source: draft-ietf-httpbis/latest/p3-payload.xml @ 874

Last change on this file since 874 was 874, checked in by fielding@…, 9 years ago

Addresses #109: Clarify entity / representation / variant terminology

Replace more entity, entities, and entity-body, as appropriate.

Addresses #183: "requested resource" in content-encoding definition

Fixed.

Clarifies #178: Content-MD5 and partial responses

New terminology makes it easier to understand what is digested.

  • Property svn:eol-style set to native
File size: 135.6 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-fields            "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc rfcedstyle="yes"?>
52<?rfc-ext allow-markup-in-artwork="yes" ?>
53<?rfc-ext include-references-in-index="yes" ?>
54<rfc obsoletes="2616" category="std" x:maturity-level="draft"
55     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
56     xmlns:x='http://purl.org/net/xml2rfc/ext'>
57<front>
58
59  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
60
61  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
62    <organization abbrev="Day Software">Day Software</organization>
63    <address>
64      <postal>
65        <street>23 Corporate Plaza DR, Suite 280</street>
66        <city>Newport Beach</city>
67        <region>CA</region>
68        <code>92660</code>
69        <country>USA</country>
70      </postal>
71      <phone>+1-949-706-5300</phone>
72      <facsimile>+1-949-706-5305</facsimile>
73      <email>fielding@gbiv.com</email>
74      <uri>http://roy.gbiv.com/</uri>
75    </address>
76  </author>
77
78  <author initials="J." surname="Gettys" fullname="Jim Gettys">
79    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
80    <address>
81      <postal>
82        <street>21 Oak Knoll Road</street>
83        <city>Carlisle</city>
84        <region>MA</region>
85        <code>01741</code>
86        <country>USA</country>
87      </postal>
88      <email>jg@freedesktop.org</email>
89      <uri>http://gettys.wordpress.com/</uri>
90    </address>
91  </author>
92 
93  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
94    <organization abbrev="HP">Hewlett-Packard Company</organization>
95    <address>
96      <postal>
97        <street>HP Labs, Large Scale Systems Group</street>
98        <street>1501 Page Mill Road, MS 1177</street>
99        <city>Palo Alto</city>
100        <region>CA</region>
101        <code>94304</code>
102        <country>USA</country>
103      </postal>
104      <email>JeffMogul@acm.org</email>
105    </address>
106  </author>
107
108  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
109    <organization abbrev="Microsoft">Microsoft Corporation</organization>
110    <address>
111      <postal>
112        <street>1 Microsoft Way</street>
113        <city>Redmond</city>
114        <region>WA</region>
115        <code>98052</code>
116        <country>USA</country>
117      </postal>
118      <email>henrikn@microsoft.com</email>
119    </address>
120  </author>
121
122  <author initials="L." surname="Masinter" fullname="Larry Masinter">
123    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
124    <address>
125      <postal>
126        <street>345 Park Ave</street>
127        <city>San Jose</city>
128        <region>CA</region>
129        <code>95110</code>
130        <country>USA</country>
131      </postal>
132      <email>LMM@acm.org</email>
133      <uri>http://larry.masinter.net/</uri>
134    </address>
135  </author>
136 
137  <author initials="P." surname="Leach" fullname="Paul J. Leach">
138    <organization abbrev="Microsoft">Microsoft Corporation</organization>
139    <address>
140      <postal>
141        <street>1 Microsoft Way</street>
142        <city>Redmond</city>
143        <region>WA</region>
144        <code>98052</code>
145      </postal>
146      <email>paulle@microsoft.com</email>
147    </address>
148  </author>
149   
150  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
151    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
152    <address>
153      <postal>
154        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
155        <street>The Stata Center, Building 32</street>
156        <street>32 Vassar Street</street>
157        <city>Cambridge</city>
158        <region>MA</region>
159        <code>02139</code>
160        <country>USA</country>
161      </postal>
162      <email>timbl@w3.org</email>
163      <uri>http://www.w3.org/People/Berners-Lee/</uri>
164    </address>
165  </author>
166
167  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
168    <organization abbrev="W3C">World Wide Web Consortium</organization>
169    <address>
170      <postal>
171        <street>W3C / ERCIM</street>
172        <street>2004, rte des Lucioles</street>
173        <city>Sophia-Antipolis</city>
174        <region>AM</region>
175        <code>06902</code>
176        <country>France</country>
177      </postal>
178      <email>ylafon@w3.org</email>
179      <uri>http://www.raubacapeu.net/people/yves/</uri>
180    </address>
181  </author>
182
183  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
184    <organization abbrev="greenbytes">greenbytes GmbH</organization>
185    <address>
186      <postal>
187        <street>Hafenweg 16</street>
188        <city>Muenster</city><region>NW</region><code>48155</code>
189        <country>Germany</country>
190      </postal>
191      <phone>+49 251 2807760</phone>
192      <facsimile>+49 251 2807761</facsimile>
193      <email>julian.reschke@greenbytes.de</email>
194      <uri>http://greenbytes.de/tech/webdav/</uri>
195    </address>
196  </author>
197
198  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
199  <workgroup>HTTPbis Working Group</workgroup>
200
201<abstract>
202<t>
203   The Hypertext Transfer Protocol (HTTP) is an application-level
204   protocol for distributed, collaborative, hypermedia information
205   systems. HTTP has been in use by the World Wide Web global information
206   initiative since 1990. This document is Part 3 of the seven-part specification
207   that defines the protocol referred to as "HTTP/1.1" and, taken together,
208   obsoletes RFC 2616.  Part 3 defines HTTP message content,
209   metadata, and content negotiation.
210</t>
211</abstract>
212
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (ietf-http-wg@w3.org). The current issues list is
217    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
218    and related documents (including fancy diffs) can be found at
219    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.10"/>.
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   This document defines HTTP/1.1 message payloads (a.k.a., content), the
230   associated metadata header fields that define how the payload is intended
231   to be interpreted by a recipient, the request header fields that
232   may influence content selection, and the various selection algorithms
233   that are collectively referred to as HTTP content negotiation.
234</t>
235<t>
236   This document is currently disorganized in order to minimize the changes
237   between drafts and enable reviewers to see the smaller errata changes.
238   The next draft will reorganize the sections to better reflect the content.
239   In particular, the sections on entities will be renamed payload and moved
240   to the first half of the document, while the sections on content negotiation
241   and associated request header fields will be moved to the second half.  The
242   current mess reflects how widely dispersed these topics and associated
243   requirements had become in <xref target="RFC2616"/>.
244</t>
245
246<section title="Terminology" anchor="terminology">
247<t>
248   This specification uses a number of terms to refer to the roles
249   played by participants in, and objects of, the HTTP communication.
250</t>
251<t>
252  <iref item="content negotiation"/>
253  <x:dfn>content negotiation</x:dfn>
254  <list>
255    <t>
256      The mechanism for selecting the appropriate representation when
257      servicing a request. The representation in any response
258      can be negotiated (including error responses).
259    </t>
260  </list>
261</t>
262<t>
263  <iref item="payload"/>
264  <x:dfn>payload</x:dfn>
265  <list>
266    <t>
267      The information transferred within a given message is called the
268      payload, consisting  of optional payload metadata and an optional
269      payload body.  The payload in HTTP is always a partial or complete
270      representation of some resource, though which resource is represented
271      is dependent on the type of message (request or response), the
272      request method, and the response status code.
273    </t>
274  </list>
275</t>
276<t>
277  <iref item="representation"/>
278  <x:dfn>representation</x:dfn>
279  <list>
280    <t>
281      A representation is information in a format that can be readily
282      communicated from one party to another.  For our purposes, a
283      representation is binary data and its associated metadata.
284      A representation of a resource is information that reflects the
285      state of that resource, as observed at some point in the past
286      or to be desired at some point in the future.
287    </t>
288  </list>
289</t>
290</section>
291
292<section title="Requirements" anchor="intro.requirements">
293<t>
294   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
295   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
296   document are to be interpreted as described in <xref target="RFC2119"/>.
297</t>
298<t>
299   An implementation is not compliant if it fails to satisfy one or more
300   of the "MUST" or "REQUIRED" level requirements for the protocols it
301   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
302   level and all the "SHOULD" level requirements for its protocols is said
303   to be "unconditionally compliant"; one that satisfies all the "MUST"
304   level requirements but not all the "SHOULD" level requirements for its
305   protocols is said to be "conditionally compliant".
306</t>
307</section>
308
309<section title="Syntax Notation" anchor="notation">
310  <x:anchor-alias value="ALPHA"/>
311  <x:anchor-alias value="CR"/>
312  <x:anchor-alias value="DIGIT"/>
313  <x:anchor-alias value="LF"/>
314  <x:anchor-alias value="OCTET"/>
315  <x:anchor-alias value="VCHAR"/>
316  <x:anchor-alias value="WSP"/>
317<t>
318  This specification uses the ABNF syntax defined in &notation; (which
319  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
320  <xref target="collected.abnf"/> shows the collected ABNF, with the list
321  rule expanded.
322</t>
323<t>
324  The following core rules are included by
325  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
326  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
327  DIGIT (decimal 0-9), DQUOTE (double quote),
328  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
329  OCTET (any 8-bit sequence of data), SP (space),
330  VCHAR (any visible USASCII character),
331  and WSP (whitespace).
332</t>
333
334<section title="Core Rules" anchor="core.rules">
335  <x:anchor-alias value="quoted-string"/>
336  <x:anchor-alias value="token"/>
337  <x:anchor-alias value="word"/>
338  <x:anchor-alias value="OWS"/>
339<t>
340  The core rules below are defined in &basic-rules;:
341</t>
342<figure><artwork type="abnf2616">
343  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
344  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
345  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
346  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
347</artwork></figure>
348</section>
349
350<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
351  <x:anchor-alias value="absolute-URI"/>
352  <x:anchor-alias value="Allow"/>
353  <x:anchor-alias value="Content-Length"/>
354  <x:anchor-alias value="Content-Range"/>
355  <x:anchor-alias value="Expires"/>
356  <x:anchor-alias value="Last-Modified"/>
357  <x:anchor-alias value="header-field"/>
358  <x:anchor-alias value="partial-URI"/>
359  <x:anchor-alias value="qvalue"/>
360<t>
361  The ABNF rules below are defined in other parts:
362</t>
363<figure><!--Part1--><artwork type="abnf2616">
364  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
365  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
366  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
367  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
368  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
369</artwork></figure>
370<figure><!--Part4--><artwork type="abnf2616">
371  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
372</artwork></figure>
373<figure><!--Part5--><artwork type="abnf2616">
374  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
375</artwork></figure>
376<figure><!--Part6--><artwork type="abnf2616">
377  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
378</artwork></figure>
379</section>
380
381</section>
382
383</section>
384
385<section title="Protocol Parameters" anchor="protocol.parameters">
386
387<section title="Character Sets" anchor="character.sets">
388<t>
389   HTTP uses the same definition of the term "character set" as that
390   described for MIME:
391</t>
392<t>
393   The term "character set" is used in this document to refer to a
394   method used with one or more tables to convert a sequence of octets
395   into a sequence of characters. Note that unconditional conversion in
396   the other direction is not required, in that not all characters may
397   be available in a given character set and a character set may provide
398   more than one sequence of octets to represent a particular character.
399   This definition is intended to allow various kinds of character
400   encoding, from simple single-table mappings such as US-ASCII to
401   complex table switching methods such as those that use ISO-2022's
402   techniques. However, the definition associated with a MIME character
403   set name &MUST; fully specify the mapping to be performed from octets
404   to characters. In particular, use of external profiling information
405   to determine the exact mapping is not permitted.
406</t>
407<x:note>
408  <t>
409    <x:h>Note:</x:h> This use of the term "character set" is more commonly
410    referred to as a "character encoding." However, since HTTP and
411    MIME share the same registry, it is important that the terminology
412    also be shared.
413  </t>
414</x:note>
415<t anchor="rule.charset">
416  <x:anchor-alias value="charset"/>
417   HTTP character sets are identified by case-insensitive tokens. The
418   complete set of tokens is defined by the IANA Character Set registry
419   (<eref target="http://www.iana.org/assignments/character-sets"/>).
420</t>
421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
422  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
423</artwork></figure>
424<t>
425   Although HTTP allows an arbitrary token to be used as a charset
426   value, any token that has a predefined value within the IANA
427   Character Set registry &MUST; represent the character set defined
428   by that registry. Applications &SHOULD; limit their use of character
429   sets to those defined by the IANA registry.
