28/03/12 15:54:24 (10 years ago)


1 edited


  • draft-ietf-httpbis/experiment/p2-semantics.xml

    r1621 r1627  
    2020  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2121  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    22   <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2322  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2423  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2524  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2625  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    27   <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    28   <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2926  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    3027  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    3734  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    3835  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    39   <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4036  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    41   <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    42   <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    43   <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    44   <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4537  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4638  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4840  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4941  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    50   <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    5142  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    52   <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    5343  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    5444  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7060  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7161  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    72   <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7362  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7463  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7968  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8069  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    81   <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8270  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8371  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8674  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8775  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    88   <!ENTITY p6-head                 "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     76  <!ENTITY p6-head                    "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     77  <!ENTITY compression-codings        "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     78  <!ENTITY transfer-codings           "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     79  <!ENTITY compress-coding            "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     80  <!ENTITY deflate-coding             "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     81  <!ENTITY gzip-coding                "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     82  <!ENTITY header-content-length      "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     83  <!ENTITY header-last-modified       "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     84  <!ENTITY header-transfer-encoding   "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     85  <!ENTITY qvalue                     "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    9087<?rfc toc="yes" ?>
    171168   Part 2 defines the semantics of HTTP messages as expressed by request
    172    methods, request header fields, response status codes, and response header
    173    fields.
     169   methods, request header fields, response status codes, response header
     170   fields, HTTP message content, metadata, and content negotiation.
     204   This document defines HTTP/1.1 message payloads (a.k.a., content), the
     205   associated metadata header fields that define how the payload is intended
     206   to be interpreted by a recipient, the request header fields that
     207   might influence content selection, and the various selection algorithms
     208   that are collectively referred to as HTTP content negotiation.<cref>FIXME</cref>
    207211   This document is currently disorganized in order to minimize the changes
    208212   between drafts and enable reviewers to see the smaller errata changes.
    211215   processing of an HTTP request message (after message parsing): resource
    212216   mapping, methods, request modifying header fields, response status,
    213    status modifying header fields, and resource metadata.  The current mess
     217   status modifying header fields, and resource metadata.
     218   Furthermore,, the sections on entities will be renamed payload and moved
     219   to the first half of the document, while the sections on content negotiation
     220   and associated request header fields will be moved to the second half.
     221   The current mess
    214222   reflects how widely dispersed these topics and associated requirements
    215223   had become in <xref target="RFC2616"/>.
     226<section title="Terminology" anchor="terminology">
     228   This specification uses a number of terms to refer to the roles
     229   played by participants in, and objects of, the HTTP communication.
     232  <iref item="content negotiation"/>
     233  <x:dfn>content negotiation</x:dfn>
     234  <list>
     235    <t>
     236      The mechanism for selecting the appropriate representation when
     237      servicing a request. The representation in any response
     238      can be negotiated (including error responses).
     239    </t>
     240  </list>
     243  <iref primary="true" item="selected representation"/>
     244  <x:dfn>selected representation</x:dfn>
     245  <list>
     246    <t>
     247      The current representation of the target resource that would have been
     248      selected in a successful response if the same request had used the
     249      method GET and excluded any conditional request header fields.
     250    </t>
     251  </list>
    218255<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
    615652   include explicit freshness information (see &p6-explicit;). A
    616653   cached POST response with a Content-Location header field
    617    (see &header-content-location;) whose value is the effective
     654   (see <xref target="header.content-location"/>) whose value is the effective
    618655   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
    945982   Many header fields use a format including (case-insensitively) named
    946    parameters (for instance, Content-Type, defined in &header-content-type;).
     983   parameters (for instance, Content-Type, defined in <xref target="header.content-type"/>).
    947984   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
    948985   parameter value enables recipients to use existing parser components. When
    949986   allowing both forms, the meaning of a parameter value ought to be
    950987   independent of the syntax used for it (for an example, see the notes on
    951    parameter handling for media types in &media-types;).
     988   parameter handling for media types in <xref target="media.types"/>).
    9971034  <ttcol>Defined in...</ttcol>
    999   <c>Accept</c> <c>&header-accept;</c>
    1000   <c>Accept-Charset</c> <c>&header-accept-charset;</c>
    1001   <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
    1002   <c>Accept-Language</c> <c>&header-accept-language;</c>
     1036  <c>Accept</c> <c><xref target="header.accept"/></c>
     1037  <c>Accept-Charset</c> <c><xref target="header.accept-charset"/></c>
     1038  <c>Accept-Encoding</c> <c><xref target="header.accept-encoding"/></c>
     1039  <c>Accept-Language</c> <c><xref target="header.accept-language"/></c>
    10031040  <c>Authorization</c> <c>&header-authorization;</c>
    10041041  <c>Expect</c> <c><xref target="header.expect"/></c>
    11071144   For most status codes the response can carry a payload, in which case a
    11081145   Content-Type header field indicates the payload's media type
    1109    (&header-content-type;).
     1146   (<xref target="header.content-type"/>).
    14751512        <t>
    14761513          Redirection offering a choice of matching resources for use by
    1477           agent-driven content negotiation (&agent-driven-negotiation;). This
     1514          agent-driven content negotiation (<xref target="agent-driven.negotiation"/>). This
    14781515          is status code 300 (Multiple Choices).
    14791516        </t>
    15331570   The target resource has more than one
    15341571   representation, each with its own specific location, and agent-driven
    1535    negotiation information (&content-negotiation;) is being provided so that
     1572   negotiation information (<xref target="content.negotiation"/>) is being provided so that
    15361573   the user (or user agent) can select a preferred representation by
    15371574   redirecting its request to that location.
    17721809   The resource identified by the request is only capable of generating
    17731810   response representations which have content characteristics not acceptable
    1774    according to the Accept and Accept-* header fields sent in the request
    1775    (see &p3-header-fields;).
     1811   according to the Accept and Accept-* header fields sent in the request.
    20602096   body).  When a complete or partial representation is enclosed in an HTTP message,
    20612097   it is referred to as the payload of the message. HTTP representations
    2062    are defined in &payload;.
     2098   are defined in <xref target="payload"/>.
     2329<section title="Protocol Parameters" anchor="protocol.parameters">
     2331<section title="Character Encodings (charset)" anchor="character.sets">
     2333   HTTP uses charset names to indicate the character encoding of a
     2334   textual representation.
     2336<t anchor="rule.charset">
     2337  <x:anchor-alias value="charset"/>
     2338   A character encoding is identified by a case-insensitive token. The
     2339   complete set of tokens is defined by the IANA Character Set registry
     2340   (<eref target="http://www.iana.org/assignments/character-sets"/>).
     2342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
     2343  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
     2346   Although HTTP allows an arbitrary token to be used as a charset
     2347   value, any token that has a predefined value within the IANA
     2348   Character Set registry &MUST; represent the character encoding defined
     2349   by that registry. Applications &SHOULD; limit their use of character
     2350   encodings to those defined within the IANA registry.
     2353   HTTP uses charset in two contexts: within an Accept-Charset request
     2354   header field (in which the charset value is an unquoted token) and as the
     2355   value of a parameter in a Content-Type header field (within a request or
     2356   response), in which case the parameter value of the charset parameter
     2357   can be quoted.
     2360   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
     2361   <xref target="RFC2277"/>.
     2365<section title="Content Codings" anchor="content.codings">
     2366  <x:anchor-alias value="content-coding"/>
     2368   Content coding values indicate an encoding transformation that has
     2369   been or can be applied to a representation. Content codings are primarily
     2370   used to allow a representation to be compressed or otherwise usefully
     2371   transformed without losing the identity of its underlying media type
     2372   and without loss of information. Frequently, the representation is stored in
     2373   coded form, transmitted directly, and only decoded by the recipient.
     2375<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
     2376  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
     2379   All content-coding values are case-insensitive. HTTP/1.1 uses
     2380   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
     2381   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
     2382   describes the content-coding, what is more important is that it
     2383   indicates what decoding mechanism will be required to remove the
     2384   encoding.
     2387   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
     2388  <list>
     2389    <t>
     2390      See &compress-coding;.
     2391    </t>
     2392  </list>
     2395   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
     2396  <list>
     2397    <t>
     2398      See &deflate-coding;.
     2399    </t>
     2400  </list>
     2403   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
     2404  <list>
     2405    <t>
     2406      See &gzip-coding;.
     2407    </t>
     2408  </list>
     2411<section title="Content Coding Registry" anchor="content.coding.registry">
     2413   The HTTP Content Coding Registry defines the name space for the content
     2414   coding names.
     2417   Registrations &MUST; include the following fields:
     2418   <list style="symbols">
     2419     <t>Name</t>
     2420     <t>Description</t>
     2421     <t>Pointer to specification text</t>
     2422   </list>
     2425   Names of content codings &MUST-NOT; overlap with names of transfer codings
     2426   (&transfer-codings;), unless the encoding transformation is identical (as
     2427   is the case for the compression codings defined in
     2428   &compression-codings;).
     2431   Values to be added to this name space require IETF Review
     2432   (see <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
     2433   conform to the purpose of content coding defined in this section.
     2436   The registry itself is maintained at
     2437   <eref target="http://www.iana.org/assignments/http-parameters"/>.
     2443<section title="Media Types" anchor="media.types">
     2444  <x:anchor-alias value="media-type"/>
     2445  <x:anchor-alias value="type"/>
     2446  <x:anchor-alias value="subtype"/>
     2448   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
     2449   and Accept (<xref target="header.accept"/>) header fields in order to provide
     2450   open and extensible data typing and type negotiation.
     2452<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"/>
     2453  <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> )
     2454  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
     2455  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
     2457<t anchor="rule.parameter">
     2458  <x:anchor-alias value="attribute"/>
     2459  <x:anchor-alias value="parameter"/>
     2460  <x:anchor-alias value="value"/>
     2461   The type/subtype &MAY; be followed by parameters in the form of
     2462   attribute/value pairs.
     2464<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"/>
     2465  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
     2466  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
     2467  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
     2470   The type, subtype, and parameter attribute names are case-insensitive.
     2471   Parameter values might or might not be case-sensitive, depending on the
     2472   semantics of the parameter name.  The presence or absence of a parameter might
     2473   be significant to the processing of a media-type, depending on its
     2474   definition within the media type registry.
     2477   A parameter value that matches the <x:ref>token</x:ref> production can be
     2478   transmitted as either a token or within a quoted-string. The quoted and
     2479   unquoted values are equivalent.
