2116  <front>
2117    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2118    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2119      <organization>MIT, Laboratory for Computer Science</organization>
2120      <address><email>timbl@w3.org</email></address>
2121    </author>
2122    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2123      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2124      <address><email>fielding@ics.uci.edu</email></address>
2125    </author>
2126    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2127      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2128      <address><email>frystyk@w3.org</email></address>
2129    </author>
2130    <date month="May" year="1996"/>
2131  </front>
2132  <seriesInfo name="RFC" value="1945"/>
2133</reference>
2134
2135<reference anchor="RFC2049">
2136  <front>
2137    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2138    <author initials="N." surname="Freed" fullname="Ned Freed">
2139      <organization>Innosoft International, Inc.</organization>
2140      <address><email>ned@innosoft.com</email></address>
2141    </author>
2142    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2143      <organization>First Virtual Holdings</organization>
2144      <address><email>nsb@nsb.fv.com</email></address>
2145    </author>
2146    <date month="November" year="1996"/>
2147  </front>
2148  <seriesInfo name="RFC" value="2049"/>
2149</reference>
2150
2151<reference anchor="RFC2068">
2152  <front>
2153    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2154    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2155      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2156      <address><email>fielding@ics.uci.edu</email></address>
2157    </author>
2158    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2159      <organization>MIT Laboratory for Computer Science</organization>
2160      <address><email>jg@w3.org</email></address>
2161    </author>
2162    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2163      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2164      <address><email>mogul@wrl.dec.com</email></address>
2165    </author>
2166    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2167      <organization>MIT Laboratory for Computer Science</organization>
2168      <address><email>frystyk@w3.org</email></address>
2169    </author>
2170    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2171      <organization>MIT Laboratory for Computer Science</organization>
2172      <address><email>timbl@w3.org</email></address>
2173    </author>
2174    <date month="January" year="1997"/>
2175  </front>
2176  <seriesInfo name="RFC" value="2068"/>
2177</reference>
2178
2179<reference anchor="RFC2076">
2180  <front>
2181    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2182    <author initials="J." surname="Palme" fullname="Jacob Palme">
2183      <organization>Stockholm University/KTH</organization>
2184      <address><email>jpalme@dsv.su.se</email></address>
2185    </author>
2186    <date month="February" year="1997"/>
2187  </front>
2188  <seriesInfo name="RFC" value="2076"/>
2189</reference>
2190
2191<reference anchor="RFC2183">
2192  <front>
2193    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2194    <author initials="R." surname="Troost" fullname="Rens Troost">
2195      <organization>New Century Systems</organization>
2196      <address><email>rens@century.com</email></address>
2197    </author>
2198    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2199      <organization>QUALCOMM Incorporated</organization>
2200      <address><email>sdorner@qualcomm.com</email></address>
2201    </author>
2202    <author initials="K." surname="Moore" fullname="Keith Moore">
2203      <organization>Department of Computer Science</organization>
2204      <address><email>moore@cs.utk.edu</email></address>
2205    </author>
2206    <date month="August" year="1997"/>
2207  </front>
2208  <seriesInfo name="RFC" value="2183"/>
2209</reference>
2210
2211<reference anchor="RFC2277">
2212  <front>
2213    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2214    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2215      <organization>UNINETT</organization>
2216      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2217    </author>
2218    <date month="January" year="1998"/>
2219  </front>
2220  <seriesInfo name="BCP" value="18"/>