430</t>
431<t>
432   HTTP uses charset in two contexts: within an Accept-Charset request
433   header (in which the charset value is an unquoted token) and as the
434   value of a parameter in a Content-Type header (within a request or
435   response), in which case the parameter value of the charset parameter
436   may be quoted.
437</t>
438<t>
439   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
440   <xref target="RFC2277"/>.
441</t>
442
443<section title="Missing Charset" anchor="missing.charset">
444<t>
445   Some HTTP/1.0 software has interpreted a Content-Type header without
446   charset parameter incorrectly to mean "recipient should guess."
447   Senders wishing to defeat this behavior &MAY; include a charset
448   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
449   it is known that it will not confuse the recipient.
450</t>
451<t>
452   Unfortunately, some older HTTP/1.0 clients did not deal properly with
453   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
454   charset label provided by the sender; and those user agents that have
455   a provision to "guess" a charset &MUST; use the charset from the
456   content-type field if they support that charset, rather than the
457   recipient's preference, when initially displaying a document. See
458   <xref target="canonicalization.and.text.defaults"/>.
459</t>
460</section>
461</section>
462
463<section title="Content Codings" anchor="content.codings">
464  <x:anchor-alias value="content-coding"/>
465<t>
466   Content coding values indicate an encoding transformation that has
467   been or can be applied to a representation. Content codings are primarily
468   used to allow a representation to be compressed or otherwise usefully
469   transformed without losing the identity of its underlying media type
470   and without loss of information. Frequently, the representation is stored in
471   coded form, transmitted directly, and only decoded by the recipient.
472</t>
473<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
474  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
475</artwork></figure>
476<t>
477   All content-coding values are case-insensitive. HTTP/1.1 uses
478   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
479   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
480   describes the content-coding, what is more important is that it
481   indicates what decoding mechanism will be required to remove the
482   encoding.
483</t>
484<t>
485   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
486  <list>
487    <t>
488      See &compress-coding;.
489    </t>
490  </list>
491</t>
492<t>
493   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
494  <list>
495    <t>
496      See &deflate-coding;.
497    </t>
498  </list>
499</t>
500<t>
501   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
502  <list>
503    <t>
504      See &gzip-coding;.
505    </t>
506  </list>
507</t>
508<t>
509   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
510  <list><t>
511        The default (identity) encoding; the use of no transformation
512        whatsoever. This content-coding is used only in the Accept-Encoding
513        header, and &SHOULD-NOT;  be used in the Content-Encoding
514        header.
515  </t></list>
516</t>
517
518<section title="Content Coding Registry" anchor="content.coding.registry">
519<t>
520   The HTTP Content Coding Registry defines the name space for the content
521   coding names.
522</t>
523<t>
524   Registrations &MUST; include the following fields:
525   <list style="symbols">
526     <t>Name</t>
527     <t>Description</t>
528     <t>Pointer to specification text</t>
529   </list>
530</t>
531<t>
532   Names of content codings &MUST-NOT; overlap with names of transfer codings
533   (&transfer-codings;), unless the encoding transformation is identical (as it
534   is the case for the compression codings defined in
535   &compression-codings;).
536</t>
537<t>
538   Values to be added to this name space require expert review and a specification
539   (see "Expert Review" and "Specification Required" in
540   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
541   conform to the purpose of content coding defined in this section.
542</t>
543<t>
544   The registry itself is maintained at
545   <eref target="http://www.iana.org/assignments/http-parameters"/>.
546</t>
547</section>
548
549</section>
550
551<section title="Media Types" anchor="media.types">
552  <x:anchor-alias value="media-type"/>
553  <x:anchor-alias value="type"/>
554  <x:anchor-alias value="subtype"/>
555<t>
556   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
557   and Accept (<xref target="header.accept"/>) header fields in order to provide
558   open and extensible data typing and type negotiation.
559</t>
560<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"/>
561  <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
562  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
563  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
564</artwork></figure>
565<t anchor="rule.parameter">
566  <x:anchor-alias value="attribute"/>
567  <x:anchor-alias value="parameter"/>
568  <x:anchor-alias value="value"/>
569   Parameters &MAY; follow the type/subtype in the form of attribute/value
570   pairs.
571</t>
572<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"/>
573  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
574  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
575  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
576</artwork></figure>
577<t>
578   The type, subtype, and parameter attribute names are case-insensitive.
579   Parameter values might or might not be case-sensitive, depending on the
580   semantics of the parameter name.  The presence or absence of a parameter might
581   be significant to the processing of a media-type, depending on its
582   definition within the media type registry.
583</t>
584<t>
585   A parameter value that matches the <x:ref>token</x:ref> production may be
586   transmitted as either a token or within a quoted-string. The quoted and
587   unquoted values are equivalent.
588</t>
589<t>
590   Note that some older HTTP applications do not recognize media type
591   parameters. When sending data to older HTTP applications,
592   implementations &SHOULD; only use media type parameters when they are
593   required by that type/subtype definition.
594</t>
595<t>
596   Media-type values are registered with the Internet Assigned Number
597   Authority (IANA). The media type registration process is
598   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
599   discouraged.
600</t>
601
602<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
603<t>
604   Internet media types are registered with a canonical form. A
605   representation transferred via HTTP messages &MUST; be in the
606   appropriate canonical form prior to its transmission except for
607   "text" types, as defined in the next paragraph.
608</t>
609<t>
610   When in canonical form, media subtypes of the "text" type use CRLF as
611   the text line break. HTTP relaxes this requirement and allows the
612   transport of text media with plain CR or LF alone representing a line
613   break when it is done consistently for an entire representation. HTTP
614   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
615   a line break in text media received via HTTP. In
616   addition, if the text is in a character encoding that does not
617   use octets 13 and 10 for CR and LF respectively, as is the case for
618   some multi-byte character encodings, HTTP allows the use of whatever octet
619   sequences are defined by that character encoding to represent the
620   equivalent of CR and LF for line breaks. This flexibility regarding
621   line breaks applies only to text media in the payload body; a bare CR
622   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
623   structures (such as header fields and multipart boundaries).
624</t>
625<t>
626   If a representation is encoded with a content-coding, the underlying
627   data &MUST; be in a form defined above prior to being encoded.
628</t>
629<t>
630   The "charset" parameter is used with some media types to define the
631   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
632   parameter is provided by the sender, media subtypes of the "text"
633   type are defined to have a default charset value of "ISO-8859-1" when
634   received via HTTP. Data in character encodings other than "ISO-8859-1" or
635   its subsets &MUST; be labeled with an appropriate charset value. See
636   <xref target="missing.charset"/> for compatibility problems.
637</t>
638</section>
639
640<section title="Multipart Types" anchor="multipart.types">
641<t>
642   MIME provides for a number of "multipart" types -- encapsulations of
643   one or more representations within a single message-body. All multipart
644   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
645   and &MUST; include a boundary parameter as part of the media type
646   value. The message body is itself a protocol element and &MUST;
647   therefore use only CRLF to represent line breaks between body-parts.
648</t>
649<t>
650   In general, HTTP treats a multipart message-body no differently than
651   any other media type: strictly as payload.  HTTP does not use the
652   multipart boundary as an indicator of message-body length.
653   <!-- jre: re-insert removed text pointing to caching? -->
654   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
655   behavior as a MIME user agent would upon receipt of a multipart type.
656   The MIME header fields within each body-part of a multipart message-body
657   do not have any significance to HTTP beyond that defined by
658   their MIME semantics.
659</t>
660<t>
661   If an application receives an unrecognized multipart subtype, the
662   application &MUST; treat it as being equivalent to "multipart/mixed".
663</t>
664<x:note>
665  <t>
666    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
667    for carrying form data suitable for processing via the POST
668    request method, as described in <xref target="RFC2388"/>.
669  </t>
670</x:note>
671</section>
672</section>
673
674<section title="Language Tags" anchor="language.tags">
675  <x:anchor-alias value="language-tag"/>
676<t>
677   A language tag, as defined in <xref target="RFC5646"/>, identifies a
678   natural language spoken, written, or otherwise conveyed by human beings for
679   communication of information to other human beings. Computer languages are
680   explicitly excluded. HTTP uses language tags within the Accept-Language and
681   Content-Language fields.
682</t>
683<t>
684   In summary, a language tag is composed of one or more parts: A primary
685   language subtag followed by a possibly empty series of subtags:
686</t>
687<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
688  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
689</artwork></figure>
690<t>
691   White space is not allowed within the tag and all tags are case-insensitive.
692   The name space of language subtags is administered by the IANA (see
693   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
694</t>
695<figure>
696  <preamble>Example tags include:</preamble>
697<artwork type="example">
698  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
699</artwork>
700</figure>
701<t>
702   See <xref target="RFC5646"/> for further information.
703</t>
704</section>
705</section>
706
707<section title="Representation" anchor="representation">
708<t>
709   Request and Response messages &MAY; transfer a representation if not otherwise
710   restricted by the request method or response status code. A representation
711   consists of entity-header fields and a representation body, although some
712   responses will only include the entity-headers.
713</t>
714<t>
715   In this section, both sender and recipient refer to either the client
716   or the server, depending on who sends and who receives the message.
717</t>
718
719<section title="Entity Header Fields" anchor="entity.header.fields">
720  <x:anchor-alias value="entity-header"/>
721  <x:anchor-alias value="extension-header"/>
722<t>
723   Entity-header fields define metadata about the representation data
724   enclosed in the message-body or, if no message-body is present, about
725   the representation that would have been transferred in a 200 response
726   to a simultaneous GET request on the Effective Request URI.
727</t>
728<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
729  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
730                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
731                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
732                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
733                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
734                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
735                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
736                 / <x:ref>Expires</x:ref>                  ; &header-expires;
737                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
738                 / <x:ref>extension-header</x:ref>
739 
740  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
741</artwork></figure>
742<t>
743   The extension-header mechanism allows additional entity-header fields
744   to be defined without changing the protocol, but these fields cannot
745   be assumed to be recognizable by the recipient. Unrecognized header
746   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
747   transparent proxies.
748</t>
749</section>
750
751<section title="Payload Body" anchor="payload.body">
752  <x:anchor-alias value="payload-body"/>
753<t>
754   The payload body (if any) sent with an HTTP request or response is in
755   a format and encoding defined by the entity-header fields.
756</t>
757<t>
758   A payload body is only present in a message when a message-body is
759   present, as described in &message-body;. The payload body is obtained
760   from the message-body by decoding any Transfer-Encoding that might
761   have been applied to ensure safe and proper transfer of the message.
762</t>
763
764<section title="Type" anchor="type">
765<t>
766   When a payload body is included with a message, the data type of that
767   body is determined via the header fields Content-Type and Content-Encoding.
768   These define a two-layer, ordered encoding model:
769</t>
770<figure><artwork type="example">
771  payload-body := Content-Encoding( Content-Type( data ) )
772</artwork></figure>
773<t>
774   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
775   message containing a payload body &SHOULD; include a Content-Type header
776   field defining the media type of that body, unless that information is
777   unknown.
778</t>
779<t>   
780   If the Content-Type header field is not present, it indicates that
781   the sender does not know the media type of the data; recipients &MAY;
782   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
783   or examine the content to determine its type.
784</t>
785<t>
786   In practice, currently-deployed servers sometimes provide a Content-Type
787   header which does not correctly convey the intended interpretation of the
788   content sent, with the result that some clients will examine the response
789   body's content and override the specified type.
790</t>
791<t>
792   Clients that do so risk drawing incorrect conclusions, which may expose
793   additional security risks (e.g., "privilege escalation"). Implementers are
794   encouraged to provide a means of disabling such "content sniffing" when it
795   is used.
796</t>
797<t>
798   Content-Encoding may be used to indicate any additional content
799   codings applied to the data, usually for the purpose of data
800   compression, that are a property of the representation.  There is
801   no default encoding.
802</t>
803</section>
804   
805</section>
806</section>
807
808<section title="Content Negotiation" anchor="content.negotiation">
809<t>
810   HTTP responses include a representation which contains information for
811   interpretation, whether by a human user or for further processing.
812   Often, the server has different ways of representing the
813   same information; for example, in different formats, languages,
814   or using different character encodings.
