source: draft-ietf-httpbis/latest/p3-payload.xml @ 228

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
18  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
19  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x=''/>">
20  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x=''/>">
21  <!ENTITY header-allow             "<xref target='Part2' x:rel='#header.allow' xmlns:x=''/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x=''/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x=''/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x=''/>">
30  <!ENTITY message-headers          "<xref target='Part1' x:rel='#message.headers' xmlns:x=''/>">
31  <!ENTITY general-syntax           "<xref target='Part1' x:rel='#general.syntax' xmlns:x=''/>">
32  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
34<?rfc toc="yes" ?>
35<?rfc symrefs="yes" ?>
36<?rfc sortrefs="yes" ?>
37<?rfc compact="yes"?>
38<?rfc subcompact="no" ?>
39<?rfc linkmailto="no" ?>
40<?rfc editing="no" ?>
41<?rfc comments="yes"?>
42<?rfc inline="yes"?>
43<?rfc-ext allow-markup-in-artwork="yes" ?>
44<?rfc-ext include-references-in-index="yes" ?>
45<rfc obsoletes="2616" category="std"
46     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
47     xmlns:x=''>
50  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
52  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
53    <organization abbrev="Day Software">Day Software</organization>
54    <address>
55      <postal>
56        <street>23 Corporate Plaza DR, Suite 280</street>
57        <city>Newport Beach</city>
58        <region>CA</region>
59        <code>92660</code>
60        <country>USA</country>
61      </postal>
62      <phone>+1-949-706-5300</phone>
63      <facsimile>+1-949-706-5305</facsimile>
64      <email></email>
65      <uri></uri>
66    </address>
67  </author>
69  <author initials="J." surname="Gettys" fullname="Jim Gettys">
70    <organization>One Laptop per Child</organization>
71    <address>
72      <postal>
73        <street>21 Oak Knoll Road</street>
74        <city>Carlisle</city>
75        <region>MA</region>
76        <code>01741</code>
77        <country>USA</country>
78      </postal>
79      <email></email>
80      <uri></uri>
81    </address>
82  </author>
84  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
85    <organization abbrev="HP">Hewlett-Packard Company</organization>
86    <address>
87      <postal>
88        <street>HP Labs, Large Scale Systems Group</street>
89        <street>1501 Page Mill Road, MS 1177</street>
90        <city>Palo Alto</city>
91        <region>CA</region>
92        <code>94304</code>
93        <country>USA</country>
94      </postal>
95      <email></email>
96    </address>
97  </author>
99  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
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        <country>USA</country>
108      </postal>
109      <email></email>
110    </address>
111  </author>
113  <author initials="L." surname="Masinter" fullname="Larry Masinter">
114    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
115    <address>
116      <postal>
117        <street>345 Park Ave</street>
118        <city>San Jose</city>
119        <region>CA</region>
120        <code>95110</code>
121        <country>USA</country>
122      </postal>
123      <email></email>
124      <uri></uri>
125    </address>
126  </author>
128  <author initials="P." surname="Leach" fullname="Paul J. Leach">
129    <organization abbrev="Microsoft">Microsoft Corporation</organization>
130    <address>
131      <postal>
132        <street>1 Microsoft Way</street>
133        <city>Redmond</city>
134        <region>WA</region>
135        <code>98052</code>
136      </postal>
137      <email></email>
138    </address>
139  </author>
141  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
142    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
143    <address>
144      <postal>
145        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
146        <street>The Stata Center, Building 32</street>
147        <street>32 Vassar Street</street>
148        <city>Cambridge</city>
149        <region>MA</region>
150        <code>02139</code>
151        <country>USA</country>
152      </postal>
153      <email></email>
154      <uri></uri>
155    </address>
156  </author>
158  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
159    <organization abbrev="W3C">World Wide Web Consortium</organization>
160    <address>
161      <postal>
162        <street>W3C / ERCIM</street>
163        <street>2004, rte des Lucioles</street>
164        <city>Sophia-Antipolis</city>
165        <region>AM</region>
166        <code>06902</code>
167        <country>France</country>
168      </postal>
169      <email></email>
170      <uri></uri>
171    </address>
172  </author>
174  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
175    <organization abbrev="greenbytes">greenbytes GmbH</organization>
176    <address>
177      <postal>
178        <street>Hafenweg 16</street>
179        <city>Muenster</city><region>NW</region><code>48155</code>
180        <country>Germany</country>
181      </postal>
182      <phone>+49 251 2807760</phone>   
183      <facsimile>+49 251 2807761</facsimile>   
184      <email></email>       
185      <uri></uri>     
186    </address>
187  </author>
189  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
193   The Hypertext Transfer Protocol (HTTP) is an application-level
194   protocol for distributed, collaborative, hypermedia information
195   systems. HTTP has been in use by the World Wide Web global information
196   initiative since 1990. This document is Part 3 of the seven-part specification
197   that defines the protocol referred to as "HTTP/1.1" and, taken together,
198   obsoletes RFC 2616.  Part 3 defines HTTP message content,
199   metadata, and content negotiation.
203<note title="Editorial Note (To be removed by RFC Editor)">
204  <t>
205    Discussion of this draft should take place on the HTTPBIS working group
206    mailing list ( The current issues list is
207    at <eref target=""/>
208    and related documents (including fancy diffs) can be found at
209    <eref target=""/>.
210  </t>
211  <t>
212    This draft incorporates those issue resolutions that were either
213    collected in the original RFC2616 errata list (<eref target=""/>),
214    or which were agreed upon on the mailing list between October 2006 and
215    November 2007 (as published in "draft-lafon-rfc2616bis-03").
216  </t>
220<section title="Introduction" anchor="introduction">
222   This document defines HTTP/1.1 message payloads (a.k.a., content), the
223   associated metadata header fields that define how the payload is intended
224   to be interpreted by a recipient, the request header fields that
225   may influence content selection, and the various selection algorithms
226   that are collectively referred to as HTTP content negotiation.
229   This document is currently disorganized in order to minimize the changes
230   between drafts and enable reviewers to see the smaller errata changes.
231   The next draft will reorganize the sections to better reflect the content.
232   In particular, the sections on entities will be renamed payload and moved
233   to the first half of the document, while the sections on content negotiation
234   and associated request header fields will be moved to the second half.  The
235   current mess reflects how widely dispersed these topics and associated
236   requirements had become in <xref target="RFC2616"/>.
239<section title="Requirements" anchor="intro.requirements">
241   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
242   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
243   document are to be interpreted as described in <xref target="RFC2119"/>.
246   An implementation is not compliant if it fails to satisfy one or more
247   of the &MUST; or &REQUIRED; level requirements for the protocols it
248   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
249   level and all the &SHOULD; level requirements for its protocols is said
250   to be "unconditionally compliant"; one that satisfies all the &MUST;
251   level requirements but not all the &SHOULD; level requirements for its
252   protocols is said to be "conditionally compliant."
257<section title="Notational Conventions and Generic Grammar" anchor="notation">
259  This specification uses the ABNF syntax defined in &notation-abnf; and
260  the core rules defined in &basic-rules;:
261  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
262  <eref target=""/>.</cref>
264<figure><artwork type="abnf2616">
265  ALPHA          = &lt;ALPHA, defined in &basic-rules;&gt;
266  DIGIT          = &lt;DIGIT, defined in &basic-rules;&gt;
267  OCTET          = &lt;OCTET, defined in &basic-rules;&gt;
269<figure><artwork type="abnf2616">
270  quoted-string  = &lt;quoted-string, defined in &basic-rules;&gt;
271  token          = &lt;token, defined in &basic-rules;&gt;
273<t anchor="abnf.dependencies">
274  The ABNF rules below are defined in other parts:
276<figure><!--Part1--><artwork type="abnf2616">
277  absoluteURI    = &lt;absoluteURI, defined in &general-syntax;&gt;
278  Content-Length = &lt;Content-Length, defined in &header-content-length;&gt;
279  relativeURI    = &lt;relativeURI, defined in &general-syntax;&gt;
280  message-header = &lt;message-header, defined in &message-headers;&gt;
282<figure><!--Part2--><artwork type="abnf2616">
283  Allow          = &lt;Allow, defined in &header-allow;&gt;
285<figure><!--Part4--><artwork type="abnf2616">
286  Last-Modified  = &lt;Last-Modified, defined in &header-last-modified;&gt;
288<figure><!--Part5--><artwork type="abnf2616">
289  Content-Range  = &lt;Content-Range, defined in &header-content-range;&gt;
291<figure><!--Part6--><artwork type="abnf2616">
292  Expires        = &lt;Expires, defined in &header-expires;&gt;
296<section title="Protocol Parameters" anchor="protocol.parameters">
298<section title="Character Sets" anchor="character.sets">
300   HTTP uses the same definition of the term "character set" as that
301   described for MIME:
304   The term "character set" is used in this document to refer to a
305   method used with one or more tables to convert a sequence of octets
306   into a sequence of characters. Note that unconditional conversion in
307   the other direction is not required, in that not all characters may
308   be available in a given character set and a character set may provide
309   more than one sequence of octets to represent a particular character.