     2482   Note that some older HTTP applications do not recognize media type
     2483   parameters. When sending data to older HTTP applications,
     2484   implementations &SHOULD; only use media type parameters when they are
     2485   required by that type/subtype definition.
     2488   Media-type values are registered with the Internet Assigned Number
     2489   Authority (IANA). The media type registration process is
     2490   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
     2491   discouraged.
     2494<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
     2496   Internet media types are registered with a canonical form. A
     2497   representation transferred via HTTP messages &MUST; be in the
     2498   appropriate canonical form prior to its transmission except for
     2499   "text" types, as defined in the next paragraph.
     2502   When in canonical form, media subtypes of the "text" type use CRLF as
     2503   the text line break. HTTP relaxes this requirement and allows the
     2504   transport of text media with plain CR or LF alone representing a line
     2505   break when it is done consistently for an entire representation. HTTP
     2506   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
     2507   a line break in text media received via HTTP. In
     2508   addition, if the text is in a character encoding that does not
     2509   use octets 13 and 10 for CR and LF respectively, as is the case for
     2510   some multi-byte character encodings, HTTP allows the use of whatever octet
     2511   sequences are defined by that character encoding to represent the
     2512   equivalent of CR and LF for line breaks. This flexibility regarding
     2513   line breaks applies only to text media in the payload body; a bare CR
     2514   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
     2515   structures (such as header fields and multipart boundaries).
     2518   If a representation is encoded with a content-coding, the underlying
     2519   data &MUST; be in a form defined above prior to being encoded.
     2523<section title="Multipart Types" anchor="multipart.types">
     2525   MIME provides for a number of "multipart" types &mdash; encapsulations of
     2526   one or more representations within a single message body. All multipart
     2527   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
     2528   and &MUST; include a boundary parameter as part of the media type
     2529   value. The message body is itself a protocol element and &MUST;
     2530   therefore use only CRLF to represent line breaks between body-parts.
     2533   In general, HTTP treats a multipart message body no differently than
     2534   any other media type: strictly as payload.  HTTP does not use the
     2535   multipart boundary as an indicator of message body length.
     2536   <!-- jre: re-insert removed text pointing to caching? -->
     2537   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
     2538   behavior as a MIME user agent would upon receipt of a multipart type.
     2539   The MIME header fields within each body-part of a multipart message body
     2540   do not have any significance to HTTP beyond that defined by
     2541   their MIME semantics.
     2544   If an application receives an unrecognized multipart subtype, the
     2545   application &MUST; treat it as being equivalent to "multipart/mixed".
     2548  <t>
     2549    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
     2550    for carrying form data suitable for processing via the POST
     2551    request method, as described in <xref target="RFC2388"/>.
     2552  </t>
     2557<section title="Language Tags" anchor="language.tags">
     2558  <x:anchor-alias value="language-tag"/>
     2560   A language tag, as defined in <xref target="RFC5646"/>, identifies a
     2561   natural language spoken, written, or otherwise conveyed by human beings for
     2562   communication of information to other human beings. Computer languages are
     2563   explicitly excluded. HTTP uses language tags within the Accept-Language and
     2564   Content-Language fields.
     2567   In summary, a language tag is composed of one or more parts: A primary
     2568   language subtag followed by a possibly empty series of subtags:
     2570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
     2571  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
     2574   White space is not allowed within the tag and all tags are case-insensitive.
     2575   The name space of language subtags is administered by the IANA (see
     2576   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
     2579  <preamble>Example tags include:</preamble>
     2580<artwork type="example">
     2581  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
     2585   See <xref target="RFC5646"/> for further information.
     2590<section title="Payload" anchor="payload">
     2592   HTTP messages &MAY; transfer a payload if not otherwise restricted by
     2593   the request method or response status code.  The payload consists of
     2594   metadata, in the form of header fields, and data, in the form of the
     2595   sequence of octets in the message body after any transfer-coding has
     2596   been decoded.
     2598<iref item="payload"/>
     2600   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
     2601   representation of some resource.  We use separate terms for payload
     2602   and representation because some messages contain only the associated
     2603   representation's header fields (e.g., responses to HEAD) or only some
     2604   part(s) of the representation (e.g., the 206 status code).
     2606<section title="Payload Header Fields" anchor="payload.header.fields">
     2607  <x:anchor-alias value="payload-header"/>
     2609   HTTP header fields that specifically define the payload, rather than the
     2610   associated representation, are referred to as "payload header fields".
     2611   The following payload header fields are defined by HTTP/1.1:
     2613<texttable align="left">
     2614  <ttcol>Header Field Name</ttcol>
     2615  <ttcol>Defined in...</ttcol>
     2617  <c>Content-Length</c> <c>&header-content-length;</c>
     2618  <c>Content-Range</c> <c>&header-content-range;</c>
     2622<section title="Payload Body" anchor="payload.body">
     2623  <x:anchor-alias value="payload-body"/>
     2625   A payload body is only present in a message when a message body is
     2626   present, as described in &message-body;. The payload body is obtained
     2627   from the message body by decoding any Transfer-Encoding that might
     2628   have been applied to ensure safe and proper transfer of the message.
     2633<section title="Representation" anchor="representation-TODO">
     2634<iref item="representation"/>
     2636   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
     2637   communicated from one party to another.  A resource representation
     2638   is information that reflects the state of that resource, as observed
     2639   at some point in the past (e.g., in a response to GET) or to be
     2640   desired at some point in the future (e.g., in a PUT request).
     2643   Most, but not all, representations transferred via HTTP are intended
     2644   to be a representation of the target resource (the resource identified
     2645   by the effective request URI).  The precise semantics of a representation
     2646   are determined by the type of message (request or response), the request
     2647   method, the response status code, and the representation metadata.
     2648   For example, the above semantic is true for the representation in any
     2649   200 (OK) response to GET and for the representation in any PUT request.
     2650   A 200 response to PUT, in contrast, contains either a representation
     2651   that describes the successful action or a representation of the target
     2652   resource, with the latter indicated by a Content-Location header field
     2653   with the same value as the effective request URI.  Likewise, response
     2654   messages with an error status code usually contain a representation that
     2655   describes the error and what next steps are suggested for resolving it.
     2658<section title="Representation Header Fields" anchor="representation.header.fields">
     2659  <x:anchor-alias value="representation-header"/>
     2661   Representation header fields define metadata about the representation data
     2662   enclosed in the message body or, if no message body is present, about
     2663   the representation that would have been transferred in a 200 response
     2664   to a simultaneous GET request with the same effective request URI.
     2667   The following header fields are defined as representation metadata:
     2669<texttable align="left">
     2670  <ttcol>Header Field Name</ttcol>
     2671  <ttcol>Defined in...</ttcol>
     2673  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
     2674  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
     2675  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
     2676  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
     2677  <c>Expires</c> <c>&header-expires;</c>
     2680   Additional header fields define metadata about the selected
     2681   representation, which might differ from the representation included
     2682   in the message for responses to some state-changing methods.
     2683   The following header fields are defined as selected representation
     2684   metadata:
     2686<texttable align="left">
     2687  <ttcol>Header Field Name</ttcol>
     2688  <ttcol>Defined in...</ttcol>
     2690  <c>ETag</c> <c>&header-etag;</c>
     2691  <c>Last-Modified</c> <c>&header-last-modified;</c>
     2695<section title="Representation Data" anchor="representation.data">
     2696  <x:anchor-alias value="representation-data"/>
     2698   The representation body associated with an HTTP message is
     2699   either provided as the payload body of the message or
     2700   referred to by the message semantics and the effective request
     2701   URI.  The representation data is in a format and encoding defined by
     2702   the representation metadata header fields.
     2705   The data type of the representation data
     2706   is determined via the header fields Content-Type and Content-Encoding.
     2707   These define a two-layer, ordered encoding model:
     2709<figure><artwork type="example">
     2710  representation-data := Content-Encoding( Content-Type( bits ) )
     2713   Content-Type specifies the media type of the underlying data, which
     2714   defines both the data format and how that data &SHOULD; be processed
     2715   by the recipient (within the scope of the request method semantics).
     2716   Any HTTP/1.1 message containing a payload body &SHOULD; include a
     2717   Content-Type header field defining the media type of the associated
     2718   representation unless that metadata is unknown to the sender.
     2719   If the Content-Type header field is not present, it indicates that
     2720   the sender does not know the media type of the representation;
     2721   recipients &MAY; either assume that the media type is
     2722   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
     2723   or examine the content to determine its type.
     2726   In practice, resource owners do not always properly configure their origin
     2727   server to provide the correct Content-Type for a given representation,
     2728   with the result that some clients will examine a response body's content
     2729   and override the specified type.
     2730   Clients that do so risk drawing incorrect conclusions, which might expose
     2731   additional security risks (e.g., "privilege escalation").  Furthermore,
     2732   it is impossible to determine the sender's intent by examining the data
     2733   format: many data formats match multiple media types that differ only in
     2734   processing semantics.  Implementers are encouraged to provide a means of
     2735   disabling such "content sniffing" when it is used.
     2738   Content-Encoding is used to indicate any additional content
     2739   codings applied to the data, usually for the purpose of data
     2740   compression, that are a property of the representation.  If
     2741   Content-Encoding is not present, then there is no additional
     2742   encoding beyond that defined by the Content-Type.
     2747<section title="Content Negotiation" anchor="content.negotiation">
     2749   HTTP responses include a representation which contains information for
     2750   interpretation, whether by a human user or for further processing.
     2751   Often, the server has different ways of representing the
     2752   same information; for example, in different formats, languages,
     2753   or using different character encodings.
     2756   HTTP clients and their users might have different or variable
     2757   capabilities, characteristics or preferences which would influence
     2758   which representation, among those available from the server,
     2759   would be best for the server to deliver. For this reason, HTTP
     2760   provides mechanisms for "content negotiation" &mdash; a process of
     2761   allowing selection of a representation of a given resource,
     2762   when more than one is available.
     2765   This specification defines two patterns of content negotiation;
     2766   "server-driven", where the server selects the representation based
     2767   upon the client's stated preferences, and "agent-driven" negotiation,
     2768   where the server provides a list of representations for the client to
     2769   choose from, based upon their metadata. In addition,  there are
     2770   other patterns: some applications use an "active content" pattern,
     2771   where the server returns active content which runs on the client
     2772   and, based on client available parameters, selects additional
     2773   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
     2774   has also been proposed.