815</t>
816<t>
817   HTTP clients and their users might have different or variable
818   capabilities, characteristics or preferences which would influence
819   which representation, among those available from the server,
820   would be best for the server to deliver. For this reason, HTTP
821   provides mechanisms for "content negotiation" -- a process of
822   allowing selection of a representation of a given resource,
823   when more than one is available.
824</t>
825<t>
826   This specification defines two patterns of content negotiation;
827   "server-driven", where the server selects the representation based
828   upon the client's stated preferences, and "agent-driven" negotiation,
829   where the server provides a list of representations for the client to
830   choose from, based upon their metadata. In addition,  there are
831   other patterns: some applications use an "active content" pattern,
832   where the server returns active content which runs on the client
833   and, based on client available parameters, selects additional
834   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
835   has also been proposed.
836</t>
837<t>
838   These patterns are all widely used, and have trade-offs in applicability
839   and practicality. In particular, when the number of preferences or
840   capabilities to be expressed by a client are large (such as when many
841   different formats are supported by a user-agent), server-driven
842   negotiation becomes unwieldy, and may not be appropriate. Conversely,
843   when the number of representations to choose from is very large,
844   agent-driven negotiation may not be appropriate.
845</t>
846<t>
847   Note that in all cases, the supplier of representations has the
848   responsibility for determining which representations might be
849   considered to be the "same information".
850</t>
851
852<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
853<t>
854   If the selection of the best representation for a response is made by
855   an algorithm located at the server, it is called server-driven
856   negotiation. Selection is based on the available representations of
857   the response (the dimensions over which it can vary; e.g., language,
858   content-coding, etc.) and the contents of particular header fields in
859   the request message or on other information pertaining to the request
860   (such as the network address of the client).
861</t>
862<t>
863   Server-driven negotiation is advantageous when the algorithm for
864   selecting from among the available representations is difficult to
865   describe to the user agent, or when the server desires to send its
866   "best guess" to the client along with the first response (hoping to
867   avoid the round-trip delay of a subsequent request if the "best
868   guess" is good enough for the user). In order to improve the server's
869   guess, the user agent &MAY; include request header fields (Accept,
870   Accept-Language, Accept-Encoding, etc.) which describe its
871   preferences for such a response.
872</t>
873<t>
874   Server-driven negotiation has disadvantages:
875  <list style="numbers">
876    <t>
877         It is impossible for the server to accurately determine what
878         might be "best" for any given user, since that would require
879         complete knowledge of both the capabilities of the user agent
880         and the intended use for the response (e.g., does the user want
881         to view it on screen or print it on paper?).
882    </t>
883    <t>
884         Having the user agent describe its capabilities in every
885         request can be both very inefficient (given that only a small
886         percentage of responses have multiple representations) and a
887         potential violation of the user's privacy.
888    </t>
889    <t>
890         It complicates the implementation of an origin server and the
891         algorithms for generating responses to a request.
892    </t>
893    <t>
894         It may limit a public cache's ability to use the same response
895         for multiple user's requests.
896    </t>
897  </list>
898</t>
899<t>
900   HTTP/1.1 includes the following request-header fields for enabling
901   server-driven negotiation through description of user agent
902   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
903   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
904   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
905   However, an origin server is not limited to these dimensions and &MAY; vary
906   the response based on any aspect of the request, including information
907   outside the request-header fields or within extension header fields
908   not defined by this specification.
909</t>
910<x:note>
911  <t>
912    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
913    because new clients might not be recognized.
914  </t>
915</x:note>
916<t>
917   The Vary header field (&header-vary;) can be used to express the parameters the
918   server uses to select a representation that is subject to server-driven
919   negotiation.
920</t>
921</section>
922
923<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
924<t>
925   With agent-driven negotiation, selection of the best representation
926   for a response is performed by the user agent after receiving an
927   initial response from the origin server. Selection is based on a list
928   of the available representations of the response included within the
929   header fields or body of the initial response, with each
930   representation identified by its own URI. Selection from among the
931   representations may be performed automatically (if the user agent is
932   capable of doing so) or manually by the user selecting from a
933   generated (possibly hypertext) menu.
934</t>
935<t>
936   Agent-driven negotiation is advantageous when the response would vary
937   over commonly-used dimensions (such as type, language, or encoding),
938   when the origin server is unable to determine a user agent's
939   capabilities from examining the request, and generally when public
940   caches are used to distribute server load and reduce network usage.
941</t>
942<t>
943   Agent-driven negotiation suffers from the disadvantage of needing a
944   second request to obtain the best alternate representation. This
945   second request is only efficient when caching is used. In addition,
946   this specification does not define any mechanism for supporting
947   automatic selection, though it also does not prevent any such
948   mechanism from being developed as an extension and used within
949   HTTP/1.1.
950</t>
951<t>
952   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
953   status codes for enabling agent-driven negotiation when the server is
954   unwilling or unable to provide a varying response using server-driven
955   negotiation.
956</t>
957</section>
958</section>
959
960<section title="Header Field Definitions" anchor="header.fields">
961<t>
962   This section defines the syntax and semantics of HTTP/1.1 header fields
963   related to the payload of messages.
964</t>
965<t>
966   For entity-header fields, both sender and recipient refer to either the
967   client or the server, depending on who sends and who receives the message.
968</t>
969
970<section title="Accept" anchor="header.accept">
971  <iref primary="true" item="Accept header" x:for-anchor=""/>
972  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
973  <x:anchor-alias value="Accept"/>
974  <x:anchor-alias value="Accept-v"/>
975  <x:anchor-alias value="accept-ext"/>
976  <x:anchor-alias value="accept-params"/>
977  <x:anchor-alias value="media-range"/>
978<t>
979   The "Accept" request-header field can be used by user agents to specify
980   response media types that are acceptable. Accept headers can be used to
981   indicate that the request is specifically limited to a small set of desired
982   types, as in the case of a request for an in-line image.
983</t>
984<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
985  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
986  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
987 
988  <x:ref>media-range</x:ref>    = ( "*/*"
989                   / ( <x:ref>type</x:ref> "/" "*" )
990                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
991                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
992  <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
993  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
994                   [ "=" <x:ref>word</x:ref> ]
995</artwork></figure>
996<t>
997   The asterisk "*" character is used to group media types into ranges,
998   with "*/*" indicating all media types and "type/*" indicating all
999   subtypes of that type. The media-range &MAY; include media type
1000   parameters that are applicable to that range.
1001</t>
1002<t>
1003   Each media-range &MAY; be followed by one or more accept-params,
1004   beginning with the "q" parameter for indicating a relative quality
1005   factor. The first "q" parameter (if any) separates the media-range
1006   parameter(s) from the accept-params. Quality factors allow the user
1007   or user agent to indicate the relative degree of preference for that
1008   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1009   default value is q=1.
1010</t>
1011<x:note>
1012  <t>
1013    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1014    parameters from Accept extension parameters is due to historical
1015    practice. Although this prevents any media type parameter named
1016    "q" from being used with a media range, such an event is believed
1017    to be unlikely given the lack of any "q" parameters in the IANA
1018    media type registry and the rare usage of any media type
1019    parameters in Accept. Future media types are discouraged from
1020    registering any parameter named "q".
1021  </t>
1022</x:note>
1023<t>
1024   The example
1025</t>
1026<figure><artwork type="example">
1027  Accept: audio/*; q=0.2, audio/basic
1028</artwork></figure>
1029<t>
1030   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1031   type if it is the best available after an 80% mark-down in quality."
1032</t>
1033<t>
1034   If no Accept header field is present, then it is assumed that the
1035   client accepts all media types. If an Accept header field is present,
1036   and if the server cannot send a response which is acceptable
1037   according to the combined Accept field value, then the server &SHOULD;
1038   send a 406 (Not Acceptable) response.
1039</t>
1040<t>
1041   A more elaborate example is
1042</t>
1043<figure><artwork type="example">
1044  Accept: text/plain; q=0.5, text/html,
1045          text/x-dvi; q=0.8, text/x-c
1046</artwork></figure>
1047<t>
1048   Verbally, this would be interpreted as "text/html and text/x-c are
1049   the preferred media types, but if they do not exist, then send the
1050   text/x-dvi representation, and if that does not exist, send the text/plain
1051   representation."
1052</t>
1053<t>
1054   Media ranges can be overridden by more specific media ranges or
1055   specific media types. If more than one media range applies to a given
1056   type, the most specific reference has precedence. For example,
1057</t>
1058<figure><artwork type="example">
1059  Accept: text/*, text/html, text/html;level=1, */*
1060</artwork></figure>
1061<t>
1062   have the following precedence:
1063   <list style="numbers">
1064    <t>text/html;level=1</t>
1065    <t>text/html</t>
1066    <t>text/*</t>
1067    <t>*/*</t>
1068   </list>
1069</t>
1070<t>
1071   The media type quality factor associated with a given type is
1072   determined by finding the media range with the highest precedence
1073   which matches that type. For example,
1074</t>
1075<figure><artwork type="example">
1076  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1077          text/html;level=2;q=0.4, */*;q=0.5
1078</artwork></figure>
1079<t>
1080   would cause the following values to be associated:
1081</t>
1082<texttable align="left">
1083  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1084  <c>text/html;level=1</c>    <c>1</c>
1085  <c>text/html</c>            <c>0.7</c>
1086  <c>text/plain</c>           <c>0.3</c>
1087  <c>image/jpeg</c>           <c>0.5</c>
1088  <c>text/html;level=2</c>    <c>0.4</c>
1089  <c>text/html;level=3</c>    <c>0.7</c>
1090</texttable>
1091<t>
1092      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1093      values for certain media ranges. However, unless the user agent is
1094      a closed system which cannot interact with other rendering agents,
1095      this default set ought to be configurable by the user.
1096</t>
1097</section>
1098
1099<section title="Accept-Charset" anchor="header.accept-charset">
1100  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1101  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1102  <x:anchor-alias value="Accept-Charset"/>
1103  <x:anchor-alias value="Accept-Charset-v"/>
1104<t>
1105   The "Accept-Charset" request-header field can be used by user agents to
1106   indicate what response character sets are acceptable. This field allows
1107   clients capable of understanding more comprehensive or special-purpose
1108   character sets to signal that capability to a server which is capable of
1109   representing documents in those character sets.
1110</t>
1111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1112  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1113          <x:ref>Accept-Charset-v</x:ref>
1114  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1115                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1116</artwork></figure>
1117<t>
1118   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1119   be given an associated quality value which represents the user's
1120   preference for that charset. The default value is q=1. An example is
1121</t>
1122<figure><artwork type="example">
1123  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1124</artwork></figure>
1125<t>
1126   The special value "*", if present in the Accept-Charset field,
1127   matches every character set (including ISO-8859-1) which is not
1128   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1129   in an Accept-Charset field, then all character sets not explicitly
1130   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1131   a quality value of 1 if not explicitly mentioned.
1132</t>
1133<t>
1134   If no Accept-Charset header is present, the default is that any
1135   character set is acceptable. If an Accept-Charset header is present,
1136   and if the server cannot send a response which is acceptable
1137   according to the Accept-Charset header, then the server &SHOULD; send
1138   an error response with the 406 (Not Acceptable) status code, though
1139   the sending of an unacceptable response is also allowed.
1140</t>
1141</section>
1142
1143<section title="Accept-Encoding" anchor="header.accept-encoding">
1144  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1145  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1146  <x:anchor-alias value="Accept-Encoding"/>
1147  <x:anchor-alias value="Accept-Encoding-v"/>
1148  <x:anchor-alias value="codings"/>
1149<t>
1150   The "Accept-Encoding" request-header field can be used by user agents to
1151   indicate what response content-codings (<xref target="content.codings"/>)
1152   are acceptable in the response.
1153</t>
1154<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1155  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1156                     <x:ref>Accept-Encoding-v</x:ref>
1157  <x:ref>Accept-Encoding-v</x:ref>  =
1158                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1159  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1160</artwork></figure>
1161<t>
1162   Each codings value &MAY; be given an associated quality value which
1163   represents the preference for that encoding. The default value is q=1.