310   This definition is intended to allow various kinds of character
311   encoding, from simple single-table mappings such as US-ASCII to
312   complex table switching methods such as those that use ISO-2022's
313   techniques. However, the definition associated with a MIME character
314   set name &MUST; fully specify the mapping to be performed from octets
315   to characters. In particular, use of external profiling information
316   to determine the exact mapping is not permitted.
319      <x:h>Note:</x:h> This use of the term "character set" is more commonly
320      referred to as a "character encoding." However, since HTTP and
321      MIME share the same registry, it is important that the terminology
322      also be shared.
325   HTTP character sets are identified by case-insensitive tokens. The
326   complete set of tokens is defined by the IANA Character Set registry
327   (<eref target=""/>).
329<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
330  charset = token
333   Although HTTP allows an arbitrary token to be used as a charset
334   value, any token that has a predefined value within the IANA
335   Character Set registry &MUST; represent the character set defined
336   by that registry. Applications &SHOULD; limit their use of character
337   sets to those defined by the IANA registry.
340   HTTP uses charset in two contexts: within an Accept-Charset request
341   header (in which the charset value is an unquoted token) and as the
342   value of a parameter in a Content-Type header (within a request or
343   response), in which case the parameter value of the charset parameter
344   may be quoted.
347   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
348   <xref target="RFC2277"/>.
351<section title="Missing Charset" anchor="missing.charset">
353   Some HTTP/1.0 software has interpreted a Content-Type header without
354   charset parameter incorrectly to mean "recipient should guess."
355   Senders wishing to defeat this behavior &MAY; include a charset
356   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
357   it is known that it will not confuse the recipient.
360   Unfortunately, some older HTTP/1.0 clients did not deal properly with
361   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
362   charset label provided by the sender; and those user agents that have
363   a provision to "guess" a charset &MUST; use the charset from the
364   content-type field if they support that charset, rather than the
365   recipient's preference, when initially displaying a document. See
366   <xref target="canonicalization.and.text.defaults"/>.
371<section title="Content Codings" anchor="content.codings">
373   Content coding values indicate an encoding transformation that has
374   been or can be applied to an entity. Content codings are primarily
375   used to allow a document to be compressed or otherwise usefully
376   transformed without losing the identity of its underlying media type
377   and without loss of information. Frequently, the entity is stored in
378   coded form, transmitted directly, and only decoded by the recipient.
380<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
381  content-coding   = token
384   All content-coding values are case-insensitive. HTTP/1.1 uses
385   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
386   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
387   describes the content-coding, what is more important is that it
388   indicates what decoding mechanism will be required to remove the
389   encoding.
392   The Internet Assigned Numbers Authority (IANA) acts as a registry for
393   content-coding value tokens. Initially, the registry contains the
394   following tokens:
397   gzip<iref item="gzip"/>
398  <list>
399    <t>
400        An encoding format produced by the file compression program
401        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
402        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
403    </t>
404  </list>
407   compress<iref item="compress"/>
408  <list><t>
409        The encoding format produced by the common UNIX file compression
410        program "compress". This format is an adaptive Lempel-Ziv-Welch
411        coding (LZW).
413        Use of program names for the identification of encoding formats
414        is not desirable and is discouraged for future encodings. Their
415        use here is representative of historical practice, not good
416        design. For compatibility with previous implementations of HTTP,
417        applications &SHOULD; consider "x-gzip" and "x-compress" to be
418        equivalent to "gzip" and "compress" respectively.
419  </t></list>
422   deflate<iref item="deflate"/>
423  <list><t>
424        The "zlib" format defined in <xref target="RFC1950"/> in combination with
425        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
426  </t></list>
429   identity<iref item="identity"/>
430  <list><t>
431        The default (identity) encoding; the use of no transformation
432        whatsoever. This content-coding is used only in the Accept-Encoding
433        header, and &SHOULD-NOT;  be used in the Content-Encoding
434        header.
435  </t></list>
438   New content-coding value tokens &SHOULD; be registered; to allow
439   interoperability between clients and servers, specifications of the
440   content coding algorithms needed to implement a new value &SHOULD; be
441   publicly available and adequate for independent implementation, and
442   conform to the purpose of content coding defined in this section.
446<section title="Media Types" anchor="media.types">
448   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
449   and Accept (<xref target="header.accept"/>) header fields in order to provide
450   open and extensible data typing and type negotiation.
452<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/>
453  media-type     = type "/" subtype *( ";" parameter )
454  type           = token
455  subtype        = token
458   Parameters &MAY; follow the type/subtype in the form of attribute/value
459   pairs.
461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
462  parameter               = attribute "=" value
463  attribute               = token
464  value                   = token | quoted-string
467   The type, subtype, and parameter attribute names are case-insensitive.
468   Parameter values might or might not be case-sensitive,
469   depending on the semantics of the parameter name. Linear white space
470   (LWS) &MUST-NOT; be used between the type and subtype, nor between an
471   attribute and its value. The presence or absence of a parameter might
472   be significant to the processing of a media-type, depending on its
473   definition within the media type registry.
476   Note that some older HTTP applications do not recognize media type
477   parameters. When sending data to older HTTP applications,
478   implementations &SHOULD; only use media type parameters when they are
479   required by that type/subtype definition.
482   Media-type values are registered with the Internet Assigned Number
483   Authority (IANA). The media type registration process is
484   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
485   discouraged.
488<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
490   Internet media types are registered with a canonical form. An
491   entity-body transferred via HTTP messages &MUST; be represented in the
492   appropriate canonical form prior to its transmission except for
493   "text" types, as defined in the next paragraph.
496   When in canonical form, media subtypes of the "text" type use CRLF as
497   the text line break. HTTP relaxes this requirement and allows the
498   transport of text media with plain CR or LF alone representing a line
499   break when it is done consistently for an entire entity-body. HTTP
500   applications &MUST; accept CRLF, bare CR, and bare LF as being
501   representative of a line break in text media received via HTTP. In
502   addition, if the text is represented in a character set that does not
503   use octets 13 and 10 for CR and LF respectively, as is the case for
504   some multi-byte character sets, HTTP allows the use of whatever octet
505   sequences are defined by that character set to represent the
506   equivalent of CR and LF for line breaks. This flexibility regarding
507   line breaks applies only to text media in the entity-body; a bare CR
508   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
509   structures (such as header fields and multipart boundaries).
512   If an entity-body is encoded with a content-coding, the underlying
513   data &MUST; be in a form defined above prior to being encoded.
516   The "charset" parameter is used with some media types to define the
517   character set (<xref target="character.sets"/>) of the data. When no explicit charset
518   parameter is provided by the sender, media subtypes of the "text"
519   type are defined to have a default charset value of "ISO-8859-1" when
520   received via HTTP. Data in character sets other than "ISO-8859-1" or
521   its subsets &MUST; be labeled with an appropriate charset value. See
522   <xref target="missing.charset"/> for compatibility problems.
526<section title="Multipart Types" anchor="multipart.types">
528   MIME provides for a number of "multipart" types -- encapsulations of
529   one or more entities within a single message-body. All multipart
530   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
531   and &MUST; include a boundary parameter as part of the media type
532   value. The message body is itself a protocol element and &MUST;
533   therefore use only CRLF to represent line breaks between body-parts.
534   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
535   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
536   original multipart contains an epilogue). These restrictions exist in
537   order to preserve the self-delimiting nature of a multipart message-body,
538   wherein the "end" of the message-body is indicated by the
539   ending multipart boundary.
542   In general, HTTP treats a multipart message-body no differently than
543   any other media type: strictly as payload. The one exception is the
544   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
545   (Partial Content) response.
546   <!-- jre: re-insert removed text pointing to caching? -->
547   In all
548   other cases, an HTTP user agent &SHOULD; follow the same or similar
549   behavior as a MIME user agent would upon receipt of a multipart type.
550   The MIME header fields within each body-part of a multipart message-body
551   do not have any significance to HTTP beyond that defined by
552   their MIME semantics.
555   In general, an HTTP user agent &SHOULD; follow the same or similar
556   behavior as a MIME user agent would upon receipt of a multipart type.
557   If an application receives an unrecognized multipart subtype, the
558   application &MUST; treat it as being equivalent to "multipart/mixed".
561      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
562      for carrying form data suitable for processing via the POST
563      request method, as described in <xref target="RFC2388"/>.
568<section title="Quality Values" anchor="quality.values">
570   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
571   numbers to indicate the relative importance ("weight") of various
572   negotiable parameters.  A weight is normalized to a real number in
573   the range 0 through 1, where 0 is the minimum and 1 the maximum
574   value. If a parameter has a quality value of 0, then content with
575   this parameter is `not acceptable' for the client. HTTP/1.1
576   applications &MUST-NOT; generate more than three digits after the
577   decimal point. User configuration of these values &SHOULD; also be
578   limited in this fashion.
580<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
581  qvalue         = ( "0" [ "." 0*3DIGIT ] )
582                 | ( "1" [ "." 0*3("0") ] )
585   "Quality values" is a misnomer, since these values merely represent
586   relative degradation in desired quality.