     2777   These patterns are all widely used, and have trade-offs in applicability
     2778   and practicality. In particular, when the number of preferences or
     2779   capabilities to be expressed by a client are large (such as when many
     2780   different formats are supported by a user-agent), server-driven
     2781   negotiation becomes unwieldy, and might not be appropriate. Conversely,
     2782   when the number of representations to choose from is very large,
     2783   agent-driven negotiation might not be appropriate.
     2786   Note that in all cases, the supplier of representations has the
     2787   responsibility for determining which representations might be
     2788   considered to be the "same information".
     2791<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
     2793   If the selection of the best representation for a response is made by
     2794   an algorithm located at the server, it is called server-driven
     2795   negotiation. Selection is based on the available representations of
     2796   the response (the dimensions over which it can vary; e.g., language,
     2797   content-coding, etc.) and the contents of particular header fields in
     2798   the request message or on other information pertaining to the request
     2799   (such as the network address of the client).
     2802   Server-driven negotiation is advantageous when the algorithm for
     2803   selecting from among the available representations is difficult to
     2804   describe to the user agent, or when the server desires to send its
     2805   "best guess" to the client along with the first response (hoping to
     2806   avoid the round-trip delay of a subsequent request if the "best
     2807   guess" is good enough for the user). In order to improve the server's
     2808   guess, the user agent &MAY; include request header fields (Accept,
     2809   Accept-Language, Accept-Encoding, etc.) which describe its
     2810   preferences for such a response.
     2813   Server-driven negotiation has disadvantages:
     2814  <list style="numbers">
     2815    <t>
     2816         It is impossible for the server to accurately determine what
     2817         might be "best" for any given user, since that would require
     2818         complete knowledge of both the capabilities of the user agent
     2819         and the intended use for the response (e.g., does the user want
     2820         to view it on screen or print it on paper?).
     2821    </t>
     2822    <t>
     2823         Having the user agent describe its capabilities in every
     2824         request can be both very inefficient (given that only a small
     2825         percentage of responses have multiple representations) and a
     2826         potential violation of the user's privacy.
     2827    </t>
     2828    <t>
     2829         It complicates the implementation of an origin server and the
     2830         algorithms for generating responses to a request.
     2831    </t>
     2832    <t>
     2833         It might limit a public cache's ability to use the same response
     2834         for multiple user's requests.
     2835    </t>
     2836  </list>
     2839   Server-driven negotiation allows the user agent to specify its preferences,
     2840   but it cannot expect responses to always honor them. For example, the origin
     2841   server might not implement server-driven negotiation, or it might decide that
     2842   sending a response that doesn't conform to them is better than sending a 406
     2843   (Not Acceptable) response.
     2846   Many of the mechanisms for expressing preferences use quality values to
     2847   declare relative preference. See qvalue; for more information.
     2850   HTTP/1.1 includes the following header fields for enabling
     2851   server-driven negotiation through description of user agent
     2852   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
     2853   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
     2854   (<xref target="header.accept-language"/>), and User-Agent (<xref target="header.user-agent"/>).
     2855   However, an origin server is not limited to these dimensions and &MAY; vary
     2856   the response based on any aspect of the request, including aspects
     2857   of the connection (e.g., IP address) or information within extension
     2858   header fields not defined by this specification.
     2861  <t>
     2862    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
     2863    because new clients might not be recognized.
     2864  </t>
     2867   The Vary header field (&header-vary;) can be used to express the parameters the
     2868   server uses to select a representation that is subject to server-driven
     2869   negotiation.
     2873<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
     2875   With agent-driven negotiation, selection of the best representation
     2876   for a response is performed by the user agent after receiving an
     2877   initial response from the origin server. Selection is based on a list
     2878   of the available representations of the response included within the
     2879   header fields or body of the initial response, with each
     2880   representation identified by its own URI. Selection from among the
     2881   representations can be performed automatically (if the user agent is
     2882   capable of doing so) or manually by the user selecting from a
     2883   generated (possibly hypertext) menu.
     2886   Agent-driven negotiation is advantageous when the response would vary
     2887   over commonly-used dimensions (such as type, language, or encoding),
     2888   when the origin server is unable to determine a user agent's
     2889   capabilities from examining the request, and generally when public
     2890   caches are used to distribute server load and reduce network usage.
     2893   Agent-driven negotiation suffers from the disadvantage of needing a
     2894   second request to obtain the best alternate representation. This
     2895   second request is only efficient when caching is used. In addition,
     2896   this specification does not define any mechanism for supporting
     2897   automatic selection, though it also does not prevent any such
     2898   mechanism from being developed as an extension and used within
     2899   HTTP/1.1.
     2902   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
     2903   status codes for enabling agent-driven negotiation when the server is
     2904   unwilling or unable to provide a varying response using server-driven
     2905   negotiation.
    22932910<section title="Header Field Definitions" anchor="header.field.definitions">
    22952912   This section defines the syntax and semantics of HTTP/1.1 header fields
    2296    related to request and response semantics.
     2913   related to request and response semantics, and to the payload of
     2914   messages.
    25463164  <t>
    2547     <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
     3165    <x:h>Note:</x:h> The Content-Location header field (<xref target="header.content-location"/>) differs
    25483166    from Location in that the Content-Location identifies the most specific
    25493167    resource corresponding to the enclosed representation.
    2753 </section>
     3372<section title="Accept" anchor="header.accept">
     3373  <iref primary="true" item="Accept header field" x:for-anchor=""/>
     3374  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
     3375  <x:anchor-alias value="Accept"/>
     3376  <x:anchor-alias value="accept-ext"/>
     3377  <x:anchor-alias value="accept-params"/>
     3378  <x:anchor-alias value="media-range"/>
     3380   The "Accept" header field can be used by user agents to specify
     3381   response media types that are acceptable. Accept header fields can be used to
     3382   indicate that the request is specifically limited to a small set of desired
     3383   types, as in the case of a request for an in-line image.
     3385<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"/>
     3386  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
     3388  <x:ref>media-range</x:ref>    = ( "*/*"
     3389                   / ( <x:ref>type</x:ref> "/" "*" )
     3390                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
     3391                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
     3392  <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> )
     3393  <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> ]
     3396   The asterisk "*" character is used to group media types into ranges,
     3397   with "*/*" indicating all media types and "type/*" indicating all
     3398   subtypes of that type. The media-range &MAY; include media type
     3399   parameters that are applicable to that range.
     3402   Each media-range &MAY; be followed by one or more accept-params,
     3403   beginning with the "q" parameter for indicating a relative quality
     3404   factor. The first "q" parameter (if any) separates the media-range
     3405   parameter(s) from the accept-params. Quality factors allow the user
     3406   or user agent to indicate the relative degree of preference for that
     3407   media-range, using the qvalue scale from 0 to 1 (qvalue;). The
     3408   default value is q=1.
     3411  <t>
     3412    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
     3413    parameters from Accept extension parameters is due to historical
     3414    practice. Although this prevents any media type parameter named
     3415    "q" from being used with a media range, such an event is believed
     3416    to be unlikely given the lack of any "q" parameters in the IANA
     3417    media type registry and the rare usage of any media type
     3418    parameters in Accept. Future media types are discouraged from
     3419    registering any parameter named "q".
     3420  </t>
     3423   The example
     3425<figure><artwork type="example">
     3426  Accept: audio/*; q=0.2, audio/basic
     3429   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
     3430   type if it is the best available after an 80% mark-down in quality".
     3433   A request without any Accept header field implies that the user agent
     3434   will accept any media type in response.
     3435   If an Accept header field is present in a request and none of the
     3436   available representations for the response have a media type that is
     3437   listed as acceptable, the origin server &MAY; either
     3438   honor the Accept header field by sending a 406 (Not Acceptable) response
     3439   or disregard the Accept header field by treating the response as if
     3440   it is not subject to content negotiation.
     3443   A more elaborate example is
     3445<figure><artwork type="example">
     3446  Accept: text/plain; q=0.5, text/html,
     3447          text/x-dvi; q=0.8, text/x-c
     3450   Verbally, this would be interpreted as "text/html and text/x-c are
     3451   the preferred media types, but if they do not exist, then send the
     3452   text/x-dvi representation, and if that does not exist, send the text/plain
     3453   representation".
     3456   Media ranges can be overridden by more specific media ranges or
     3457   specific media types. If more than one media range applies to a given
     3458   type, the most specific reference has precedence. For example,
     3460<figure><artwork type="example">
     3461  Accept: text/*, text/plain, text/plain;format=flowed, */*
     3464   have the following precedence:
     3465   <list style="numbers">
     3466    <t>text/plain;format=flowed</t>
     3467    <t>text/plain</t>
     3468    <t>text/*</t>
     3469    <t>*/*</t>
     3470   </list>
     3473   The media type quality factor associated with a given type is
     3474   determined by finding the media range with the highest precedence
     3475   which matches that type. For example,
     3477<figure><artwork type="example">
     3478  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
     3479          text/html;level=2;q=0.4, */*;q=0.5
     3482   would cause the following values to be associated:
     3484<texttable align="left">
     3485  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
     3486  <c>text/html;level=1</c>    <c>1</c>
     3487  <c>text/html</c>            <c>0.7</c>
     3488  <c>text/plain</c>           <c>0.3</c>
     3489  <c>image/jpeg</c>           <c>0.5</c>
     3490  <c>text/html;level=2</c>    <c>0.4</c>
     3491  <c>text/html;level=3</c>    <c>0.7</c>
     3494      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
     3495      values for certain media ranges. However, unless the user agent is
     3496      a closed system which cannot interact with other rendering agents,
     3497      this default set ought to be configurable by the user.
     3501<section title="Accept-Charset" anchor="header.accept-charset">
     3502  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
     3503  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
     3504  <x:anchor-alias value="Accept-Charset"/>
     3506   The "Accept-Charset" header field can be used by user agents to
     3507   indicate what character encodings are acceptable in a response
     3508   payload. This field allows
     3509   clients capable of understanding more comprehensive or special-purpose
     3510   character encodings to signal that capability to a server which is capable of
     3511   representing documents in those character encodings.
     3513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
     3514  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
     3515                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
     3518   Character encoding values (a.k.a., charsets) are described in
     3519   <xref target="character.sets"/>. Each charset &MAY; be given an
     3520   associated quality value which represents the user's preference
     3521   for that charset. The default value is q=1. An example is
     3523<figure><artwork type="example">
     3524  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
     3527   The special value "*", if present in the Accept-Charset field,
     3528   matches every character encoding which is not mentioned elsewhere in the
     3529   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
     3530   all character encodings not explicitly mentioned get a quality value of 0.
