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Timestamp:
28/03/12 15:54:24 (9 years ago)
Author:
julian.reschke@…
Message:

exp

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  • draft-ietf-httpbis/experiment/p3-payload.xml

    r1604 r1627  
    2323  <!ENTITY field-components         "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2424  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    25   <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2625  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2726  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     
    117116<abstract>
    118117<t>
    119    The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
    120    distributed, collaborative, hypertext information systems. HTTP has been in
    121    use by the World Wide Web global information initiative since 1990. This
    122    document is Part 3 of the seven-part specification that defines the protocol
    123    referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
    124 </t>
    125 <t>
    126    Part 3 defines HTTP message content, metadata, and content negotiation.
    127118</t>
    128119</abstract>
    129120
    130 <note title="Editorial Note (To be removed by RFC Editor)">
    131   <t>
    132     Discussion of this draft should take place on the HTTPBIS working group
    133     mailing list (ietf-http-wg@w3.org), which is archived at
    134     <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
    135   </t>
    136   <t>
    137     The current issues list is at
    138     <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
    139     documents (including fancy diffs) can be found at
    140     <eref target="http://tools.ietf.org/wg/httpbis/"/>.
    141   </t>
    142   <t>
    143     The changes in this draft are summarized in <xref target="changes.since.19"/>.
    144   </t>
    145 </note>
    146121</front>
    147122<middle>
    148 <section title="Introduction" anchor="introduction">
    149 <t>
    150    This document defines HTTP/1.1 message payloads (a.k.a., content), the
    151    associated metadata header fields that define how the payload is intended
    152    to be interpreted by a recipient, the request header fields that
    153    might influence content selection, and the various selection algorithms
    154    that are collectively referred to as HTTP content negotiation.
    155 </t>
    156 <t>
    157    This document is currently disorganized in order to minimize the changes
    158    between drafts and enable reviewers to see the smaller errata changes.
    159    A future draft will reorganize the sections to better reflect the content.
    160    In particular, the sections on entities will be renamed payload and moved
    161    to the first half of the document, while the sections on content negotiation
    162    and associated request header fields will be moved to the second half.  The
    163    current mess reflects how widely dispersed these topics and associated
    164    requirements had become in <xref target="RFC2616"/>.
    165 </t>
    166 
    167 <section title="Terminology" anchor="terminology">
    168 <t>
    169    This specification uses a number of terms to refer to the roles
    170    played by participants in, and objects of, the HTTP communication.
    171 </t>
    172 <t>
    173   <iref item="content negotiation"/>
    174   <x:dfn>content negotiation</x:dfn>
    175   <list>
    176     <t>
    177       The mechanism for selecting the appropriate representation when
    178       servicing a request. The representation in any response
    179       can be negotiated (including error responses).
    180     </t>
    181   </list>
    182 </t>
    183 <t>
    184   <iref primary="true" item="selected representation"/>
    185   <x:dfn>selected representation</x:dfn>
    186   <list>
    187     <t>
    188       The current representation of the target resource that would have been
    189       selected in a successful response if the same request had used the
    190       method GET and excluded any conditional request header fields.
    191     </t>
    192   </list>
    193 </t>
    194 </section>
    195 
    196 <section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
    197 <t>
    198    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    199    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
    200    document are to be interpreted as described in <xref target="RFC2119"/>.
    201 </t>
    202 <t>
    203    This document defines conformance criteria for several roles in HTTP
    204    communication, including Senders, Recipients, Clients, Servers, User-Agents,
    205    Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
    206    for definitions of these terms.
    207 </t>
    208 <t>
    209    An implementation is considered conformant if it complies with all of the
    210    requirements associated with its role(s). Note that SHOULD-level requirements
    211    are relevant here, unless one of the documented exceptions is applicable.
    212 </t>
    213 <t>
    214    This document also uses ABNF to define valid protocol elements
    215    (<xref target="notation"/>). In addition to the prose requirements placed
    216    upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
    217 </t>
    218 <t>
    219    Unless noted otherwise, Recipients &MAY; take steps to recover a usable
    220    protocol element from an invalid construct. However, HTTP does not define
    221    specific error handling mechanisms, except in cases where it has direct
    222    impact on security. This is because different uses of the protocol require
    223    different error handling strategies; for example, a Web browser may wish to
    224    transparently recover from a response where the Location header field
    225    doesn't parse according to the ABNF, whereby in a systems control protocol
    226    using HTTP, this type of error recovery could lead to dangerous consequences.