590<section title="Language Tags" anchor="language.tags">
592   A language tag identifies a natural language spoken, written, or
593   otherwise conveyed by human beings for communication of information
594   to other human beings. Computer languages are explicitly excluded.
595   HTTP uses language tags within the Accept-Language and Content-Language
596   fields.
599   The syntax and registry of HTTP language tags is the same as that
600   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
601   or more parts: A primary language tag and a possibly empty series of
602   subtags:
604<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/>
605  language-tag  = primary-tag *( "-" subtag )
606  primary-tag   = 1*8ALPHA
607  subtag        = 1*8ALPHA
610   White space is not allowed within the tag and all tags are case-insensitive.
611   The name space of language tags is administered by the
612   IANA. Example tags include:
614<figure><artwork type="example">
615    en, en-US, en-cockney, i-cherokee, x-pig-latin
618   where any two-letter primary-tag is an ISO-639 language abbreviation
619   and any two-letter initial subtag is an ISO-3166 country code. (The
620   last three tags above are not registered tags; all but the last are
621   examples of tags which could be registered in future.)
626<section title="Entity" anchor="entity">
628   Request and Response messages &MAY; transfer an entity if not otherwise
629   restricted by the request method or response status code. An entity
630   consists of entity-header fields and an entity-body, although some
631   responses will only include the entity-headers.
634   In this section, both sender and recipient refer to either the client
635   or the server, depending on who sends and who receives the entity.
638<section title="Entity Header Fields" anchor="entity.header.fields">
640   Entity-header fields define metainformation about the entity-body or,
641   if no body is present, about the resource identified by the request.
643<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
644  entity-header  = Allow                    ; &header-allow;
645                 | Content-Encoding         ; <xref target="header.content-encoding"/>
646                 | Content-Language         ; <xref target="header.content-language"/>
647                 | Content-Length           ; &header-content-length;
648                 | Content-Location         ; <xref target="header.content-location"/>
649                 | Content-MD5              ; <xref target="header.content-md5"/>
650                 | Content-Range            ; &header-content-range;
651                 | Content-Type             ; <xref target="header.content-type"/>
652                 | Expires                  ; &header-expires;
653                 | Last-Modified            ; &header-last-modified;
654                 | extension-header
656  extension-header = message-header
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.
667<section title="Entity Body" anchor="entity.body">
669   The entity-body (if any) sent with an HTTP request or response is in
670   a format and encoding defined by the entity-header fields.
672<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
673  entity-body    = *OCTET
676   An entity-body is only present in a message when a message-body is
677   present, as described in &message-body;. The entity-body is obtained
678   from the message-body by decoding any Transfer-Encoding that might
679   have been applied to ensure safe and proper transfer of the message.
682<section title="Type" anchor="type">
684   When an entity-body is included with a message, the data type of that
685   body is determined via the header fields Content-Type and Content-Encoding.
686   These define a two-layer, ordered encoding model:
688<figure><artwork type="example">
689    entity-body := Content-Encoding( Content-Type( data ) )
692   Content-Type specifies the media type of the underlying data.
693   Content-Encoding may be used to indicate any additional content
694   codings applied to the data, usually for the purpose of data
695   compression, that are a property of the requested resource. There is
696   no default encoding.
699   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
700   Content-Type header field defining the media type of that body. If
701   and only if the media type is not given by a Content-Type field, the
702   recipient &MAY; attempt to guess the media type via inspection of its
703   content and/or the name extension(s) of the URI used to identify the
704   resource. If the media type remains unknown, the recipient &SHOULD;
705   treat it as type "application/octet-stream".
709<section title="Entity Length" anchor="entity.length">
711   The entity-length of a message is the length of the message-body
712   before any transfer-codings have been applied. &message-length; defines
713   how the transfer-length of a message-body is determined.
719<section title="Content Negotiation" anchor="content.negotiation">
721   Most HTTP responses include an entity which contains information for
722   interpretation by a human user. Naturally, it is desirable to supply
723   the user with the "best available" entity corresponding to the
724   request. Unfortunately for servers and caches, not all users have the
725   same preferences for what is "best," and not all user agents are
726   equally capable of rendering all entity types. For that reason, HTTP
727   has provisions for several mechanisms for "content negotiation" --
728   the process of selecting the best representation for a given response
729   when there are multiple representations available.
730  <list><t>
731      <x:h>Note:</x:h> This is not called "format negotiation" because the
732      alternate representations may be of the same media type, but use
733      different capabilities of that type, be in different languages,
734      etc.
735  </t></list>
738   Any response containing an entity-body &MAY; be subject to negotiation,
739   including error responses.
742   There are two kinds of content negotiation which are possible in
743   HTTP: server-driven and agent-driven negotiation. These two kinds of
744   negotiation are orthogonal and thus may be used separately or in
745   combination. One method of combination, referred to as transparent
746   negotiation, occurs when a cache uses the agent-driven negotiation
747   information provided by the origin server in order to provide
748   server-driven negotiation for subsequent requests.
751<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
753   If the selection of the best representation for a response is made by
754   an algorithm located at the server, it is called server-driven
755   negotiation. Selection is based on the available representations of
756   the response (the dimensions over which it can vary; e.g. language,
757   content-coding, etc.) and the contents of particular header fields in
758   the request message or on other information pertaining to the request
759   (such as the network address of the client).
762   Server-driven negotiation is advantageous when the algorithm for
763   selecting from among the available representations is difficult to
764   describe to the user agent, or when the server desires to send its
765   "best guess" to the client along with the first response (hoping to
766   avoid the round-trip delay of a subsequent request if the "best
767   guess" is good enough for the user). In order to improve the server's
768   guess, the user agent &MAY; include request header fields (Accept,
769   Accept-Language, Accept-Encoding, etc.) which describe its
770   preferences for such a response.
773   Server-driven negotiation has disadvantages:
774  <list style="numbers">
775    <t>
776         It is impossible for the server to accurately determine what
777         might be "best" for any given user, since that would require
778         complete knowledge of both the capabilities of the user agent
779         and the intended use for the response (e.g., does the user want
780         to view it on screen or print it on paper?).
781    </t>
782    <t>
783         Having the user agent describe its capabilities in every
784         request can be both very inefficient (given that only a small
785         percentage of responses have multiple representations) and a
786         potential violation of the user's privacy.
787    </t>
788    <t>
789         It complicates the implementation of an origin server and the
790         algorithms for generating responses to a request.
791    </t>
792    <t>
793         It may limit a public cache's ability to use the same response
794         for multiple user's requests.
795    </t>
796  </list>
799   HTTP/1.1 includes the following request-header fields for enabling
800   server-driven negotiation through description of user agent
801   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
802   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
803   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
804   origin server is not limited to these dimensions and &MAY; vary the
805   response based on any aspect of the request, including information
806   outside the request-header fields or within extension header fields
807   not defined by this specification.
810   The Vary header field (&header-vary;) can be used to express the parameters the
811   server uses to select a representation that is subject to server-driven
812   negotiation.
816<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
818   With agent-driven negotiation, selection of the best representation
819   for a response is performed by the user agent after receiving an
820   initial response from the origin server. Selection is based on a list
821   of the available representations of the response included within the
822   header fields or entity-body of the initial response, with each
823   representation identified by its own URI. Selection from among the
824   representations may be performed automatically (if the user agent is
825   capable of doing so) or manually by the user selecting from a
826   generated (possibly hypertext) menu.
829   Agent-driven negotiation is advantageous when the response would vary
830   over commonly-used dimensions (such as type, language, or encoding),
831   when the origin server is unable to determine a user agent's
832   capabilities from examining the request, and generally when public
833   caches are used to distribute server load and reduce network usage.
836   Agent-driven negotiation suffers from the disadvantage of needing a
837   second request to obtain the best alternate representation. This
838   second request is only efficient when caching is used. In addition,
839   this specification does not define any mechanism for supporting
840   automatic selection, though it also does not prevent any such
841   mechanism from being developed as an extension and used within
842   HTTP/1.1.
845   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
846   status codes for enabling agent-driven negotiation when the server is
847   unwilling or unable to provide a varying response using server-driven
848   negotiation.
852<section title="Transparent Negotiation" anchor="transparent.negotiation">
854   Transparent negotiation is a combination of both server-driven and
855   agent-driven negotiation. When a cache is supplied with a form of the
856   list of available representations of the response (as in agent-driven
857   negotiation) and the dimensions of variance are completely understood
858   by the cache, then the cache becomes capable of performing server-driven
859   negotiation on behalf of the origin server for subsequent
860   requests on that resource.
863   Transparent negotiation has the advantage of distributing the
864   negotiation work that would otherwise be required of the origin
865   server and also removing the second request delay of agent-driven
866   negotiation when the cache is able to correctly guess the right
867   response.
870   This specification does not define any mechanism for transparent
871   negotiation, though it also does not prevent any such mechanism from
872   being developed as an extension that could be used within HTTP/1.1.
877<section title="Header Field Definitions" anchor="header.fields">
879   This section defines the syntax and semantics of HTTP/1.1 header fields
880   related to the payload of messages.
883   For entity-header fields, both sender and recipient refer to either the
884   client or the server, depending on who sends and who receives the entity.