     3533   A request without any Accept-Charset header field implies that the user
     3534   agent will accept any character encoding in response.
     3535   If an Accept-Charset header field is present in a request and none of the
     3536   available representations for the response have a character encoding that
     3537   is listed as acceptable, the origin server &MAY; either honor the
     3538   Accept-Charset header field by sending a 406 (Not Acceptable) response or
     3539   disregard the Accept-Charset header field by treating the response as if
     3540   it is not subject to content negotiation.
     3544<section title="Accept-Encoding" anchor="header.accept-encoding">
     3545  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
     3546  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
     3547  <x:anchor-alias value="Accept-Encoding"/>
     3548  <x:anchor-alias value="codings"/>
     3550   The "Accept-Encoding" header field can be used by user agents to
     3551   indicate what response content-codings (<xref target="content.codings"/>)
     3552   are acceptable in the response.  An "identity" token is used as a synonym
     3553   for "no encoding" in order to communicate when no encoding is preferred.
     3555<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
     3556  <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> ] )
     3557  <x:ref>codings</x:ref>          = <x:ref>content-coding</x:ref> / "identity" / "*"
     3560   Each codings value &MAY; be given an associated quality value which
     3561   represents the preference for that encoding. The default value is q=1.
     3564   For example,
     3566<figure><artwork type="example">
     3567  Accept-Encoding: compress, gzip
     3568  Accept-Encoding:
     3569  Accept-Encoding: *
     3570  Accept-Encoding: compress;q=0.5, gzip;q=1.0
     3571  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
     3574   A server tests whether a content-coding for a given representation is
     3575   acceptable, according to an Accept-Encoding field, using these rules:
     3576  <list style="numbers">
     3577      <t>The special "*" symbol in an Accept-Encoding field matches any
     3578         available content-coding not explicitly listed in the header
     3579         field.</t>
     3581      <t>If the representation has no content-coding, then it is acceptable
     3582         by default unless specifically excluded by the Accept-Encoding field
     3583         stating either "identity;q=0" or "*;q=0" without a more specific
     3584         entry for "identity".</t>
     3586      <t>If the representation's content-coding is one of the content-codings
     3587         listed in the Accept-Encoding field, then it is acceptable unless
     3588         it is accompanied by a qvalue of 0. (As defined in qvalue;, a
     3589         qvalue of 0 means "not acceptable".)</t>
     3591      <t>If multiple content-codings are acceptable, then the acceptable
     3592         content-coding with the highest non-zero qvalue is preferred.</t>
     3593  </list>
     3596   An Accept-Encoding header field with a combined field-value that is empty
     3597   implies that the user agent does not want any content-coding in response.
     3598   If an Accept-Encoding header field is present in a request and none of the
     3599   available representations for the response have a content-coding that
     3600   is listed as acceptable, the origin server &SHOULD; send a response
     3601   without any content-coding.
     3604   A request without an Accept-Encoding header field implies that the user
     3605   agent will accept any content-coding in response, but a representation
     3606   without content-coding is preferred for compatibility with the widest
     3607   variety of user agents.
     3610  <t>
     3611    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
     3612    associated with content-codings. This means that qvalues will not
     3613    work and are not permitted with x-gzip or x-compress.
     3614  </t>
     3618<section title="Accept-Language" anchor="header.accept-language">
     3619  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
     3620  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
     3621  <x:anchor-alias value="Accept-Language"/>
     3622  <x:anchor-alias value="language-range"/>
     3624   The "Accept-Language" header field can be used by user agents to
     3625   indicate the set of natural languages that are preferred in the response.
     3626   Language tags are defined in <xref target="language.tags"/>.
     3628<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
     3629  <x:ref>Accept-Language</x:ref> =
     3630                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
     3631  <x:ref>language-range</x:ref>  =
     3632            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
     3635   Each language-range can be given an associated quality value which
     3636   represents an estimate of the user's preference for the languages
     3637   specified by that range. The quality value defaults to "q=1". For
     3638   example,
     3640<figure><artwork type="example">
     3641  Accept-Language: da, en-gb;q=0.8, en;q=0.7
     3644   would mean: "I prefer Danish, but will accept British English and
     3645   other types of English".
     3646   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
     3649   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
     3650   several matching schemes. Implementations can offer the most appropriate
     3651   matching scheme for their requirements.
     3654  <t>
     3655    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
     3656    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
     3657    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
     3658  </t>
     3661   It might be contrary to the privacy expectations of the user to send
     3662   an Accept-Language header field with the complete linguistic preferences of
     3663   the user in every request. For a discussion of this issue, see
     3664   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
     3667   As intelligibility is highly dependent on the individual user, it is
     3668   recommended that client applications make the choice of linguistic
     3669   preference available to the user. If the choice is not made
     3670   available, then the Accept-Language header field &MUST-NOT; be given in
     3671   the request.
     3674  <t>
     3675    <x:h>Note:</x:h> When making the choice of linguistic preference available to
     3676    the user, we remind implementors of  the fact that users are not
     3677    familiar with the details of language matching as described above,
     3678    and ought to be provided appropriate guidance. As an example, users
     3679    might assume that on selecting "en-gb", they will be served any
     3680    kind of English document if British English is not available. A
     3681    user agent might suggest in such a case to add "en" to get the
     3682    best matching behavior.
     3683  </t>
     3687<section title="Content-Encoding" anchor="header.content-encoding">
     3688  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
     3689  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
     3690  <x:anchor-alias value="Content-Encoding"/>
     3692   The "Content-Encoding" header field indicates what content-codings
     3693   have been applied to the representation beyond those inherent in the media
     3694   type, and thus what decoding mechanisms have to be applied in order to obtain
     3695   the media-type referenced by the Content-Type header field.
     3696   Content-Encoding is primarily used to allow a representation to be
     3697   compressed without losing the identity of its underlying media type.
     3699<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
     3700  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
     3703   Content codings are defined in <xref target="content.codings"/>. An example of its use is
     3705<figure><artwork type="example">
     3706  Content-Encoding: gzip
     3709   The content-coding is a characteristic of the representation.
     3710   Typically, the representation body is stored with this
     3711   encoding and is only decoded before rendering or analogous usage.
     3712   However, a transforming proxy &MAY; modify the content-coding if the
     3713   new coding is known to be acceptable to the recipient, unless the
     3714   "no-transform" cache-control directive is present in the message.
     3717   If the media type includes an inherent encoding, such as a data format
     3718   that is always compressed, then that encoding would not be restated as
     3719   a Content-Encoding even if it happens to be the same algorithm as one
     3720   of the content-codings.  Such a content-coding would only be listed if,
     3721   for some bizarre reason, it is applied a second time to form the
     3722   representation.  Likewise, an origin server might choose to publish the
     3723   same payload data as multiple representations that differ only in whether
     3724   the coding is defined as part of Content-Type or Content-Encoding, since
     3725   some user agents will behave differently in their handling of each
     3726   response (e.g., open a "Save as ..." dialog instead of automatic
     3727   decompression and rendering of content).
     3730   A representation that has a content-coding applied to it &MUST; include
     3731   a Content-Encoding header field (<xref target="header.content-encoding"/>)
     3732   that lists the content-coding(s) applied.
     3735   If multiple encodings have been applied to a representation, the content
     3736   codings &MUST; be listed in the order in which they were applied.
     3737   Additional information about the encoding parameters &MAY; be provided
     3738   by other header fields not defined by this specification.
     3741   If the content-coding of a representation in a request message is not
     3742   acceptable to the origin server, the server &SHOULD; respond with a
     3743   status code of 415 (Unsupported Media Type).
     3747<section title="Content-Language" anchor="header.content-language">
     3748  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
     3749  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
     3750  <x:anchor-alias value="Content-Language"/>
     3752   The "Content-Language" header field describes the natural
     3753   language(s) of the intended audience for the representation. Note that this might
     3754   not be equivalent to all the languages used within the representation.
     3756<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
     3757  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
     3760   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
     3761   Content-Language is to allow a user to identify and differentiate
     3762   representations according to the user's own preferred language. Thus, if the
     3763   body content is intended only for a Danish-literate audience, the
     3764   appropriate field is
     3766<figure><artwork type="example">
     3767  Content-Language: da
     3770   If no Content-Language is specified, the default is that the content
     3771   is intended for all language audiences. This might mean that the
     3772   sender does not consider it to be specific to any natural language,
     3773   or that the sender does not know for which language it is intended.
     3776   Multiple languages &MAY; be listed for content that is intended for
     3777   multiple audiences. For example, a rendition of the "Treaty of
     3778   Waitangi", presented simultaneously in the original Maori and English
     3779   versions, would call for
     3781<figure><artwork type="example">
     3782  Content-Language: mi, en
     3785   However, just because multiple languages are present within a representation
     3786   does not mean that it is intended for multiple linguistic audiences.
     3787   An example would be a beginner's language primer, such as "A First
     3788   Lesson in Latin", which is clearly intended to be used by an
     3789   English-literate audience. In this case, the Content-Language would
     3790   properly only include "en".
     3793   Content-Language &MAY; be applied to any media type &mdash; it is not
     3794   limited to textual documents.
     3798<section title="Content-Location" anchor="header.content-location">
     3799  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
     3800  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
     3801  <x:anchor-alias value="Content-Location"/>
     3803   The "Content-Location" header field supplies a URI that can be used
     3804   as a specific identifier for the representation in this message.
     3805   In other words, if one were to perform a GET on this URI at the time
     3806   of this message's generation, then a 200 response would contain the
     3807   same representation that is enclosed as payload in this message.
     3809<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
     3810  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
     3813   The Content-Location value is not a replacement for the effective
     3814   Request URI (&effective-request-uri;).  It is representation metadata.
     3815   It has the same syntax and semantics as the header field of the same name
     3816   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
     3817   However, its appearance in an HTTP message has some special implications
     3818   for HTTP recipients.
     3821   If Content-Location is included in a response message and its value
     3822   is the same as the effective request URI, then the response payload
     3823   &SHOULD; be considered a current representation of that resource.
     3824   For a GET or HEAD request, this is the same as the default semantics
     3825   when no Content-Location is provided by the server.  For a state-changing
     3826   request like PUT or POST, it implies that the server's response contains
     3827   the new representation of that resource, thereby distinguishing it from
     3828   representations that might only report about the action (e.g., "It worked!").
     3829   This allows authoring applications to update their local copies without
     3830   the need for a subsequent GET request.