    227 </t>
    228 </section>
    229 
    230 <section title="Syntax Notation" anchor="notation">
    231   <x:anchor-alias value="ALPHA"/>
    232   <x:anchor-alias value="CR"/>
    233   <x:anchor-alias value="DIGIT"/>
    234   <x:anchor-alias value="LF"/>
    235   <x:anchor-alias value="OCTET"/>
    236   <x:anchor-alias value="VCHAR"/>
    237 <t>
    238    This specification uses the Augmented Backus-Naur Form (ABNF) notation
    239    of <xref target="RFC5234"/> with the list rule extension defined in
    240    &notation;.  <xref target="collected.abnf"/> shows the collected ABNF
    241    with the list rule expanded.
    242 </t>
    243 <t>
    244   The following core rules are included by
    245   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
    246   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
    247   DIGIT (decimal 0-9), DQUOTE (double quote),
    248   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
    249   OCTET (any 8-bit sequence of data), SP (space), and
    250   VCHAR (any visible US-ASCII character).
    251 </t>
    252 
    253 <section title="Core Rules" anchor="core.rules">
    254   <x:anchor-alias value="token"/>
    255   <x:anchor-alias value="word"/>
    256   <x:anchor-alias value="OWS"/>
    257 <t>
    258   The core rules below are defined in <xref target="Part1"/>:
    259 </t>
     123<section title="">
    260124<figure><artwork type="abnf2616">
    261   <x:ref>OWS</x:ref>            = &lt;OWS, defined in &whitespace;&gt;
    262   <x:ref>token</x:ref>          = &lt;token, defined in &field-components;&gt;
    263   <x:ref>word</x:ref>           = &lt;word, defined in &field-components;&gt;
     125foo = bar
    264126</artwork></figure>
    265 </section>
    266 
    267 <section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
    268   <x:anchor-alias value="absolute-URI"/>
    269   <x:anchor-alias value="partial-URI"/>
    270   <x:anchor-alias value="qvalue"/>
    271 <t>
    272   The ABNF rules below are defined in other parts:
    273 </t>
    274 <figure><!--Part1--><artwork type="abnf2616">
    275   <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
    276   <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
    277   <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
    278 </artwork></figure>
    279 </section>
    280 
    281 </section>
    282 
    283 </section>
    284 
    285 <section title="Protocol Parameters" anchor="protocol.parameters">
    286 
    287 <section title="Character Encodings (charset)" anchor="character.sets">
    288 <t>
    289    HTTP uses charset names to indicate the character encoding of a
    290    textual representation.
    291 </t>
    292 <t anchor="rule.charset">
    293   <x:anchor-alias value="charset"/>
    294    A character encoding is identified by a case-insensitive token. The
    295    complete set of tokens is defined by the IANA Character Set registry
    296    (<eref target="http://www.iana.org/assignments/character-sets"/>).
    297 </t>
    298 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
    299   <x:ref>charset</x:ref> = <x:ref>token</x:ref>
    300 </artwork></figure>
    301 <t>
    302    Although HTTP allows an arbitrary token to be used as a charset
    303    value, any token that has a predefined value within the IANA
    304    Character Set registry &MUST; represent the character encoding defined
    305    by that registry. Applications &SHOULD; limit their use of character
    306    encodings to those defined within the IANA registry.
    307 </t>
    308 <t>
    309    HTTP uses charset in two contexts: within an Accept-Charset request
    310    header field (in which the charset value is an unquoted token) and as the
    311    value of a parameter in a Content-Type header field (within a request or
    312    response), in which case the parameter value of the charset parameter
    313    can be quoted.
    314 </t>
    315 <t>
    316    Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
    317    <xref target="RFC2277"/>.
    318 </t>
    319 </section>
    320 
    321 <section title="Content Codings" anchor="content.codings">
    322   <x:anchor-alias value="content-coding"/>
    323 <t>
    324    Content coding values indicate an encoding transformation that has
    325    been or can be applied to a representation. Content codings are primarily
    326    used to allow a representation to be compressed or otherwise usefully
    327    transformed without losing the identity of its underlying media type
    328    and without loss of information. Frequently, the representation is stored in
    329    coded form, transmitted directly, and only decoded by the recipient.