2221  <seriesInfo name="RFC" value="2277"/>
2222</reference>
2223
2224<reference anchor="RFC2388">
2225  <front>
2226    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2227    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2228      <organization>Xerox Palo Alto Research Center</organization>
2229      <address><email>masinter@parc.xerox.com</email></address>
2230    </author>
2231    <date year="1998" month="August"/>
2232  </front>
2233  <seriesInfo name="RFC" value="2388"/>
2234</reference>
2235
2236<reference anchor="RFC2557">
2237  <front>
2238    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2239    <author initials="F." surname="Palme" fullname="Jacob Palme">
2240      <organization>Stockholm University and KTH</organization>
2241      <address><email>jpalme@dsv.su.se</email></address>
2242    </author>
2243    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2244      <organization>Microsoft Corporation</organization>
2245      <address><email>alexhop@microsoft.com</email></address>
2246    </author>
2247    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2248      <organization>Lotus Development Corporation</organization>
2249      <address><email>Shelness@lotus.com</email></address>
2250    </author>
2251    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2252      <organization/>
2253      <address><email>stef@nma.com</email></address>
2254    </author>
2255    <date year="1999" month="March"/>
2256  </front>
2257  <seriesInfo name="RFC" value="2557"/>
2258</reference>
2259
2260<reference anchor="RFC2616">
2261  <front>
2262    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2263    <author initials="R." surname="Fielding" fullname="R. Fielding">
2264      <organization>University of California, Irvine</organization>
2265      <address><email>fielding@ics.uci.edu</email></address>
2266    </author>
2267    <author initials="J." surname="Gettys" fullname="J. Gettys">
2268      <organization>W3C</organization>
2269      <address><email>jg@w3.org</email></address>
2270    </author>
2271    <author initials="J." surname="Mogul" fullname="J. Mogul">
2272      <organization>Compaq Computer Corporation</organization>
2273      <address><email>mogul@wrl.dec.com</email></address>
2274    </author>
2275    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2276      <organization>MIT Laboratory for Computer Science</organization>
2277      <address><email>frystyk@w3.org</email></address>
2278    </author>
2279    <author initials="L." surname="Masinter" fullname="L. Masinter">
2280      <organization>Xerox Corporation</organization>
2281      <address><email>masinter@parc.xerox.com</email></address>
2282    </author>
2283    <author initials="P." surname="Leach" fullname="P. Leach">
2284      <organization>Microsoft Corporation</organization>
2285      <address><email>paulle@microsoft.com</email></address>
2286    </author>
2287    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2288      <organization>W3C</organization>
2289      <address><email>timbl@w3.org</email></address>
2290    </author>
2291    <date month="June" year="1999"/>
2292  </front>
2293  <seriesInfo name="RFC" value="2616"/>
2294</reference>
2295
2296<reference anchor="RFC3629">
2297  <front>
2298    <title>UTF-8, a transformation format of ISO 10646</title>
2299    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2300      <organization>Alis Technologies</organization>
2301      <address><email>fyergeau@alis.com</email></address>
2302    </author>
2303    <date month="November" year="2003"/>
2304  </front>
2305  <seriesInfo name="RFC" value="3629"/>
2306  <seriesInfo name="STD" value="63"/>
2307</reference>
2308
2309<reference anchor="RFC3864">
2310  <front>
2311    <title>Registration Procedures for Message Header Fields</title>
2312    <author initials="G." surname="Klyne" fullname="G. Klyne">
2313      <organization>Nine by Nine</organization>
2314      <address><email>GK-IETF@ninebynine.org</email></address>
2315    </author>
2316    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
2317      <organization>BEA Systems</organization>
2318      <address><email>mnot@pobox.com</email></address>
2319    </author>
2320    <author initials="J." surname="Mogul" fullname="J. Mogul">
2321      <organization>HP Labs</organization>
2322      <address><email>JeffMogul@acm.org</email></address>
2323    </author>
2324    <date year="2004" month="September"/>
