source: draft-ietf-httpbis/latest/p3-payload.xml @ 1642

Last change on this file since 1642 was 1642, checked in by julian.reschke@…, 8 years ago

Step 4 of p2/p3-merge (see #351)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 105.7 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='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 "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture             "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY abnf-extension           "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY acks                     "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY whitespace               "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY field-components         "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-etag              "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY http-date                "<xref target='Part2' x:rel='#http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45]>
46<?rfc toc="yes" ?>
47<?rfc symrefs="yes" ?>
48<?rfc sortrefs="yes" ?>
49<?rfc compact="yes"?>
50<?rfc subcompact="no" ?>
51<?rfc linkmailto="no" ?>
52<?rfc editing="no" ?>
53<?rfc comments="yes"?>
54<?rfc inline="yes"?>
55<?rfc rfcedstyle="yes"?>
56<?rfc-ext allow-markup-in-artwork="yes" ?>
57<?rfc-ext include-references-in-index="yes" ?>
58<rfc obsoletes="2616" category="std" x:maturity-level="proposed"
59     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
60     xmlns:x='http://purl.org/net/xml2rfc/ext'>
61<x:link rel="prev" basename="p2-semantics"/>
62<x:link rel="next" basename="p4-conditional"/>
63<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
64<front>
65
66  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
67
68  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
69    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
70    <address>
71      <postal>
72        <street>345 Park Ave</street>
73        <city>San Jose</city>
74        <region>CA</region>
75        <code>95110</code>
76        <country>USA</country>
77      </postal>
78      <email>fielding@gbiv.com</email>
79      <uri>http://roy.gbiv.com/</uri>
80    </address>
81  </author>
82
83  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
84    <organization abbrev="W3C">World Wide Web Consortium</organization>
85    <address>
86      <postal>
87        <street>W3C / ERCIM</street>
88        <street>2004, rte des Lucioles</street>
89        <city>Sophia-Antipolis</city>
90        <region>AM</region>
91        <code>06902</code>
92        <country>France</country>
93      </postal>
94      <email>ylafon@w3.org</email>
95      <uri>http://www.raubacapeu.net/people/yves/</uri>
96    </address>
97  </author>
98
99  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
100    <organization abbrev="greenbytes">greenbytes GmbH</organization>
101    <address>
102      <postal>
103        <street>Hafenweg 16</street>
104        <city>Muenster</city><region>NW</region><code>48155</code>
105        <country>Germany</country>
106      </postal>
107      <phone>+49 251 2807760</phone>
108      <facsimile>+49 251 2807761</facsimile>
109      <email>julian.reschke@greenbytes.de</email>
110      <uri>http://greenbytes.de/tech/webdav/</uri>
111    </address>
112  </author>
113
114  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
115  <workgroup>HTTPbis Working Group</workgroup>
116
117<abstract>
118<t>
119  This part is now obsolete. Please see HTTPbis, Part 2.
120</t>
121</abstract>
122</front>
123<middle>
124<section title="Introduction" anchor="introduction">
125<t>
126  This part is now obsolete. Please see HTTPbis, Part 2.
127</t>
128
129<section title="Syntax Notation" anchor="notation">
130  <x:anchor-alias value="ALPHA"/>
131  <x:anchor-alias value="CR"/>
132  <x:anchor-alias value="DIGIT"/>
133  <x:anchor-alias value="LF"/>
134  <x:anchor-alias value="OCTET"/>
135  <x:anchor-alias value="VCHAR"/>
136
137<section title="Core Rules" anchor="core.rules">
138  <x:anchor-alias value="token"/>
139  <x:anchor-alias value="word"/>
140  <x:anchor-alias value="OWS"/>
141</section>
142
143<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
144  <x:anchor-alias value="absolute-URI"/>
145  <x:anchor-alias value="partial-URI"/>
146  <x:anchor-alias value="qvalue"/>
147</section>
148
149</section>
150
151</section>
152
153<section title="Protocol Parameters" anchor="protocol.parameters">
154
155<section title="Character Encodings (charset)" anchor="character.sets">
156<t>
157   HTTP uses charset names to indicate the character encoding of a
158   textual representation.
159</t>
160<t anchor="rule.charset">
161  <x:anchor-alias value="charset"/>
162   A character encoding is identified by a case-insensitive token. The
163   complete set of tokens is defined by the IANA Character Set registry
164   (<eref target="http://www.iana.org/assignments/character-sets"/>).
165</t>
166<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
167  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
168</artwork></figure>
169<t>
170   Although HTTP allows an arbitrary token to be used as a charset
171   value, any token that has a predefined value within the IANA
172   Character Set registry &MUST; represent the character encoding defined
173   by that registry. Applications &SHOULD; limit their use of character
174   encodings to those defined within the IANA registry.
175</t>
176<t>
177   HTTP uses charset in two contexts: within an Accept-Charset request
178   header field (in which the charset value is an unquoted token) and as the
179   value of a parameter in a Content-Type header field (within a request or
180   response), in which case the parameter value of the charset parameter
181   can be quoted.
182</t>
183<t>
184   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
185   <xref target="RFC2277"/>.
186</t>
187</section>
188
189<section title="Content Codings" anchor="content.codings">
190  <x:anchor-alias value="content-coding"/>
191<t>
192   Content coding values indicate an encoding transformation that has
193   been or can be applied to a representation. Content codings are primarily
194   used to allow a representation to be compressed or otherwise usefully
195   transformed without losing the identity of its underlying media type
196   and without loss of information. Frequently, the representation is stored in
197   coded form, transmitted directly, and only decoded by the recipient.
198</t>
199<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
200  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
201</artwork></figure>
202<t>
203   All content-coding values are case-insensitive. HTTP/1.1 uses
204   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
205   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
206   describes the content-coding, what is more important is that it
207   indicates what decoding mechanism will be required to remove the
208   encoding.
209</t>
210<t>
211   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
212  <list>
213    <t>
214      See &compress-coding;.
215    </t>
216  </list>
217</t>
218<t>
219   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
220  <list>
221    <t>
222      See &deflate-coding;.
223    </t>
224  </list>
225</t>
226<t>
227   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
228  <list>
229    <t>
230      See &gzip-coding;.
231    </t>
232  </list>
233</t>
234
235<section title="Content Coding Registry" anchor="content.coding.registry">
236<t>
237   The HTTP Content Coding Registry defines the name space for the content
238   coding names.
239</t>
240<t>
241   Registrations &MUST; include the following fields:
242   <list style="symbols">
243     <t>Name</t>
244     <t>Description</t>
245     <t>Pointer to specification text</t>
246   </list>
247</t>
248<t>
249   Names of content codings &MUST-NOT; overlap with names of transfer codings
250   (&transfer-codings;), unless the encoding transformation is identical (as
251   is the case for the compression codings defined in
252   &compression-codings;).
253</t>
254<t>
255   Values to be added to this name space require IETF Review
256   (see <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
257   conform to the purpose of content coding defined in this section.
258</t>
259<t>
260   The registry itself is maintained at
261   <eref target="http://www.iana.org/assignments/http-parameters"/>.
262</t>
263</section>
264
265</section>
266
267<section title="Media Types" anchor="media.types">
268  <x:anchor-alias value="media-type"/>
269  <x:anchor-alias value="type"/>
270  <x:anchor-alias value="subtype"/>
271<t>
272   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
273   and Accept (<xref target="header.accept"/>) header fields in order to provide
274   open and extensible data typing and type negotiation.
275</t>
276<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"/>
277  <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> )
278  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
279  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
280</artwork></figure>
281<t anchor="rule.parameter">
282  <x:anchor-alias value="attribute"/>
283  <x:anchor-alias value="parameter"/>
284  <x:anchor-alias value="value"/>
285   The type/subtype &MAY; be followed by parameters in the form of
286   attribute/value pairs.
287</t>
288<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"/>
289  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
290  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
291  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
292</artwork></figure>
293<t>
294   The type, subtype, and parameter attribute names are case-insensitive.
295   Parameter values might or might not be case-sensitive, depending on the
296   semantics of the parameter name.  The presence or absence of a parameter might
297   be significant to the processing of a media-type, depending on its
298   definition within the media type registry.
299</t>
300<t>
301   A parameter value that matches the <x:ref>token</x:ref> production can be
302   transmitted as either a token or within a quoted-string. The quoted and
303   unquoted values are equivalent.
304</t>
305<t>
306   Note that some older HTTP applications do not recognize media type
307   parameters. When sending data to older HTTP applications,
308   implementations &SHOULD; only use media type parameters when they are
309   required by that type/subtype definition.
310</t>
311<t>
312   Media-type values are registered with the Internet Assigned Number
313   Authority (IANA). The media type registration process is
314   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
315   discouraged.
316</t>
317
318<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
319<t>
320   Internet media types are registered with a canonical form. A
321   representation transferred via HTTP messages &MUST; be in the
322   appropriate canonical form prior to its transmission except for
323   "text" types, as defined in the next paragraph.
324</t>
325<t>
326   When in canonical form, media subtypes of the "text" type use CRLF as
327   the text line break. HTTP relaxes this requirement and allows the
328   transport of text media with plain CR or LF alone representing a line
329   break when it is done consistently for an entire representation. HTTP
330   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
331   a line break in text media received via HTTP. In
332   addition, if the text is in a character encoding that does not
333   use octets 13 and 10 for CR and LF respectively, as is the case for
334   some multi-byte character encodings, HTTP allows the use of whatever octet
335   sequences are defined by that character encoding to represent the
336   equivalent of CR and LF for line breaks. This flexibility regarding
337   line breaks applies only to text media in the payload body; a bare CR
338   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
339   structures (such as header fields and multipart boundaries).
340</t>
341<t>
342   If a representation is encoded with a content-coding, the underlying
343   data &MUST; be in a form defined above prior to being encoded.
344</t>
345</section>
346
347<section title="Multipart Types" anchor="multipart.types">
348<t>
349   MIME provides for a number of "multipart" types &mdash; encapsulations of
350   one or more representations within a single message body. All multipart
351   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
352   and &MUST; include a boundary parameter as part of the media type
353   value. The message body is itself a protocol element and &MUST;
354   therefore use only CRLF to represent line breaks between body-parts.