    330 </t>
    331 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
    332   <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
    333 </artwork></figure>
    334 <t>
    335    All content-coding values are case-insensitive. HTTP/1.1 uses
    336    content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
    337    Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
    338    describes the content-coding, what is more important is that it
    339    indicates what decoding mechanism will be required to remove the
    340    encoding.
    341 </t>
    342 <t>
    343    compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
    344   <list>
    345     <t>
    346       See &compress-coding;.
    347     </t>
    348   </list>
    349 </t>
    350 <t>
    351    deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
    352   <list>
    353     <t>
    354       See &deflate-coding;.
    355     </t>
    356   </list>
    357 </t>
    358 <t>
    359    gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
    360   <list>
    361     <t>
    362       See &gzip-coding;.
    363     </t>
    364   </list>
    365 </t>
    366 
    367 <section title="Content Coding Registry" anchor="content.coding.registry">
    368 <t>
    369    The HTTP Content Coding Registry defines the name space for the content
    370    coding names.
    371 </t>
    372 <t>
    373    Registrations &MUST; include the following fields:
    374    <list style="symbols">
    375      <t>Name</t>
    376      <t>Description</t>
    377      <t>Pointer to specification text</t>
    378    </list>
    379 </t>
    380 <t>
    381    Names of content codings &MUST-NOT; overlap with names of transfer codings
    382    (&transfer-codings;), unless the encoding transformation is identical (as
    383    is the case for the compression codings defined in
    384    &compression-codings;).
    385 </t>
    386 <t>
    387    Values to be added to this name space require IETF Review
    388    (see <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
    389    conform to the purpose of content coding defined in this section.
    390 </t>
    391 <t>
    392    The registry itself is maintained at
    393    <eref target="http://www.iana.org/assignments/http-parameters"/>.
    394 </t>
    395 </section>
    396 
    397 </section>
    398 
    399 <section title="Media Types" anchor="media.types">
    400   <x:anchor-alias value="media-type"/>
    401   <x:anchor-alias value="type"/>
    402   <x:anchor-alias value="subtype"/>
    403 <t>
    404    HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
    405    and Accept (<xref target="header.accept"/>) header fields in order to provide
    406    open and extensible data typing and type negotiation.
    407 </t>
    408 <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"/>
    409   <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> )
    410   <x:ref>type</x:ref>       = <x:ref>token</x:ref>
    411   <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
    412 </artwork></figure>
    413 <t anchor="rule.parameter">
    414   <x:anchor-alias value="attribute"/>
    415   <x:anchor-alias value="parameter"/>
    416   <x:anchor-alias value="value"/>
    417    The type/subtype &MAY; be followed by parameters in the form of
    418    attribute/value pairs.
    419 </t>
    420 <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"/>
    421   <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
    422   <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
    423   <x:ref>value</x:ref>          = <x:ref>word</x:ref>
    424 </artwork></figure>
    425 <t>
    426    The type, subtype, and parameter attribute names are case-insensitive.
    427    Parameter values might or might not be case-sensitive, depending on the
    428    semantics of the parameter name.  The presence or absence of a parameter might
    429    be significant to the processing of a media-type, depending on its
    430    definition within the media type registry.
    431 </t>
    432 <t>
    433    A parameter value that matches the <x:ref>token</x:ref> production can be
    434    transmitted as either a token or within a quoted-string. The quoted and
    435    unquoted values are equivalent.
    436 </t>
    437 <t>
    438    Note that some older HTTP applications do not recognize media type
    439    parameters. When sending data to older HTTP applications,
    440    implementations &SHOULD; only use media type parameters when they are
    441    required by that type/subtype definition.
    442 </t>
    443 <t>
    444    Media-type values are registered with the Internet Assigned Number
    445    Authority (IANA). The media type registration process is
    446    outlined in <xref target="RFC4288"/>. Use of non-registered media types is
    447    discouraged.
    448 </t>
    449 
    450 <section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
    451 <t>
    452    Internet media types are registered with a canonical form. A
    453    representation transferred via HTTP messages &MUST; be in the
    454    appropriate canonical form prior to its transmission except for
    455    "text" types, as defined in the next paragraph.