1164</t>
1165<t>
1166   Examples of its use are:
1167</t>
1168<figure><artwork type="example">
1169  Accept-Encoding: compress, gzip
1170  Accept-Encoding:
1171  Accept-Encoding: *
1172  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1173  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1174</artwork></figure>
1175<t>
1176   A server tests whether a content-coding is acceptable, according to
1177   an Accept-Encoding field, using these rules:
1178  <list style="numbers">
1179      <t>If the content-coding is one of the content-codings listed in
1180         the Accept-Encoding field, then it is acceptable, unless it is
1181         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1182         qvalue of 0 means "not acceptable.")</t>
1183
1184      <t>The special "*" symbol in an Accept-Encoding field matches any
1185         available content-coding not explicitly listed in the header
1186         field.</t>
1187
1188      <t>If multiple content-codings are acceptable, then the acceptable
1189         content-coding with the highest non-zero qvalue is preferred.</t>
1190
1191      <t>The "identity" content-coding is always acceptable, unless
1192         specifically refused because the Accept-Encoding field includes
1193         "identity;q=0", or because the field includes "*;q=0" and does
1194         not explicitly include the "identity" content-coding. If the
1195         Accept-Encoding field-value is empty, then only the "identity"
1196         encoding is acceptable.</t>
1197  </list>
1198</t>
1199<t>
1200   If an Accept-Encoding field is present in a request, and if the
1201   server cannot send a response which is acceptable according to the
1202   Accept-Encoding header, then the server &SHOULD; send an error response
1203   with the 406 (Not Acceptable) status code.
1204</t>
1205<t>
1206   If no Accept-Encoding field is present in a request, the server &MAY;
1207   assume that the client will accept any content coding. In this case,
1208   if "identity" is one of the available content-codings, then the
1209   server &SHOULD; use the "identity" content-coding, unless it has
1210   additional information that a different content-coding is meaningful
1211   to the client.
1212</t>
1213<x:note>
1214  <t>
1215    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1216    and if the "identity" content-coding is unavailable, then
1217    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1218    "gzip" and "compress") are preferred; some older clients
1219    improperly display messages sent with other content-codings.  The
1220    server might also make this decision based on information about
1221    the particular user-agent or client.
1222  </t>
1223</x:note>
1224<x:note>
1225  <t>
1226    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1227    associated with content-codings. This means that qvalues will not
1228    work and are not permitted with x-gzip or x-compress.
1229  </t>
1230</x:note>
1231</section>
1232
1233<section title="Accept-Language" anchor="header.accept-language">
1234  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1235  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1236  <x:anchor-alias value="Accept-Language"/>
1237  <x:anchor-alias value="Accept-Language-v"/>
1238  <x:anchor-alias value="language-range"/>
1239<t>
1240   The "Accept-Language" request-header field can be used by user agents to
1241   indicate the set of natural languages that are preferred in the response.
1242   Language tags are defined in <xref target="language.tags"/>.
1243</t>
1244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1245  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1246                    <x:ref>Accept-Language-v</x:ref>
1247  <x:ref>Accept-Language-v</x:ref> =
1248                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1249  <x:ref>language-range</x:ref>    =
1250            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1251</artwork></figure>
1252<t>
1253   Each language-range can be given an associated quality value which
1254   represents an estimate of the user's preference for the languages
1255   specified by that range. The quality value defaults to "q=1". For
1256   example,
1257</t>
1258<figure><artwork type="example">
1259  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1260</artwork></figure>
1261<t>
1262   would mean: "I prefer Danish, but will accept British English and
1263   other types of English."
1264   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1265</t>
1266<t>
1267   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1268   several matching schemes. Implementations can offer the most appropriate
1269   matching scheme for their requirements.
1270</t>
1271<x:note>
1272  <t>
1273    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1274    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1275    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1276  </t>
1277</x:note>
1278<t>
1279   It might be contrary to the privacy expectations of the user to send
1280   an Accept-Language header with the complete linguistic preferences of
1281   the user in every request. For a discussion of this issue, see
1282   <xref target="privacy.issues.connected.to.accept.headers"/>.
1283</t>
1284<t>
1285   As intelligibility is highly dependent on the individual user, it is
1286   recommended that client applications make the choice of linguistic
1287   preference available to the user. If the choice is not made
1288   available, then the Accept-Language header field &MUST-NOT; be given in
1289   the request.
1290</t>
1291<x:note>
1292  <t>
1293    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1294    the user, we remind implementors of  the fact that users are not
1295    familiar with the details of language matching as described above,
1296    and should provide appropriate guidance. As an example, users
1297    might assume that on selecting "en-gb", they will be served any
1298    kind of English document if British English is not available. A
1299    user agent might suggest in such a case to add "en" to get the
1300    best matching behavior.
1301  </t>
1302</x:note>
1303</section>
1304
1305<section title="Content-Encoding" anchor="header.content-encoding">
1306  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1307  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1308  <x:anchor-alias value="Content-Encoding"/>
1309  <x:anchor-alias value="Content-Encoding-v"/>
1310<t>
1311   The "Content-Encoding" entity-header field indicates what content-codings
1312   have been applied to the representation, and thus what decoding mechanisms
1313   must be applied in order to obtain the media-type referenced by the
1314   Content-Type header field. Content-Encoding is primarily used to allow a
1315   representation to be compressed without losing the identity of its underlying
1316   media type.
1317</t>
1318<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1319  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1320  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1321</artwork></figure>
1322<t>
1323   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1324</t>
1325<figure><artwork type="example">
1326  Content-Encoding: gzip
1327</artwork></figure>
1328<t>
1329   The content-coding is a characteristic of the representation.
1330   Typically, the representation body is stored with this
1331   encoding and is only decoded before rendering or analogous usage.
1332   However, a non-transparent proxy &MAY; modify the content-coding if the
1333   new coding is known to be acceptable to the recipient, unless the
1334   "no-transform" cache-control directive is present in the message.
1335</t>
1336<t>
1337   If the content-coding of a representation is not "identity", then the
1338   representation metadata &MUST; include a Content-Encoding header
1339   field (<xref target="header.content-encoding"/>)
1340   that lists the non-identity content-coding(s) used.
1341</t>
1342<t>
1343   If the content-coding of a representation in a request message is not
1344   acceptable to the origin server, the server &SHOULD; respond with a
1345   status code of 415 (Unsupported Media Type).
1346</t>
1347<t>
1348   If multiple encodings have been applied to a representation, the content
1349   codings &MUST; be listed in the order in which they were applied.
1350   Additional information about the encoding parameters &MAY; be provided
1351   by other header fields not defined by this specification.
1352</t>
1353</section>
1354
1355<section title="Content-Language" anchor="header.content-language">
1356  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1357  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1358  <x:anchor-alias value="Content-Language"/>
1359  <x:anchor-alias value="Content-Language-v"/>
1360<t>
1361   The "Content-Language" entity-header field describes the natural
1362   language(s) of the intended audience for the representation. Note that this might
1363   not be equivalent to all the languages used within the representation.
1364</t>
1365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1366  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1367  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1368</artwork></figure>
1369<t>
1370   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1371   Content-Language is to allow a user to identify and differentiate
1372   representations according to the user's own preferred language. Thus, if the
1373   body content is intended only for a Danish-literate audience, the
1374   appropriate field is
1375</t>
1376<figure><artwork type="example">
1377  Content-Language: da
1378</artwork></figure>
1379<t>
1380   If no Content-Language is specified, the default is that the content
1381   is intended for all language audiences. This might mean that the
1382   sender does not consider it to be specific to any natural language,
1383   or that the sender does not know for which language it is intended.
1384</t>
1385<t>
1386   Multiple languages &MAY; be listed for content that is intended for
1387   multiple audiences. For example, a rendition of the "Treaty of
1388   Waitangi," presented simultaneously in the original Maori and English
1389   versions, would call for
1390</t>
1391<figure><artwork type="example">
1392  Content-Language: mi, en
1393</artwork></figure>
1394<t>
1395   However, just because multiple languages are present within a representation
1396   does not mean that it is intended for multiple linguistic audiences.
1397   An example would be a beginner's language primer, such as "A First
1398   Lesson in Latin," which is clearly intended to be used by an
1399   English-literate audience. In this case, the Content-Language would
1400   properly only include "en".
1401</t>
1402<t>
1403   Content-Language &MAY; be applied to any media type -- it is not
1404   limited to textual documents.
1405</t>
1406</section>
1407
1408<section title="Content-Location" anchor="header.content-location">
1409  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1410  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1411  <x:anchor-alias value="Content-Location"/>
1412  <x:anchor-alias value="Content-Location-v"/>
1413<t>
1414   The "Content-Location" header field supplies a URI that can be used
1415   as a specific identifier for the representation in this message.
1416   In other words, if one were to perform a GET on this URI at the time
1417   of this message's generation, then a 200 response would contain the
1418   same representation that is enclosed as payload in this message.
1419</t>
1420<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1421  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1422                    <x:ref>Content-Location-v</x:ref>
1423  <x:ref>Content-Location-v</x:ref> =
1424                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1425</artwork></figure>
1426<t>
1427   The Content-Location value is not a replacement for the Effective
1428   Request URI (&effective-request-uri;).  It is representation metadata.
1429   It has the same syntax and semantics as the header field of the same name
1430   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1431   However, its appearance in an HTTP message has some special implications
1432   for HTTP recipients.
1433</t>
1434<t>
1435   If Content-Location is included in a response message and its value
1436   is the same as the Effective Request URI, then the response payload
1437   &SHOULD; be considered the current representation of that resource.
1438   For a GET or HEAD request, this is the same as the default semantics
1439   when no Content-Location is provided by the server.  For a state-changing
1440   method like PUT or POST, it implies that the server's response contains
1441   the new representation of that resource, thereby distinguishing it from
1442   representations that might only report about the action (e.g., "It worked!").
1443   This allows authoring applications to update their local copies without
1444   the need for a subsequent GET request.
1445</t>
1446<t>
1447   If Content-Location is included in a response message and its value
1448   differs from the Effective Request URI, then the origin server is
1449   informing recipients that this representation has its own, presumably
1450   more specific, identifier.  For a GET or HEAD request, this is an
1451   indication that the Effective Request URI identifies a resource that
1452   is subject to content negotiation and the representation selected for
1453   this response can also be found at the identified URI.  For other
1454   methods, such a Content-Location indicates that this representation
1455   contains a report on the action's status and the same report is
1456   available (for future access with GET) at the given URI.  For
1457   example, a purchase transaction made via the POST method may
1458   include a receipt document as the payload of the 200 response;
1459   the Content-Location value provides an identifier for retrieving
1460   a copy of that same receipt in the future.
1461</t>
1462<t>
1463   If Content-Location is included in a request message, then it &MAY;
1464   be interpreted by the origin server as an indication of where the
1465   user agent originally obtained the content of the enclosed
1466   representation (prior to any subsequent modification of the content
1467   by that user agent).  In other words, the user agent is providing
1468   the same representation metadata that it received with the original
1469   representation.  However, such interpretation &MUST-NOT; be used to
1470   alter the semantics of the method requested by the client.  For
1471   example, if a client makes a PUT request on a negotiated resource
1472   and the origin server accepts that PUT (without redirection), then the
1473   new set of values for that resource is expected to be consistent with
1474   the one representation supplied in that PUT; the Content-Location
1475   cannot be used as a form of reverse content selection that
1476   identifies only one of the negotiated representations to be updated.
1477   If the user agent had wanted the latter semantics, it would have applied
1478   the PUT directly to the Content-Location URI.
1479</t>
1480<t>
1481   A Content-Location field received in a request message is transitory
1482   information that &SHOULD-NOT; be saved with other representation
1483   metadata for use in later responses.  The Content-Location's value
1484   might be saved for use in other contexts, such as within source links
1485   or other metadata.
1486</t>
1487<t>
1488   A cache cannot assume that a representation with a Content-Location
1489   different from the URI used to retrieve it can be used to respond to
1490   later requests on that Content-Location URI.
1491</t>
1492<t>
1493   If the Content-Location value is a partial URI, it is
1494   interpreted relative to the Effective Request URI.
1495</t>
1496</section>
1497
1498<section title="Content-MD5" anchor="header.content-md5">
1499  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1500  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1501  <x:anchor-alias value="Content-MD5"/>
1502  <x:anchor-alias value="Content-MD5-v"/>
1503<t>
1504   The "Content-MD5" entity-header field, as defined in <xref target="RFC1864"/>, is
1505   an MD5 digest of the payload body that provides an end-to-end message
1506   integrity check (MIC) of the payload body (the message-body after any
1507   transfer-coding is decoded). Note that a MIC is good for
1508   detecting accidental modification of the payload body in transit, but is not
1509   proof against malicious attacks.