887<section title="Accept" anchor="header.accept">
888  <iref primary="true" item="Accept header" x:for-anchor=""/>
889  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
891   The Accept request-header field can be used to specify certain media
892   types which are acceptable for the response. Accept headers can be
893   used to indicate that the request is specifically limited to a small
894   set of desired types, as in the case of a request for an in-line
895   image.
897<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-extension"/>
898  Accept         = "Accept" ":"
899                   #( media-range [ accept-params ] )
901  media-range    = ( "*/*"
902                   | ( type "/" "*" )
903                   | ( type "/" subtype )
904                   ) *( ";" parameter )
905  accept-params  = ";" "q" "=" qvalue *( accept-extension )
906  accept-extension = ";" token [ "=" ( token | quoted-string ) ]
909   The asterisk "*" character is used to group media types into ranges,
910   with "*/*" indicating all media types and "type/*" indicating all
911   subtypes of that type. The media-range &MAY; include media type
912   parameters that are applicable to that range.
915   Each media-range &MAY; be followed by one or more accept-params,
916   beginning with the "q" parameter for indicating a relative quality
917   factor. The first "q" parameter (if any) separates the media-range
918   parameter(s) from the accept-params. Quality factors allow the user
919   or user agent to indicate the relative degree of preference for that
920   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
921   default value is q=1.
922  <list><t>
923      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
924      parameters from Accept extension parameters is due to historical
925      practice. Although this prevents any media type parameter named
926      "q" from being used with a media range, such an event is believed
927      to be unlikely given the lack of any "q" parameters in the IANA
928      media type registry and the rare usage of any media type
929      parameters in Accept. Future media types are discouraged from
930      registering any parameter named "q".
931  </t></list>
934   The example
936<figure><artwork type="example">
937    Accept: audio/*; q=0.2, audio/basic
940   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
941   type if it is the best available after an 80% mark-down in quality."
944   If no Accept header field is present, then it is assumed that the
945   client accepts all media types. If an Accept header field is present,
946   and if the server cannot send a response which is acceptable
947   according to the combined Accept field value, then the server &SHOULD;
948   send a 406 (Not Acceptable) response.
951   A more elaborate example is
953<figure><artwork type="example">
954    Accept: text/plain; q=0.5, text/html,
955            text/x-dvi; q=0.8, text/x-c
958   Verbally, this would be interpreted as "text/html and text/x-c are
959   the preferred media types, but if they do not exist, then send the
960   text/x-dvi entity, and if that does not exist, send the text/plain
961   entity."
964   Media ranges can be overridden by more specific media ranges or
965   specific media types. If more than one media range applies to a given
966   type, the most specific reference has precedence. For example,
968<figure><artwork type="example">
969    Accept: text/*, text/html, text/html;level=1, */*
972   have the following precedence:
974<figure><artwork type="example">
975    1) text/html;level=1
976    2) text/html
977    3) text/*
978    4) */*
981   The media type quality factor associated with a given type is
982   determined by finding the media range with the highest precedence
983   which matches that type. For example,
985<figure><artwork type="example">
986    Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
987            text/html;level=2;q=0.4, */*;q=0.5
990   would cause the following values to be associated:
992<figure><artwork type="example">
993    text/html;level=1         = 1
994    text/html                 = 0.7
995    text/plain                = 0.3
996    image/jpeg                = 0.5
997    text/html;level=2         = 0.4
998    text/html;level=3         = 0.7
1001      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1002      values for certain media ranges. However, unless the user agent is
1003      a closed system which cannot interact with other rendering agents,
1004      this default set ought to be configurable by the user.
1008<section title="Accept-Charset" anchor="header.accept-charset">
1009  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1010  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1012   The Accept-Charset request-header field can be used to indicate what
1013   character sets are acceptable for the response. This field allows
1014   clients capable of understanding more comprehensive or special-purpose
1015   character sets to signal that capability to a server which is
1016   capable of representing documents in those character sets.
1018<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
1019  Accept-Charset = "Accept-Charset" ":"
1020          1#( ( charset | "*" ) [ ";" "q" "=" qvalue ] )
1023   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1024   be given an associated quality value which represents the user's
1025   preference for that charset. The default value is q=1. An example is
1027<figure><artwork type="example">
1028   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1031   The special value "*", if present in the Accept-Charset field,
1032   matches every character set (including ISO-8859-1) which is not
1033   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1034   in an Accept-Charset field, then all character sets not explicitly
1035   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1036   a quality value of 1 if not explicitly mentioned.
1039   If no Accept-Charset header is present, the default is that any
1040   character set is acceptable. If an Accept-Charset header is present,
1041   and if the server cannot send a response which is acceptable
1042   according to the Accept-Charset header, then the server &SHOULD; send
1043   an error response with the 406 (Not Acceptable) status code, though
1044   the sending of an unacceptable response is also allowed.
1048<section title="Accept-Encoding" anchor="header.accept-encoding">
1049  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1050  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1052   The Accept-Encoding request-header field is similar to Accept, but
1053   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1054   the response.
1056<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
1057  Accept-Encoding  = "Accept-Encoding" ":"
1058                     #( codings [ ";" "q" "=" qvalue ] )
1059  codings          = ( content-coding | "*" )
1062   Examples of its use are:
1064<figure><artwork type="example">
1065    Accept-Encoding: compress, gzip
1066    Accept-Encoding:
1067    Accept-Encoding: *
1068    Accept-Encoding: compress;q=0.5, gzip;q=1.0
1069    Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1072   A server tests whether a content-coding is acceptable, according to
1073   an Accept-Encoding field, using these rules:
1074  <list style="numbers">
1075      <t>If the content-coding is one of the content-codings listed in
1076         the Accept-Encoding field, then it is acceptable, unless it is
1077         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1078         qvalue of 0 means "not acceptable.")</t>
1080      <t>The special "*" symbol in an Accept-Encoding field matches any
1081         available content-coding not explicitly listed in the header
1082         field.</t>
1084      <t>If multiple content-codings are acceptable, then the acceptable
1085         content-coding with the highest non-zero qvalue is preferred.</t>
1087      <t>The "identity" content-coding is always acceptable, unless
1088         specifically refused because the Accept-Encoding field includes
1089         "identity;q=0", or because the field includes "*;q=0" and does
1090         not explicitly include the "identity" content-coding. If the
1091         Accept-Encoding field-value is empty, then only the "identity"
1092         encoding is acceptable.</t>
1093  </list>
1096   If an Accept-Encoding field is present in a request, and if the
1097   server cannot send a response which is acceptable according to the
1098   Accept-Encoding header, then the server &SHOULD; send an error response
1099   with the 406 (Not Acceptable) status code.
1102   If no Accept-Encoding field is present in a request, the server &MAY;
1103   assume that the client will accept any content coding. In this case,
1104   if "identity" is one of the available content-codings, then the
1105   server &SHOULD; use the "identity" content-coding, unless it has
1106   additional information that a different content-coding is meaningful
1107   to the client.
1108  <list><t>
1109      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1110      and if the "identity" content-coding is unavailable, then
1111      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1112      "gzip" and "compress") are preferred; some older clients
1113      improperly display messages sent with other content-codings.  The
1114      server might also make this decision based on information about
1115      the particular user-agent or client.
1116    </t><t>
1117      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1118      associated with content-codings. This means that qvalues will not
1119      work and are not permitted with x-gzip or x-compress.
1120    </t></list>
1124<section title="Accept-Language" anchor="header.accept-language">
1125  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1126  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1128   The Accept-Language request-header field is similar to Accept, but
1129   restricts the set of natural languages that are preferred as a
1130   response to the request. Language tags are defined in <xref target="language.tags"/>.
1132<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1133  Accept-Language = "Accept-Language" ":"
1134                    1#( language-range [ ";" "q" "=" qvalue ] )
1135  language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
1138   Each language-range &MAY; be given an associated quality value which
1139   represents an estimate of the user's preference for the languages
1140   specified by that range. The quality value defaults to "q=1". For
1141   example,
1143<figure><artwork type="example">
1144    Accept-Language: da, en-gb;q=0.8, en;q=0.7
1147   would mean: "I prefer Danish, but will accept British English and
1148   other types of English." A language-range matches a language-tag if
1149   it exactly equals the tag, or if it exactly equals a prefix of the
1150   tag such that the first tag character following the prefix is "-".
1151   The special range "*", if present in the Accept-Language field,
1152   matches every tag not matched by any other range present in the
1153   Accept-Language field.
1154  <list><t>
1155      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1156      language tags are assigned to languages in such a way that it is
1157      always true that if a user understands a language with a certain
1158      tag, then this user will also understand all languages with tags
1159      for which this tag is a prefix. The prefix rule simply allows the
1160      use of prefix tags if this is the case.
1161  </t></list>
1164   The language quality factor assigned to a language-tag by the
1165   Accept-Language field is the quality value of the longest language-range
1166   in the field that matches the language-tag. If no language-range
1167   in the field matches the tag, the language quality factor
1168   assigned is 0. If no Accept-Language header is present in the
1169   request, the server
1170   &SHOULD; assume that all languages are equally acceptable. If an
1171   Accept-Language header is present, then all languages which are
1172   assigned a quality factor greater than 0 are acceptable.