     3833   If Content-Location is included in a response message and its value
     3834   differs from the effective request URI, then the origin server is
     3835   informing recipients that this representation has its own, presumably
     3836   more specific, identifier.  For a GET or HEAD request, this is an
     3837   indication that the effective request URI identifies a resource that
     3838   is subject to content negotiation and the selected representation for
     3839   this response can also be found at the identified URI.  For other
     3840   methods, such a Content-Location indicates that this representation
     3841   contains a report on the action's status and the same report is
     3842   available (for future access with GET) at the given URI.  For
     3843   example, a purchase transaction made via a POST request might
     3844   include a receipt document as the payload of the 200 response;
     3845   the Content-Location value provides an identifier for retrieving
     3846   a copy of that same receipt in the future.
     3849   If Content-Location is included in a request message, then it &MAY;
     3850   be interpreted by the origin server as an indication of where the
     3851   user agent originally obtained the content of the enclosed
     3852   representation (prior to any subsequent modification of the content
     3853   by that user agent).  In other words, the user agent is providing
     3854   the same representation metadata that it received with the original
     3855   representation.  However, such interpretation &MUST-NOT; be used to
     3856   alter the semantics of the method requested by the client.  For
     3857   example, if a client makes a PUT request on a negotiated resource
     3858   and the origin server accepts that PUT (without redirection), then the
     3859   new set of values for that resource is expected to be consistent with
     3860   the one representation supplied in that PUT; the Content-Location
     3861   cannot be used as a form of reverse content selection that
     3862   identifies only one of the negotiated representations to be updated.
     3863   If the user agent had wanted the latter semantics, it would have applied
     3864   the PUT directly to the Content-Location URI.
     3867   A Content-Location field received in a request message is transitory
     3868   information that &SHOULD-NOT; be saved with other representation
     3869   metadata for use in later responses.  The Content-Location's value
     3870   might be saved for use in other contexts, such as within source links
     3871   or other metadata.
     3874   A cache cannot assume that a representation with a Content-Location
     3875   different from the URI used to retrieve it can be used to respond to
     3876   later requests on that Content-Location URI.
     3879   If the Content-Location value is a partial URI, the partial URI is
     3880   interpreted relative to the effective request URI.
     3884<section title="Content-Type" anchor="header.content-type">
     3885  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
     3886  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
     3887  <x:anchor-alias value="Content-Type"/>
     3889   The "Content-Type" header field indicates the media type of the
     3890   representation. In the case of responses to the HEAD method, the media type is
     3891   that which would have been sent had the request been a GET.
     3893<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
     3894  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
     3897   Media types are defined in <xref target="media.types"/>. An example of the field is
     3899<figure><artwork type="example">
     3900  Content-Type: text/html; charset=ISO-8859-4
     3903   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
    27553910<section title="IANA Considerations" anchor="IANA.considerations">
    30284183   <ttcol>Reference</ttcol>
     4185   <c>Accept</c>
     4186   <c>http</c>
     4187   <c>standard</c>
     4188   <c>
     4189      <xref target="header.accept"/>
     4190   </c>
     4191   <c>Accept-Charset</c>
     4192   <c>http</c>
     4193   <c>standard</c>
     4194   <c>
     4195      <xref target="header.accept-charset"/>
     4196   </c>
     4197   <c>Accept-Encoding</c>
     4198   <c>http</c>
     4199   <c>standard</c>
     4200   <c>
     4201      <xref target="header.accept-encoding"/>
     4202   </c>
     4203   <c>Accept-Language</c>
     4204   <c>http</c>
     4205   <c>standard</c>
     4206   <c>
     4207      <xref target="header.accept-language"/>
     4208   </c>
    30304209   <c>Allow</c>
    30314210   <c>http</c>
    30334212   <c>
    30344213      <xref target="header.allow"/>
     4214   </c>
     4215   <c>Content-Encoding</c>
     4216   <c>http</c>
     4217   <c>standard</c>
     4218   <c>
     4219      <xref target="header.content-encoding"/>
     4220   </c>
     4221   <c>Content-Language</c>
     4222   <c>http</c>
     4223   <c>standard</c>
     4224   <c>
     4225      <xref target="header.content-language"/>
     4226   </c>
     4227   <c>Content-Location</c>
     4228   <c>http</c>
     4229   <c>standard</c>
     4230   <c>
     4231      <xref target="header.content-location"/>
     4232   </c>
     4233   <c>Content-Type</c>
     4234   <c>http</c>
     4235   <c>standard</c>
     4236   <c>
     4237      <xref target="header.content-type"/>
    30354238   </c>
    30364239   <c>Date</c>
    30574260   <c>
    30584261      <xref target="header.location"/>
     4262   </c>
     4263   <c>MIME-Version</c>
     4264   <c>http</c>
     4265   <c>standard</c>
     4266   <c>
     4267      <xref target="mime-version"/>
    30594268   </c>
    30604269   <c>Max-Forwards</c>
     4307<section title="Content Coding Registry" anchor="content.coding.registration">
     4309   The registration procedure for HTTP Content Codings is now defined
     4310   by <xref target="content.coding.registry"/> of this document.
     4313   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
     4314   shall be updated with the registration below:
     4316<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
     4317   <ttcol>Name</ttcol>
     4318   <ttcol>Description</ttcol>
     4319   <ttcol>Reference</ttcol>
     4320   <c>compress</c>
     4321   <c>UNIX "compress" program method</c>
     4322   <c>
     4323      &compress-coding;
     4324   </c>
     4325   <c>deflate</c>
     4326   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
     4327   the "zlib" data format (<xref target="RFC1950"/>)
     4328   </c>
     4329   <c>
     4330      &deflate-coding;
     4331   </c>
     4332   <c>gzip</c>
     4333   <c>Same as GNU zip <xref target="RFC1952"/></c>
     4334   <c>
     4335      &gzip-coding;
     4336   </c>
     4337   <c>identity</c>
     4338   <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
     4339   <c>
     4340      <xref target="header.accept-encoding"/>
     4341   </c>
     4471<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
     4473   Accept header fields can reveal information about the user to all
     4474   servers which are accessed. The Accept-Language header field in particular
     4475   can reveal information the user would consider to be of a private
     4476   nature, because the understanding of particular languages is often
     4477   strongly correlated to the membership of a particular ethnic group.
     4478   User agents which offer the option to configure the contents of an
     4479   Accept-Language header field to be sent in every request are strongly
     4480   encouraged to let the configuration process include a message which
     4481   makes the user aware of the loss of privacy involved.
     4484   An approach that limits the loss of privacy would be for a user agent
     4485   to omit the sending of Accept-Language header fields by default, and to ask
     4486   the user whether or not to start sending Accept-Language header fields to a
     4487   server if it detects, by looking for any Vary header fields
     4488   generated by the server, that such sending could improve the quality
     4489   of service.
     4492   Elaborate user-customized accept header fields sent in every request,
     4493   in particular if these include quality values, can be used by servers
     4494   as relatively reliable and long-lived user identifiers. Such user
     4495   identifiers would allow content providers to do click-trail tracking,
     4496   and would allow collaborating content providers to match cross-server
     4497   click-trails or form submissions of individual users. Note that for
     4498   many users not behind a proxy, the network address of the host
     4499   running the user agent will also serve as a long-lived user
     4500   identifier. In environments where proxies are used to enhance
     4501   privacy, user agents ought to be conservative in offering accept
     4502   header configuration options to end users. As an extreme privacy
     4503   measure, proxies could filter the accept header fields in relayed requests.
     4504   General purpose user agents which provide a high degree of header
     4505   configurability &SHOULD; warn users about the loss of privacy which can
     4506   be involved.
    3257 <reference anchor="Part3">
    3258   <front>
    3259     <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
    3260     <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    3261       <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    3262       <address><email>fielding@gbiv.com</email></address>
    3263     </author>
    3264     <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    3265       <organization abbrev="W3C">World Wide Web Consortium</organization>
    3266       <address><email>ylafon@w3.org</email></address>
    3267     </author>
    3268     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    3269       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    3270       <address><email>julian.reschke@greenbytes.de</email></address>
    3271     </author>
    3272     <date month="&ID-MONTH;" year="&ID-YEAR;"/>
    3273   </front>
    3274   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
    3275   <x:source href="p3-payload.xml" basename="p3-payload"/>
    3276 </reference>
    32784542<reference anchor="Part4">
    32794543  <front>
     4630<reference anchor="RFC1950">
     4631  <front>
     4632    <title>ZLIB Compressed Data Format Specification version 3.3</title>
     4633    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
     4634      <organization>Aladdin Enterprises</organization>
     4635      <address><email>ghost@aladdin.com</email></address>
     4636    </author>
     4637    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
     4638    <date month="May" year="1996"/>
     4639  </front>
     4640  <seriesInfo name="RFC" value="1950"/>
     4641  <!--<annotation>
     4642    RFC 1950 is an Informational RFC, thus it might be less stable than
     4643    this specification. On the other hand, this downward reference was
     4644    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
     4645    therefore it is unlikely to cause problems in practice. See also
     4646    <xref target="BCP97"/>.
     4647  </annotation>-->
     4650<reference anchor="RFC1951">
     4651  <front>
     4652    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
     4653    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
     4654      <organization>Aladdin Enterprises</organization>
     4655      <address><email>ghost@aladdin.com</email></address>
     4656    </author>
     4657    <date month="May" year="1996"/>
     4658  </front>
     4659  <seriesInfo name="RFC" value="1951"/>
     4660  <!--<annotation>
     4661    RFC 1951 is an Informational RFC, thus it might be less stable than
     4662    this specification. On the other hand, this downward reference was
     4663    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
     4664    therefore it is unlikely to cause problems in practice. See also
     4665    <xref target="BCP97"/>.
     4666  </annotation>-->
     4669<reference anchor="RFC1952">
     4670  <front>
     4671    <title>GZIP file format specification version 4.3</title>
     4672    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
     4673      <organization>Aladdin Enterprises</organization>
     4674      <address><email>ghost@aladdin.com</email></address>
     4675    </author>
     4676    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
     4677      <address><email>gzip@prep.ai.mit.edu</email></address>
     4678    </author>
     4679    <author initials="M." surname="Adler" fullname="Mark Adler">
     4680      <address><email>madler@alumni.caltech.edu</email></address>
     4681    </author>
     4682    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
     4683      <address><email>ghost@aladdin.com</email></address>
     4684    </author>
     4685    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
     4686      <address><email>randeg@alumni.rpi.edu</email></address>
     4687    </author>
     4688    <date month="May" year="1996"/>
     4689  </front>
     4690  <seriesInfo name="RFC" value="1952"/>
     4691  <!--<annotation>
     4692    RFC 1952 is an Informational RFC, thus it might be less stable than
     4693    this specification. On the other hand, this downward reference was
     4694    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
     4695    therefore it is unlikely to cause problems in practice. See also
     4696    <xref target="BCP97"/>.