355</t>
356<t>
357   In general, HTTP treats a multipart message body no differently than
358   any other media type: strictly as payload.  HTTP does not use the
359   multipart boundary as an indicator of message body length.
360   <!-- jre: re-insert removed text pointing to caching? -->
361   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
362   behavior as a MIME user agent would upon receipt of a multipart type.
363   The MIME header fields within each body-part of a multipart message body
364   do not have any significance to HTTP beyond that defined by
365   their MIME semantics.
366</t>
367<t>
368   If an application receives an unrecognized multipart subtype, the
369   application &MUST; treat it as being equivalent to "multipart/mixed".
370</t>
371<x:note>
372  <t>
373    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
374    for carrying form data suitable for processing via the POST
375    request method, as described in <xref target="RFC2388"/>.
376  </t>
377</x:note>
378</section>
379</section>
380
381<section title="Language Tags" anchor="language.tags">
382  <x:anchor-alias value="language-tag"/>
383<t>
384   A language tag, as defined in <xref target="RFC5646"/>, identifies a
385   natural language spoken, written, or otherwise conveyed by human beings for
386   communication of information to other human beings. Computer languages are
387   explicitly excluded. HTTP uses language tags within the Accept-Language and
388   Content-Language fields.
389</t>
390<t>
391   In summary, a language tag is composed of one or more parts: A primary
392   language subtag followed by a possibly empty series of subtags:
393</t>
394<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
395  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
396</artwork></figure>
397<t>
398   White space is not allowed within the tag and all tags are case-insensitive.
399   The name space of language subtags is administered by the IANA (see
400   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
401</t>
402<figure>
403  <preamble>Example tags include:</preamble>
404<artwork type="example">
405  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
406</artwork>
407</figure>
408<t>
409   See <xref target="RFC5646"/> for further information.
410</t>
411</section>
412</section>
413
414<section title="Payload" anchor="payload">
415<t>
416   HTTP messages &MAY; transfer a payload if not otherwise restricted by
417   the request method or response status code.  The payload consists of
418   metadata, in the form of header fields, and data, in the form of the
419   sequence of octets in the message body after any transfer-coding has
420   been decoded.
421</t>
422<iref item="payload"/>
423<t>   
424   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
425   representation of some resource.  We use separate terms for payload
426   and representation because some messages contain only the associated
427   representation's header fields (e.g., responses to HEAD) or only some
428   part(s) of the representation (e.g., the 206 status code).
429</t>
430<section title="Payload Header Fields" anchor="payload.header.fields">
431  <x:anchor-alias value="payload-header"/>
432<t>
433   HTTP header fields that specifically define the payload, rather than the
434   associated representation, are referred to as "payload header fields".
435   The following payload header fields are defined by HTTP/1.1:
436</t>
437<texttable align="left">
438  <ttcol>Header Field Name</ttcol>
439  <ttcol>Defined in...</ttcol>
440
441  <c>Content-Length</c> <c>&header-content-length;</c>
442  <c>Content-Range</c> <c>&header-content-range;</c>
443</texttable>
444</section>
445
446<section title="Payload Body" anchor="payload.body">
447  <x:anchor-alias value="payload-body"/>
448<t>
449   A payload body is only present in a message when a message body is
450   present, as described in &message-body;. The payload body is obtained
451   from the message body by decoding any Transfer-Encoding that might
452   have been applied to ensure safe and proper transfer of the message.
453</t>
454</section>
455</section>
456
457<section title="Representation" anchor="representation">
458<iref item="representation"/>
459<t>
460   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
461   communicated from one party to another.  A resource representation
462   is information that reflects the state of that resource, as observed
463   at some point in the past (e.g., in a response to GET) or to be
464   desired at some point in the future (e.g., in a PUT request).
465</t>
466<t>
467   Most, but not all, representations transferred via HTTP are intended
468   to be a representation of the target resource (the resource identified
469   by the effective request URI).  The precise semantics of a representation
470   are determined by the type of message (request or response), the request
471   method, the response status code, and the representation metadata.
472   For example, the above semantic is true for the representation in any
473   200 (OK) response to GET and for the representation in any PUT request.
474   A 200 response to PUT, in contrast, contains either a representation
475   that describes the successful action or a representation of the target
476   resource, with the latter indicated by a Content-Location header field
477   with the same value as the effective request URI.  Likewise, response
478   messages with an error status code usually contain a representation that
479   describes the error and what next steps are suggested for resolving it.
480</t>
481
482<section title="Representation Header Fields" anchor="representation.header.fields">
483  <x:anchor-alias value="representation-header"/>
484<t>
485   Representation header fields define metadata about the representation data
486   enclosed in the message body or, if no message body is present, about
487   the representation that would have been transferred in a 200 response
488   to a simultaneous GET request with the same effective request URI.
489</t>
490<t>
491   The following header fields are defined as representation metadata:
492</t>
493<texttable align="left">
494  <ttcol>Header Field Name</ttcol>
495  <ttcol>Defined in...</ttcol>
496
497  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
498  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
499  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
500  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
501  <c>Expires</c> <c>&header-expires;</c>
502</texttable>
503<t>
504   Additional header fields define metadata about the selected
505   representation, which might differ from the representation included
506   in the message for responses to some state-changing methods.
507   The following header fields are defined as selected representation
508   metadata:
509</t>
510<texttable align="left">
511  <ttcol>Header Field Name</ttcol>
512  <ttcol>Defined in...</ttcol>
513
514  <c>ETag</c> <c>&header-etag;</c>
515  <c>Last-Modified</c> <c>&header-last-modified;</c>
516</texttable>
517</section>
518
519<section title="Representation Data" anchor="representation.data">
520  <x:anchor-alias value="representation-data"/>
521<t>
522   The representation body associated with an HTTP message is
523   either provided as the payload body of the message or
524   referred to by the message semantics and the effective request
525   URI.  The representation data is in a format and encoding defined by
526   the representation metadata header fields.
527</t>
528<t>
529   The data type of the representation data
530   is determined via the header fields Content-Type and Content-Encoding.
531   These define a two-layer, ordered encoding model:
532</t>
533<figure><artwork type="example">
534  representation-data := Content-Encoding( Content-Type( bits ) )
535</artwork></figure>
536<t>
537   Content-Type specifies the media type of the underlying data, which
538   defines both the data format and how that data &SHOULD; be processed
539   by the recipient (within the scope of the request method semantics).
540   Any HTTP/1.1 message containing a payload body &SHOULD; include a
541   Content-Type header field defining the media type of the associated
542   representation unless that metadata is unknown to the sender.
543   If the Content-Type header field is not present, it indicates that
544   the sender does not know the media type of the representation;
545   recipients &MAY; either assume that the media type is
546   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
547   or examine the content to determine its type.
548</t>
549<t>
550   In practice, resource owners do not always properly configure their origin
551   server to provide the correct Content-Type for a given representation,
552   with the result that some clients will examine a response body's content
553   and override the specified type.
554   Clients that do so risk drawing incorrect conclusions, which might expose
555   additional security risks (e.g., "privilege escalation").  Furthermore,
556   it is impossible to determine the sender's intent by examining the data
557   format: many data formats match multiple media types that differ only in
558   processing semantics.  Implementers are encouraged to provide a means of
559   disabling such "content sniffing" when it is used.
560</t>
561<t>
562   Content-Encoding is used to indicate any additional content
563   codings applied to the data, usually for the purpose of data
564   compression, that are a property of the representation.  If
565   Content-Encoding is not present, then there is no additional
566   encoding beyond that defined by the Content-Type.
567</t>
568</section>
569</section>
570
571<section title="Content Negotiation" anchor="content.negotiation">
572<t>
573   HTTP responses include a representation which contains information for
574   interpretation, whether by a human user or for further processing.
575   Often, the server has different ways of representing the
576   same information; for example, in different formats, languages,
577   or using different character encodings.
578</t>
579<t>
580   HTTP clients and their users might have different or variable
581   capabilities, characteristics or preferences which would influence
582   which representation, among those available from the server,
583   would be best for the server to deliver. For this reason, HTTP
584   provides mechanisms for "content negotiation" &mdash; a process of
585   allowing selection of a representation of a given resource,
586   when more than one is available.
587</t>
588<t>
589   This specification defines two patterns of content negotiation;
590   "server-driven", where the server selects the representation based
591   upon the client's stated preferences, and "agent-driven" negotiation,
592   where the server provides a list of representations for the client to
593   choose from, based upon their metadata. In addition,  there are
594   other patterns: some applications use an "active content" pattern,
595   where the server returns active content which runs on the client
596   and, based on client available parameters, selects additional
597   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
598   has also been proposed.
599</t>
600<t>
601   These patterns are all widely used, and have trade-offs in applicability
602   and practicality. In particular, when the number of preferences or
603   capabilities to be expressed by a client are large (such as when many
604   different formats are supported by a user-agent), server-driven
605   negotiation becomes unwieldy, and might not be appropriate. Conversely,
606   when the number of representations to choose from is very large,
607   agent-driven negotiation might not be appropriate.
608</t>
609<t>
610   Note that in all cases, the supplier of representations has the
611   responsibility for determining which representations might be
612   considered to be the "same information".
613</t>
614
615<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
616<t>
617   If the selection of the best representation for a response is made by
618   an algorithm located at the server, it is called server-driven
619   negotiation. Selection is based on the available representations of
620   the response (the dimensions over which it can vary; e.g., language,
621   content-coding, etc.) and the contents of particular header fields in
622   the request message or on other information pertaining to the request
623   (such as the network address of the client).
624</t>
625<t>
626   Server-driven negotiation is advantageous when the algorithm for
627   selecting from among the available representations is difficult to
628   describe to the user agent, or when the server desires to send its
629   "best guess" to the client along with the first response (hoping to
630   avoid the round-trip delay of a subsequent request if the "best
631   guess" is good enough for the user). In order to improve the server's
632   guess, the user agent &MAY; include request header fields (Accept,
633   Accept-Language, Accept-Encoding, etc.) which describe its
634   preferences for such a response.