1510</t>
1511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1512  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1513  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1514</artwork></figure>
1515<t>
1516   The Content-MD5 header field &MAY; be generated by an origin server or
1517   client to function as an integrity check of the payload body. Only
1518   origin servers or user agents &MAY; generate the Content-MD5 header field;
1519   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1520   value as an end-to-end integrity check. Any recipient &MAY; check that
1521   the digest value in this header field matches a corresponding digest
1522   calculated on payload body as received.
1523</t>
1524<t>
1525   The MD5 digest is computed based on the content of the payload body,
1526   including any content-coding, but not including any transfer-coding
1527   applied to the message-body because such transfer-codings might be
1528   applied or removed anywhere along the request/response chain.
1529   If the message is received with a transfer-coding, that encoding &MUST;
1530   be decoded prior to checking the Content-MD5 value against the received
1531   payload.
1532</t>
1533<t>
1534   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1535   composite media-types (e.g., multipart/* and message/rfc822), but
1536   this does not change how the digest is computed as defined in the
1537   preceding paragraph.
1538</t>
1539<t>
1540   There are several consequences of this. The payload for composite
1541   types &MAY; contain many body-parts, each with its own MIME and HTTP
1542   headers (including Content-MD5, Content-Transfer-Encoding, and
1543   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1544   or Content-Encoding header, it is assumed that the content
1545   of the body-part has had the encoding applied, and the body-part is
1546   included in the Content-MD5 digest as is -- i.e., after the
1547   application. The Transfer-Encoding header field is not allowed within
1548   body-parts.
1549</t>
1550<t>
1551   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1552   computing or checking the digest: the line break convention used in
1553   the text actually transmitted &MUST; be left unaltered when computing
1554   the digest.
1555</t>
1556<x:note>
1557  <t>
1558    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1559    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1560    in which the application of Content-MD5 to HTTP entity-bodies
1561    differs from its application to MIME entity-bodies. One is that
1562    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1563    does use Transfer-Encoding and Content-Encoding. Another is that
1564    HTTP more frequently uses binary content types than MIME, so it is
1565    worth noting that, in such cases, the byte order used to compute
1566    the digest is the transmission byte order defined for the type.
1567    Lastly, HTTP allows transmission of text types with any of several
1568    line break conventions and not just the canonical form using CRLF.
1569  </t>
1570</x:note>
1571</section>
1572
1573<section title="Content-Type" anchor="header.content-type">
1574  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1575  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1576  <x:anchor-alias value="Content-Type"/>
1577  <x:anchor-alias value="Content-Type-v"/>
1578<t>
1579   The "Content-Type" entity-header field indicates the media type of the
1580   representation. In the case of responses to the HEAD method, the media type is
1581   that which would have been sent had the request been a GET.
1582</t>
1583<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1584  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1585  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1586</artwork></figure>
1587<t>
1588   Media types are defined in <xref target="media.types"/>. An example of the field is
1589</t>
1590<figure><artwork type="example">
1591  Content-Type: text/html; charset=ISO-8859-4
1592</artwork></figure>
1593<t>
1594   Further discussion of methods for identifying the media type of a
1595   representation is provided in <xref target="type"/>.
1596</t>
1597</section>
1598
1599</section>
1600
1601<section title="IANA Considerations" anchor="IANA.considerations">
1602<section title="Message Header Registration" anchor="message.header.registration">
1603<t>
1604   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1605   with the permanent registrations below (see <xref target="RFC3864"/>):
1606</t>
1607<?BEGININC p3-payload.iana-headers ?>
1608<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1609<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1610   <ttcol>Header Field Name</ttcol>
1611   <ttcol>Protocol</ttcol>
1612   <ttcol>Status</ttcol>
1613   <ttcol>Reference</ttcol>
1614
1615   <c>Accept</c>
1616   <c>http</c>
1617   <c>standard</c>
1618   <c>
1619      <xref target="header.accept"/>
1620   </c>
1621   <c>Accept-Charset</c>
1622   <c>http</c>
1623   <c>standard</c>
1624   <c>
1625      <xref target="header.accept-charset"/>
1626   </c>
1627   <c>Accept-Encoding</c>
1628   <c>http</c>
1629   <c>standard</c>
1630   <c>
1631      <xref target="header.accept-encoding"/>
1632   </c>
1633   <c>Accept-Language</c>
1634   <c>http</c>
1635   <c>standard</c>
1636   <c>
1637      <xref target="header.accept-language"/>
1638   </c>
1639   <c>Content-Disposition</c>
1640   <c>http</c>
1641   <c/>
1642   <c>
1643      <xref target="content-disposition"/>
1644   </c>
1645   <c>Content-Encoding</c>
1646   <c>http</c>
1647   <c>standard</c>
1648   <c>
1649      <xref target="header.content-encoding"/>
1650   </c>
1651   <c>Content-Language</c>
1652   <c>http</c>
1653   <c>standard</c>
1654   <c>
1655      <xref target="header.content-language"/>
1656   </c>
1657   <c>Content-Location</c>
1658   <c>http</c>
1659   <c>standard</c>
1660   <c>
1661      <xref target="header.content-location"/>
1662   </c>
1663   <c>Content-MD5</c>
1664   <c>http</c>
1665   <c>standard</c>
1666   <c>
1667      <xref target="header.content-md5"/>
1668   </c>
1669   <c>Content-Type</c>
1670   <c>http</c>
1671   <c>standard</c>
1672   <c>
1673      <xref target="header.content-type"/>
1674   </c>
1675   <c>MIME-Version</c>
1676   <c>http</c>
1677   <c/>
1678   <c>
1679      <xref target="mime-version"/>
1680   </c>
1681</texttable>
1682<!--(END)-->
1683<?ENDINC p3-payload.iana-headers ?>
1684<t>
1685   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1686</t>
1687</section>
1688
1689<section title="Content Coding Registry" anchor="content.coding.registration">
1690<t>
1691   The registration procedure for HTTP Content Codings is now defined
1692   by <xref target="content.coding.registry"/> of this document.
1693</t>
1694<t>
1695   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1696   should be updated with the registration below:
1697</t>
1698<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1699   <ttcol>Name</ttcol>
1700   <ttcol>Description</ttcol>
1701   <ttcol>Reference</ttcol>
1702   <c>compress</c>
1703   <c>UNIX "compress" program method</c>
1704   <c>
1705      &compress-coding;
1706   </c>
1707   <c>deflate</c>
1708   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1709   the "zlib" data format (<xref target="RFC1950"/>)
1710   </c>
1711   <c>
1712      &deflate-coding;
1713   </c>
1714   <c>gzip</c>
1715   <c>Same as GNU zip <xref target="RFC1952"/></c>
1716   <c>
1717      &gzip-coding;
1718   </c>
1719   <c>identity</c>
1720   <c>No transformation</c>
1721   <c>
1722      <xref target="content.codings"/>
1723   </c>
1724</texttable>
1725</section>
1726
1727</section>
1728
1729<section title="Security Considerations" anchor="security.considerations">
1730<t>
1731   This section is meant to inform application developers, information
1732   providers, and users of the security limitations in HTTP/1.1 as
1733   described by this document. The discussion does not include
1734   definitive solutions to the problems revealed, though it does make
1735   some suggestions for reducing security risks.
1736</t>
1737
1738<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1739<t>
1740   Accept request-headers can reveal information about the user to all
1741   servers which are accessed. The Accept-Language header in particular
1742   can reveal information the user would consider to be of a private
1743   nature, because the understanding of particular languages is often
1744   strongly correlated to the membership of a particular ethnic group.
1745   User agents which offer the option to configure the contents of an
1746   Accept-Language header to be sent in every request are strongly
1747   encouraged to let the configuration process include a message which
1748   makes the user aware of the loss of privacy involved.
1749</t>
1750<t>
1751   An approach that limits the loss of privacy would be for a user agent
1752   to omit the sending of Accept-Language headers by default, and to ask
1753   the user whether or not to start sending Accept-Language headers to a
1754   server if it detects, by looking for any Vary response-header fields
1755   generated by the server, that such sending could improve the quality
1756   of service.
1757</t>
1758<t>
1759   Elaborate user-customized accept header fields sent in every request,
1760   in particular if these include quality values, can be used by servers
1761   as relatively reliable and long-lived user identifiers. Such user
1762   identifiers would allow content providers to do click-trail tracking,
1763   and would allow collaborating content providers to match cross-server
1764   click-trails or form submissions of individual users. Note that for
1765   many users not behind a proxy, the network address of the host
1766   running the user agent will also serve as a long-lived user
1767   identifier. In environments where proxies are used to enhance
1768   privacy, user agents ought to be conservative in offering accept
1769   header configuration options to end users. As an extreme privacy
1770   measure, proxies could filter the accept headers in relayed requests.
1771   General purpose user agents which provide a high degree of header
1772   configurability &SHOULD; warn users about the loss of privacy which can
1773   be involved.
1774</t>
1775</section>
1776
1777<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1778<t>
1779   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1780   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1781   serious security considerations. Content-Disposition is not part of
1782   the HTTP standard, but since it is widely implemented, we are
1783   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1784   for details.