2325  </front>
2326  <seriesInfo name="BCP" value="90"/>
2327  <seriesInfo name="RFC" value="3864"/>
2328</reference>
2329
2330<reference anchor="RFC4288">
2331  <front>
2332    <title>Media Type Specifications and Registration Procedures</title>
2333    <author initials="N." surname="Freed" fullname="N. Freed">
2334      <organization>Sun Microsystems</organization>
2335      <address>
2336        <email>ned.freed@mrochek.com</email>
2337      </address>
2338    </author>
2339    <author initials="J." surname="Klensin" fullname="J. Klensin">
2340      <organization/>
2341      <address>
2342        <email>klensin+ietf@jck.com</email>
2343      </address>
2344    </author>
2345    <date year="2005" month="December"/>
2346  </front>
2347  <seriesInfo name="BCP" value="13"/>
2348  <seriesInfo name="RFC" value="4288"/>
2349</reference>
2350
2351<reference anchor="RFC5322">
2352  <front>
2353    <title>Internet Message Format</title>
2354    <author initials="P." surname="Resnick" fullname="P. Resnick">
2355      <organization>Qualcomm Incorporated</organization>
2356    </author>
2357    <date year="2008" month="October"/>
2358  </front> 
2359  <seriesInfo name="RFC" value="5322"/>
2360</reference>
2361
2362<reference anchor="BCP97">
2363  <front>
2364    <title>Handling Normative References to Standards-Track Documents</title>
2365    <author initials="J." surname="Klensin" fullname="J. Klensin">
2366      <organization/>
2367      <address>
2368        <email>klensin+ietf@jck.com</email>
2369      </address>
2370    </author>
2371    <author initials="S." surname="Hartman" fullname="S. Hartman">
2372      <organization>MIT</organization>
2373      <address>
2374        <email>hartmans-ietf@mit.edu</email>
2375      </address>
2376    </author>
2377    <date year="2007" month="June"/>
2378  </front>
2379  <seriesInfo name="BCP" value="97"/>
2380  <seriesInfo name="RFC" value="4897"/>
2381</reference>
2382
2383
2384</references>
2385
2386<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2387<t>
2388   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
2389   allow entities to be transmitted in an open variety of
2390   representations and with extensible mechanisms. However, RFC 2045
2391   discusses mail, and HTTP has a few features that are different from
2392   those described in RFC 2045. These differences were carefully chosen
2393   to optimize performance over binary connections, to allow greater
2394   freedom in the use of new media types, to make date comparisons
2395   easier, and to acknowledge the practice of some early HTTP servers
2396   and clients.
2397</t>
2398<t>
2399   This appendix describes specific areas where HTTP differs from RFC
2400   2045. Proxies and gateways to strict MIME environments SHOULD be
2401   aware of these differences and provide the appropriate conversions
2402   where necessary. Proxies and gateways from MIME environments to HTTP
2403   also need to be aware of the differences because some conversions
2404   might be required.
2405</t>
2406
2407<section title="MIME-Version" anchor="mime-version">
2408  <iref primary="true" item="MIME-Version header"/>
2409  <iref primary="true" item="Headers" subitem="MIME-Version"/>
2410 
2411 
2412<t>
2413   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages MAY
2414   include a single MIME-Version general-header field to indicate what
2415   version of the MIME protocol was used to construct the message. Use
2416   of the MIME-Version header field indicates that the message is in
2417   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2418   Proxies/gateways are responsible for ensuring full compliance (where
2419   possible) when exporting HTTP messages to strict MIME environments.
2420</t>
2421<figure><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/><artwork type="abnf2616"><![CDATA[
2422  MIME-Version   = "MIME-Version" ":" OWS MIME-Version-v
2423  MIME-Version-v = 1*DIGIT "." 1*DIGIT
2424]]></artwork></figure>
2425<t>
2426   MIME version "1.0" is the default for use in HTTP/1.1. However,
2427   HTTP/1.1 message parsing and semantics are defined by this document
2428   and not the MIME specification.
2429</t>
2430</section>
2431
2432<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2433<t>
2434   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2435   canonical form prior to being transferred, as described in Section 4 of <xref target="RFC2049"/>.