    456 </t>
    457 <t>
    458    When in canonical form, media subtypes of the "text" type use CRLF as
    459    the text line break. HTTP relaxes this requirement and allows the
    460    transport of text media with plain CR or LF alone representing a line
    461    break when it is done consistently for an entire representation. HTTP
    462    applications &MUST; accept CRLF, bare CR, and bare LF as indicating
    463    a line break in text media received via HTTP. In
    464    addition, if the text is in a character encoding that does not
    465    use octets 13 and 10 for CR and LF respectively, as is the case for
    466    some multi-byte character encodings, HTTP allows the use of whatever octet
    467    sequences are defined by that character encoding to represent the
    468    equivalent of CR and LF for line breaks. This flexibility regarding
    469    line breaks applies only to text media in the payload body; a bare CR
    470    or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
    471    structures (such as header fields and multipart boundaries).
    472 </t>
    473 <t>
    474    If a representation is encoded with a content-coding, the underlying
    475    data &MUST; be in a form defined above prior to being encoded.
    476 </t>
    477 </section>
    478 
    479 <section title="Multipart Types" anchor="multipart.types">
    480 <t>
    481    MIME provides for a number of "multipart" types &mdash; encapsulations of
    482    one or more representations within a single message body. All multipart
    483    types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
    484    and &MUST; include a boundary parameter as part of the media type
    485    value. The message body is itself a protocol element and &MUST;
    486    therefore use only CRLF to represent line breaks between body-parts.
    487 </t>
    488 <t>
    489    In general, HTTP treats a multipart message body no differently than
    490    any other media type: strictly as payload.  HTTP does not use the
    491    multipart boundary as an indicator of message body length.
    492    <!-- jre: re-insert removed text pointing to caching? -->
    493    In all other respects, an HTTP user agent &SHOULD; follow the same or similar
    494    behavior as a MIME user agent would upon receipt of a multipart type.
    495    The MIME header fields within each body-part of a multipart message body
    496    do not have any significance to HTTP beyond that defined by
    497    their MIME semantics.
    498 </t>
    499 <t>
    500    If an application receives an unrecognized multipart subtype, the
    501    application &MUST; treat it as being equivalent to "multipart/mixed".
    502 </t>
    503 <x:note>
    504   <t>
    505     <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
    506     for carrying form data suitable for processing via the POST
    507     request method, as described in <xref target="RFC2388"/>.
    508   </t>
    509 </x:note>
    510 </section>
    511 </section>
    512 
    513 <section title="Language Tags" anchor="language.tags">
    514   <x:anchor-alias value="language-tag"/>
    515 <t>
    516    A language tag, as defined in <xref target="RFC5646"/>, identifies a
    517    natural language spoken, written, or otherwise conveyed by human beings for
    518    communication of information to other human beings. Computer languages are
    519    explicitly excluded. HTTP uses language tags within the Accept-Language and
    520    Content-Language fields.
    521 </t>
    522 <t>
    523    In summary, a language tag is composed of one or more parts: A primary
    524    language subtag followed by a possibly empty series of subtags:
    525 </t>
    526 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
    527   <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
    528 </artwork></figure>
    529 <t>
    530    White space is not allowed within the tag and all tags are case-insensitive.
    531    The name space of language subtags is administered by the IANA (see
    532    <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
    533 </t>
    534 <figure>
    535   <preamble>Example tags include:</preamble>
    536 <artwork type="example">
    537   en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
    538 </artwork>
    539 </figure>
    540 <t>
    541    See <xref target="RFC5646"/> for further information.
    542 </t>
    543 </section>
    544 </section>
    545 
    546 <section title="Payload" anchor="payload">
    547 <t>
    548    HTTP messages &MAY; transfer a payload if not otherwise restricted by
    549    the request method or response status code.  The payload consists of
    550    metadata, in the form of header fields, and data, in the form of the
    551    sequence of octets in the message body after any transfer-coding has
    552    been decoded.
    553 </t>
    554 <iref item="payload"/>
    555 <t>   
    556    A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
    557    representation of some resource.  We use separate terms for payload
    558    and representation because some messages contain only the associated
    559    representation's header fields (e.g., responses to HEAD) or only some
    560    part(s) of the representation (e.g., the 206 status code).
    561 </t>
    562 <section title="Payload Header Fields" anchor="payload.header.fields">
    563   <x:anchor-alias value="payload-header"/>
    564 <t>
    565    HTTP header fields that specifically define the payload, rather than the
    566    associated representation, are referred to as "payload header fields".