1785</t>
1786</section>
1787
1788</section>
1789
1790<section title="Acknowledgments" anchor="ack">
1791</section>
1792</middle>
1793<back>
1794
1795<references title="Normative References">
1796
1797<reference anchor="ISO-8859-1">
1798  <front>
1799    <title>
1800     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1801    </title>
1802    <author>
1803      <organization>International Organization for Standardization</organization>
1804    </author>
1805    <date year="1998"/>
1806  </front>
1807  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1808</reference>
1809
1810<reference anchor="Part1">
1811  <front>
1812    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1813    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1814      <organization abbrev="Day Software">Day Software</organization>
1815      <address><email>fielding@gbiv.com</email></address>
1816    </author>
1817    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1818      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1819      <address><email>jg@freedesktop.org</email></address>
1820    </author>
1821    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1822      <organization abbrev="HP">Hewlett-Packard Company</organization>
1823      <address><email>JeffMogul@acm.org</email></address>
1824    </author>
1825    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1826      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1827      <address><email>henrikn@microsoft.com</email></address>
1828    </author>
1829    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1830      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1831      <address><email>LMM@acm.org</email></address>
1832    </author>
1833    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1834      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1835      <address><email>paulle@microsoft.com</email></address>
1836    </author>
1837    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1838      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1839      <address><email>timbl@w3.org</email></address>
1840    </author>
1841    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1842      <organization abbrev="W3C">World Wide Web Consortium</organization>
1843      <address><email>ylafon@w3.org</email></address>
1844    </author>
1845    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1846      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1847      <address><email>julian.reschke@greenbytes.de</email></address>
1848    </author>
1849    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1850  </front>
1851  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1852  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1853</reference>
1854
1855<reference anchor="Part2">
1856  <front>
1857    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1858    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1859      <organization abbrev="Day Software">Day Software</organization>
1860      <address><email>fielding@gbiv.com</email></address>
1861    </author>
1862    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1863      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1864      <address><email>jg@freedesktop.org</email></address>
1865    </author>
1866    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1867      <organization abbrev="HP">Hewlett-Packard Company</organization>
1868      <address><email>JeffMogul@acm.org</email></address>
1869    </author>
1870    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1871      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1872      <address><email>henrikn@microsoft.com</email></address>
1873    </author>
1874    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1875      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1876      <address><email>LMM@acm.org</email></address>
1877    </author>
1878    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1879      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1880      <address><email>paulle@microsoft.com</email></address>
1881    </author>
1882    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1883      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1884      <address><email>timbl@w3.org</email></address>
1885    </author>
1886    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1887      <organization abbrev="W3C">World Wide Web Consortium</organization>
1888      <address><email>ylafon@w3.org</email></address>
1889    </author>
1890    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1891      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1892      <address><email>julian.reschke@greenbytes.de</email></address>
1893    </author>
1894    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1895  </front>
1896  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1897  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1898</reference>
1899
1900<reference anchor="Part4">
1901  <front>
1902    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1903    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1904      <organization abbrev="Day Software">Day Software</organization>
1905      <address><email>fielding@gbiv.com</email></address>
1906    </author>
1907    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1908      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1909      <address><email>jg@freedesktop.org</email></address>
1910    </author>
1911    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1912      <organization abbrev="HP">Hewlett-Packard Company</organization>
1913      <address><email>JeffMogul@acm.org</email></address>
1914    </author>
1915    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1916      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1917      <address><email>henrikn@microsoft.com</email></address>
1918    </author>
1919    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1920      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1921      <address><email>LMM@acm.org</email></address>
1922    </author>
1923    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1924      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1925      <address><email>paulle@microsoft.com</email></address>
1926    </author>
1927    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1928      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1929      <address><email>timbl@w3.org</email></address>
1930    </author>
1931    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1932      <organization abbrev="W3C">World Wide Web Consortium</organization>
1933      <address><email>ylafon@w3.org</email></address>
1934    </author>
1935    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1936      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1937      <address><email>julian.reschke@greenbytes.de</email></address>
1938    </author>
1939    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1940  </front>
1941  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1942  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1943</reference>
1944
1945<reference anchor="Part5">
1946  <front>
1947    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1948    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1949      <organization abbrev="Day Software">Day Software</organization>
1950      <address><email>fielding@gbiv.com</email></address>
1951    </author>
1952    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1953      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1954      <address><email>jg@freedesktop.org</email></address>
1955    </author>
1956    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1957      <organization abbrev="HP">Hewlett-Packard Company</organization>
1958      <address><email>JeffMogul@acm.org</email></address>
1959    </author>
1960    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1961      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1962      <address><email>henrikn@microsoft.com</email></address>
1963    </author>
1964    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1965      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1966      <address><email>LMM@acm.org</email></address>
1967    </author>
1968    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1969      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1970      <address><email>paulle@microsoft.com</email></address>
1971    </author>
1972    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1973      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1974      <address><email>timbl@w3.org</email></address>
1975    </author>
1976    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1977      <organization abbrev="W3C">World Wide Web Consortium</organization>
1978      <address><email>ylafon@w3.org</email></address>
1979    </author>
1980    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1981      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1982      <address><email>julian.reschke@greenbytes.de</email></address>
1983    </author>
1984    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1985  </front>
1986  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1987  <x:source href="p5-range.xml" basename="p5-range"/>
1988</reference>
1989
1990<reference anchor="Part6">
1991  <front>
1992    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1993    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1994      <organization abbrev="Day Software">Day Software</organization>
1995      <address><email>fielding@gbiv.com</email></address>
1996    </author>
1997    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1998      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1999      <address><email>jg@freedesktop.org</email></address>
2000    </author>
2001    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2002      <organization abbrev="HP">Hewlett-Packard Company</organization>
2003      <address><email>JeffMogul@acm.org</email></address>
2004    </author>
2005    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2006      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2007      <address><email>henrikn@microsoft.com</email></address>
2008    </author>
2009    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2010      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2011      <address><email>LMM@acm.org</email></address>
2012    </author>
2013    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2014      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2015      <address><email>paulle@microsoft.com</email></address>
2016    </author>
2017    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2018      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2019      <address><email>timbl@w3.org</email></address>
2020    </author>
2021    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2022      <organization abbrev="W3C">World Wide Web Consortium</organization>
2023      <address><email>ylafon@w3.org</email></address>
2024    </author>
2025    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2026      <address><email>mnot@mnot.net</email></address>
2027    </author>
2028    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2029      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2030      <address><email>julian.reschke@greenbytes.de</email></address>
2031    </author>
2032    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2033  </front>
2034  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2035  <x:source href="p6-cache.xml" basename="p6-cache"/>
2036</reference>
2037
2038<reference anchor="RFC1864">
2039  <front>
2040    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2041    <author initials="J." surname="Myers" fullname="John G. Myers">
2042      <organization>Carnegie Mellon University</organization>
2043      <address><email>jgm+@cmu.edu</email></address>
2044    </author>
2045    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2046      <organization>Dover Beach Consulting, Inc.</organization>
2047      <address><email>mrose@dbc.mtview.ca.us</email></address>
2048    </author>
2049    <date month="October" year="1995"/>
2050  </front>
2051  <seriesInfo name="RFC" value="1864"/>
2052</reference>
2053
2054<reference anchor="RFC1950">
2055  <front>
2056    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2057    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2058      <organization>Aladdin Enterprises</organization>
2059      <address><email>ghost@aladdin.com</email></address>
2060    </author>
2061    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2062    <date month="May" year="1996"/>
2063  </front>
2064  <seriesInfo name="RFC" value="1950"/>
2065  <annotation>
2066    RFC 1950 is an Informational RFC, thus it may be less stable than
2067    this specification. On the other hand, this downward reference was
2068    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2069    therefore it is unlikely to cause problems in practice. See also
2070    <xref target="BCP97"/>.
2071  </annotation>
2072</reference>
2073
2074<reference anchor="RFC1951">
2075  <front>
2076    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2077    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2078      <organization>Aladdin Enterprises</organization>
2079      <address><email>ghost@aladdin.com</email></address>
2080    </author>
2081    <date month="May" year="1996"/>
2082  </front>
2083  <seriesInfo name="RFC" value="1951"/>
2084  <annotation>
2085    RFC 1951 is an Informational RFC, thus it may be less stable than
2086    this specification. On the other hand, this downward reference was
2087    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2088    therefore it is unlikely to cause problems in practice. See also
2089    <xref target="BCP97"/>.
2090  </annotation>
2091</reference>
2092
2093<reference anchor="RFC1952">
2094  <front>
2095    <title>GZIP file format specification version 4.3</title>
2096    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2097      <organization>Aladdin Enterprises</organization>
2098      <address><email>ghost@aladdin.com</email></address>
2099    </author>
2100    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2101      <address><email>gzip@prep.ai.mit.edu</email></address>
2102    </author>
2103    <author initials="M." surname="Adler" fullname="Mark Adler">
2104      <address><email>madler@alumni.caltech.edu</email></address>
2105    </author>
2106    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2107      <address><email>ghost@aladdin.com</email></address>
2108    </author>
2109    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2110      <address><email>randeg@alumni.rpi.edu</email></address>
2111    </author>
2112    <date month="May" year="1996"/>
2113  </front>
2114  <seriesInfo name="RFC" value="1952"/>
2115  <annotation>
2116    RFC 1952 is an Informational RFC, thus it may be less stable than
2117    this specification. On the other hand, this downward reference was
2118    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2119    therefore it is unlikely to cause problems in practice. See also
2120    <xref target="BCP97"/>.
2121  </annotation>
2122</reference>
2123
2124<reference anchor="RFC2045">
2125  <front>
2126    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2127    <author initials="N." surname="Freed" fullname="Ned Freed">
2128      <organization>Innosoft International, Inc.</organization>
2129      <address><email>ned@innosoft.com</email></address>
2130    </author>
2131    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2132      <organization>First Virtual Holdings</organization>
2133      <address><email>nsb@nsb.fv.com</email></address>
2134    </author>
2135    <date month="November" year="1996"/>
2136  </front>
2137  <seriesInfo name="RFC" value="2045"/>
2138</reference>
2139
2140<reference anchor="RFC2046">
2141  <front>
2142    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2143    <author initials="N." surname="Freed" fullname="Ned Freed">
2144      <organization>Innosoft International, Inc.</organization>
2145      <address><email>ned@innosoft.com</email></address>
2146    </author>
2147    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2148      <organization>First Virtual Holdings</organization>
2149      <address><email>nsb@nsb.fv.com</email></address>
2150    </author>
2151    <date month="November" year="1996"/>
2152  </front>
2153  <seriesInfo name="RFC" value="2046"/>
2154</reference>
2155
2156<reference anchor="RFC2119">
2157  <front>
2158    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2159    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2160      <organization>Harvard University</organization>
2161      <address><email>sob@harvard.edu</email></address>
2162    </author>
2163    <date month="March" year="1997"/>
2164  </front>
2165  <seriesInfo name="BCP" value="14"/>
2166  <seriesInfo name="RFC" value="2119"/>
2167</reference>
2168
2169<reference anchor='RFC4647'>
2170  <front>
2171    <title>Matching of Language Tags</title>
2172    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2173      <organization>Yahoo! Inc.</organization>
2174      <address><email>addison@inter-locale.com</email></address>
2175    </author>
2176    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2177      <organization>Google</organization>
2178      <address><email>mark.davis@macchiato.com</email></address>
2179    </author>
2180    <date year='2006' month='September' />
2181  </front>
2182  <seriesInfo name='BCP' value='47' />
2183  <seriesInfo name='RFC' value='4647' />
2184</reference>
2185
2186<reference anchor="RFC5234">
2187  <front>
2188    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2189    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2190      <organization>Brandenburg InternetWorking</organization>
2191      <address>
2192        <email>dcrocker@bbiw.net</email>
2193      </address> 
2194    </author>
2195    <author initials="P." surname="Overell" fullname="Paul Overell">
2196      <organization>THUS plc.</organization>
2197      <address>
2198        <email>paul.overell@thus.net</email>
2199      </address>
2200    </author>
2201    <date month="January" year="2008"/>
2202  </front>
2203  <seriesInfo name="STD" value="68"/>
2204  <seriesInfo name="RFC" value="5234"/>
2205</reference>
2206
2207<reference anchor='RFC5646'>
2208  <front>
2209    <title>Tags for Identifying Languages</title>
2210    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2211      <organization>Lab126</organization>
2212      <address><email>addison@inter-locale.com</email></address>
2213    </author>
2214    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2215      <organization>Google</organization>
2216      <address><email>mark.davis@google.com</email></address>
2217    </author>
2218    <date month='September' year='2009' />
2219  </front>
2220  <seriesInfo name='BCP' value='47' />
2221  <seriesInfo name='RFC' value='5646' />
2222</reference>
2223
2224</references>
2225
2226<references title="Informative References">
2227
2228<reference anchor="RFC1945">
2229  <front>