2436   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2437   allowed for subtypes of the "text" media type when transmitted over
2438   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2439   line breaks as CRLF and forbids the use of CR or LF outside of line
2440   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2441   line break within text content when a message is transmitted over
2442   HTTP.
2443</t>
2444<t>
2445   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2446   environment SHOULD translate all line breaks within the text media
2447   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2448   canonical form of CRLF. Note, however, that this might be complicated
2449   by the presence of a Content-Encoding and by the fact that HTTP
2450   allows the use of some character sets which do not use octets 13 and
2451   10 to represent CR and LF, as is the case for some multi-byte
2452   character sets.
2453</t>
2454<t>
2455   Implementors should note that conversion will break any cryptographic
2456   checksums applied to the original content unless the original content
2457   is already in canonical form. Therefore, the canonical form is
2458   recommended for any content that uses such checksums in HTTP.
2459</t>
2460</section>
2461
2462
2463<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2464<t>
2465   HTTP/1.1 uses a restricted set of date formats (Section 3.2 of <xref target="Part1"/>) to
2466   simplify the process of date comparison. Proxies and gateways from
2467   other protocols SHOULD ensure that any Date header field present in a
2468   message conforms to one of the HTTP/1.1 formats and rewrite the date
2469   if necessary.
2470</t>
2471</section>
2472
2473<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2474<t>
2475   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2476   Content-Encoding header field. Since this acts as a modifier on the
2477   media type, proxies and gateways from HTTP to MIME-compliant
2478   protocols MUST either change the value of the Content-Type header
2479   field or decode the entity-body before forwarding the message. (Some
2480   experimental applications of Content-Type for Internet mail have used
2481   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2482   a function equivalent to Content-Encoding. However, this parameter is
2483   not part of RFC 2045).
2484</t>
2485</section>
2486
2487<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2488<t>
2489   HTTP does not use the Content-Transfer-Encoding field of RFC
2490   2045. Proxies and gateways from MIME-compliant protocols to HTTP MUST
2491   remove any Content-Transfer-Encoding
2492   prior to delivering the response message to an HTTP client.
2493</t>
2494<t>
2495   Proxies and gateways from HTTP to MIME-compliant protocols are
2496   responsible for ensuring that the message is in the correct format
2497   and encoding for safe transport on that protocol, where "safe
2498   transport" is defined by the limitations of the protocol being used.
2499   Such a proxy or gateway SHOULD label the data with an appropriate
2500   Content-Transfer-Encoding if doing so will improve the likelihood of
2501   safe transport over the destination protocol.
2502</t>
2503</section>
2504
2505<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2506<t>
2507   HTTP/1.1 introduces the Transfer-Encoding header field (Section 8.7 of <xref target="Part1"/>).
2508   Proxies/gateways MUST remove any transfer-coding prior to
2509   forwarding a message via a MIME-compliant protocol.
2510</t>
2511</section>
2512
2513<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2514<t>
2515   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2516   need to be aware of MIME line length limitations. Since HTTP does not
2517   have this limitation, HTTP does not fold long lines. MHTML messages
2518   being transported by HTTP follow all conventions of MHTML, including
2519   line length limitations and folding, canonicalization, etc., since
2520   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2521   does not interpret the content or any MIME header lines that might be
2522   contained therein.
2523</t>
2524</section>
2525</section>
2526
2527<section title="Additional Features" anchor="additional.features">
2528<t>
2529   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2530   existing HTTP implementations, but not consistently and correctly
2531   across most HTTP/1.1 applications. Implementors are advised to be
2532   aware of these features, but cannot rely upon their presence in, or
2533   interoperability with, other HTTP/1.1 applications. Some of these
2534   describe proposed experimental features, and some describe features
2535   that experimental deployment found lacking that are now addressed in
2536   the base HTTP/1.1 specification.