    567    The following payload header fields are defined by HTTP/1.1:
    568 </t>
    569 <texttable align="left">
    570   <ttcol>Header Field Name</ttcol>
    571   <ttcol>Defined in...</ttcol>
    572 
    573   <c>Content-Length</c> <c>&header-content-length;</c>
    574   <c>Content-Range</c> <c>&header-content-range;</c>
    575 </texttable>
    576 </section>
    577 
    578 <section title="Payload Body" anchor="payload.body">
    579   <x:anchor-alias value="payload-body"/>
    580 <t>
    581    A payload body is only present in a message when a message body is
    582    present, as described in &message-body;. The payload body is obtained
    583    from the message body by decoding any Transfer-Encoding that might
    584    have been applied to ensure safe and proper transfer of the message.
    585 </t>
    586 </section>
    587 </section>
    588 
    589 <section title="Representation" anchor="representation">
    590 <iref item="representation"/>
    591 <t>
    592    A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
    593    communicated from one party to another.  A resource representation
    594    is information that reflects the state of that resource, as observed
    595    at some point in the past (e.g., in a response to GET) or to be
    596    desired at some point in the future (e.g., in a PUT request).
    597 </t>
    598 <t>
    599    Most, but not all, representations transferred via HTTP are intended
    600    to be a representation of the target resource (the resource identified
    601    by the effective request URI).  The precise semantics of a representation
    602    are determined by the type of message (request or response), the request
    603    method, the response status code, and the representation metadata.
    604    For example, the above semantic is true for the representation in any
    605    200 (OK) response to GET and for the representation in any PUT request.
    606    A 200 response to PUT, in contrast, contains either a representation
    607    that describes the successful action or a representation of the target
    608    resource, with the latter indicated by a Content-Location header field
    609    with the same value as the effective request URI.  Likewise, response
    610    messages with an error status code usually contain a representation that
    611    describes the error and what next steps are suggested for resolving it.
    612 </t>
    613 
    614 <section title="Representation Header Fields" anchor="representation.header.fields">
    615   <x:anchor-alias value="representation-header"/>
    616 <t>
    617    Representation header fields define metadata about the representation data
    618    enclosed in the message body or, if no message body is present, about
    619    the representation that would have been transferred in a 200 response
    620    to a simultaneous GET request with the same effective request URI.
    621 </t>
    622 <t>
    623    The following header fields are defined as representation metadata:
    624 </t>
    625 <texttable align="left">
    626   <ttcol>Header Field Name</ttcol>
    627   <ttcol>Defined in...</ttcol>
    628 
    629   <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
    630   <c>Content-Language</c> <c><xref target="header.content-language"/></c>
    631   <c>Content-Location</c> <c><xref target="header.content-location"/></c>
    632   <c>Content-Type</c> <c><xref target="header.content-type"/></c>
    633   <c>Expires</c> <c>&header-expires;</c>
    634 </texttable>
    635 <t>
    636    Additional header fields define metadata about the selected
    637    representation, which might differ from the representation included
    638    in the message for responses to some state-changing methods.
    639    The following header fields are defined as selected representation
    640    metadata:
    641 </t>
    642 <texttable align="left">
    643   <ttcol>Header Field Name</ttcol>
    644   <ttcol>Defined in...</ttcol>
    645 
    646   <c>ETag</c> <c>&header-etag;</c>
    647   <c>Last-Modified</c> <c>&header-last-modified;</c>
    648 </texttable>
    649 </section>
    650 
    651 <section title="Representation Data" anchor="representation.data">
    652   <x:anchor-alias value="representation-data"/>
    653 <t>
    654    The representation body associated with an HTTP message is
    655    either provided as the payload body of the message or
    656    referred to by the message semantics and the effective request
    657    URI.  The representation data is in a format and encoding defined by
    658    the representation metadata header fields.
    659 </t>
    660 <t>
    661    The data type of the representation data
    662    is determined via the header fields Content-Type and Content-Encoding.
    663    These define a two-layer, ordered encoding model:
    664 </t>
    665 <figure><artwork type="example">
    666   representation-data := Content-Encoding( Content-Type( bits ) )
    667 </artwork></figure>
    668 <t>
    669    Content-Type specifies the media type of the underlying data, which
    670    defines both the data format and how that data &SHOULD; be processed
    671    by the recipient (within the scope of the request method semantics).
    672    Any HTTP/1.1 message containing a payload body &SHOULD; include a
    673    Content-Type header field defining the media type of the associated
    674    representation unless that metadata is unknown to the sender.