     4697  </annotation>-->
     4700<reference anchor="RFC2045">
     4701  <front>
     4702    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
     4703    <author initials="N." surname="Freed" fullname="Ned Freed">
     4704      <organization>Innosoft International, Inc.</organization>
     4705      <address><email>ned@innosoft.com</email></address>
     4706    </author>
     4707    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
     4708      <organization>First Virtual Holdings</organization>
     4709      <address><email>nsb@nsb.fv.com</email></address>
     4710    </author>
     4711    <date month="November" year="1996"/>
     4712  </front>
     4713  <seriesInfo name="RFC" value="2045"/>
     4716<reference anchor="RFC2046">
     4717  <front>
     4718    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
     4719    <author initials="N." surname="Freed" fullname="Ned Freed">
     4720      <organization>Innosoft International, Inc.</organization>
     4721      <address><email>ned@innosoft.com</email></address>
     4722    </author>
     4723    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
     4724      <organization>First Virtual Holdings</organization>
     4725      <address><email>nsb@nsb.fv.com</email></address>
     4726    </author>
     4727    <date month="November" year="1996"/>
     4728  </front>
     4729  <seriesInfo name="RFC" value="2046"/>
    33664732<reference anchor="RFC2119">
    33674733  <front>
    33754741  <seriesInfo name="BCP" value="14"/>
    33764742  <seriesInfo name="RFC" value="2119"/>
     4745<reference anchor='RFC2295'>
     4746  <front>
     4747    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
     4748    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
     4749      <organization>Technische Universiteit Eindhoven</organization>
     4750      <address>
     4751        <email>koen@win.tue.nl</email>
     4752      </address>
     4753    </author>
     4754    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
     4755      <organization>Hewlett-Packard Company</organization>
     4756      <address>
     4757        <email>mutz@hpl.hp.com</email>
     4758      </address>
     4759    </author>
     4760    <date year='1998' month='March'/>
     4761  </front>
     4762  <seriesInfo name='RFC' value='2295'/>
     4795<reference anchor="RFC4288">
     4796  <front>
     4797    <title>Media Type Specifications and Registration Procedures</title>
     4798    <author initials="N." surname="Freed" fullname="N. Freed">
     4799      <organization>Sun Microsystems</organization>
     4800      <address>
     4801        <email>ned.freed@mrochek.com</email>
     4802      </address>
     4803    </author>
     4804    <author initials="J." surname="Klensin" fullname="J. Klensin">
     4805      <address>
     4806        <email>klensin+ietf@jck.com</email>
     4807      </address>
     4808    </author>
     4809    <date year="2005" month="December"/>
     4810  </front>
     4811  <seriesInfo name="BCP" value="13"/>
     4812  <seriesInfo name="RFC" value="4288"/>
     4815<reference anchor='RFC4647'>
     4816  <front>
     4817    <title>Matching of Language Tags</title>
     4818    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
     4819      <organization>Yahoo! Inc.</organization>
     4820      <address><email>addison@inter-locale.com</email></address>
     4821    </author>
     4822    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
     4823      <organization>Google</organization>
     4824      <address><email>mark.davis@macchiato.com</email></address>
     4825    </author>
     4826    <date year='2006' month='September' />
     4827  </front>
     4828  <seriesInfo name='BCP' value='47' />
     4829  <seriesInfo name='RFC' value='4647' />
    34094832<reference anchor="RFC5234">
    34104833  <front>
     4853<reference anchor='RFC5646'>
     4854  <front>
     4855    <title>Tags for Identifying Languages</title>
     4856    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
     4857      <organization>Lab126</organization>
     4858      <address><email>addison@inter-locale.com</email></address>
     4859    </author>
     4860    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
     4861      <organization>Google</organization>
     4862      <address><email>mark.davis@google.com</email></address>
     4863    </author>
     4864    <date month='September' year='2009' />
     4865  </front>
     4866  <seriesInfo name='BCP' value='47' />
     4867  <seriesInfo name='RFC' value='5646' />
     4907<reference anchor="RFC2049">
     4908  <front>
     4909    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
     4910    <author initials="N." surname="Freed" fullname="Ned Freed">
     4911      <organization>Innosoft International, Inc.</organization>
     4912      <address><email>ned@innosoft.com</email></address>
     4913    </author>
     4914    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
     4915      <organization>First Virtual Holdings</organization>
     4916      <address><email>nsb@nsb.fv.com</email></address>
     4917    </author>
     4918    <date month="November" year="1996"/>
     4919  </front>
     4920  <seriesInfo name="RFC" value="2049"/>
    34674923<reference anchor="RFC2068">
    34684924  <front>
     4951<reference anchor="RFC2076">
     4952  <front>
     4953    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
     4954    <author initials="J." surname="Palme" fullname="Jacob Palme">
     4955      <organization>Stockholm University/KTH</organization>
     4956      <address><email>jpalme@dsv.su.se</email></address>
     4957    </author>
     4958    <date month="February" year="1997"/>
     4959  </front>
     4960  <seriesInfo name="RFC" value="2076"/>
     4963<reference anchor="RFC2277">
     4964  <front>
     4965    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
     4966    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
     4967      <organization>UNINETT</organization>
     4968      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
     4969    </author>
     4970    <date month="January" year="1998"/>
     4971  </front>
     4972  <seriesInfo name="BCP" value="18"/>
     4973  <seriesInfo name="RFC" value="2277"/>
     4976<reference anchor="RFC2388">
     4977  <front>
     4978    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
     4979    <author initials="L." surname="Masinter" fullname="Larry Masinter">
     4980      <organization>Xerox Palo Alto Research Center</organization>
     4981      <address><email>masinter@parc.xerox.com</email></address>
     4982    </author>
     4983    <date year="1998" month="August"/>
     4984  </front>
     4985  <seriesInfo name="RFC" value="2388"/>
     4988<reference anchor="RFC2557">
     4989  <front>
     4990    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
     4991    <author initials="F." surname="Palme" fullname="Jacob Palme">
     4992      <organization>Stockholm University and KTH</organization>
     4993      <address><email>jpalme@dsv.su.se</email></address>
     4994    </author>
     4995    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
     4996      <organization>Microsoft Corporation</organization>
     4997      <address><email>alexhop@microsoft.com</email></address>
     4998    </author>
     4999    <author initials="N." surname="Shelness" fullname="Nick Shelness">
     5000      <organization>Lotus Development Corporation</organization>
     5001      <address><email>Shelness@lotus.com</email></address>
     5002    </author>
     5003    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
     5004      <address><email>stef@nma.com</email></address>
     5005    </author>
     5006    <date year="1999" month="March"/>
     5007  </front>
     5008  <seriesInfo name="RFC" value="2557"/>
    34955011<reference anchor="RFC2616">
    34965012  <front>
    35435059  </front>
    35445060  <seriesInfo name='RFC' value='2817' />
     5063<reference anchor="RFC3629">
     5064  <front>
     5065    <title>UTF-8, a transformation format of ISO 10646</title>
     5066    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
     5067      <organization>Alis Technologies</organization>
     5068      <address><email>fyergeau@alis.com</email></address>
     5069    </author>
     5070    <date month="November" year="2003"/>
     5071  </front>
     5072  <seriesInfo name="STD" value="63"/>
     5073  <seriesInfo name="RFC" value="3629"/>
     5157<reference anchor="RFC6151">
     5158  <front>
     5159    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
     5160    <author initials="S." surname="Turner" fullname="S. Turner"/>
     5161    <author initials="L." surname="Chen" fullname="L. Chen"/>
     5162    <date year="2011" month="March" />
     5163  </front>
     5164  <seriesInfo name="RFC" value="6151" />
     5167<reference anchor="RFC6266">
     5168  <front>
     5169    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
     5170    in the Hypertext Transfer Protocol (HTTP)</title>
     5171    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
     5172      <organization abbrev="greenbytes">greenbytes GmbH</organization>
     5173      <address>
     5174        <email>julian.reschke@greenbytes.de</email>
     5175      </address>
     5176    </author>
     5177    <date month="June" year="2011"/>
     5178  </front>
     5179  <seriesInfo name='RFC' value='6266' />
    36285182<reference anchor="draft-reschke-http-status-308">
    36295183        <front>
     5198<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
     5200   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
     5201   allow a message body to be transmitted in an open variety of
     5202   representations and with extensible mechanisms. However, RFC 2045
     5203   discusses mail, and HTTP has a few features that are different from
     5204   those described in MIME. These differences were carefully chosen
     5205   to optimize performance over binary connections, to allow greater
     5206   freedom in the use of new media types, to make date comparisons
     5207   easier, and to acknowledge the practice of some early HTTP servers
     5208   and clients.
     5211   This appendix describes specific areas where HTTP differs from MIME.
     5212   Proxies and gateways to strict MIME environments &SHOULD; be
     5213   aware of these differences and provide the appropriate conversions
     5214   where necessary. Proxies and gateways from MIME environments to HTTP
     5215   also need to be aware of the differences because some conversions
     5216   might be required.
     5219<section title="MIME-Version" anchor="mime-version">
     5220  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
     5221  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
     5222  <x:anchor-alias value="MIME-Version"/>
     5224   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
     5225   include a single MIME-Version header field to indicate what
     5226   version of the MIME protocol was used to construct the message. Use
     5227   of the MIME-Version header field indicates that the message is in
     5228   full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
     5229   Proxies/gateways are responsible for ensuring full conformance (where
     5230   possible) when exporting HTTP messages to strict MIME environments.
     5232<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
     5233  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
     5236   MIME version "1.0" is the default for use in HTTP/1.1. However,
     5237   HTTP/1.1 message parsing and semantics are defined by this document
     5238   and not the MIME specification.
     5242<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
     5244   MIME requires that an Internet mail body-part be converted to
     5245   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
     5246   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
     5247   allowed for subtypes of the "text" media type when transmitted over
     5248   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
     5249   line breaks as CRLF and forbids the use of CR or LF outside of line
     5250   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
     5251   line break within text content when a message is transmitted over
     5252   HTTP.
     5255   Where it is possible, a proxy or gateway from HTTP to a strict MIME
     5256   environment &SHOULD; translate all line breaks within the text media
     5257   types described in <xref target="canonicalization.and.text.defaults"/>
     5258   of this document to the RFC 2049
     5259   canonical form of CRLF. Note, however, that this might be complicated
     5260   by the presence of a Content-Encoding and by the fact that HTTP
     5261   allows the use of some character encodings which do not use octets 13 and
     5262   10 to represent CR and LF, respectively, as is the case for some multi-byte
     5263   character encodings.