1175   It might be contrary to the privacy expectations of the user to send
1176   an Accept-Language header with the complete linguistic preferences of
1177   the user in every request. For a discussion of this issue, see
1178   <xref target=""/>.
1181   As intelligibility is highly dependent on the individual user, it is
1182   recommended that client applications make the choice of linguistic
1183   preference available to the user. If the choice is not made
1184   available, then the Accept-Language header field &MUST-NOT; be given in
1185   the request.
1186  <list><t>
1187      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1188      the user, we remind implementors of  the fact that users are not
1189      familiar with the details of language matching as described above,
1190      and should provide appropriate guidance. As an example, users
1191      might assume that on selecting "en-gb", they will be served any
1192      kind of English document if British English is not available. A
1193      user agent might suggest in such a case to add "en" to get the
1194      best matching behavior.
1195  </t></list>
1199<section title="Content-Encoding" anchor="header.content-encoding">
1200  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1201  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1203   The Content-Encoding entity-header field is used as a modifier to the
1204   media-type. When present, its value indicates what additional content
1205   codings have been applied to the entity-body, and thus what decoding
1206   mechanisms must be applied in order to obtain the media-type
1207   referenced by the Content-Type header field. Content-Encoding is
1208   primarily used to allow a document to be compressed without losing
1209   the identity of its underlying media type.
1211<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1212  Content-Encoding  = "Content-Encoding" ":" 1#content-coding
1215   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1217<figure><artwork type="example">
1218    Content-Encoding: gzip
1221   The content-coding is a characteristic of the entity identified by
1222   the Request-URI. Typically, the entity-body is stored with this
1223   encoding and is only decoded before rendering or analogous usage.
1224   However, a non-transparent proxy &MAY; modify the content-coding if the
1225   new coding is known to be acceptable to the recipient, unless the
1226   "no-transform" cache-control directive is present in the message.
1229   If the content-coding of an entity is not "identity", then the
1230   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1231   that lists the non-identity content-coding(s) used.
1234   If the content-coding of an entity in a request message is not
1235   acceptable to the origin server, the server &SHOULD; respond with a
1236   status code of 415 (Unsupported Media Type).
1239   If multiple encodings have been applied to an entity, the content
1240   codings &MUST; be listed in the order in which they were applied.
1241   Additional information about the encoding parameters &MAY; be provided
1242   by other entity-header fields not defined by this specification.
1246<section title="Content-Language" anchor="header.content-language">
1247  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1248  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1250   The Content-Language entity-header field describes the natural
1251   language(s) of the intended audience for the enclosed entity. Note
1252   that this might not be equivalent to all the languages used within
1253   the entity-body.
1255<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1256  Content-Language  = "Content-Language" ":" 1#language-tag
1259   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1260   Content-Language is to allow a user to identify and differentiate
1261   entities according to the user's own preferred language. Thus, if the
1262   body content is intended only for a Danish-literate audience, the
1263   appropriate field is
1265<figure><artwork type="example">
1266    Content-Language: da
1269   If no Content-Language is specified, the default is that the content
1270   is intended for all language audiences. This might mean that the
1271   sender does not consider it to be specific to any natural language,
1272   or that the sender does not know for which language it is intended.
1275   Multiple languages &MAY; be listed for content that is intended for
1276   multiple audiences. For example, a rendition of the "Treaty of
1277   Waitangi," presented simultaneously in the original Maori and English
1278   versions, would call for
1280<figure><artwork type="example">
1281    Content-Language: mi, en
1284   However, just because multiple languages are present within an entity
1285   does not mean that it is intended for multiple linguistic audiences.
1286   An example would be a beginner's language primer, such as "A First
1287   Lesson in Latin," which is clearly intended to be used by an
1288   English-literate audience. In this case, the Content-Language would
1289   properly only include "en".
1292   Content-Language &MAY; be applied to any media type -- it is not
1293   limited to textual documents.
1297<section title="Content-Location" anchor="header.content-location">
1298  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1299  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1301   The Content-Location entity-header field &MAY; be used to supply the
1302   resource location for the entity enclosed in the message when that
1303   entity is accessible from a location separate from the requested
1304   resource's URI. A server &SHOULD; provide a Content-Location for the
1305   variant corresponding to the response entity; especially in the case
1306   where a resource has multiple entities associated with it, and those
1307   entities actually have separate locations by which they might be
1308   individually accessed, the server &SHOULD; provide a Content-Location
1309   for the particular variant which is returned.
1311<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1312  Content-Location = "Content-Location" ":"
1313                    ( absoluteURI | relativeURI )
1316   The value of Content-Location also defines the base URI for the
1317   entity.
1320   The Content-Location value is not a replacement for the original
1321   requested URI; it is only a statement of the location of the resource
1322   corresponding to this particular entity at the time of the request.
1323   Future requests &MAY; specify the Content-Location URI as the request-URI
1324   if the desire is to identify the source of that particular
1325   entity.
1328   A cache cannot assume that an entity with a Content-Location
1329   different from the URI used to retrieve it can be used to respond to
1330   later requests on that Content-Location URI. However, the Content-Location
1331   can be used to differentiate between multiple entities
1332   retrieved from a single requested resource, as described in &caching-neg-resp;.
1335   If the Content-Location is a relative URI, the relative URI is
1336   interpreted relative to the Request-URI.
1339   The meaning of the Content-Location header in PUT or POST requests is
1340   undefined; servers are free to ignore it in those cases.
1344<section title="Content-MD5" anchor="header.content-md5">
1345  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1346  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1348   The Content-MD5 entity-header field, as defined in <xref target="RFC1864"/>, is
1349   an MD5 digest of the entity-body for the purpose of providing an
1350   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1351   MIC is good for detecting accidental modification of the entity-body
1352   in transit, but is not proof against malicious attacks.)
1354<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="md5-digest"/>
1355  Content-MD5   = "Content-MD5" ":" md5-digest
1356  md5-digest    = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1359   The Content-MD5 header field &MAY; be generated by an origin server or
1360   client to function as an integrity check of the entity-body. Only
1361   origin servers or clients &MAY; generate the Content-MD5 header field;
1362   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1363   value as an end-to-end integrity check. Any recipient of the entity-body,
1364   including gateways and proxies, &MAY; check that the digest value
1365   in this header field matches that of the entity-body as received.
1368   The MD5 digest is computed based on the content of the entity-body,
1369   including any content-coding that has been applied, but not including
1370   any transfer-encoding applied to the message-body. If the message is
1371   received with a transfer-encoding, that encoding &MUST; be removed
1372   prior to checking the Content-MD5 value against the received entity.
1375   This has the result that the digest is computed on the octets of the
1376   entity-body exactly as, and in the order that, they would be sent if
1377   no transfer-encoding were being applied.
1380   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1381   composite media-types (e.g., multipart/* and message/rfc822), but
1382   this does not change how the digest is computed as defined in the
1383   preceding paragraph.
1386   There are several consequences of this. The entity-body for composite
1387   types &MAY; contain many body-parts, each with its own MIME and HTTP
1388   headers (including Content-MD5, Content-Transfer-Encoding, and
1389   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1390   or Content-Encoding header, it is assumed that the content
1391   of the body-part has had the encoding applied, and the body-part is
1392   included in the Content-MD5 digest as is -- i.e., after the
1393   application. The Transfer-Encoding header field is not allowed within
1394   body-parts.
1397   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1398   computing or checking the digest: the line break convention used in
1399   the text actually transmitted &MUST; be left unaltered when computing
1400   the digest.
1401  <list><t>
1402      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1403      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1404      in which the application of Content-MD5 to HTTP entity-bodies
1405      differs from its application to MIME entity-bodies. One is that
1406      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1407      does use Transfer-Encoding and Content-Encoding. Another is that
1408      HTTP more frequently uses binary content types than MIME, so it is
1409      worth noting that, in such cases, the byte order used to compute
1410      the digest is the transmission byte order defined for the type.
1411      Lastly, HTTP allows transmission of text types with any of several
1412      line break conventions and not just the canonical form using CRLF.
1413  </t></list>
1417<section title="Content-Type" anchor="header.content-type">
1418  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1419  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1421   The Content-Type entity-header field indicates the media type of the
1422   entity-body sent to the recipient or, in the case of the HEAD method,
1423   the media type that would have been sent had the request been a GET.
1425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1426  Content-Type   = "Content-Type" ":" media-type
1429   Media types are defined in <xref target="media.types"/>. An example of the field is
1431<figure><artwork type="example">
1432    Content-Type: text/html; charset=ISO-8859-4
1435   Further discussion of methods for identifying the media type of an
1436   entity is provided in <xref target="type"/>.
1442<section title="IANA Considerations" anchor="IANA.considerations">
1444   <cref>TBD.</cref>
1448<section title="Security Considerations" anchor="security.considerations">
1450   This section is meant to inform application developers, information
1451   providers, and users of the security limitations in HTTP/1.1 as
1452   described by this document. The discussion does not include
1453   definitive solutions to the problems revealed, though it does make
1454   some suggestions for reducing security risks.