635</t>
636<t>
637   Server-driven negotiation has disadvantages:
638  <list style="numbers">
639    <t>
640         It is impossible for the server to accurately determine what
641         might be "best" for any given user, since that would require
642         complete knowledge of both the capabilities of the user agent
643         and the intended use for the response (e.g., does the user want
644         to view it on screen or print it on paper?).
645    </t>
646    <t>
647         Having the user agent describe its capabilities in every
648         request can be both very inefficient (given that only a small
649         percentage of responses have multiple representations) and a
650         potential violation of the user's privacy.
651    </t>
652    <t>
653         It complicates the implementation of an origin server and the
654         algorithms for generating responses to a request.
655    </t>
656    <t>
657         It might limit a public cache's ability to use the same response
658         for multiple user's requests.
659    </t>
660  </list>
661</t>
662<t>
663   Server-driven negotiation allows the user agent to specify its preferences,
664   but it cannot expect responses to always honor them. For example, the origin
665   server might not implement server-driven negotiation, or it might decide that
666   sending a response that doesn't conform to them is better than sending a 406
667   (Not Acceptable) response.
668</t>
669<t>
670   Many of the mechanisms for expressing preferences use quality values to
671   declare relative preference. See &qvalue; for more information.
672</t>
673<t>
674   HTTP/1.1 includes the following header fields for enabling
675   server-driven negotiation through description of user agent
676   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
677   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
678   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
679   However, an origin server is not limited to these dimensions and &MAY; vary
680   the response based on any aspect of the request, including aspects
681   of the connection (e.g., IP address) or information within extension
682   header fields not defined by this specification.
683</t>
684<x:note>
685  <t>
686    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
687    because new clients might not be recognized.
688  </t>
689</x:note>
690<t>
691   The Vary header field (&header-vary;) can be used to express the parameters the
692   server uses to select a representation that is subject to server-driven
693   negotiation.
694</t>
695</section>
696
697<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
698<t>
699   With agent-driven negotiation, selection of the best representation
700   for a response is performed by the user agent after receiving an
701   initial response from the origin server. Selection is based on a list
702   of the available representations of the response included within the
703   header fields or body of the initial response, with each
704   representation identified by its own URI. Selection from among the
705   representations can be performed automatically (if the user agent is
706   capable of doing so) or manually by the user selecting from a
707   generated (possibly hypertext) menu.
708</t>
709<t>
710   Agent-driven negotiation is advantageous when the response would vary
711   over commonly-used dimensions (such as type, language, or encoding),
712   when the origin server is unable to determine a user agent's
713   capabilities from examining the request, and generally when public
714   caches are used to distribute server load and reduce network usage.
715</t>
716<t>
717   Agent-driven negotiation suffers from the disadvantage of needing a
718   second request to obtain the best alternate representation. This
719   second request is only efficient when caching is used. In addition,
720   this specification does not define any mechanism for supporting
721   automatic selection, though it also does not prevent any such
722   mechanism from being developed as an extension and used within
723   HTTP/1.1.
724</t>
725<t>
726   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
727   status codes for enabling agent-driven negotiation when the server is
728   unwilling or unable to provide a varying response using server-driven
729   negotiation.
730</t>
731</section>
732</section>
733
734<section title="Header Field Definitions" anchor="header.field.definitions">
735<t>
736   This section defines the syntax and semantics of HTTP/1.1 header fields
737   related to the payload of messages.
738</t>
739
740<section title="Accept" anchor="header.accept">
741  <iref primary="true" item="Accept header field" x:for-anchor=""/>
742  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
743  <x:anchor-alias value="Accept"/>
744  <x:anchor-alias value="accept-ext"/>
745  <x:anchor-alias value="accept-params"/>
746  <x:anchor-alias value="media-range"/>
747<t>
748   The "Accept" header field can be used by user agents to specify
749   response media types that are acceptable. Accept header fields can be used to
750   indicate that the request is specifically limited to a small set of desired
751   types, as in the case of a request for an in-line image.
752</t>
753<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
754  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
755 
756  <x:ref>media-range</x:ref>    = ( "*/*"
757                   / ( <x:ref>type</x:ref> "/" "*" )
758                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
759                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
760  <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> )
761  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
762</artwork></figure>
763<t>
764   The asterisk "*" character is used to group media types into ranges,
765   with "*/*" indicating all media types and "type/*" indicating all
766   subtypes of that type. The media-range &MAY; include media type
767   parameters that are applicable to that range.
768</t>
769<t>
770   Each media-range &MAY; be followed by one or more accept-params,
771   beginning with the "q" parameter for indicating a relative quality
772   factor. The first "q" parameter (if any) separates the media-range
773   parameter(s) from the accept-params. Quality factors allow the user
774   or user agent to indicate the relative degree of preference for that
775   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
776   default value is q=1.
777</t>
778<x:note>
779  <t>
780    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
781    parameters from Accept extension parameters is due to historical
782    practice. Although this prevents any media type parameter named
783    "q" from being used with a media range, such an event is believed
784    to be unlikely given the lack of any "q" parameters in the IANA
785    media type registry and the rare usage of any media type
786    parameters in Accept. Future media types are discouraged from
787    registering any parameter named "q".
788  </t>
789</x:note>
790<t>
791   The example
792</t>
793<figure><artwork type="example">
794  Accept: audio/*; q=0.2, audio/basic
795</artwork></figure>
796<t>
797   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
798   type if it is the best available after an 80% mark-down in quality".
799</t>
800<t>
801   A request without any Accept header field implies that the user agent
802   will accept any media type in response.
803   If an Accept header field is present in a request and none of the
804   available representations for the response have a media type that is
805   listed as acceptable, the origin server &MAY; either
806   honor the Accept header field by sending a 406 (Not Acceptable) response
807   or disregard the Accept header field by treating the response as if
808   it is not subject to content negotiation.
809</t>
810<t>
811   A more elaborate example is
812</t>
813<figure><artwork type="example">
814  Accept: text/plain; q=0.5, text/html,
815          text/x-dvi; q=0.8, text/x-c
816</artwork></figure>
817<t>
818   Verbally, this would be interpreted as "text/html and text/x-c are
819   the preferred media types, but if they do not exist, then send the
820   text/x-dvi representation, and if that does not exist, send the text/plain
821   representation".
822</t>
823<t>
824   Media ranges can be overridden by more specific media ranges or
825   specific media types. If more than one media range applies to a given
826   type, the most specific reference has precedence. For example,
827</t>
828<figure><artwork type="example">
829  Accept: text/*, text/plain, text/plain;format=flowed, */*
830</artwork></figure>
831<t>
832   have the following precedence:
833   <list style="numbers">
834    <t>text/plain;format=flowed</t>
835    <t>text/plain</t>
836    <t>text/*</t>
837    <t>*/*</t>
838   </list>
839</t>
840<t>
841   The media type quality factor associated with a given type is
842   determined by finding the media range with the highest precedence
843   which matches that type. For example,
844</t>
845<figure><artwork type="example">
846  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
847          text/html;level=2;q=0.4, */*;q=0.5
848</artwork></figure>
849<t>
850   would cause the following values to be associated:
851</t>
852<texttable align="left">
853  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
854  <c>text/html;level=1</c>    <c>1</c>
855  <c>text/html</c>            <c>0.7</c>
856  <c>text/plain</c>           <c>0.3</c>
857  <c>image/jpeg</c>           <c>0.5</c>
858  <c>text/html;level=2</c>    <c>0.4</c>
859  <c>text/html;level=3</c>    <c>0.7</c>
860</texttable>
861<t>
862      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
863      values for certain media ranges. However, unless the user agent is
864      a closed system which cannot interact with other rendering agents,
865      this default set ought to be configurable by the user.
866</t>
867</section>
868
869<section title="Accept-Charset" anchor="header.accept-charset">
870  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
871  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
872  <x:anchor-alias value="Accept-Charset"/>
873<t>
874   The "Accept-Charset" header field can be used by user agents to
875   indicate what character encodings are acceptable in a response
876   payload. This field allows
877   clients capable of understanding more comprehensive or special-purpose
878   character encodings to signal that capability to a server which is capable of
879   representing documents in those character encodings.
880</t>
881<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
882  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
883                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
884</artwork></figure>
885<t>
886   Character encoding values (a.k.a., charsets) are described in
887   <xref target="character.sets"/>. Each charset &MAY; be given an
888   associated quality value which represents the user's preference
889   for that charset. The default value is q=1. An example is
890</t>
891<figure><artwork type="example">
892  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
893</artwork></figure>
894<t>
895   The special value "*", if present in the Accept-Charset field,
896   matches every character encoding which is not mentioned elsewhere in the
897   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
898   all character encodings not explicitly mentioned get a quality value of 0.
899</t>
900<t>
901   A request without any Accept-Charset header field implies that the user
902   agent will accept any character encoding in response.
903   If an Accept-Charset header field is present in a request and none of the
904   available representations for the response have a character encoding that
905   is listed as acceptable, the origin server &MAY; either honor the
906   Accept-Charset header field by sending a 406 (Not Acceptable) response or
907   disregard the Accept-Charset header field by treating the response as if
908   it is not subject to content negotiation.
909</t>
910</section>
911
912<section title="Accept-Encoding" anchor="header.accept-encoding">
913  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
914  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
915  <x:anchor-alias value="Accept-Encoding"/>
916  <x:anchor-alias value="codings"/>
917<t>
918   The "Accept-Encoding" header field can be used by user agents to
919   indicate what response content-codings (<xref target="content.codings"/>)
920   are acceptable in the response.  An "identity" token is used as a synonym
921   for "no encoding" in order to communicate when no encoding is preferred.
922</t>
923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
924  <x:ref>Accept-Encoding</x:ref>  = #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
925  <x:ref>codings</x:ref>          = <x:ref>content-coding</x:ref> / "identity" / "*"
926</artwork></figure>
927<t>
928   Each codings value &MAY; be given an associated quality value which
929   represents the preference for that encoding. The default value is q=1.