2230    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2231    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2232      <organization>MIT, Laboratory for Computer Science</organization>
2233      <address><email>timbl@w3.org</email></address>
2234    </author>
2235    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2236      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2237      <address><email>fielding@ics.uci.edu</email></address>
2238    </author>
2239    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2240      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2241      <address><email>frystyk@w3.org</email></address>
2242    </author>
2243    <date month="May" year="1996"/>
2244  </front>
2245  <seriesInfo name="RFC" value="1945"/>
2246</reference>
2247
2248<reference anchor="RFC2049">
2249  <front>
2250    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2251    <author initials="N." surname="Freed" fullname="Ned Freed">
2252      <organization>Innosoft International, Inc.</organization>
2253      <address><email>ned@innosoft.com</email></address>
2254    </author>
2255    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2256      <organization>First Virtual Holdings</organization>
2257      <address><email>nsb@nsb.fv.com</email></address>
2258    </author>
2259    <date month="November" year="1996"/>
2260  </front>
2261  <seriesInfo name="RFC" value="2049"/>
2262</reference>
2263
2264<reference anchor="RFC2068">
2265  <front>
2266    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2267    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2268      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2269      <address><email>fielding@ics.uci.edu</email></address>
2270    </author>
2271    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2272      <organization>MIT Laboratory for Computer Science</organization>
2273      <address><email>jg@w3.org</email></address>
2274    </author>
2275    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2276      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2277      <address><email>mogul@wrl.dec.com</email></address>
2278    </author>
2279    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2280      <organization>MIT Laboratory for Computer Science</organization>
2281      <address><email>frystyk@w3.org</email></address>
2282    </author>
2283    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2284      <organization>MIT Laboratory for Computer Science</organization>
2285      <address><email>timbl@w3.org</email></address>
2286    </author>
2287    <date month="January" year="1997"/>
2288  </front>
2289  <seriesInfo name="RFC" value="2068"/>
2290</reference>
2291
2292<reference anchor="RFC2076">
2293  <front>
2294    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2295    <author initials="J." surname="Palme" fullname="Jacob Palme">
2296      <organization>Stockholm University/KTH</organization>
2297      <address><email>jpalme@dsv.su.se</email></address>
2298    </author>
2299    <date month="February" year="1997"/>
2300  </front>
2301  <seriesInfo name="RFC" value="2076"/>
2302</reference>
2303
2304<reference anchor="RFC2183">
2305  <front>
2306    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2307    <author initials="R." surname="Troost" fullname="Rens Troost">
2308      <organization>New Century Systems</organization>
2309      <address><email>rens@century.com</email></address>
2310    </author>
2311    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2312      <organization>QUALCOMM Incorporated</organization>
2313      <address><email>sdorner@qualcomm.com</email></address>
2314    </author>
2315    <author initials="K." surname="Moore" fullname="Keith Moore">
2316      <organization>Department of Computer Science</organization>
2317      <address><email>moore@cs.utk.edu</email></address>
2318    </author>
2319    <date month="August" year="1997"/>
2320  </front>
2321  <seriesInfo name="RFC" value="2183"/>
2322</reference>
2323
2324<reference anchor="RFC2277">
2325  <front>
2326    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2327    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2328      <organization>UNINETT</organization>
2329      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2330    </author>
2331    <date month="January" year="1998"/>
2332  </front>
2333  <seriesInfo name="BCP" value="18"/>
2334  <seriesInfo name="RFC" value="2277"/>
2335</reference>
2336
2337<reference anchor='RFC2295'>
2338  <front>
2339    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2340    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2341      <organization>Technische Universiteit Eindhoven</organization>
2342      <address>
2343        <email>koen@win.tue.nl</email>
2344      </address>
2345    </author>
2346    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2347      <organization>Hewlett-Packard Company</organization>
2348      <address>
2349        <email>mutz@hpl.hp.com</email>
2350      </address>
2351    </author>
2352    <date year='1998' month='March'/>
2353  </front>
2354  <seriesInfo name='RFC' value='2295'/>
2355</reference>
2356
2357<reference anchor="RFC2388">
2358  <front>
2359    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2360    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2361      <organization>Xerox Palo Alto Research Center</organization>
2362      <address><email>masinter@parc.xerox.com</email></address>
2363    </author>
2364    <date year="1998" month="August"/>
2365  </front>
2366  <seriesInfo name="RFC" value="2388"/>
2367</reference>
2368
2369<reference anchor="RFC2557">
2370  <front>
2371    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2372    <author initials="F." surname="Palme" fullname="Jacob Palme">
2373      <organization>Stockholm University and KTH</organization>
2374      <address><email>jpalme@dsv.su.se</email></address>
2375    </author>
2376    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2377      <organization>Microsoft Corporation</organization>
2378      <address><email>alexhop@microsoft.com</email></address>
2379    </author>
2380    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2381      <organization>Lotus Development Corporation</organization>
2382      <address><email>Shelness@lotus.com</email></address>
2383    </author>
2384    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2385      <address><email>stef@nma.com</email></address>
2386    </author>
2387    <date year="1999" month="March"/>
2388  </front>
2389  <seriesInfo name="RFC" value="2557"/>
2390</reference>
2391
2392<reference anchor="RFC2616">
2393  <front>
2394    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2395    <author initials="R." surname="Fielding" fullname="R. Fielding">
2396      <organization>University of California, Irvine</organization>
2397      <address><email>fielding@ics.uci.edu</email></address>
2398    </author>
2399    <author initials="J." surname="Gettys" fullname="J. Gettys">
2400      <organization>W3C</organization>
2401      <address><email>jg@w3.org</email></address>
2402    </author>
2403    <author initials="J." surname="Mogul" fullname="J. Mogul">
2404      <organization>Compaq Computer Corporation</organization>
2405      <address><email>mogul@wrl.dec.com</email></address>
2406    </author>
2407    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2408      <organization>MIT Laboratory for Computer Science</organization>
2409      <address><email>frystyk@w3.org</email></address>
2410    </author>
2411    <author initials="L." surname="Masinter" fullname="L. Masinter">
2412      <organization>Xerox Corporation</organization>
2413      <address><email>masinter@parc.xerox.com</email></address>
2414    </author>
2415    <author initials="P." surname="Leach" fullname="P. Leach">
2416      <organization>Microsoft Corporation</organization>
2417      <address><email>paulle@microsoft.com</email></address>
2418    </author>
2419    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2420      <organization>W3C</organization>
2421      <address><email>timbl@w3.org</email></address>
2422    </author>
2423    <date month="June" year="1999"/>
2424  </front>
2425  <seriesInfo name="RFC" value="2616"/>
2426</reference>
2427
2428<reference anchor="RFC3629">
2429  <front>
2430    <title>UTF-8, a transformation format of ISO 10646</title>
2431    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2432      <organization>Alis Technologies</organization>
2433      <address><email>fyergeau@alis.com</email></address>
2434    </author>
2435    <date month="November" year="2003"/>
2436  </front>
2437  <seriesInfo name="RFC" value="3629"/>
2438  <seriesInfo name="STD" value="63"/>
2439</reference>
2440
2441<reference anchor='RFC3864'>
2442  <front>
2443    <title>Registration Procedures for Message Header Fields</title>
2444    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2445      <organization>Nine by Nine</organization>
2446      <address><email>GK-IETF@ninebynine.org</email></address>
2447    </author>
2448    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2449      <organization>BEA Systems</organization>
2450      <address><email>mnot@pobox.com</email></address>
2451    </author>
2452    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2453      <organization>HP Labs</organization>
2454      <address><email>JeffMogul@acm.org</email></address>
2455    </author>
2456    <date year='2004' month='September' />
2457  </front>
2458  <seriesInfo name='BCP' value='90' />
2459  <seriesInfo name='RFC' value='3864' />
2460</reference>
2461
2462<reference anchor="RFC4288">
2463  <front>
2464    <title>Media Type Specifications and Registration Procedures</title>
2465    <author initials="N." surname="Freed" fullname="N. Freed">
2466      <organization>Sun Microsystems</organization>
2467      <address>
2468        <email>ned.freed@mrochek.com</email>
2469      </address>
2470    </author>
2471    <author initials="J." surname="Klensin" fullname="J. Klensin">
2472      <address>
2473        <email>klensin+ietf@jck.com</email>
2474      </address>
2475    </author>
2476    <date year="2005" month="December"/>
2477  </front>
2478  <seriesInfo name="BCP" value="13"/>
2479  <seriesInfo name="RFC" value="4288"/>
2480</reference>
2481
2482<reference anchor='RFC5226'>
2483  <front>
2484    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2485    <author initials='T.' surname='Narten' fullname='T. Narten'>
2486      <organization>IBM</organization>
2487      <address><email>narten@us.ibm.com</email></address>
2488    </author>
2489    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2490      <organization>Google</organization>
2491      <address><email>Harald@Alvestrand.no</email></address>
2492    </author>
2493    <date year='2008' month='May' />
2494  </front>
2495  <seriesInfo name='BCP' value='26' />
2496  <seriesInfo name='RFC' value='5226' />
2497</reference>
2498
2499<reference anchor="RFC5322">
2500  <front>
2501    <title>Internet Message Format</title>
2502    <author initials="P." surname="Resnick" fullname="P. Resnick">
2503      <organization>Qualcomm Incorporated</organization>
2504    </author>
2505    <date year="2008" month="October"/>
2506  </front> 
2507  <seriesInfo name="RFC" value="5322"/>
2508</reference>
2509
2510<reference anchor='BCP97'>
2511  <front>
2512    <title>Handling Normative References to Standards-Track Documents</title>
2513    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2514      <address>
2515        <email>klensin+ietf@jck.com</email>
2516      </address>
2517    </author>
2518    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2519      <organization>MIT</organization>
2520      <address>
2521        <email>hartmans-ietf@mit.edu</email>
2522      </address>
2523    </author>
2524    <date year='2007' month='June' />
2525  </front>
2526  <seriesInfo name='BCP' value='97' />
2527  <seriesInfo name='RFC' value='4897' />
2528</reference>
2529
2530
2531</references>
2532
2533<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2534<t>
2535   HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC5322"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2536   allow a message-body to be transmitted in an open variety of
2537   representations and with extensible mechanisms. However, RFC 2045
2538   discusses mail, and HTTP has a few features that are different from
2539   those described in MIME. These differences were carefully chosen
2540   to optimize performance over binary connections, to allow greater
2541   freedom in the use of new media types, to make date comparisons
2542   easier, and to acknowledge the practice of some early HTTP servers
2543   and clients.
2544</t>
2545<t>
2546   This appendix describes specific areas where HTTP differs from MIME.
2547   Proxies and gateways to strict MIME environments &SHOULD; be
2548   aware of these differences and provide the appropriate conversions
2549   where necessary. Proxies and gateways from MIME environments to HTTP
2550   also need to be aware of the differences because some conversions
2551   might be required.
2552</t>
2553
2554<section title="MIME-Version" anchor="mime-version">
2555  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2556  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2557  <x:anchor-alias value="MIME-Version"/>
2558  <x:anchor-alias value="MIME-Version-v"/>
2559<t>
2560   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2561   include a single MIME-Version general-header field to indicate what
2562   version of the MIME protocol was used to construct the message. Use
2563   of the MIME-Version header field indicates that the message is in
2564   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2565   Proxies/gateways are responsible for ensuring full compliance (where
2566   possible) when exporting HTTP messages to strict MIME environments.
2567</t>
2568<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2569  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2570  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2571</artwork></figure>
2572<t>
2573   MIME version "1.0" is the default for use in HTTP/1.1. However,
2574   HTTP/1.1 message parsing and semantics are defined by this document
2575   and not the MIME specification.
2576</t>
2577</section>
2578
2579<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2580<t>
2581   MIME requires that an Internet mail body-part be converted to
2582   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2583   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2584   allowed for subtypes of the "text" media type when transmitted over
2585   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2586   line breaks as CRLF and forbids the use of CR or LF outside of line
2587   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2588   line break within text content when a message is transmitted over
2589   HTTP.
2590</t>
2591<t>
2592   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2593   environment &SHOULD; translate all line breaks within the text media
2594   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2595   canonical form of CRLF. Note, however, that this might be complicated
2596   by the presence of a Content-Encoding and by the fact that HTTP
2597   allows the use of some character sets which do not use octets 13 and
2598   10 to represent CR and LF, as is the case for some multi-byte
2599   character sets.
2600</t>
2601<t>
2602   Implementors should note that conversion will break any cryptographic
2603   checksums applied to the original content unless the original content
2604   is already in canonical form. Therefore, the canonical form is
2605   recommended for any content that uses such checksums in HTTP.
2606</t>
2607</section>
2608
2609
2610<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2611<t>
2612   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2613   simplify the process of date comparison. Proxies and gateways from
2614   other protocols &SHOULD; ensure that any Date header field present in a
2615   message conforms to one of the HTTP/1.1 formats and rewrite the date
2616   if necessary.
2617</t>
2618</section>
2619
2620<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2621<t>
2622   MIME does not include any concept equivalent to HTTP/1.1's
2623   Content-Encoding header field. Since this acts as a modifier on the
2624   media type, proxies and gateways from HTTP to MIME-compliant
2625   protocols &MUST; either change the value of the Content-Type header
2626   field or decode the representation before forwarding the message. (Some
2627   experimental applications of Content-Type for Internet mail have used
2628   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2629   a function equivalent to Content-Encoding. However, this parameter is
2630   not part of the MIME standards).
2631</t>
2632</section>
2633
2634<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2635<t>
2636   HTTP does not use the Content-Transfer-Encoding field of MIME.
2637   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2638   remove any Content-Transfer-Encoding
2639   prior to delivering the response message to an HTTP client.
2640</t>
2641<t>
2642   Proxies and gateways from HTTP to MIME-compliant protocols are
2643   responsible for ensuring that the message is in the correct format
2644   and encoding for safe transport on that protocol, where "safe
2645   transport" is defined by the limitations of the protocol being used.
2646   Such a proxy or gateway &SHOULD; label the data with an appropriate
2647   Content-Transfer-Encoding if doing so will improve the likelihood of
2648   safe transport over the destination protocol.
2649</t>
2650</section>
2651
2652<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2653<t>
2654   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2655   Proxies/gateways &MUST; remove any transfer-coding prior to
2656   forwarding a message via a MIME-compliant protocol.
2657</t>
2658</section>
2659
2660<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2661<t>
2662   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2663   need to be aware of MIME line length limitations. Since HTTP does not
2664   have this limitation, HTTP does not fold long lines. MHTML messages
2665   being transported by HTTP follow all conventions of MHTML, including
2666   line length limitations and folding, canonicalization, etc., since
2667   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2668   does not interpret the content or any MIME header lines that might be
2669   contained therein.
2670</t>
2671</section>
2672</section>
2673
2674<section title="Additional Features" anchor="additional.features">
2675<t>
2676   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2677   existing HTTP implementations, but not consistently and correctly
2678   across most HTTP/1.1 applications. Implementors are advised to be
2679   aware of these features, but cannot rely upon their presence in, or
2680   interoperability with, other HTTP/1.1 applications. Some of these
2681   describe proposed experimental features, and some describe features
2682   that experimental deployment found lacking that are now addressed in
2683   the base HTTP/1.1 specification.