1457<section title="Privacy Issues Connected to Accept Headers" anchor="">
1459   Accept request-headers can reveal information about the user to all
1460   servers which are accessed. The Accept-Language header in particular
1461   can reveal information the user would consider to be of a private
1462   nature, because the understanding of particular languages is often
1463   strongly correlated to the membership of a particular ethnic group.
1464   User agents which offer the option to configure the contents of an
1465   Accept-Language header to be sent in every request are strongly
1466   encouraged to let the configuration process include a message which
1467   makes the user aware of the loss of privacy involved.
1470   An approach that limits the loss of privacy would be for a user agent
1471   to omit the sending of Accept-Language headers by default, and to ask
1472   the user whether or not to start sending Accept-Language headers to a
1473   server if it detects, by looking for any Vary response-header fields
1474   generated by the server, that such sending could improve the quality
1475   of service.
1478   Elaborate user-customized accept header fields sent in every request,
1479   in particular if these include quality values, can be used by servers
1480   as relatively reliable and long-lived user identifiers. Such user
1481   identifiers would allow content providers to do click-trail tracking,
1482   and would allow collaborating content providers to match cross-server
1483   click-trails or form submissions of individual users. Note that for
1484   many users not behind a proxy, the network address of the host
1485   running the user agent will also serve as a long-lived user
1486   identifier. In environments where proxies are used to enhance
1487   privacy, user agents ought to be conservative in offering accept
1488   header configuration options to end users. As an extreme privacy
1489   measure, proxies could filter the accept headers in relayed requests.
1490   General purpose user agents which provide a high degree of header
1491   configurability &SHOULD; warn users about the loss of privacy which can
1492   be involved.
1496<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1498   <xref target="RFC1806"/>, from which the often implemented Content-Disposition
1499   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1500   serious security considerations. Content-Disposition is not part of
1501   the HTTP standard, but since it is widely implemented, we are
1502   documenting its use and risks for implementors. See <xref target="RFC2183"/>
1503   (which updates <xref target="RFC1806"/>) for details.
1509<section title="Acknowledgments" anchor="ack">
1514<references title="Normative References">
1516<reference anchor="ISO-8859-1">
1517  <front>
1518    <title>
1519     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1520    </title>
1521    <author>
1522      <organization>International Organization for Standardization</organization>
1523    </author>
1524    <date year="1998"/>
1525  </front>
1526  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1529<reference anchor="Part1">
1530  <front>
1531    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1532    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1533      <organization abbrev="Day Software">Day Software</organization>
1534      <address><email></email></address>
1535    </author>
1536    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1537      <organization>One Laptop per Child</organization>
1538      <address><email></email></address>
1539    </author>
1540    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1541      <organization abbrev="HP">Hewlett-Packard Company</organization>
1542      <address><email></email></address>
1543    </author>
1544    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1545      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1546      <address><email></email></address>
1547    </author>
1548    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1549      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1550      <address><email></email></address>
1551    </author>
1552    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1553      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1554      <address><email></email></address>
1555    </author>
1556    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1557      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1558      <address><email></email></address>
1559    </author>
1560    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1561      <organization abbrev="W3C">World Wide Web Consortium</organization>
1562      <address><email></email></address>
1563    </author>
1564    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1565      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1566      <address><email></email></address>
1567    </author>
1568    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1569  </front>
1570  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1571  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1574<reference anchor="Part2">
1575  <front>
1576    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1577    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1578      <organization abbrev="Day Software">Day Software</organization>
1579      <address><email></email></address>
1580    </author>
1581    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1582      <organization>One Laptop per Child</organization>
1583      <address><email></email></address>
1584    </author>
1585    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1586      <organization abbrev="HP">Hewlett-Packard Company</organization>
1587      <address><email></email></address>
1588    </author>
1589    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1590      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1591      <address><email></email></address>
1592    </author>
1593    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1594      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1595      <address><email></email></address>
1596    </author>
1597    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1598      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1599      <address><email></email></address>
1600    </author>
1601    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1602      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1603      <address><email></email></address>
1604    </author>
1605    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1606      <organization abbrev="W3C">World Wide Web Consortium</organization>
1607      <address><email></email></address>
1608    </author>
1609    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1610      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1611      <address><email></email></address>
1612    </author>
1613    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1614  </front>
1615  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1616  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1619<reference anchor="Part4">
1620  <front>
1621    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1622    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1623      <organization abbrev="Day Software">Day Software</organization>
1624      <address><email></email></address>
1625    </author>
1626    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1627      <organization>One Laptop per Child</organization>
1628      <address><email></email></address>
1629    </author>
1630    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1631      <organization abbrev="HP">Hewlett-Packard Company</organization>
1632      <address><email></email></address>
1633    </author>
1634    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1635      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1636      <address><email></email></address>
1637    </author>
1638    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1639      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1640      <address><email></email></address>
1641    </author>
1642    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1643      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1644      <address><email></email></address>
1645    </author>
1646    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1647      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1648      <address><email></email></address>
1649    </author>
1650    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1651      <organization abbrev="W3C">World Wide Web Consortium</organization>
1652      <address><email></email></address>
1653    </author>
1654    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1655      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1656      <address><email></email></address>
1657    </author>
1658    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1659  </front>
1660  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1661  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1664<reference anchor="Part5">
1665  <front>
1666    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1667    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1668      <organization abbrev="Day Software">Day Software</organization>
1669      <address><email></email></address>
1670    </author>
1671    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1672      <organization>One Laptop per Child</organization>
1673      <address><email></email></address>
1674    </author>
1675    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1676      <organization abbrev="HP">Hewlett-Packard Company</organization>
1677      <address><email></email></address>
1678    </author>
1679    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1680      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1681      <address><email></email></address>
1682    </author>
1683    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1684      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1685      <address><email></email></address>
1686    </author>
1687    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1688      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1689      <address><email></email></address>
1690    </author>
1691    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1692      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1693      <address><email></email></address>
1694    </author>
1695    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1696      <organization abbrev="W3C">World Wide Web Consortium</organization>
1697      <address><email></email></address>
1698    </author>
1699    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1700      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1701      <address><email></email></address>
1702    </author>
1703    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1704  </front>
1705  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1706  <x:source href="p5-range.xml" basename="p5-range"/>
1709<reference anchor="Part6">
1710  <front>
1711    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1712    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1713      <organization abbrev="Day Software">Day Software</organization>
1714      <address><email></email></address>
1715    </author>
1716    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1717      <organization>One Laptop per Child</organization>
1718      <address><email></email></address>
1719    </author>
1720    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1721      <organization abbrev="HP">Hewlett-Packard Company</organization>
1722      <address><email></email></address>
1723    </author>
1724    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1725      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1726      <address><email></email></address>
1727    </author>
1728    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1729      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1730      <address><email></email></address>
1731    </author>
1732    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1733      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1734      <address><email></email></address>
1735    </author>
1736    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1737      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1738      <address><email></email></address>
1739    </author>
1740    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1741      <organization abbrev="W3C">World Wide Web Consortium</organization>
1742      <address><email></email></address>
1743    </author>
1744    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1745      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1746      <address><email></email></address>
1747    </author>
1748    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1749  </front>
1750  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1751  <x:source href="p6-cache.xml" basename="p6-cache"/>
1754<reference anchor="RFC1766">
1755  <front>
1756    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1757    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1758      <organization>UNINETT</organization>
1759      <address><email></email></address>
1760    </author>
1761    <date month="March" year="1995"/>
1762  </front>
1763  <seriesInfo name="RFC" value="1766"/>
1766<reference anchor="RFC1864">
1767  <front>
1768    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1769    <author initials="J." surname="Myers" fullname="John G. Myers">
1770      <organization>Carnegie Mellon University</organization>
1771      <address><email></email></address>
1772    </author>
1773    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1774      <organization>Dover Beach Consulting, Inc.</organization>
1775      <address><email></email></address>
1776    </author>
1777    <date month="October" year="1995"/>
1778  </front>
1779  <seriesInfo name="RFC" value="1864"/>
1782<reference anchor="RFC1950">
1783  <front>
1784    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1785    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1786      <organization>Aladdin Enterprises</organization>
1787      <address><email></email></address>
1788    </author>
1789    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1790      <organization/>
1791    </author>
1792    <date month="May" year="1996"/>
1793  </front>
1794  <seriesInfo name="RFC" value="1950"/>
1795  <annotation>
1796    RFC1950 is an Informational RFC, thus it may be less stable than
1797    this specification. On the other hand, this downward reference was
1798    present since <xref target="RFC2068"/> (published in 1997), therefore it is unlikely
1799    to cause problems in practice.
1800  </annotation>
1803<reference anchor="RFC1951">
1804  <front>
1805    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1806    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1807      <organization>Aladdin Enterprises</organization>
1808      <address><email></email></address>
1809    </author>
1810    <date month="May" year="1996"/>
1811  </front>
1812  <seriesInfo name="RFC" value="1951"/>
1813  <annotation>
1814    RFC1951 is an Informational RFC, thus it may be less stable than
1815    this specification. On the other hand, this downward reference was
1816    present since <xref target="RFC2068"/> (published in 1997), therefore it is unlikely
1817    to cause problems in practice.