930</t>
931<t>
932   For example,
933</t>
934<figure><artwork type="example">
935  Accept-Encoding: compress, gzip
936  Accept-Encoding:
937  Accept-Encoding: *
938  Accept-Encoding: compress;q=0.5, gzip;q=1.0
939  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
940</artwork></figure>
941<t>
942   A server tests whether a content-coding for a given representation is
943   acceptable, according to an Accept-Encoding field, using these rules:
944  <list style="numbers">
945      <t>The special "*" symbol in an Accept-Encoding field matches any
946         available content-coding not explicitly listed in the header
947         field.</t>
948
949      <t>If the representation has no content-coding, then it is acceptable
950         by default unless specifically excluded by the Accept-Encoding field
951         stating either "identity;q=0" or "*;q=0" without a more specific
952         entry for "identity".</t>
953
954      <t>If the representation's content-coding is one of the content-codings
955         listed in the Accept-Encoding field, then it is acceptable unless
956         it is accompanied by a qvalue of 0. (As defined in &qvalue;, a
957         qvalue of 0 means "not acceptable".)</t>
958
959      <t>If multiple content-codings are acceptable, then the acceptable
960         content-coding with the highest non-zero qvalue is preferred.</t>
961  </list>
962</t>
963<t>
964   An Accept-Encoding header field with a combined field-value that is empty
965   implies that the user agent does not want any content-coding in response.
966   If an Accept-Encoding header field is present in a request and none of the
967   available representations for the response have a content-coding that
968   is listed as acceptable, the origin server &SHOULD; send a response
969   without any content-coding.
970</t>
971<t>
972   A request without an Accept-Encoding header field implies that the user
973   agent will accept any content-coding in response, but a representation
974   without content-coding is preferred for compatibility with the widest
975   variety of user agents.
976</t>
977<x:note>
978  <t>
979    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
980    associated with content-codings. This means that qvalues will not
981    work and are not permitted with x-gzip or x-compress.
982  </t>
983</x:note>
984</section>
985
986<section title="Accept-Language" anchor="header.accept-language">
987  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
988  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
989  <x:anchor-alias value="Accept-Language"/>
990  <x:anchor-alias value="language-range"/>
991<t>
992   The "Accept-Language" header field can be used by user agents to
993   indicate the set of natural languages that are preferred in the response.
994   Language tags are defined in <xref target="language.tags"/>.
995</t>
996<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
997  <x:ref>Accept-Language</x:ref> =
998                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
999  <x:ref>language-range</x:ref>  =
1000            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1001</artwork></figure>
1002<t>
1003   Each language-range can be given an associated quality value which
1004   represents an estimate of the user's preference for the languages
1005   specified by that range. The quality value defaults to "q=1". For
1006   example,
1007</t>
1008<figure><artwork type="example">
1009  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1010</artwork></figure>
1011<t>
1012   would mean: "I prefer Danish, but will accept British English and
1013   other types of English".
1014   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1015</t>
1016<t>
1017   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1018   several matching schemes. Implementations can offer the most appropriate
1019   matching scheme for their requirements.
1020</t>
1021<x:note>
1022  <t>
1023    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1024    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1025    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1026  </t>
1027</x:note>
1028<t>
1029   It might be contrary to the privacy expectations of the user to send
1030   an Accept-Language header field with the complete linguistic preferences of
1031   the user in every request. For a discussion of this issue, see
1032   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1033</t>
1034<t>
1035   As intelligibility is highly dependent on the individual user, it is
1036   recommended that client applications make the choice of linguistic
1037   preference available to the user. If the choice is not made
1038   available, then the Accept-Language header field &MUST-NOT; be given in
1039   the request.
1040</t>
1041<x:note>
1042  <t>
1043    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1044    the user, we remind implementors of  the fact that users are not
1045    familiar with the details of language matching as described above,
1046    and ought to be provided appropriate guidance. As an example, users
1047    might assume that on selecting "en-gb", they will be served any
1048    kind of English document if British English is not available. A
1049    user agent might suggest in such a case to add "en" to get the
1050    best matching behavior.
1051  </t>
1052</x:note>
1053</section>
1054
1055<section title="Content-Encoding" anchor="header.content-encoding">
1056  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1057  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
1058  <x:anchor-alias value="Content-Encoding"/>
1059<t>
1060   The "Content-Encoding" header field indicates what content-codings
1061   have been applied to the representation beyond those inherent in the media
1062   type, and thus what decoding mechanisms have to be applied in order to obtain
1063   the media-type referenced by the Content-Type header field.
1064   Content-Encoding is primarily used to allow a representation to be
1065   compressed without losing the identity of its underlying media type.
1066</t>
1067<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1068  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
1069</artwork></figure>
1070<t>
1071   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1072</t>
1073<figure><artwork type="example">
1074  Content-Encoding: gzip
1075</artwork></figure>
1076<t>
1077   The content-coding is a characteristic of the representation.
1078   Typically, the representation body is stored with this
1079   encoding and is only decoded before rendering or analogous usage.
1080   However, a transforming proxy &MAY; modify the content-coding if the
1081   new coding is known to be acceptable to the recipient, unless the
1082   "no-transform" cache-control directive is present in the message.
1083</t>
1084<t>
1085   If the media type includes an inherent encoding, such as a data format
1086   that is always compressed, then that encoding would not be restated as
1087   a Content-Encoding even if it happens to be the same algorithm as one
1088   of the content-codings.  Such a content-coding would only be listed if,
1089   for some bizarre reason, it is applied a second time to form the
1090   representation.  Likewise, an origin server might choose to publish the
1091   same payload data as multiple representations that differ only in whether
1092   the coding is defined as part of Content-Type or Content-Encoding, since
1093   some user agents will behave differently in their handling of each
1094   response (e.g., open a "Save as ..." dialog instead of automatic
1095   decompression and rendering of content).
1096</t>
1097<t>
1098   A representation that has a content-coding applied to it &MUST; include
1099   a Content-Encoding header field (<xref target="header.content-encoding"/>)
1100   that lists the content-coding(s) applied.
1101</t>
1102<t>
1103   If multiple encodings have been applied to a representation, the content
1104   codings &MUST; be listed in the order in which they were applied.
1105   Additional information about the encoding parameters &MAY; be provided
1106   by other header fields not defined by this specification.
1107</t>
1108<t>
1109   If the content-coding of a representation in a request message is not
1110   acceptable to the origin server, the server &SHOULD; respond with a
1111   status code of 415 (Unsupported Media Type).
1112</t>
1113</section>
1114
1115<section title="Content-Language" anchor="header.content-language">
1116  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1117  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
1118  <x:anchor-alias value="Content-Language"/>
1119<t>
1120   The "Content-Language" header field describes the natural
1121   language(s) of the intended audience for the representation. Note that this might
1122   not be equivalent to all the languages used within the representation.
1123</t>
1124<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1125  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
1126</artwork></figure>
1127<t>
1128   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1129   Content-Language is to allow a user to identify and differentiate
1130   representations according to the user's own preferred language. Thus, if the
1131   body content is intended only for a Danish-literate audience, the
1132   appropriate field is
1133</t>
1134<figure><artwork type="example">
1135  Content-Language: da
1136</artwork></figure>
1137<t>
1138   If no Content-Language is specified, the default is that the content
1139   is intended for all language audiences. This might mean that the
1140   sender does not consider it to be specific to any natural language,
1141   or that the sender does not know for which language it is intended.
1142</t>
1143<t>
1144   Multiple languages &MAY; be listed for content that is intended for
1145   multiple audiences. For example, a rendition of the "Treaty of
1146   Waitangi", presented simultaneously in the original Maori and English
1147   versions, would call for
1148</t>
1149<figure><artwork type="example">
1150  Content-Language: mi, en
1151</artwork></figure>
1152<t>
1153   However, just because multiple languages are present within a representation
1154   does not mean that it is intended for multiple linguistic audiences.
1155   An example would be a beginner's language primer, such as "A First
1156   Lesson in Latin", which is clearly intended to be used by an
1157   English-literate audience. In this case, the Content-Language would
1158   properly only include "en".
1159</t>
1160<t>
1161   Content-Language &MAY; be applied to any media type &mdash; it is not
1162   limited to textual documents.
1163</t>
1164</section>
1165
1166<section title="Content-Location" anchor="header.content-location">
1167  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1168  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
1169  <x:anchor-alias value="Content-Location"/>
1170<t>
1171   The "Content-Location" header field supplies a URI that can be used
1172   as a specific identifier for the representation in this message.
1173   In other words, if one were to perform a GET on this URI at the time
1174   of this message's generation, then a 200 response would contain the
1175   same representation that is enclosed as payload in this message.
1176</t>
1177<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1178  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1179</artwork></figure>
1180<t>
1181   The Content-Location value is not a replacement for the effective
1182   Request URI (&effective-request-uri;).  It is representation metadata.
1183   It has the same syntax and semantics as the header field of the same name
1184   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1185   However, its appearance in an HTTP message has some special implications
1186   for HTTP recipients.
1187</t>
1188<t>
1189   If Content-Location is included in a response message and its value
1190   is the same as the effective request URI, then the response payload
1191   &SHOULD; be considered a current representation of that resource.
1192   For a GET or HEAD request, this is the same as the default semantics
1193   when no Content-Location is provided by the server.  For a state-changing
1194   request like PUT or POST, it implies that the server's response contains
1195   the new representation of that resource, thereby distinguishing it from
1196   representations that might only report about the action (e.g., "It worked!").
1197   This allows authoring applications to update their local copies without
1198   the need for a subsequent GET request.
1199</t>
1200<t>
1201   If Content-Location is included in a response message and its value
1202   differs from the effective request URI, then the origin server is
1203   informing recipients that this representation has its own, presumably
1204   more specific, identifier.  For a GET or HEAD request, this is an
1205   indication that the effective request URI identifies a resource that
1206   is subject to content negotiation and the selected representation for
1207   this response can also be found at the identified URI.  For other
1208   methods, such a Content-Location indicates that this representation
1209   contains a report on the action's status and the same report is
1210   available (for future access with GET) at the given URI.  For
1211   example, a purchase transaction made via a POST request might
1212   include a receipt document as the payload of the 200 response;
1213   the Content-Location value provides an identifier for retrieving
1214   a copy of that same receipt in the future.