     5266   Conversion will break any cryptographic
     5267   checksums applied to the original content unless the original content
     5268   is already in canonical form. Therefore, the canonical form is
     5269   recommended for any content that uses such checksums in HTTP.
     5274<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
     5276   HTTP/1.1 uses a restricted set of date formats (<xref target="http.date"/>) to
     5277   simplify the process of date comparison. Proxies and gateways from
     5278   other protocols &SHOULD; ensure that any Date header field present in a
     5279   message conforms to one of the HTTP/1.1 formats and rewrite the date
     5280   if necessary.
     5284<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
     5286   MIME does not include any concept equivalent to HTTP/1.1's
     5287   Content-Encoding header field. Since this acts as a modifier on the
     5288   media type, proxies and gateways from HTTP to MIME-compliant
     5289   protocols &MUST; either change the value of the Content-Type header
     5290   field or decode the representation before forwarding the message. (Some
     5291   experimental applications of Content-Type for Internet mail have used
     5292   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
     5293   a function equivalent to Content-Encoding. However, this parameter is
     5294   not part of the MIME standards).
     5298<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
     5299  <iref item="Content-Transfer-Encoding header field" x:for-anchor=""/>
     5300  <iref item="Header Fields" subitem="Content-Transfer-Encoding" x:for-anchor=""/>
     5302   HTTP does not use the Content-Transfer-Encoding field of MIME.
     5303   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
     5304   remove any Content-Transfer-Encoding
     5305   prior to delivering the response message to an HTTP client.
     5308   Proxies and gateways from HTTP to MIME-compliant protocols are
     5309   responsible for ensuring that the message is in the correct format
     5310   and encoding for safe transport on that protocol, where "safe
     5311   transport" is defined by the limitations of the protocol being used.
     5312   Such a proxy or gateway &SHOULD; label the data with an appropriate
     5313   Content-Transfer-Encoding if doing so will improve the likelihood of
     5314   safe transport over the destination protocol.
     5318<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
     5320   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
     5321   Proxies/gateways &MUST; remove any transfer-coding prior to
     5322   forwarding a message via a MIME-compliant protocol.
     5326<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
     5328   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
     5329   need to be aware of MIME line length limitations. Since HTTP does not
     5330   have this limitation, HTTP does not fold long lines. MHTML messages
     5331   being transported by HTTP follow all conventions of MHTML, including
     5332   line length limitations and folding, canonicalization, etc., since
     5333   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
     5334   does not interpret the content or any MIME header lines that might be
     5335   contained therein.
     5340<section title="Additional Features" anchor="additional.features">
     5342   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
     5343   existing HTTP implementations, but not consistently and correctly
     5344   across most HTTP/1.1 applications. Implementors are advised to be
     5345   aware of these features, but cannot rely upon their presence in, or
     5346   interoperability with, other HTTP/1.1 applications. Some of these
     5347   describe proposed experimental features, and some describe features
     5348   that experimental deployment found lacking that are now addressed in
     5349   the base HTTP/1.1 specification.
     5352   A number of other header fields, such as Content-Disposition and Title,
     5353   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
     5354   and <xref target="RFC2076"/>).
    36445358<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
    37325446  (<xref target="header.server"/>)
     5449  Clarify contexts that charset is used in.
     5450  (<xref target="character.sets"/>)
     5453  Registration of Content Codings now requires IETF Review
     5454  (<xref target="content.coding.registry"/>)
     5457  Remove the default character encoding for text media types; the default
     5458  now is whatever the media type definition says.
     5459  (<xref target="canonicalization.and.text.defaults"/>)
     5462  Change ABNF productions for header fields to only define the field value.
     5463  (<xref target="header.field.definitions"/>)
     5466  Remove definition of Content-MD5 header field because it was inconsistently
     5467  implemented with respect to partial responses, and also because of known
     5468  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
     5469  (<xref target="header.field.definitions"/>)
     5472  Remove ISO-8859-1 special-casing in Accept-Charset.
     5473  (<xref target="header.accept-charset"/>)
     5476  Remove base URI setting semantics for Content-Location due to poor
     5477  implementation support, which was caused by too many broken servers emitting
     5478  bogus Content-Location header fields, and also the potentially undesirable effect
     5479  of potentially breaking relative links in content-negotiated resources.
     5480  (<xref target="header.content-location"/>)
     5483  Remove reference to non-existant identity transfer-coding value tokens.
     5484  (<xref target="no.content-transfer-encoding"/>)
     5487  Remove discussion of Content-Disposition header field, it is now defined
     5488  by <xref target="RFC6266"/>.
     5489  (<xref target="additional.features"/>)
    37395496<artwork type="abnf" name="p2-semantics.parsed-abnf">
     5497<x:ref>Accept</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
     5498 OWS media-range [ accept-params ] ] ) ]
     5499<x:ref>Accept-Charset</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
     5500 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
     5501 qvalue ] ] )
     5502<x:ref>Accept-Encoding</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
     5503 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
     5504<x:ref>Accept-Language</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
     5505 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
     5506 ] )
    37405507<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
    37425509<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
     5511<x:ref>Content-Encoding</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
     5512 content-coding ] )
     5513<x:ref>Content-Language</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
     5514 language-tag ] )
     5515<x:ref>Content-Location</x:ref> = absolute-URI / partial-URI
     5516<x:ref>Content-Type</x:ref> = media-type
    37445518<x:ref>Date</x:ref> = HTTP-date
    37545528<x:ref>Location</x:ref> = URI-reference
     5530<x:ref>MIME-Version</x:ref> = 1*DIGIT "." 1*DIGIT
    37565532<x:ref>Max-Forwards</x:ref> = 1*DIGIT
    37605536<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
    37615538<x:ref>Referer</x:ref> = absolute-URI / partial-URI
    37625539<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
    37665543<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
    37675545<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
    37695547<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
     5549<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
     5550<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
    37705552<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
     5553<x:ref>attribute</x:ref> = token
     5555<x:ref>charset</x:ref> = token
     5557<x:ref>codings</x:ref> = content-coding / "identity" / "*"
    37725559<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
     5560<x:ref>content-coding</x:ref> = token
    37745562<x:ref>date1</x:ref> = day SP month SP year
    37755564<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
    37765566<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
    37775567<x:ref>day</x:ref> = 2DIGIT
    37945584<x:ref>expect-name</x:ref> = token
    37955586<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
    37965588<x:ref>expect-value</x:ref> = token / quoted-string
    37975589<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
    38005592<x:ref>hour</x:ref> = 2DIGIT
     5594<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
     5596<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
    38025598<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
     5600<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
     5601 ";" OWS parameter )
     5602<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
    38035603<x:ref>method</x:ref> = token
    38045604<x:ref>minute</x:ref> = 2DIGIT
    38185618<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
    38195620<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
     5622<x:ref>parameter</x:ref> = attribute "=" value
    38215624<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
    38225626<x:ref>product</x:ref> = token [ "/" product-version ]
    38235627<x:ref>product-version</x:ref> = token
    38275631<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
    38285633<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
    38295635<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
    38315637<x:ref>second</x:ref> = 2DIGIT
    38325639<x:ref>status-code</x:ref> = 3DIGIT
     5641<x:ref>subtype</x:ref> = token
    38345643<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
    38355645<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
     5647<x:ref>type</x:ref> = token
     5649<x:ref>value</x:ref> = word
    38375651<x:ref>year</x:ref> = 4DIGIT
    38405654<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
     5655; qvalue UNDEFINED
     5656; word UNDEFINED
     5657; Accept defined but not used
     5658; Accept-Charset defined but not used
     5659; Accept-Encoding defined but not used
     5660; Accept-Language defined but not used
    38415661; Allow defined but not used
     5662; Content-Encoding defined but not used
     5663; Content-Language defined but not used
     5664; Content-Location defined but not used
     5665; Content-Type defined but not used
    38425666; Date defined but not used
    38435667; Expect defined but not used
    38445668; From defined but not used
    38455669; Location defined but not used
     5670; MIME-Version defined but not used
    38465671; Max-Forwards defined but not used
    38475672; Referer defined but not used
    3916 <section title="Since draft-ietf-httpbis-p2-semantics-01">
     5741<section title="Since draft-ietf-httpbis-p3-payload-00">
    39185743  Closed issues:
    39195744  <list style="symbols">
    39205745    <t>
     5746      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
     5747      "Media Type Registrations"
     5748      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
     5749    </t>
     5750    <t>
     5751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
     5752      "Clarification regarding quoting of charset values"
     5753      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
     5754    </t>
     5755    <t>
     5756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
     5757      "Remove 'identity' token references"
     5758      (<eref target="http://purl.org/NET/http-errata#identity"/>)
     5759    </t>
     5760    <t>
     5761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
     5762      "Accept-Encoding BNF"
     5763    </t>
     5764    <t>
     5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
     5766      "Normative and Informative references"
     5767    </t>
     5768    <t>
     5769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
     5770      "RFC1700 references"
     5771    </t>
     5772    <t>
     5773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
     5774      "Updating to RFC4288"
     5775    </t>
     5776    <t>
     5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
     5778      "Informative references"
     5779    </t>
     5780    <t>
     5781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
     5782      "ISO-8859-1 Reference"
     5783    </t>
     5784    <t>
     5785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
     5786      "Encoding References Normative"
     5787    </t>
     5788    <t>
     5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
     5790      "Normative up-to-date references"
     5791    </t>
     5792  </list>
     5796<section title="Since draft-ietf-httpbis-p2-semantics-01">
     5798  Closed issues:
     5799  <list style="symbols">
     5800    <t>
    39215801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
    39225802      "PUT side effects"
     5827<section title="Since draft-ietf-httpbis-p3-payload-01">
     5829  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
     5830  <list style="symbols">
     5831    <t>
     5832      Add explicit references to BNF syntax and rules imported from other parts of the specification.
     5833    </t>
     5834  </list>
    39475838<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
    4000 <section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
     5891<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.3.02">
    40025893  Closed issues:
    40035894  <list style="symbols">
    40045895    <t>
     5896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
     5897      "Quoting Charsets"
     5898    </t>
     5899    <t>
     5900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
     5901      "Classification for Allow header"
     5902    </t>
     5903    <t>
     5904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
     5905      "missing default for qvalue in description of Accept-Encoding"
     5906    </t>
     5907  </list>
     5910  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
     5911  <list style="symbols">
     5912    <t>
     5913      Reference RFC 3984, and update header field registrations for headers defined
     5914      in this document.