1818  </annotation>
1821<reference anchor="RFC1952">
1822  <front>
1823    <title>GZIP file format specification version 4.3</title>
1824    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1825      <organization>Aladdin Enterprises</organization>
1826      <address><email></email></address>
1827    </author>
1828    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1829      <organization/>
1830      <address><email></email></address>
1831    </author>
1832    <author initials="M." surname="Adler" fullname="Mark Adler">
1833      <organization/>
1834      <address><email></email></address>
1835    </author>
1836    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1837      <organization/>
1838      <address><email></email></address>
1839    </author>
1840    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1841      <organization/>
1842      <address><email></email></address>
1843    </author>
1844    <date month="May" year="1996"/>
1845  </front>
1846  <seriesInfo name="RFC" value="1952"/>
1847  <annotation>
1848    RFC1952 is an Informational RFC, thus it may be less stable than
1849    this specification. On the other hand, this downward reference was
1850    present since <xref target="RFC2068"/> (published in 1997), therefore it is unlikely
1851    to cause problems in practice.
1852  </annotation>
1855<reference anchor="RFC2045">
1856  <front>
1857    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1858    <author initials="N." surname="Freed" fullname="Ned Freed">
1859      <organization>Innosoft International, Inc.</organization>
1860      <address><email></email></address>
1861    </author>
1862    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1863      <organization>First Virtual Holdings</organization>
1864      <address><email></email></address>
1865    </author>
1866    <date month="November" year="1996"/>
1867  </front>
1868  <seriesInfo name="RFC" value="2045"/>
1871<reference anchor="RFC2046">
1872  <front>
1873    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1874    <author initials="N." surname="Freed" fullname="Ned Freed">
1875      <organization>Innosoft International, Inc.</organization>
1876      <address><email></email></address>
1877    </author>
1878    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1879      <organization>First Virtual Holdings</organization>
1880      <address><email></email></address>
1881    </author>
1882    <date month="November" year="1996"/>
1883  </front>
1884  <seriesInfo name="RFC" value="2046"/>
1887<reference anchor="RFC2119">
1888  <front>
1889    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1890    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1891      <organization>Harvard University</organization>
1892      <address><email></email></address>
1893    </author>
1894    <date month="March" year="1997"/>
1895  </front>
1896  <seriesInfo name="BCP" value="14"/>
1897  <seriesInfo name="RFC" value="2119"/>
1902<references title="Informative References">
1904<reference anchor="RFC1806">
1905  <front>
1906    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header</title>
1907    <author initials="R." surname="Troost" fullname="Rens Troost">
1908      <organization>New Century Systems</organization>
1909      <address><email></email></address>
1910    </author>
1911    <author initials="S." surname="Dorner" fullname="Steve Dorner">
1912      <organization>QUALCOMM Incorporated</organization>
1913      <address><email></email></address>
1914    </author>
1915    <date month="June" year="1995"/>
1916  </front>
1917  <seriesInfo name="RFC" value="1806"/>
1920<reference anchor="RFC1945">
1921  <front>
1922    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
1923    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1924      <organization>MIT, Laboratory for Computer Science</organization>
1925      <address><email></email></address>
1926    </author>
1927    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
1928      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1929      <address><email></email></address>
1930    </author>
1931    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1932      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
1933      <address><email></email></address>
1934    </author>
1935    <date month="May" year="1996"/>
1936  </front>
1937  <seriesInfo name="RFC" value="1945"/>
1940<reference anchor="RFC2049">
1941  <front>
1942    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
1943    <author initials="N." surname="Freed" fullname="Ned Freed">
1944      <organization>Innosoft International, Inc.</organization>
1945      <address><email></email></address>
1946    </author>
1947    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1948      <organization>First Virtual Holdings</organization>
1949      <address><email></email></address>
1950    </author>
1951    <date month="November" year="1996"/>
1952  </front>
1953  <seriesInfo name="RFC" value="2049"/>
1956<reference anchor="RFC2068">
1957  <front>
1958    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
1959    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
1960      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1961      <address><email></email></address>
1962    </author>
1963    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1964      <organization>MIT Laboratory for Computer Science</organization>
1965      <address><email></email></address>
1966    </author>
1967    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1968      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
1969      <address><email></email></address>
1970    </author>
1971    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1972      <organization>MIT Laboratory for Computer Science</organization>
1973      <address><email></email></address>
1974    </author>
1975    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1976      <organization>MIT Laboratory for Computer Science</organization>
1977      <address><email></email></address>
1978    </author>
1979    <date month="January" year="1997"/>
1980  </front>
1981  <seriesInfo name="RFC" value="2068"/>
1984<reference anchor="RFC2076">
1985  <front>
1986    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
1987    <author initials="J." surname="Palme" fullname="Jacob Palme">
1988      <organization>Stockholm University/KTH</organization>
1989      <address><email></email></address>
1990    </author>
1991    <date month="February" year="1997"/>
1992  </front>
1993  <seriesInfo name="RFC" value="2076"/>
1996<reference anchor="RFC2183">
1997  <front>
1998    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
1999    <author initials="R." surname="Troost" fullname="Rens Troost">
2000      <organization>New Century Systems</organization>
2001      <address><email></email></address>
2002    </author>
2003    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2004      <organization>QUALCOMM Incorporated</organization>
2005      <address><email></email></address>
2006    </author>
2007    <author initials="K." surname="Moore" fullname="Keith Moore">
2008      <organization>Department of Computer Science</organization>
2009      <address><email></email></address>
2010    </author>
2011    <date month="August" year="1997"/>
2012  </front>
2013  <seriesInfo name="RFC" value="2183"/>
2016<reference anchor="RFC2277">
2017  <front>
2018    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2019    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2020      <organization>UNINETT</organization>
2021      <address><email></email></address>
2022    </author>
2023    <date month="January" year="1998"/>
2024  </front>
2025  <seriesInfo name="BCP" value="18"/>
2026  <seriesInfo name="RFC" value="2277"/>
2029<reference anchor="RFC2388">
2030  <front>
2031    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2032    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2033      <organization>Xerox Palo Alto Research Center</organization>
2034      <address><email></email></address>
2035    </author>
2036    <date year="1998" month="August"/>
2037  </front>
2038  <seriesInfo name="RFC" value="2388"/>
2041<reference anchor="RFC2557">
2042  <front>
2043    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2044    <author initials="F." surname="Palme" fullname="Jacob Palme">
2045      <organization>Stockholm University and KTH</organization>
2046      <address><email></email></address>
2047    </author>
2048    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2049      <organization>Microsoft Corporation</organization>
2050      <address><email></email></address>
2051    </author>
2052    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2053      <organization>Lotus Development Corporation</organization>
2054      <address><email></email></address>
2055    </author>
2056    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2057      <organization/>
2058      <address><email></email></address>
2059    </author>
2060    <date year="1999" month="March"/>
2061  </front>
2062  <seriesInfo name="RFC" value="2557"/>
2065<reference anchor="RFC2616">
2066  <front>
2067    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2068    <author initials="R." surname="Fielding" fullname="R. Fielding">
2069      <organization>University of California, Irvine</organization>
2070      <address><email></email></address>
2071    </author>
2072    <author initials="J." surname="Gettys" fullname="J. Gettys">
2073      <organization>W3C</organization>
2074      <address><email></email></address>
2075    </author>
2076    <author initials="J." surname="Mogul" fullname="J. Mogul">
2077      <organization>Compaq Computer Corporation</organization>
2078      <address><email></email></address>
2079    </author>
2080    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2081      <organization>MIT Laboratory for Computer Science</organization>
2082      <address><email></email></address>
2083    </author>
2084    <author initials="L." surname="Masinter" fullname="L. Masinter">
2085      <organization>Xerox Corporation</organization>
2086      <address><email></email></address>
2087    </author>
2088    <author initials="P." surname="Leach" fullname="P. Leach">
2089      <organization>Microsoft Corporation</organization>
2090      <address><email></email></address>
2091    </author>
2092    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2093      <organization>W3C</organization>
2094      <address><email></email></address>
2095    </author>
2096    <date month="June" year="1999"/>
2097  </front>
2098  <seriesInfo name="RFC" value="2616"/>
2101<reference anchor="RFC2822">
2102  <front>
2103    <title>Internet Message Format</title>
2104    <author initials="P." surname="Resnick" fullname="P. Resnick">
2105      <organization>QUALCOMM Incorporated</organization>
2106    </author>
2107    <date year="2001" month="April"/>
2108  </front>
2109  <seriesInfo name="RFC" value="2822"/>
2112<reference anchor="RFC3629">
2113  <front>
2114    <title>UTF-8, a transformation format of ISO 10646</title>
2115    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2116      <organization>Alis Technologies</organization>
2117      <address><email></email></address>
2118    </author>
2119    <date month="November" year="2003"/>
2120  </front>
2121  <seriesInfo name="RFC" value="3629"/>
2122  <seriesInfo name="STD" value="63"/>
2125<reference anchor="RFC4288">
2126  <front>
2127    <title>Media Type Specifications and Registration Procedures</title>
2128    <author initials="N." surname="Freed" fullname="N. Freed">
2129      <organization>Sun Microsystems</organization>
2130      <address>
2131        <email></email>
2132      </address>
2133    </author>
2134    <author initials="J." surname="Klensin" fullname="J. Klensin">
2135      <organization/>
2136      <address>
2137        <email></email>
2138      </address>
2139    </author>
2140    <date year="2005" month="December"/>
2141  </front>
2142  <seriesInfo name="BCP" value="13"/>
2143  <seriesInfo name="RFC" value="4288"/>
2148<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2150   HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC2822"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2151   allow entities to be transmitted in an open variety of
2152   representations and with extensible mechanisms. However, RFC 2045
2153   discusses mail, and HTTP has a few features that are different from
2154   those described in RFC 2045. These differences were carefully chosen
2155   to optimize performance over binary connections, to allow greater
2156   freedom in the use of new media types, to make date comparisons
2157   easier, and to acknowledge the practice of some early HTTP servers
2158   and clients.