1215</t>
1216<t>
1217   If Content-Location is included in a request message, then it &MAY;
1218   be interpreted by the origin server as an indication of where the
1219   user agent originally obtained the content of the enclosed
1220   representation (prior to any subsequent modification of the content
1221   by that user agent).  In other words, the user agent is providing
1222   the same representation metadata that it received with the original
1223   representation.  However, such interpretation &MUST-NOT; be used to
1224   alter the semantics of the method requested by the client.  For
1225   example, if a client makes a PUT request on a negotiated resource
1226   and the origin server accepts that PUT (without redirection), then the
1227   new set of values for that resource is expected to be consistent with
1228   the one representation supplied in that PUT; the Content-Location
1229   cannot be used as a form of reverse content selection that
1230   identifies only one of the negotiated representations to be updated.
1231   If the user agent had wanted the latter semantics, it would have applied
1232   the PUT directly to the Content-Location URI.
1233</t>
1234<t>
1235   A Content-Location field received in a request message is transitory
1236   information that &SHOULD-NOT; be saved with other representation
1237   metadata for use in later responses.  The Content-Location's value
1238   might be saved for use in other contexts, such as within source links
1239   or other metadata.
1240</t>
1241<t>
1242   A cache cannot assume that a representation with a Content-Location
1243   different from the URI used to retrieve it can be used to respond to
1244   later requests on that Content-Location URI.
1245</t>
1246<t>
1247   If the Content-Location value is a partial URI, the partial URI is
1248   interpreted relative to the effective request URI.
1249</t>
1250</section>
1251
1252<section title="Content-Type" anchor="header.content-type">
1253  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1254  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
1255  <x:anchor-alias value="Content-Type"/>
1256<t>
1257   The "Content-Type" header field indicates the media type of the
1258   representation. In the case of responses to the HEAD method, the media type is
1259   that which would have been sent had the request been a GET.
1260</t>
1261<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1262  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
1263</artwork></figure>
1264<t>
1265   Media types are defined in <xref target="media.types"/>. An example of the field is
1266</t>
1267<figure><artwork type="example">
1268  Content-Type: text/html; charset=ISO-8859-4
1269</artwork></figure>
1270<t>
1271   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1272</t>
1273</section>
1274
1275</section>
1276
1277<section title="IANA Considerations" anchor="IANA.considerations">
1278
1279<section title="Content Coding Registry" anchor="content.coding.registration">
1280<t>
1281   The registration procedure for HTTP Content Codings is now defined
1282   by <xref target="content.coding.registry"/> of this document.
1283</t>
1284<t>
1285   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1286   shall be updated with the registration below:
1287</t>
1288<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1289   <ttcol>Name</ttcol>
1290   <ttcol>Description</ttcol>
1291   <ttcol>Reference</ttcol>
1292   <c>compress</c>
1293   <c>UNIX "compress" program method</c>
1294   <c>
1295      &compress-coding;
1296   </c>
1297   <c>deflate</c>
1298   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1299   the "zlib" data format (<xref target="RFC1950"/>)
1300   </c>
1301   <c>
1302      &deflate-coding;
1303   </c>
1304   <c>gzip</c>
1305   <c>Same as GNU zip <xref target="RFC1952"/></c>
1306   <c>
1307      &gzip-coding;
1308   </c>
1309   <c>identity</c>
1310   <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
1311   <c>
1312      <xref target="header.accept-encoding"/>
1313   </c>
1314</texttable>
1315</section>
1316
1317</section>
1318
1319<section title="Security Considerations" anchor="security.considerations">
1320<t>
1321   This section is meant to inform application developers, information
1322   providers, and users of the security limitations in HTTP/1.1 as
1323   described by this document. The discussion does not include
1324   definitive solutions to the problems revealed, though it does make
1325   some suggestions for reducing security risks.
1326</t>
1327
1328<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1329<t>
1330   Accept header fields can reveal information about the user to all
1331   servers which are accessed. The Accept-Language header field in particular
1332   can reveal information the user would consider to be of a private
1333   nature, because the understanding of particular languages is often
1334   strongly correlated to the membership of a particular ethnic group.
1335   User agents which offer the option to configure the contents of an
1336   Accept-Language header field to be sent in every request are strongly
1337   encouraged to let the configuration process include a message which
1338   makes the user aware of the loss of privacy involved.
1339</t>
1340<t>
1341   An approach that limits the loss of privacy would be for a user agent
1342   to omit the sending of Accept-Language header fields by default, and to ask
1343   the user whether or not to start sending Accept-Language header fields to a
1344   server if it detects, by looking for any Vary header fields
1345   generated by the server, that such sending could improve the quality
1346   of service.
1347</t>
1348<t>
1349   Elaborate user-customized accept header fields sent in every request,
1350   in particular if these include quality values, can be used by servers
1351   as relatively reliable and long-lived user identifiers. Such user
1352   identifiers would allow content providers to do click-trail tracking,
1353   and would allow collaborating content providers to match cross-server
1354   click-trails or form submissions of individual users. Note that for
1355   many users not behind a proxy, the network address of the host
1356   running the user agent will also serve as a long-lived user
1357   identifier. In environments where proxies are used to enhance
1358   privacy, user agents ought to be conservative in offering accept
1359   header configuration options to end users. As an extreme privacy
1360   measure, proxies could filter the accept header fields in relayed requests.
1361   General purpose user agents which provide a high degree of header
1362   configurability &SHOULD; warn users about the loss of privacy which can
1363   be involved.
1364</t>
1365</section>
1366
1367</section>
1368
1369</middle>
1370<back>
1371
1372<references title="Normative References">
1373
1374<reference anchor="Part1">
1375  <front>
1376    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1377    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1378      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1379      <address><email>fielding@gbiv.com</email></address>
1380    </author>
1381    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1382      <organization abbrev="W3C">World Wide Web Consortium</organization>
1383      <address><email>ylafon@w3.org</email></address>
1384    </author>
1385    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1386      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1387      <address><email>julian.reschke@greenbytes.de</email></address>
1388    </author>
1389    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1390  </front>
1391  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1392  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1393</reference>
1394
1395<reference anchor="Part2">
1396  <front>
1397    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1398    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1399      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1400      <address><email>fielding@gbiv.com</email></address>
1401    </author>
1402    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1403      <organization abbrev="W3C">World Wide Web Consortium</organization>
1404      <address><email>ylafon@w3.org</email></address>
1405    </author>
1406    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1407      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1408      <address><email>julian.reschke@greenbytes.de</email></address>
1409    </author>
1410    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1411  </front>
1412  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1413  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1414</reference>
1415
1416<reference anchor="Part4">
1417  <front>
1418    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1419    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1420      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1421      <address><email>fielding@gbiv.com</email></address>
1422    </author>
1423    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1424      <organization abbrev="W3C">World Wide Web Consortium</organization>
1425      <address><email>ylafon@w3.org</email></address>
1426    </author>
1427    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1428      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1429      <address><email>julian.reschke@greenbytes.de</email></address>
1430    </author>
1431    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1432  </front>
1433  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1434  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1435</reference>
1436
1437<reference anchor="Part5">
1438  <front>
1439    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1440    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1441      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1442      <address><email>fielding@gbiv.com</email></address>
1443    </author>
1444    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1445      <organization abbrev="W3C">World Wide Web Consortium</organization>
1446      <address><email>ylafon@w3.org</email></address>
1447    </author>
1448    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1449      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1450      <address><email>julian.reschke@greenbytes.de</email></address>
1451    </author>
1452    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1453  </front>
1454  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1455  <x:source href="p5-range.xml" basename="p5-range"/>
1456</reference>
1457
1458<reference anchor="Part6">
1459  <front>
1460    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1461    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1462      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1463      <address><email>fielding@gbiv.com</email></address>
1464    </author>
1465    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1466      <organization abbrev="W3C">World Wide Web Consortium</organization>
1467      <address><email>ylafon@w3.org</email></address>
1468    </author>
1469    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1470      <organization>Rackspace</organization>
1471      <address><email>mnot@mnot.net</email></address>
1472    </author>
1473    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1474      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1475      <address><email>julian.reschke@greenbytes.de</email></address>
1476    </author>
1477    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1478  </front>
1479  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1480  <x:source href="p6-cache.xml" basename="p6-cache"/>
1481</reference>
1482
1483<reference anchor="RFC1950">
1484  <front>
1485    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1486    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1487      <organization>Aladdin Enterprises</organization>
1488      <address><email>ghost@aladdin.com</email></address>
1489    </author>
1490    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1491    <date month="May" year="1996"/>
1492  </front>
1493  <seriesInfo name="RFC" value="1950"/>
1494  <!--<annotation>
1495    RFC 1950 is an Informational RFC, thus it might be less stable than
1496    this specification. On the other hand, this downward reference was
1497    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1498    therefore it is unlikely to cause problems in practice. See also
1499    <xref target="BCP97"/>.
1500  </annotation>-->
1501</reference>
1502
1503<reference anchor="RFC1951">
1504  <front>
1505    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1506    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1507      <organization>Aladdin Enterprises</organization>
1508      <address><email>ghost@aladdin.com</email></address>
1509    </author>
1510    <date month="May" year="1996"/>
1511  </front>
1512  <seriesInfo name="RFC" value="1951"/>
1513  <!--<annotation>
1514    RFC 1951 is an Informational RFC, thus it might be less stable than
1515    this specification. On the other hand, this downward reference was
1516    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1517    therefore it is unlikely to cause problems in practice. See also
1518    <xref target="BCP97"/>.