2684</t>
2685<t>
2686   A number of other headers, such as Content-Disposition and Title,
2687   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2688</t>
2689
2690<section title="Content-Disposition" anchor="content-disposition">
2691<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2692<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2693  <x:anchor-alias value="content-disposition"/>
2694  <x:anchor-alias value="content-disposition-v"/>
2695  <x:anchor-alias value="disposition-type"/>
2696  <x:anchor-alias value="disposition-parm"/>
2697  <x:anchor-alias value="disp-extension-parm"/>
2698  <x:anchor-alias value="disp-extension-token"/>
2699  <x:anchor-alias value="filename-parm"/>
2700<t>
2701   The "Content-Disposition" response-header field has been proposed as a
2702   means for the origin server to suggest a default filename if the user
2703   requests that the content is saved to a file. This usage is derived
2704   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2705</t>
2706<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/>
2707  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2708                        <x:ref>content-disposition-v</x:ref>
2709  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2710                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2711  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2712  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2713  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2714  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2715  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" <x:ref>word</x:ref>
2716</artwork></figure>
2717<t>
2718   An example is
2719</t>
2720<figure><artwork type="example">
2721  Content-Disposition: attachment; filename="fname.ext"
2722</artwork></figure>
2723<t>
2724   The receiving user agent &SHOULD-NOT;  respect any directory path
2725   information present in the filename-parm parameter, which is the only
2726   parameter believed to apply to HTTP implementations at this time. The
2727   filename &SHOULD; be treated as a terminal component only.
2728</t>
2729<t>
2730   If this header is used in a response with the application/octet-stream
2731   content-type, the implied suggestion is that the user agent
2732   should not display the response, but directly enter a "save response
2733   as..." dialog.
2734</t>
2735<t>
2736   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2737</t>
2738</section>
2739</section>
2740
2741<section title="Compatibility with Previous Versions" anchor="compatibility">
2742<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2743<t>
2744   Charset wildcarding is introduced to avoid explosion of character set
2745   names in accept headers. (<xref target="header.accept-charset"/>)
2746</t>
2747<t>
2748   Content-Base was deleted from the specification: it was not
2749   implemented widely, and there is no simple, safe way to introduce it
2750   without a robust extension mechanism. In addition, it is used in a
2751   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2752</t>
2753<t>
2754   A content-coding of "identity" was introduced, to solve problems
2755   discovered in caching. (<xref target="content.codings"/>)
2756</t>
2757<t>
2758   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
2759   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
2760   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2761</t>
2762</section>
2763
2764<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2765<t>
2766  Clarify contexts that charset is used in.
2767  (<xref target="character.sets"/>)
2768</t>
2769<t>
2770  Remove base URI setting semantics for Content-Location due to poor
2771  implementation support, which was caused by too many broken servers emitting
2772  bogus Content-Location headers, and also the potentially undesirable effect
2773  of potentially breaking relative links in content-negotiated resources.
2774  (<xref target="header.content-location"/>)
2775</t>
2776<t>
2777  Remove reference to non-existant identity transfer-coding value tokens.
2778  (<xref target="no.content-transfer-encoding"/>)
2779</t>
2780</section>
2781
2782</section>
2783
2784<?BEGININC p3-payload.abnf-appendix ?>
2785<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2786<figure>
2787<artwork type="abnf" name="p3-payload.parsed-abnf">
2788<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2789<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2790<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2791 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2792 qvalue ] ] )
2793<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2794<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2795 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2796<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2797<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2798 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2799 ] )
2800<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2801 OWS media-range [ accept-params ] ] ) ]
2802
2803<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2804<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2805 content-coding ] )
2806<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2807<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2808 language-tag ] )
2809<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2810<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2811<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2812<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2813<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2814<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2815<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2816<x:ref>Content-Type-v</x:ref> = media-type
2817
2818<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2819
2820<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2821
2822<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2823<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2824
2825<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2826
2827<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2828<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2829<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2830<x:ref>attribute</x:ref> = token
2831
2832<x:ref>charset</x:ref> = token
2833<x:ref>codings</x:ref> = ( content-coding / "*" )
2834<x:ref>content-coding</x:ref> = token
2835<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2836 content-disposition-v
2837<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2838 disposition-parm )
2839
2840<x:ref>disp-extension-parm</x:ref> = token "=" word
2841<x:ref>disp-extension-token</x:ref> = token
2842<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2843<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2844
2845<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2846 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2847 Expires / Last-Modified / extension-header
2848<x:ref>extension-header</x:ref> = header-field
2849
2850<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2851
2852<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 3.2&gt;
2853
2854<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2855<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2856
2857<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2858 ";" OWS parameter )
2859<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2860
2861<x:ref>parameter</x:ref> = attribute "=" value
2862<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2863
2864<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2865<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2866
2867<x:ref>subtype</x:ref> = token
2868
2869<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2870<x:ref>type</x:ref> = token
2871
2872<x:ref>value</x:ref> = word
2873
2874<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2875</artwork>
2876</figure>
2877<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2878; Accept defined but not used
2879; Accept-Charset defined but not used
2880; Accept-Encoding defined but not used
2881; Accept-Language defined but not used
2882; MIME-Version defined but not used
2883; content-disposition defined but not used
2884; entity-header defined but not used
2885</artwork></figure></section>
2886<?ENDINC p3-payload.abnf-appendix ?>
2887
2888<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2889
2890<section title="Since RFC2616">
2891<t>
2892  Extracted relevant partitions from <xref target="RFC2616"/>.
2893</t>
2894</section>
2895
2896<section title="Since draft-ietf-httpbis-p3-payload-00">
2897<t>
2898  Closed issues:
2899  <list style="symbols"> 
2900    <t>
2901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2902      "Media Type Registrations"
2903      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2904    </t>
2905    <t>
2906      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2907      "Clarification regarding quoting of charset values"
2908      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2909    </t>
2910    <t>
2911      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2912      "Remove 'identity' token references"
2913      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2914    </t>
2915    <t>
2916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2917      "Accept-Encoding BNF"
2918    </t>
2919    <t>
2920      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2921      "Normative and Informative references"
2922    </t>
2923    <t>
2924      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2925      "RFC1700 references"
2926    </t>
2927    <t>
2928      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2929      "Updating to RFC4288"
2930    </t>
2931    <t>
2932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2933      "Informative references"
2934    </t>
2935    <t>
2936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2937      "ISO-8859-1 Reference"
2938    </t>
2939    <t>
2940      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2941      "Encoding References Normative"
2942    </t>
2943    <t>
2944      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2945      "Normative up-to-date references"
2946    </t>
2947  </list>
2948</t>
2949</section>
2950
2951<section title="Since draft-ietf-httpbis-p3-payload-01">
2952<t>
2953  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2954  <list style="symbols"> 
2955    <t>
2956      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2957    </t>
2958  </list>
2959</t>
2960</section>
2961
2962<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2963<t>
2964  Closed issues:
2965  <list style="symbols"> 
2966    <t>
2967      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2968      "Quoting Charsets"
2969    </t>
2970    <t>
2971      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2972      "Classification for Allow header"
2973    </t>
2974    <t>
2975      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2976      "missing default for qvalue in description of Accept-Encoding"
2977    </t>
2978  </list>
2979</t>
2980<t>
2981  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2982  <list style="symbols"> 
2983    <t>
2984      Reference RFC 3984, and update header registrations for headers defined
2985      in this document.
2986    </t>
2987  </list>
2988</t>
2989</section>
2990
2991<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2992<t>
2993  Closed issues:
2994  <list style="symbols"> 
2995    <t>
2996      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2997      "Quoting Charsets"
2998    </t>
2999    <t>
3000      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
3001      "language tag matching (Accept-Language) vs RFC4647"
3002    </t>
3003    <t>
3004      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
3005      "RFC 1806 has been replaced by RFC2183"
3006    </t>
3007  </list>
3008</t>
3009<t>
3010  Other changes:
3011  <list style="symbols"> 
3012    <t>
3013      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
3014      "Encoding References Normative" -- rephrase the annotation and reference
3015      <xref target="BCP97"/>.
3016    </t>
3017  </list>
3018</t>
3019 </section>
3020
3021<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
3022<t>
3023  Closed issues:
3024  <list style="symbols"> 
3025    <t>
3026      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3027      "RFC 2822 is updated by RFC 5322"
3028    </t>
3029  </list>
3030</t>
3031<t>
3032  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3033  <list style="symbols"> 
3034    <t>
3035      Use "/" instead of "|" for alternatives.
3036    </t>
3037    <t>
3038      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3039      whitespace ("OWS") and required whitespace ("RWS").
3040    </t>
3041    <t>
3042      Rewrite ABNFs to spell out whitespace rules, factor out
3043      header value format definitions.
3044    </t>
3045  </list>
3046</t>
3047</section>
3048
3049<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
3050<t>
3051  Closed issues:
3052  <list style="symbols"> 
3053    <t>
3054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
3055      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3056    </t>
3057  </list>
3058</t>
3059<t>
3060  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3061  <list style="symbols"> 
3062    <t>
3063      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3064    </t>
3065  </list>
3066</t>
3067<t>
3068  Other changes:
3069  <list style="symbols"> 
3070    <t>
3071      Move definition of quality values into Part 1.
3072    </t>
3073  </list>
3074</t>
3075</section>
3076
3077<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3078<t>
3079  Closed issues:
3080  <list style="symbols"> 
3081    <t>
3082      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3083      "Content-Location isn't special"
3084    </t>
3085    <t>
3086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3087      "Content Sniffing"
3088    </t>
3089  </list>
3090</t>
3091</section>
3092
3093<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3094<t>
3095  Closed issues:
3096  <list style="symbols"> 
3097    <t>
3098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3099      "Updated reference for language tags"
3100    </t>
3101    <t>
3102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3103      "Clarify rules for determining what entities a response carries"
3104    </t>
3105    <t>
3106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
3107      "Content-Location base-setting problems"
3108    </t>
3109    <t>
3110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3111      "Content Sniffing"
3112    </t>
3113    <t>
3114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3115      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3116    </t>
3117    <t>
3118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
3119      "move definitions of gzip/deflate/compress to part 1"
3120    </t>
3121  </list>
3122</t>
3123<t>
3124  Partly resolved issues:
3125  <list style="symbols"> 
3126    <t>
3127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3128      "update IANA requirements wrt Transfer-Coding values" (add the
3129      IANA Considerations subsection)
3130    </t>
3131    <t>
3132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3133      "update IANA requirements wrt Content-Coding values" (add the
3134      IANA Considerations subsection)
3135    </t>
3136  </list>
3137</t>
3138</section>
3139
3140<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3141<t>
3142  Closed issues:
3143  <list style="symbols"> 
3144    <t>
3145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3146      "Content Negotiation for media types"
3147    </t>
3148    <t>
3149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3150      "Accept-Language: which RFC4647 filtering?"
3151    </t>
3152  </list>
3153</t>
3154</section>
3155
3156<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3157<t>
3158  Closed issues:
3159  <list style="symbols"> 
3160    <t>
3161      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
3162      "IANA registry for content/transfer encodings"
3163    </t>
3164    <t>
3165      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3166      "Content Sniffing"
3167    </t>
3168    <t>
3169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
3170      "use of term "word" when talking about header structure"
3171    </t>
3172  </list>
3173</t>
3174<t>
3175  Partly resolved issues:
3176  <list style="symbols"> 
3177    <t>
3178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
3179      "Term for the requested resource's URI"
3180    </t>
3181  </list>
3182</t>
3183</section>
3184
3185<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
3186<t>
3187  Closed issues:
3188  <list style="symbols"> 
3189    <t>
3190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
3191      "Clarify 'Requested Variant'"
3192    </t>
3193    <t>
3194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3195      "Content-Location isn't special"
3196    </t>
3197    <t>
3198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
3199      "Delimiting messages with multipart/byteranges"
3200    </t>
3201    <t>
3202      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
3203      "Clarify entity / representation / variant terminology"
3204    </t>
3205    <t>
3206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
3207      "confusing req. language for Content-Location"
3208    </t>
3209    <t>
3210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
3211      "Content-Location on 304 responses"
3212    </t>
3213  </list>
3214</t>
3215</section>
3216
3217</section>
3218
3219</back>
3220</rfc>
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