2537</t>
2538<t>
2539   A number of other headers, such as Content-Disposition and Title,
2540   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2541</t>
2542
2543<section title="Content-Disposition" anchor="content-disposition">
2544<iref item="Headers" subitem="Content-Disposition" primary="true"/>
2545<iref item="Content-Disposition header" primary="true"/>
2546 
2547 
2548 
2549 
2550 
2551 
2552 
2553<t>
2554   The Content-Disposition response-header field has been proposed as a
2555   means for the origin server to suggest a default filename if the user
2556   requests that the content is saved to a file. This usage is derived
2557   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2558</t>
2559<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[
2560  content-disposition = "Content-Disposition" ":" OWS
2561                        content-disposition-v
2562  content-disposition-v = disposition-type
2563                          *( OWS ";" OWS disposition-parm )
2564  disposition-type = "attachment" / disp-extension-token
2565  disposition-parm = filename-parm / disp-extension-parm
2566  filename-parm = "filename" "=" quoted-string
2567  disp-extension-token = token
2568  disp-extension-parm = token "=" ( token / quoted-string )
2569]]></artwork></figure>
2570<t>
2571   An example is
2572</t>
2573<figure><artwork type="example"><![CDATA[
2574  Content-Disposition: attachment; filename="fname.ext"
2575]]></artwork></figure>
2576<t>
2577   The receiving user agent SHOULD NOT  respect any directory path
2578   information present in the filename-parm parameter, which is the only
2579   parameter believed to apply to HTTP implementations at this time. The
2580   filename SHOULD be treated as a terminal component only.
2581</t>
2582<t>
2583   If this header is used in a response with the application/octet-stream
2584   content-type, the implied suggestion is that the user agent
2585   should not display the response, but directly enter a `save response
2586   as...' dialog.
2587</t>
2588<t>
2589   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2590</t>
2591</section>
2592</section>
2593
2594<section title="Compatibility with Previous Versions" anchor="compatibility">
2595<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2596<t>
2597   Transfer-coding and message lengths all interact in ways that
2598   required fixing exactly when chunked encoding is used (to allow for
2599   transfer encoding that may not be self delimiting); it was important
2600   to straighten out exactly how message lengths are computed.
2601   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2602   <xref target="Part5"/> and <xref target="Part6"/>).
2603</t>
2604<t>
2605   Charset wildcarding is introduced to avoid explosion of character set
2606   names in accept headers. (<xref target="header.accept-charset"/>)
2607</t>
2608<t>
2609   Content-Base was deleted from the specification: it was not
2610   implemented widely, and there is no simple, safe way to introduce it
2611   without a robust extension mechanism. In addition, it is used in a
2612   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2613</t>
2614<t>
2615   A content-coding of "identity" was introduced, to solve problems
2616   discovered in caching. (<xref target="content.codings"/>)
2617</t>
2618<t>
2619   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
2620   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
2621   specification, but not commonly implemented. See Section 19.6.2 of <xref target="RFC2068"/>.
2622</t>
2623</section>
2624
2625<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2626<t>
2627  Clarify contexts that charset is used in.
2628  (<xref target="character.sets"/>)