1519  </annotation>-->
1520</reference>
1521
1522<reference anchor="RFC1952">
1523  <front>
1524    <title>GZIP file format specification version 4.3</title>
1525    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1526      <organization>Aladdin Enterprises</organization>
1527      <address><email>ghost@aladdin.com</email></address>
1528    </author>
1529    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1530      <address><email>gzip@prep.ai.mit.edu</email></address>
1531    </author>
1532    <author initials="M." surname="Adler" fullname="Mark Adler">
1533      <address><email>madler@alumni.caltech.edu</email></address>
1534    </author>
1535    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1536      <address><email>ghost@aladdin.com</email></address>
1537    </author>
1538    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1539      <address><email>randeg@alumni.rpi.edu</email></address>
1540    </author>
1541    <date month="May" year="1996"/>
1542  </front>
1543  <seriesInfo name="RFC" value="1952"/>
1544  <!--<annotation>
1545    RFC 1952 is an Informational RFC, thus it might be less stable than
1546    this specification. On the other hand, this downward reference was
1547    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1548    therefore it is unlikely to cause problems in practice. See also
1549    <xref target="BCP97"/>.
1550  </annotation>-->
1551</reference>
1552
1553<reference anchor="RFC2045">
1554  <front>
1555    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1556    <author initials="N." surname="Freed" fullname="Ned Freed">
1557      <organization>Innosoft International, Inc.</organization>
1558      <address><email>ned@innosoft.com</email></address>
1559    </author>
1560    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1561      <organization>First Virtual Holdings</organization>
1562      <address><email>nsb@nsb.fv.com</email></address>
1563    </author>
1564    <date month="November" year="1996"/>
1565  </front>
1566  <seriesInfo name="RFC" value="2045"/>
1567</reference>
1568
1569<reference anchor="RFC2046">
1570  <front>
1571    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1572    <author initials="N." surname="Freed" fullname="Ned Freed">
1573      <organization>Innosoft International, Inc.</organization>
1574      <address><email>ned@innosoft.com</email></address>
1575    </author>
1576    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1577      <organization>First Virtual Holdings</organization>
1578      <address><email>nsb@nsb.fv.com</email></address>
1579    </author>
1580    <date month="November" year="1996"/>
1581  </front>
1582  <seriesInfo name="RFC" value="2046"/>
1583</reference>
1584
1585<reference anchor='RFC4647'>
1586  <front>
1587    <title>Matching of Language Tags</title>
1588    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
1589      <organization>Yahoo! Inc.</organization>
1590      <address><email>addison@inter-locale.com</email></address>
1591    </author>
1592    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
1593      <organization>Google</organization>
1594      <address><email>mark.davis@macchiato.com</email></address>
1595    </author>
1596    <date year='2006' month='September' />
1597  </front>
1598  <seriesInfo name='BCP' value='47' />
1599  <seriesInfo name='RFC' value='4647' />
1600</reference>
1601
1602<reference anchor='RFC5646'>
1603  <front>
1604    <title>Tags for Identifying Languages</title>
1605    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
1606      <organization>Lab126</organization>
1607      <address><email>addison@inter-locale.com</email></address>
1608    </author>
1609    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
1610      <organization>Google</organization>
1611      <address><email>mark.davis@google.com</email></address>
1612    </author>
1613    <date month='September' year='2009' />
1614  </front>
1615  <seriesInfo name='BCP' value='47' />
1616  <seriesInfo name='RFC' value='5646' />
1617</reference>
1618
1619</references>
1620
1621<references title="Informative References">
1622
1623<reference anchor="RFC1945">
1624  <front>
1625    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
1626    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1627      <organization>MIT, Laboratory for Computer Science</organization>
1628      <address><email>timbl@w3.org</email></address>
1629    </author>
1630    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
1631      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1632      <address><email>fielding@ics.uci.edu</email></address>
1633    </author>
1634    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1635      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
1636      <address><email>frystyk@w3.org</email></address>
1637    </author>
1638    <date month="May" year="1996"/>
1639  </front>
1640  <seriesInfo name="RFC" value="1945"/>
1641</reference>
1642
1643<reference anchor="RFC2049">
1644  <front>
1645    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
1646    <author initials="N." surname="Freed" fullname="Ned Freed">
1647      <organization>Innosoft International, Inc.</organization>
1648      <address><email>ned@innosoft.com</email></address>
1649    </author>
1650    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1651      <organization>First Virtual Holdings</organization>
1652      <address><email>nsb@nsb.fv.com</email></address>
1653    </author>
1654    <date month="November" year="1996"/>
1655  </front>
1656  <seriesInfo name="RFC" value="2049"/>
1657</reference>
1658
1659<reference anchor="RFC2068">
1660  <front>
1661    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
1662    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
1663      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1664      <address><email>fielding@ics.uci.edu</email></address>
1665    </author>
1666    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1667      <organization>MIT Laboratory for Computer Science</organization>
1668      <address><email>jg@w3.org</email></address>
1669    </author>
1670    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1671      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
1672      <address><email>mogul@wrl.dec.com</email></address>
1673    </author>
1674    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1675      <organization>MIT Laboratory for Computer Science</organization>
1676      <address><email>frystyk@w3.org</email></address>
1677    </author>
1678    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1679      <organization>MIT Laboratory for Computer Science</organization>
1680      <address><email>timbl@w3.org</email></address>
1681    </author>
1682    <date month="January" year="1997"/>
1683  </front>
1684  <seriesInfo name="RFC" value="2068"/>
1685</reference>
1686
1687<reference anchor="RFC2076">
1688  <front>
1689    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
1690    <author initials="J." surname="Palme" fullname="Jacob Palme">
1691      <organization>Stockholm University/KTH</organization>
1692      <address><email>jpalme@dsv.su.se</email></address>
1693    </author>
1694    <date month="February" year="1997"/>
1695  </front>
1696  <seriesInfo name="RFC" value="2076"/>
1697</reference>
1698
1699<reference anchor="RFC2277">
1700  <front>
1701    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
1702    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1703      <organization>UNINETT</organization>
1704      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1705    </author>
1706    <date month="January" year="1998"/>
1707  </front>
1708  <seriesInfo name="BCP" value="18"/>
1709  <seriesInfo name="RFC" value="2277"/>
1710</reference>
1711
1712<reference anchor='RFC2295'>
1713  <front>
1714    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
1715    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
1716      <organization>Technische Universiteit Eindhoven</organization>
1717      <address>
1718        <email>koen@win.tue.nl</email>
1719      </address>
1720    </author>
1721    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
1722      <organization>Hewlett-Packard Company</organization>
1723      <address>
1724        <email>mutz@hpl.hp.com</email>
1725      </address>
1726    </author>
1727    <date year='1998' month='March'/>
1728  </front>
1729  <seriesInfo name='RFC' value='2295'/>
1730</reference>
1731
1732<reference anchor="RFC2388">
1733  <front>
1734    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
1735    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1736      <organization>Xerox Palo Alto Research Center</organization>
1737      <address><email>masinter@parc.xerox.com</email></address>
1738    </author>
1739    <date year="1998" month="August"/>
1740  </front>
1741  <seriesInfo name="RFC" value="2388"/>
1742</reference>
1743
1744<reference anchor="RFC2557">
1745  <front>
1746    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
1747    <author initials="F." surname="Palme" fullname="Jacob Palme">
1748      <organization>Stockholm University and KTH</organization>
1749      <address><email>jpalme@dsv.su.se</email></address>
1750    </author>
1751    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
1752      <organization>Microsoft Corporation</organization>
1753      <address><email>alexhop@microsoft.com</email></address>
1754    </author>
1755    <author initials="N." surname="Shelness" fullname="Nick Shelness">
1756      <organization>Lotus Development Corporation</organization>
1757      <address><email>Shelness@lotus.com</email></address>
1758    </author>
1759    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
1760      <address><email>stef@nma.com</email></address>
1761    </author>
1762    <date year="1999" month="March"/>
1763  </front>
1764  <seriesInfo name="RFC" value="2557"/>
1765</reference>
1766
1767<reference anchor="RFC2616">
1768  <front>
1769    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1770    <author initials="R." surname="Fielding" fullname="R. Fielding">
1771      <organization>University of California, Irvine</organization>
1772      <address><email>fielding@ics.uci.edu</email></address>
1773    </author>
1774    <author initials="J." surname="Gettys" fullname="J. Gettys">
1775      <organization>W3C</organization>
1776      <address><email>jg@w3.org</email></address>
1777    </author>
1778    <author initials="J." surname="Mogul" fullname="J. Mogul">
1779      <organization>Compaq Computer Corporation</organization>
1780      <address><email>mogul@wrl.dec.com</email></address>
1781    </author>
1782    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1783      <organization>MIT Laboratory for Computer Science</organization>
1784      <address><email>frystyk@w3.org</email></address>
1785    </author>
1786    <author initials="L." surname="Masinter" fullname="L. Masinter">
1787      <organization>Xerox Corporation</organization>
1788      <address><email>masinter@parc.xerox.com</email></address>
1789    </author>
1790    <author initials="P." surname="Leach" fullname="P. Leach">
1791      <organization>Microsoft Corporation</organization>
1792      <address><email>paulle@microsoft.com</email></address>
1793    </author>
1794    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1795      <organization>W3C</organization>
1796      <address><email>timbl@w3.org</email></address>
1797    </author>
1798    <date month="June" year="1999"/>
1799  </front>
1800  <seriesInfo name="RFC" value="2616"/>
1801</reference>
1802
1803<reference anchor="RFC3629">
1804  <front>
1805    <title>UTF-8, a transformation format of ISO 10646</title>
1806    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
1807      <organization>Alis Technologies</organization>
1808      <address><email>fyergeau@alis.com</email></address>
1809    </author>
1810    <date month="November" year="2003"/>
1811  </front>
1812  <seriesInfo name="STD" value="63"/>
1813  <seriesInfo name="RFC" value="3629"/>
1814</reference>
1815
1816<reference anchor="RFC4288">
1817  <front>
1818    <title>Media Type Specifications and Registration Procedures</title>
1819    <author initials="N." surname="Freed" fullname="N. Freed">
1820      <organization>Sun Microsystems</organization>
1821      <address>