2161   This appendix describes specific areas where HTTP differs from RFC
2162   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2163   aware of these differences and provide the appropriate conversions
2164   where necessary. Proxies and gateways from MIME environments to HTTP
2165   also need to be aware of the differences because some conversions
2166   might be required.
2168<section title="MIME-Version" anchor="mime-version">
2170   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2171   include a single MIME-Version general-header field to indicate what
2172   version of the MIME protocol was used to construct the message. Use
2173   of the MIME-Version header field indicates that the message is in
2174   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2175   Proxies/gateways are responsible for ensuring full compliance (where
2176   possible) when exporting HTTP messages to strict MIME environments.
2178<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2179  MIME-Version   = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
2182   MIME version "1.0" is the default for use in HTTP/1.1. However,
2183   HTTP/1.1 message parsing and semantics are defined by this document
2184   and not the MIME specification.
2188<section title="Conversion to Canonical Form" anchor="">
2190   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2191   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2192   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2193   allowed for subtypes of the "text" media type when transmitted over
2194   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2195   line breaks as CRLF and forbids the use of CR or LF outside of line
2196   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2197   line break within text content when a message is transmitted over
2198   HTTP.
2201   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2202   environment &SHOULD; translate all line breaks within the text media
2203   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2204   canonical form of CRLF. Note, however, that this might be complicated
2205   by the presence of a Content-Encoding and by the fact that HTTP
2206   allows the use of some character sets which do not use octets 13 and
2207   10 to represent CR and LF, as is the case for some multi-byte
2208   character sets.
2211   Implementors should note that conversion will break any cryptographic
2212   checksums applied to the original content unless the original content
2213   is already in canonical form. Therefore, the canonical form is
2214   recommended for any content that uses such checksums in HTTP.
2218<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2220   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2221   Content-Encoding header field. Since this acts as a modifier on the
2222   media type, proxies and gateways from HTTP to MIME-compliant
2223   protocols &MUST; either change the value of the Content-Type header
2224   field or decode the entity-body before forwarding the message. (Some
2225   experimental applications of Content-Type for Internet mail have used
2226   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2227   a function equivalent to Content-Encoding. However, this parameter is
2228   not part of RFC 2045).
2232<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2234   HTTP does not use the Content-Transfer-Encoding field of RFC
2235   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2236   remove any Content-Transfer-Encoding
2237   prior to delivering the response message to an HTTP client.
2240   Proxies and gateways from HTTP to MIME-compliant protocols are
2241   responsible for ensuring that the message is in the correct format
2242   and encoding for safe transport on that protocol, where "safe
2243   transport" is defined by the limitations of the protocol being used.
2244   Such a proxy or gateway &SHOULD; label the data with an appropriate
2245   Content-Transfer-Encoding if doing so will improve the likelihood of
2246   safe transport over the destination protocol.
2250<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2252   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2253   Proxies/gateways &MUST; remove any transfer-coding prior to
2254   forwarding a message via a MIME-compliant protocol.
2258<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2260   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2261   need to be aware of MIME line length limitations. Since HTTP does not
2262   have this limitation, HTTP does not fold long lines. MHTML messages
2263   being transported by HTTP follow all conventions of MHTML, including
2264   line length limitations and folding, canonicalization, etc., since
2265   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2266   does not interpret the content or any MIME header lines that might be
2267   contained therein.
2272<section title="Additional Features" anchor="additional.features">
2274   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2275   existing HTTP implementations, but not consistently and correctly
2276   across most HTTP/1.1 applications. Implementors are advised to be
2277   aware of these features, but cannot rely upon their presence in, or
2278   interoperability with, other HTTP/1.1 applications. Some of these
2279   describe proposed experimental features, and some describe features
2280   that experimental deployment found lacking that are now addressed in
2281   the base HTTP/1.1 specification.
2284   A number of other headers, such as Content-Disposition and Title,
2285   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2288<section title="Content-Disposition" anchor="content-disposition">
2289<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2290<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2292   The Content-Disposition response-header field has been proposed as a
2293   means for the origin server to suggest a default filename if the user
2294   requests that the content is saved to a file. This usage is derived
2295   from the definition of Content-Disposition in <xref target="RFC1806"/>.
2297<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><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"/>
2298  content-disposition = "Content-Disposition" ":"
2299                        disposition-type *( ";" disposition-parm )
2300  disposition-type = "attachment" | disp-extension-token
2301  disposition-parm = filename-parm | disp-extension-parm
2302  filename-parm = "filename" "=" quoted-string
2303  disp-extension-token = token
2304  disp-extension-parm = token "=" ( token | quoted-string )
2307   An example is
2309<figure><artwork type="example">
2310     Content-Disposition: attachment; filename="fname.ext"
2313   The receiving user agent &SHOULD-NOT;  respect any directory path
2314   information present in the filename-parm parameter, which is the only
2315   parameter believed to apply to HTTP implementations at this time. The
2316   filename &SHOULD; be treated as a terminal component only.
2319   If this header is used in a response with the application/octet-stream
2320   content-type, the implied suggestion is that the user agent
2321   should not display the response, but directly enter a `save response
2322   as...' dialog.
2325   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2330<section title="Compatibility with Previous Versions" anchor="compatibility">
2331<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2333   Transfer-coding and message lengths all interact in ways that
2334   required fixing exactly when chunked encoding is used (to allow for
2335   transfer encoding that may not be self delimiting); it was important
2336   to straighten out exactly how message lengths are computed.
2337   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2338   <xref target="Part5"/> and <xref target="Part6"/>).
2341   Charset wildcarding is introduced to avoid explosion of character set
2342   names in accept headers. (<xref target="header.accept-charset"/>)
2345   Content-Base was deleted from the specification: it was not
2346   implemented widely, and there is no simple, safe way to introduce it
2347   without a robust extension mechanism. In addition, it is used in a
2348   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2351   A content-coding of "identity" was introduced, to solve problems
2352   discovered in caching. (<xref target="content.codings"/>)
2355   Quality Values of zero should indicate that "I don't want something"
2356   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2359   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
2360   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
2361   specification, but not commonly implemented. See <xref target="RFC2068"/>.
2365<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2367  Clarify contexts that charset is used in.
2368  (<xref target="character.sets"/>)
2371  Remove reference to non-existant identity transfer-coding value tokens.
2372  (<xref target="no.content-transfer-encoding"/>)
2378<section title="Change Log (to be removed by RFC Editor before publication)">
2380<section title="Since RFC2616">
2382  Extracted relevant partitions from <xref target="RFC2616"/>.
2386<section title="Since draft-ietf-httpbis-p3-payload-00">
2388  Closed issues:
2389  <list style="symbols">
2390    <t>
2391      <eref target=""/>:
2392      "Media Type Registrations"
2393      (<eref target=""/>)
2394    </t>
2395    <t>
2396      <eref target=""/>:
2397      "Clarification regarding quoting of charset values"
2398      (<eref target=""/>)
2399    </t>
2400    <t>
2401      <eref target=""/>:
2402      "Remove 'identity' token references"
2403      (<eref target=""/>)
2404    </t>
2405    <t>
2406      <eref target=""/>:
2407      "Accept-Encoding BNF"
2408    </t>
2409    <t>
2410      <eref target=""/>:
2411      "Normative and Informative references"
2412    </t>
2413    <t>
2414      <eref target=""/>:
2415      "RFC1700 references"
2416    </t>
2417    <t>
2418      <eref target=""/>:
2419      "Updating to RFC4288"
2420    </t>
2421    <t>
2422      <eref target=""/>:
2423      "Informative references"
2424    </t>
2425    <t>
2426      <eref target=""/>:
2427      "ISO-8859-1 Reference"
2428    </t>
2429    <t>
2430      <eref target=""/>:
2431      "Encoding References Normative"
2432    </t>
2433    <t>
2434      <eref target=""/>:
2435      "Normative up-to-date references"
2436    </t>
2437  </list>
2441<section title="Since draft-ietf-httpbis-p3-payload-01">
2443  Ongoing work on ABNF conversion (<eref target=""/>):
2444  <list style="symbols">
2445    <t>
2446      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2447    </t>
2448  </list>
2452<section title="Since draft-ietf-httpbis-p3-payload-02">
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