2629</t>
2630<t>
2631  Remove reference to non-existant identity transfer-coding value tokens.
2632  (<xref target="no.content-transfer-encoding"/>)
2633</t>
2634</section>
2635
2636</section>
2637
2638<section title="Collected ABNF" anchor="collected.abnf">
2639<figure>
2640<artwork type="abnf" name="p3-payload.parsed-abnf"><![CDATA[
2641Accept = "Accept:" OWS Accept-v
2642Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v
2643Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2644 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2645 qvalue ] ] )
2646Accept-Encoding = "Accept-Encoding:" OWS Accept-Encoding-v
2647Accept-Encoding-v = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2648 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2649Accept-Language = "Accept-Language:" OWS Accept-Language-v
2650Accept-Language-v = *( "," OWS ) language-range [ OWS ";" OWS "q="
2651 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2652 ] )
2653Accept-v = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2654 OWS media-range [ accept-params ] ] ) ]
2655
2656Content-Encoding = "Content-Encoding:" OWS Content-Encoding-v
2657Content-Encoding-v = *( "," OWS ) content-coding *( OWS "," [ OWS
2658 content-coding ] )
2659Content-Language = "Content-Language:" OWS Content-Language-v
2660Content-Language-v = *( "," OWS ) language-tag *( OWS "," [ OWS
2661 language-tag ] )
2662Content-Length = <Content-Length, defined in [Part1], Section 8.2>
2663Content-Location = "Content-Location:" OWS Content-Location-v
2664Content-Location-v = absolute-URI / partial-URI
2665Content-MD5 = "Content-MD5:" OWS Content-MD5-v
2666Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]>
2667Content-Range = <Content-Range, defined in [Part5], Section 5.2>
2668Content-Type = "Content-Type:" OWS Content-Type-v
2669Content-Type-v = media-type
2670
2671Expires = <Expires, defined in [Part6], Section 3.3>
2672
2673Last-Modified = <Last-Modified, defined in [Part4], Section 6.6>
2674
2675MIME-Version = "MIME-Version:" OWS MIME-Version-v
2676MIME-Version-v = 1*DIGIT "." 1*DIGIT
2677
2678OWS = <OWS, defined in [Part1], Section 1.2.2>
2679
2680absolute-URI = <absolute-URI, defined in [Part1], Section 2.1>
2681accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2682accept-params = OWS ";" OWS "q=" qvalue *accept-ext
2683attribute = token
2684
2685charset = token
2686codings = ( content-coding / "*" )
2687content-coding = token
2688content-disposition = "Content-Disposition:" OWS
2689 content-disposition-v
2690content-disposition-v = disposition-type *( OWS ";" OWS
2691 disposition-parm )
2692
2693disp-extension-parm = token "=" ( token / quoted-string )
2694disp-extension-token = token
2695disposition-parm = filename-parm / disp-extension-parm
2696disposition-type = "attachment" / disp-extension-token
2697
2698entity-body = *OCTET
2699entity-header = Content-Encoding / Content-Language / Content-Length
2700 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2701 Expires / Last-Modified / extension-header
2702extension-header = message-header
2703
2704filename-parm = "filename=" quoted-string
2705
2706language-range = <language-range, defined in [RFC4647], Section 2.1>
2707language-tag = primary-tag *( "-" subtag )
2708
2709media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2710 ";" OWS parameter )
2711media-type = type "/" subtype *( OWS ";" OWS parameter )