1822        <email>ned.freed@mrochek.com</email>
1823      </address>
1824    </author>
1825    <author initials="J." surname="Klensin" fullname="J. Klensin">
1826      <address>
1827        <email>klensin+ietf@jck.com</email>
1828      </address>
1829    </author>
1830    <date year="2005" month="December"/>
1831  </front>
1832  <seriesInfo name="BCP" value="13"/>
1833  <seriesInfo name="RFC" value="4288"/>
1834</reference>
1835
1836<reference anchor='RFC5226'>
1837  <front>
1838    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
1839    <author initials='T.' surname='Narten' fullname='T. Narten'>
1840      <organization>IBM</organization>
1841      <address><email>narten@us.ibm.com</email></address>
1842    </author>
1843    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
1844      <organization>Google</organization>
1845      <address><email>Harald@Alvestrand.no</email></address>
1846    </author>
1847    <date year='2008' month='May' />
1848  </front>
1849  <seriesInfo name='BCP' value='26' />
1850  <seriesInfo name='RFC' value='5226' />
1851</reference>
1852
1853<reference anchor="RFC5322">
1854  <front>
1855    <title>Internet Message Format</title>
1856    <author initials="P." surname="Resnick" fullname="P. Resnick">
1857      <organization>Qualcomm Incorporated</organization>
1858    </author>
1859    <date year="2008" month="October"/>
1860  </front> 
1861  <seriesInfo name="RFC" value="5322"/>
1862</reference>
1863
1864<reference anchor="RFC6151">
1865  <front>
1866    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
1867    <author initials="S." surname="Turner" fullname="S. Turner"/>
1868    <author initials="L." surname="Chen" fullname="L. Chen"/>
1869    <date year="2011" month="March" />
1870  </front>
1871  <seriesInfo name="RFC" value="6151" />
1872</reference>
1873
1874<!--<reference anchor='BCP97'>
1875  <front>
1876    <title>Handling Normative References to Standards-Track Documents</title>
1877    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
1878      <address>
1879        <email>klensin+ietf@jck.com</email>
1880      </address>
1881    </author>
1882    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
1883      <organization>MIT</organization>
1884      <address>
1885        <email>hartmans-ietf@mit.edu</email>
1886      </address>
1887    </author>
1888    <date year='2007' month='June' />
1889  </front>
1890  <seriesInfo name='BCP' value='97' />
1891  <seriesInfo name='RFC' value='4897' />
1892</reference>-->
1893
1894<reference anchor="RFC6266">
1895  <front>
1896    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
1897    in the Hypertext Transfer Protocol (HTTP)</title>
1898    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
1899      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1900      <address>
1901        <email>julian.reschke@greenbytes.de</email>
1902      </address>
1903    </author>
1904    <date month="June" year="2011"/>
1905  </front>
1906  <seriesInfo name='RFC' value='6266' />
1907</reference>
1908
1909</references>
1910
1911<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
1912<t>
1913   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
1914   allow a message body to be transmitted in an open variety of
1915   representations and with extensible mechanisms. However, RFC 2045
1916   discusses mail, and HTTP has a few features that are different from
1917   those described in MIME. These differences were carefully chosen
1918   to optimize performance over binary connections, to allow greater
1919   freedom in the use of new media types, to make date comparisons
1920   easier, and to acknowledge the practice of some early HTTP servers
1921   and clients.
1922</t>
1923<t>
1924   This appendix describes specific areas where HTTP differs from MIME.
1925   Proxies and gateways to strict MIME environments &SHOULD; be
1926   aware of these differences and provide the appropriate conversions
1927   where necessary. Proxies and gateways from MIME environments to HTTP
1928   also need to be aware of the differences because some conversions
1929   might be required.
1930</t>
1931
1932<section title="MIME-Version" anchor="mime-version">
1933  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
1934  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
1935  <x:anchor-alias value="MIME-Version"/>
1936<t>
1937   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
1938   include a single MIME-Version header field to indicate what
1939   version of the MIME protocol was used to construct the message. Use
1940   of the MIME-Version header field indicates that the message is in
1941   full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
1942   Proxies/gateways are responsible for ensuring full conformance (where
1943   possible) when exporting HTTP messages to strict MIME environments.
1944</t>
1945<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
1946  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
1947</artwork></figure>
1948<t>
1949   MIME version "1.0" is the default for use in HTTP/1.1. However,
1950   HTTP/1.1 message parsing and semantics are defined by this document
1951   and not the MIME specification.
1952</t>
1953</section>
1954
1955<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
1956<t>
1957   MIME requires that an Internet mail body-part be converted to
1958   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
1959   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
1960   allowed for subtypes of the "text" media type when transmitted over
1961   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
1962   line breaks as CRLF and forbids the use of CR or LF outside of line
1963   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
1964   line break within text content when a message is transmitted over
1965   HTTP.
1966</t>
1967<t>
1968   Where it is possible, a proxy or gateway from HTTP to a strict MIME
1969   environment &SHOULD; translate all line breaks within the text media
1970   types described in <xref target="canonicalization.and.text.defaults"/>
1971   of this document to the RFC 2049
1972   canonical form of CRLF. Note, however, that this might be complicated
1973   by the presence of a Content-Encoding and by the fact that HTTP
1974   allows the use of some character encodings which do not use octets 13 and
1975   10 to represent CR and LF, respectively, as is the case for some multi-byte
1976   character encodings.
1977</t>
1978<t>
1979   Conversion will break any cryptographic
1980   checksums applied to the original content unless the original content
1981   is already in canonical form. Therefore, the canonical form is
1982   recommended for any content that uses such checksums in HTTP.
1983</t>
1984</section>
1985
1986
1987<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
1988<t>
1989   HTTP/1.1 uses a restricted set of date formats (&http-date;) to
1990   simplify the process of date comparison. Proxies and gateways from
1991   other protocols &SHOULD; ensure that any Date header field present in a
1992   message conforms to one of the HTTP/1.1 formats and rewrite the date
1993   if necessary.
1994</t>
1995</section>
1996
1997<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
1998<t>
1999   MIME does not include any concept equivalent to HTTP/1.1's
2000   Content-Encoding header field. Since this acts as a modifier on the
2001   media type, proxies and gateways from HTTP to MIME-compliant
2002   protocols &MUST; either change the value of the Content-Type header
2003   field or decode the representation before forwarding the message. (Some
2004   experimental applications of Content-Type for Internet mail have used
2005   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2006   a function equivalent to Content-Encoding. However, this parameter is
2007   not part of the MIME standards).
2008</t>
2009</section>
2010
2011<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2012  <iref item="Content-Transfer-Encoding header field" x:for-anchor=""/>
2013  <iref item="Header Fields" subitem="Content-Transfer-Encoding" x:for-anchor=""/>
2014<t>
2015   HTTP does not use the Content-Transfer-Encoding field of MIME.
2016   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2017   remove any Content-Transfer-Encoding
2018   prior to delivering the response message to an HTTP client.
2019</t>
2020<t>
2021   Proxies and gateways from HTTP to MIME-compliant protocols are
2022   responsible for ensuring that the message is in the correct format
2023   and encoding for safe transport on that protocol, where "safe
2024   transport" is defined by the limitations of the protocol being used.
2025   Such a proxy or gateway &SHOULD; label the data with an appropriate
2026   Content-Transfer-Encoding if doing so will improve the likelihood of
2027   safe transport over the destination protocol.
2028</t>
2029</section>
2030
2031<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2032<t>
2033   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2034   Proxies/gateways &MUST; remove any transfer-coding prior to
2035   forwarding a message via a MIME-compliant protocol.
2036</t>
2037</section>
2038
2039<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2040<t>
2041   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2042   need to be aware of MIME line length limitations. Since HTTP does not
2043   have this limitation, HTTP does not fold long lines. MHTML messages
2044   being transported by HTTP follow all conventions of MHTML, including
2045   line length limitations and folding, canonicalization, etc., since
2046   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2047   does not interpret the content or any MIME header lines that might be
2048   contained therein.
2049</t>
2050</section>
2051</section>
2052
2053<section title="Additional Features" anchor="additional.features">
2054<t>
2055   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2056   existing HTTP implementations, but not consistently and correctly
2057   across most HTTP/1.1 applications. Implementors are advised to be
2058   aware of these features, but cannot rely upon their presence in, or
2059   interoperability with, other HTTP/1.1 applications. Some of these
2060   describe proposed experimental features, and some describe features
2061   that experimental deployment found lacking that are now addressed in
2062   the base HTTP/1.1 specification.
2063</t>
2064<t>
2065   A number of other header fields, such as Content-Disposition and Title,
2066   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
2067   and <xref target="RFC2076"/>).
2068</t>
2069</section>
2070
2071<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2072<t>
2073  Clarify contexts that charset is used in.
2074  (<xref target="character.sets"/>)
2075</t>
2076<t>
2077  Registration of Content Codings now requires IETF Review
2078  (<xref target="content.coding.registry"/>)
2079</t>
2080<t>
2081  Remove the default character encoding for text media types; the default
2082  now is whatever the media type definition says.
2083  (<xref target="canonicalization.and.text.defaults"/>)
2084</t>
2085<t>
2086  Change ABNF productions for header fields to only define the field value.
2087  (<xref target="header.field.definitions"/>)
2088</t>
2089<t>
2090  Remove definition of Content-MD5 header field because it was inconsistently
2091  implemented with respect to partial responses, and also because of known
2092  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
2093  (<xref target="header.field.definitions"/>)
2094</t>
2095<t>
2096  Remove ISO-8859-1 special-casing in Accept-Charset.
2097  (<xref target="header.accept-charset"/>)
2098</t>
2099<t>
2100  Remove base URI setting semantics for Content-Location due to poor
2101  implementation support, which was caused by too many broken servers emitting
2102  bogus Content-Location header fields, and also the potentially undesirable effect
2103  of potentially breaking relative links in content-negotiated resources.
2104  (<xref target="header.content-location"/>)
2105</t>
2106<t>
2107  Remove reference to non-existant identity transfer-coding value tokens.
2108  (<xref target="no.content-transfer-encoding"/>)
2109</t>
2110<t>
2111  Remove discussion of Content-Disposition header field, it is now defined
2112  by <xref target="RFC6266"/>.