     5915    </t>
     5916  </list>
     5920<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
     5922  Closed issues:
     5923  <list style="symbols">
     5924    <t>
    40055925      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
    40065926      "OPTIONS request bodies"
    4029 <section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
     5949<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.3.03">
    40315951  Closed issues:
    40325952  <list style="symbols">
    40335953    <t>
     5954      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
     5955      "Quoting Charsets"
     5956    </t>
     5957    <t>
     5958      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
     5959      "language tag matching (Accept-Language) vs RFC4647"
     5960    </t>
     5961    <t>
     5962      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
     5963      "RFC 1806 has been replaced by RFC2183"
     5964    </t>
     5965  </list>
     5968  Other changes:
     5969  <list style="symbols">
     5970    <t>
     5971      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
     5972      "Encoding References Normative" &mdash; rephrase the annotation and reference
     5973      BCP97.
     5974    </t>
     5975  </list>
     5979<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
     5981  Closed issues:
     5982  <list style="symbols">
     5983    <t>
    40345984      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
    40355985      "Content-*"
    4061 <section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
     6011<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.3.04">
    40636013  Closed issues:
    40646014  <list style="symbols">
    40656015    <t>
     6016      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
     6017      "RFC 2822 is updated by RFC 5322"
     6018    </t>
     6019  </list>
     6022  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
     6023  <list style="symbols">
     6024    <t>
     6025      Use "/" instead of "|" for alternatives.
     6026    </t>
     6027    <t>
     6028      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
     6029      whitespace ("OWS") and required whitespace ("RWS").
     6030    </t>
     6031    <t>
     6032      Rewrite ABNFs to spell out whitespace rules, factor out
     6033      header field value format definitions.
     6034    </t>
     6035  </list>
     6039<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
     6041  Closed issues:
     6042  <list style="symbols">
     6043    <t>
    40666044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
    40676045      "reason-phrase BNF"
    4081 <section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
     6059<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.3.05">
    40836061  Closed issues:
    40846062  <list style="symbols">
    40856063    <t>
     6064      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
     6065      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
     6066    </t>
     6067  </list>
     6070  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
     6071  <list style="symbols">
     6072    <t>
     6073      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
     6074    </t>
     6075  </list>
     6078  Other changes:
     6079  <list style="symbols">
     6080    <t>
     6081      Move definition of quality values into Part 1.
     6082    </t>
     6083  </list>
     6087<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
     6089  Closed issues:
     6090  <list style="symbols">
     6091    <t>
    40866092      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
    40876093      "Clarify when Referer is sent"
    4101 <section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
     6107<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.3.06">
    41036109  Closed issues:
    41046110  <list style="symbols">
    41056111    <t>
     6112      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
     6113      "Content-Location isn't special"
     6114    </t>
     6115    <t>
     6116      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
     6117      "Content Sniffing"
     6118    </t>
     6119  </list>
     6123<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
     6125  Closed issues:
     6126  <list style="symbols">
     6127    <t>
    41066128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
    41076129      "Idempotency"
    41436165      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
    41446166      "Are OPTIONS and TRACE safe?"
     6167    </t>
     6168  </list>
     6172<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.3-07">
     6174  Closed issues:
     6175  <list style="symbols">
     6176    <t>
     6177      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
     6178      "Updated reference for language tags"
     6179    </t>
     6180    <t>
     6181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
     6182      "Clarify rules for determining what entities a response carries"
     6183    </t>
     6184    <t>
     6185      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
     6186      "Content-Location base-setting problems"
     6187    </t>
     6188    <t>
     6189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
     6190      "Content Sniffing"
     6191    </t>
     6192    <t>
     6193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
     6194      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
     6195    </t>
     6196    <t>
     6197      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
     6198      "move definitions of gzip/deflate/compress to part 1"
     6199    </t>
     6200  </list>
     6203  Partly resolved issues:
     6204  <list style="symbols">
     6205    <t>
     6206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
     6207      "update IANA requirements wrt Transfer-Coding values" (add the
     6208      IANA Considerations subsection)
     6209    </t>
     6210    <t>
     6211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
     6212      "update IANA requirements wrt Content-Coding values" (add the
     6213      IANA Considerations subsection)
    41456214    </t>
    41466215  </list>
    4163 <section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
     6232<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.3.08">
    41656234  Closed issues:
    41666235  <list style="symbols">
    41676236    <t>
     6237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
     6238      "Content Negotiation for media types"
     6239    </t>
     6240    <t>
     6241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
     6242      "Accept-Language: which RFC4647 filtering?"
     6243    </t>
     6244  </list>
     6248<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
     6250  Closed issues:
     6251  <list style="symbols">
     6252    <t>
    41686253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
    41696254      "Fragment combination / precedence during redirects"
    4188 <section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
     6273<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.3.09">
    41906275  Closed issues:
    41916276  <list style="symbols">
    41926277    <t>
     6278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
     6279      "MIME-Version not listed in P1, general header fields"
     6280    </t>
     6281    <t>
     6282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
     6283      "IANA registry for content/transfer encodings"
     6284    </t>
     6285    <t>
     6286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
     6287      "Content Sniffing"
     6288    </t>
     6289    <t>
     6290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
     6291      "use of term "word" when talking about header structure"
     6292    </t>
     6293  </list>
     6296  Partly resolved issues:
     6297  <list style="symbols">
     6298    <t>
     6299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
     6300      "Term for the requested resource's URI"
     6301    </t>
     6302  </list>
     6306<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
     6308  Closed issues:
     6309  <list style="symbols">
     6310    <t>
    41936311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
    41946312      "Clarify 'Requested Variant'"
    4220 <section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
     6338<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.3.10">
    42226340  Closed issues:
    42236341  <list style="symbols">
    42246342    <t>
     6343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
     6344      "Clarify 'Requested Variant'"
     6345    </t>
     6346    <t>
     6347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
     6348      "Content-Location isn't special"
     6349    </t>
     6350    <t>
     6351      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
     6352      "Delimiting messages with multipart/byteranges"
     6353    </t>
     6354    <t>
     6355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
     6356      "Clarify entity / representation / variant terminology"
     6357    </t>
     6358    <t>
     6359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
     6360      "confusing req. language for Content-Location"
     6361    </t>
     6362    <t>
     6363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
     6364      "Content-Location on 304 responses"
     6365    </t>
     6366    <t>
     6367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
     6368      "'requested resource' in content-encoding definition"
     6369    </t>
     6370    <t>
     6371      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
     6372      "consider removing the 'changes from 2068' sections"
     6373    </t>
     6374  </list>
     6377  Partly resolved issues:
     6378  <list style="symbols">
     6379    <t>
     6380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
     6381      "Content-MD5 and partial responses"
     6382    </t>
     6383  </list>
     6387<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
     6389  Closed issues:
     6390  <list style="symbols">
     6391    <t>
    42256392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
    42266393      "Considerations for new status codes"
    42336400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
    42346401      "User-Agent guidelines" (relating to the 'User-Agent' header field)
     6402    </t>
     6403  </list>
     6407<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.3.11">
     6409  Closed issues:
     6410  <list style="symbols">
     6411    <t>
     6412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
     6413      "Factor out Content-Disposition"
    42356414    </t>
    42366415  </list>
    4327 <section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
     6506<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.3.12">
    43296508  Closed issues:
    43306509  <list style="symbols">
    43316510    <t>
     6511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
     6512      "Header Classification"
     6513    </t>
     6514    <t>
    43326515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
    43336516      "untangle ABNFs for header fields"
    43346517    </t>
    43356518    <t>
     6519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
     6520      "potentially misleading MAY in media-type def"
     6521    </t>
     6522  </list>
     6526<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
     6528  Closed issues:
     6529  <list style="symbols">
     6530    <t>
     6531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
     6532      "untangle ABNFs for header fields"
     6533    </t>
     6534    <t>
    43366535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
    43376536      "message body in CONNECT request"
    4343 <section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
     6542<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.3.13">
    43456544  Closed issues:
    43466545  <list style="symbols">
    43476546    <t>
     6547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
     6548      "Default charsets for text media types"
     6549    </t>
     6550    <t>
     6551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
     6552      "Content-MD5 and partial responses"
     6553    </t>
     6554    <t>
     6555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
     6556      "untangle ABNFs for header fields"
     6557    </t>
     6558    <t>
     6559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
     6560      "confusing undefined parameter in media range example"
     6561    </t>
     6562  </list>
     6566<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
     6568  Closed issues:
     6569  <list style="symbols">
     6570    <t>
    43486571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
    43496572      "Clarify status code for rate limiting"
     6590<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.3.14">
     6592  None.
    43676596<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
    4383 <section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
     6612<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.3.15">
    43856614  Closed issues:
    43866615  <list style="symbols">
    43876616    <t>
     6617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
     6618      "Strength of requirements on Accept re: 406"
     6619    </t>
     6620  </list>
     6624<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
     6626  Closed issues:
     6627  <list style="symbols">
     6628    <t>
    43886629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
    43896630      "Redirects and non-GET methods"
    44006641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
    44016642      "clarify 303 redirect on HEAD"
     6643    </t>
     6644  </list>
     6648<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.3.16">
     6650  Closed issues:
     6651  <list style="symbols">
     6652    <t>
     6653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
     6654      "Document HTTP's error-handling philosophy"
    44026655    </t>
    44036656  </list>
    4440 <section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
     6693<section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.since.3.17">
    44426695  Closed issues:
    44436696  <list style="symbols">
    44446697    <t>
     6698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
     6699      "intended maturity level vs normative references"
     6700    </t>
     6701  </list>
     6705<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
     6707  Closed issues:
     6708  <list style="symbols">
     6709    <t>
    44456710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
    44466711      "Combining HEAD responses"
     6749<section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.since.3.18">
     6751  Closed issues:
     6752  <list style="symbols">
     6753    <t>
     6754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
     6755      "is ETag a representation header field?"
     6756    </t>
     6757    <t>
     6758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/338"/>:
     6759      "Content-Location doesn't constrain the cardinality of representations"
     6760    </t>
     6761    <t>
     6762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
     6763      "make IANA policy definitions consistent"
     6764    </t>
     6765  </list>
    44846769<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
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