2712message-header = <message-header, defined in [Part1], Section 4.2>
2713
2714parameter = attribute "=" value
2715partial-URI = <partial-URI, defined in [Part1], Section 2.1>
2716primary-tag = 1*8ALPHA
2717
2718quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
2719qvalue = <qvalue, defined in [Part1], Section 3.5>
2720
2721subtag = 1*8ALPHA
2722subtype = token
2723
2724token = <token, defined in [Part1], Section 1.2.2>
2725type = token
2726
2727value = token / quoted-string
2728
2729
2730]]></artwork>
2731</figure>
2732<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
2733; Accept defined but not used
2734; Accept-Charset defined but not used
2735; Accept-Encoding defined but not used
2736; Accept-Language defined but not used
2737; MIME-Version defined but not used
2738; content-disposition defined but not used
2739; entity-body defined but not used
2740; entity-header defined but not used
2741]]></artwork></figure></section>
2742
2743<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2744
2745<section title="Since RFC2616">
2746<t>
2747  Extracted relevant partitions from <xref target="RFC2616"/>.
2748</t>
2749</section>
2750
2751<section title="Since draft-ietf-httpbis-p3-payload-00">
2752<t>
2753  Closed issues:
2754  <list style="symbols"> 
2755    <t>
2756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2757      "Media Type Registrations"
2758      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2759    </t>
2760    <t>
2761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2762      "Clarification regarding quoting of charset values"
2763      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2764    </t>
2765    <t>
2766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2767      "Remove 'identity' token references"
2768      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2769    </t>
2770    <t>
2771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2772      "Accept-Encoding BNF"
2773    </t>
2774    <t>
2775      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2776      "Normative and Informative references"
2777    </t>
2778    <t>
2779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2780      "RFC1700 references"
2781    </t>
2782    <t>
2783      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2784      "Updating to RFC4288"
2785    </t>
2786    <t>
2787      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2788      "Informative references"
2789    </t>
2790    <t>
2791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2792      "ISO-8859-1 Reference"
2793    </t>
2794    <t>
2795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2796      "Encoding References Normative"
2797    </t>
2798    <t>
2799      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2800      "Normative up-to-date references"
2801    </t>
2802  </list>
2803</t>
2804</section>
2805
2806<section title="Since draft-ietf-httpbis-p3-payload-01">
2807<t>
2808  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2809  <list style="symbols"> 
2810    <t>
2811      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2812    </t>
2813  </list>
2814</t>
2815</section>
2816
2817<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2818<t>
2819  Closed issues:
2820  <list style="symbols"> 
2821    <t>
2822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2823      "Quoting Charsets"
2824    </t>
2825    <t>
2826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2827      "Classification for Allow header"
2828    </t>
2829    <t>
2830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2831      "missing default for qvalue in description of Accept-Encoding"
2832    </t>
2833  </list>
2834</t>
2835<t>
2836  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2837  <list style="symbols"> 
2838    <t>
2839      Reference RFC 3984, and update header registrations for headers defined
2840      in this document.
2841    </t>
2842  </list>
2843</t>
2844</section>
2845
2846<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2847<t>
2848  Closed issues:
2849  <list style="symbols"> 
2850    <t>
2851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2852      "Quoting Charsets"
2853    </t>
2854    <t>
2855      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2856      "language tag matching (Accept-Language) vs RFC4647"
2857    </t>
2858    <t>
2859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2860      "RFC 1806 has been replaced by RFC2183"
2861    </t>
2862  </list>
2863</t>
2864<t>
2865  Other changes:
2866  <list style="symbols"> 
2867    <t>
2868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2869      "Encoding References Normative" -- rephrase the annotation and reference
2870      <xref target="BCP97"/>.
2871    </t>
2872  </list>
2873</t>
2874 </section>
2875
2876<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2877<t>
2878  Closed issues:
2879  <list style="symbols"> 
2880    <t>
2881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2882      "RFC 2822 is updated by RFC 5322"
2883    </t>
2884  </list>
2885</t>
2886<t>
2887  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2888  <list style="symbols"> 
2889    <t>
2890      Use "/" instead of "|" for alternatives.
2891    </t>
2892    <t>
2893      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2894      whitespace ("OWS") and required whitespace ("RWS").
2895    </t>
2896    <t>
2897      Rewrite ABNFs to spell out whitespace rules, factor out
2898      header value format definitions.
2899    </t>
2900  </list>
2901</t>
2902</section>
2903
2904<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2905<t>
2906  Closed issues:
2907  <list style="symbols"> 
2908    <t>
2909      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2910      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2911    </t>
2912  </list>
2913</t>
2914<t>
2915  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2916  <list style="symbols"> 
2917    <t>
2918      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2919    </t>
2920  </list>
2921</t>
2922<t>
2923  Other changes:
2924  <list style="symbols"> 
2925    <t>
2926      Move definition of quality values into Part 1.
2927    </t>
2928  </list>
2929</t>
2930</section>
2931
2932<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2933<t>
2934  Closed issues:
2935  <list style="symbols"> 
2936    <t>
2937      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2938      "Content-Location isn't special"
2939    </t>
2940    <t>
2941      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2942      "Content Sniffing"
2943    </t>
2944  </list>
2945</t>
2946</section>
2947
2948</section>
2949
2950</back>
2951</rfc>
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