2113  (<xref target="additional.features"/>)
2114</t>
2115</section>
2116
2117<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2118
2119<section title="Since RFC 2616">
2120<t>
2121  Extracted relevant partitions from <xref target="RFC2616"/>.
2122</t>
2123</section>
2124
2125<section title="Since draft-ietf-httpbis-p3-payload-00">
2126<t>
2127  Closed issues:
2128  <list style="symbols"> 
2129    <t>
2130      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2131      "Media Type Registrations"
2132      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2133    </t>
2134    <t>
2135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2136      "Clarification regarding quoting of charset values"
2137      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2138    </t>
2139    <t>
2140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2141      "Remove 'identity' token references"
2142      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2143    </t>
2144    <t>
2145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2146      "Accept-Encoding BNF"
2147    </t>
2148    <t>
2149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2150      "Normative and Informative references"
2151    </t>
2152    <t>
2153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2154      "RFC1700 references"
2155    </t>
2156    <t>
2157      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2158      "Updating to RFC4288"
2159    </t>
2160    <t>
2161      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2162      "Informative references"
2163    </t>
2164    <t>
2165      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2166      "ISO-8859-1 Reference"
2167    </t>
2168    <t>
2169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2170      "Encoding References Normative"
2171    </t>
2172    <t>
2173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2174      "Normative up-to-date references"
2175    </t>
2176  </list>
2177</t>
2178</section>
2179
2180<section title="Since draft-ietf-httpbis-p3-payload-01">
2181<t>
2182  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2183  <list style="symbols"> 
2184    <t>
2185      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2186    </t>
2187  </list>
2188</t>
2189</section>
2190
2191<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2192<t>
2193  Closed issues:
2194  <list style="symbols"> 
2195    <t>
2196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2197      "Quoting Charsets"
2198    </t>
2199    <t>
2200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2201      "Classification for Allow header"
2202    </t>
2203    <t>
2204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2205      "missing default for qvalue in description of Accept-Encoding"
2206    </t>
2207  </list>
2208</t>
2209<t>
2210  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2211  <list style="symbols"> 
2212    <t>
2213      Reference RFC 3984, and update header field registrations for headers defined
2214      in this document.
2215    </t>
2216  </list>
2217</t>
2218</section>
2219
2220<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2221<t>
2222  Closed issues:
2223  <list style="symbols"> 
2224    <t>
2225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2226      "Quoting Charsets"
2227    </t>
2228    <t>
2229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2230      "language tag matching (Accept-Language) vs RFC4647"
2231    </t>
2232    <t>
2233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2234      "RFC 1806 has been replaced by RFC2183"
2235    </t>
2236  </list>
2237</t>
2238<t>
2239  Other changes:
2240  <list style="symbols"> 
2241    <t>
2242      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2243      "Encoding References Normative" &mdash; rephrase the annotation and reference
2244      BCP97.
2245    </t>
2246  </list>
2247</t>
2248 </section>
2249
2250<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2251<t>
2252  Closed issues:
2253  <list style="symbols"> 
2254    <t>
2255      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2256      "RFC 2822 is updated by RFC 5322"
2257    </t>
2258  </list>
2259</t>
2260<t>
2261  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2262  <list style="symbols"> 
2263    <t>
2264      Use "/" instead of "|" for alternatives.
2265    </t>
2266    <t>
2267      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2268      whitespace ("OWS") and required whitespace ("RWS").
2269    </t>
2270    <t>
2271      Rewrite ABNFs to spell out whitespace rules, factor out
2272      header field value format definitions.
2273    </t>
2274  </list>
2275</t>
2276</section>
2277
2278<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2279<t>
2280  Closed issues:
2281  <list style="symbols"> 
2282    <t>
2283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2284      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2285    </t>
2286  </list>
2287</t>
2288<t>
2289  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2290  <list style="symbols"> 
2291    <t>
2292      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2293    </t>
2294  </list>
2295</t>
2296<t>
2297  Other changes:
2298  <list style="symbols"> 
2299    <t>
2300      Move definition of quality values into Part 1.
2301    </t>
2302  </list>
2303</t>
2304</section>
2305
2306<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2307<t>
2308  Closed issues:
2309  <list style="symbols"> 
2310    <t>
2311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2312      "Content-Location isn't special"
2313    </t>
2314    <t>
2315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2316      "Content Sniffing"
2317    </t>
2318  </list>
2319</t>
2320</section>
2321
2322<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2323<t>
2324  Closed issues:
2325  <list style="symbols"> 
2326    <t>
2327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2328      "Updated reference for language tags"
2329    </t>
2330    <t>
2331      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2332      "Clarify rules for determining what entities a response carries"
2333    </t>
2334    <t>
2335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2336      "Content-Location base-setting problems"
2337    </t>
2338    <t>
2339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2340      "Content Sniffing"
2341    </t>
2342    <t>
2343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2344      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2345    </t>
2346    <t>
2347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2348      "move definitions of gzip/deflate/compress to part 1"
2349    </t>
2350  </list>
2351</t>
2352<t>
2353  Partly resolved issues:
2354  <list style="symbols"> 
2355    <t>
2356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2357      "update IANA requirements wrt Transfer-Coding values" (add the
2358      IANA Considerations subsection)
2359    </t>
2360    <t>
2361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2362      "update IANA requirements wrt Content-Coding values" (add the
2363      IANA Considerations subsection)
2364    </t>
2365  </list>
2366</t>
2367</section>
2368
2369<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2370<t>
2371  Closed issues:
2372  <list style="symbols"> 
2373    <t>
2374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
2375      "Content Negotiation for media types"
2376    </t>
2377    <t>
2378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
2379      "Accept-Language: which RFC4647 filtering?"
2380    </t>
2381  </list>
2382</t>
2383</section>
2384
2385<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
2386<t>
2387  Closed issues:
2388  <list style="symbols"> 
2389    <t>
2390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
2391      "MIME-Version not listed in P1, general header fields"
2392    </t>
2393    <t>
2394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
2395      "IANA registry for content/transfer encodings"
2396    </t>
2397    <t>
2398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2399      "Content Sniffing"
2400    </t>
2401    <t>
2402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
2403      "use of term "word" when talking about header structure"
2404    </t>
2405  </list>
2406</t>
2407<t>
2408  Partly resolved issues:
2409  <list style="symbols"> 
2410    <t>
2411      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2412      "Term for the requested resource's URI"
2413    </t>
2414  </list>
2415</t>
2416</section>
2417
2418<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
2419<t>
2420  Closed issues:
2421  <list style="symbols"> 
2422    <t>
2423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
2424      "Clarify 'Requested Variant'"
2425    </t>
2426    <t>
2427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2428      "Content-Location isn't special"
2429    </t>
2430    <t>
2431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
2432      "Delimiting messages with multipart/byteranges"
2433    </t>
2434    <t>
2435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
2436      "Clarify entity / representation / variant terminology"
2437    </t>
2438    <t>
2439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
2440      "confusing req. language for Content-Location"
2441    </t>
2442    <t>
2443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
2444      "Content-Location on 304 responses"
2445    </t>
2446    <t>
2447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
2448      "'requested resource' in content-encoding definition"
2449    </t>
2450    <t>
2451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
2452      "consider removing the 'changes from 2068' sections"
2453    </t>
2454  </list>
2455</t>
2456<t>
2457  Partly resolved issues:
2458  <list style="symbols"> 
2459    <t>
2460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2461      "Content-MD5 and partial responses"
2462    </t>
2463  </list>
2464</t>
2465</section>
2466
2467<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
2468<t>
2469  Closed issues:
2470  <list style="symbols"> 
2471    <t>
2472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
2473      "Factor out Content-Disposition"
2474    </t>
2475  </list>
2476</t>
2477</section>
2478
2479<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
2480<t>
2481  Closed issues:
2482  <list style="symbols"> 
2483    <t>
2484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
2485      "Header Classification"
2486    </t>
2487    <t>
2488      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2489      "untangle ABNFs for header fields"
2490    </t>
2491    <t>
2492      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
2493      "potentially misleading MAY in media-type def"
2494    </t>
2495  </list>
2496</t>
2497</section>
2498
2499<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
2500<t>
2501  Closed issues:
2502  <list style="symbols"> 
2503    <t>
2504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
2505      "Default charsets for text media types"
2506    </t>
2507    <t>
2508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2509      "Content-MD5 and partial responses"
2510    </t>
2511    <t>
2512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2513      "untangle ABNFs for header fields"
2514    </t>
2515    <t>
2516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
2517      "confusing undefined parameter in media range example"
2518    </t>
2519  </list>
2520</t>
2521</section>
2522
2523<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
2524<t>
2525  None.
2526</t>
2527</section>
2528
2529<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
2530<t>
2531  Closed issues:
2532  <list style="symbols"> 
2533    <t>
2534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
2535      "Strength of requirements on Accept re: 406"
2536    </t>
2537  </list>
2538</t>
2539</section>
2540
2541<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
2542<t>
2543  Closed issues:
2544  <list style="symbols"> 
2545    <t>
2546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
2547      "Document HTTP's error-handling philosophy"
2548    </t>
2549  </list>
2550</t>
2551</section>
2552
2553<section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.since.17">
2554<t>
2555  Closed issues:
2556  <list style="symbols"> 
2557    <t>
2558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
2559      "intended maturity level vs normative references"
2560    </t>
2561  </list>
2562</t>
2563</section>
2564
2565<section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.since.18">
2566<t>
2567  Closed issues:
2568  <list style="symbols">
2569    <t>
2570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
2571      "is ETag a representation header field?"
2572    </t>
2573    <t>
2574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/338"/>:
2575      "Content-Location doesn't constrain the cardinality of representations"
2576    </t>
2577    <t>
2578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
2579      "make IANA policy definitions consistent"
2580    </t>
2581  </list>
2582</t>
2583</section>
2584
2585<section title="Since draft-ietf-httpbis-p3-payload-19" anchor="changes.since.19">
2586<t>
2587  None yet.
2588</t>
2589</section>
2590
2591</section>
2592
2593</back>
2594</rfc>
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