    675    If the Content-Type header field is not present, it indicates that
    676    the sender does not know the media type of the representation;
    677    recipients &MAY; either assume that the media type is
    678    "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
    679    or examine the content to determine its type.
    680 </t>
    681 <t>
    682    In practice, resource owners do not always properly configure their origin
    683    server to provide the correct Content-Type for a given representation,
    684    with the result that some clients will examine a response body's content
    685    and override the specified type.
    686    Clients that do so risk drawing incorrect conclusions, which might expose
    687    additional security risks (e.g., "privilege escalation").  Furthermore,
    688    it is impossible to determine the sender's intent by examining the data
    689    format: many data formats match multiple media types that differ only in
    690    processing semantics.  Implementers are encouraged to provide a means of
    691    disabling such "content sniffing" when it is used.
    692 </t>
    693 <t>
    694    Content-Encoding is used to indicate any additional content
    695    codings applied to the data, usually for the purpose of data
    696    compression, that are a property of the representation.  If
    697    Content-Encoding is not present, then there is no additional
    698    encoding beyond that defined by the Content-Type.
    699 </t>
    700 </section>
    701 </section>
    702 
    703 <section title="Content Negotiation" anchor="content.negotiation">
    704 <t>
    705    HTTP responses include a representation which contains information for
    706    interpretation, whether by a human user or for further processing.
    707    Often, the server has different ways of representing the
    708    same information; for example, in different formats, languages,
    709    or using different character encodings.
    710 </t>
    711 <t>
    712    HTTP clients and their users might have different or variable
    713    capabilities, characteristics or preferences which would influence
    714    which representation, among those available from the server,
    715    would be best for the server to deliver. For this reason, HTTP
    716    provides mechanisms for "content negotiation" &mdash; a process of
    717    allowing selection of a representation of a given resource,
    718    when more than one is available.
    719 </t>
    720 <t>
    721    This specification defines two patterns of content negotiation;
    722    "server-driven", where the server selects the representation based
    723    upon the client's stated preferences, and "agent-driven" negotiation,
    724    where the server provides a list of representations for the client to
    725    choose from, based upon their metadata. In addition,  there are
    726    other patterns: some applications use an "active content" pattern,
    727    where the server returns active content which runs on the client
    728    and, based on client available parameters, selects additional
    729    resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
    730    has also been proposed.
    731 </t>
    732 <t>
    733    These patterns are all widely used, and have trade-offs in applicability
    734    and practicality. In particular, when the number of preferences or
    735    capabilities to be expressed by a client are large (such as when many
    736    different formats are supported by a user-agent), server-driven
    737    negotiation becomes unwieldy, and might not be appropriate. Conversely,
    738    when the number of representations to choose from is very large,
    739    agent-driven negotiation might not be appropriate.
    740 </t>
    741 <t>
    742    Note that in all cases, the supplier of representations has the
    743    responsibility for determining which representations might be
    744    considered to be the "same information".
    745 </t>
    746 
    747 <section title="Server-driven Negotiation" anchor="server-driven.negotiation">
    748 <t>
    749    If the selection of the best representation for a response is made by
    750    an algorithm located at the server, it is called server-driven
    751    negotiation. Selection is based on the available representations of
    752    the response (the dimensions over which it can vary; e.g., language,
    753    content-coding, etc.) and the contents of particular header fields in
    754    the request message or on other information pertaining to the request
    755    (such as the network address of the client).
    756 </t>
    757 <t>
    758    Server-driven negotiation is advantageous when the algorithm for
    759    selecting from among the available representations is difficult to
    760    describe to the user agent, or when the server desires to send its
    761    "best guess" to the client along with the first response (hoping to
    762    avoid the round-trip delay of a subsequent request if the "best
    763    guess" is good enough for the user). In order to improve the server's
    764    guess, the user agent &MAY; include request header fields (Accept,
    765    Accept-Language, Accept-Encoding, etc.) which describe its
    766    preferences for such a response.
    767 </t>
    768 <t>
    769    Server-driven negotiation has disadvantages:
    770   <list style="numbers">
    771     <t>
    772          It is impossible for the server to accurately determine what
    773          might be "best" for any given user, since that would require
    774          complete knowledge of both the capabilities of the user agent
    775          and the intended use for the response (e.g., does the user want
    776          to view it on screen or print it on paper?).
    777     </t>
    778     <t>
    779          Having the user agent describe its capabilities in every
    780          request can be both very inefficient (given that only a small
    781          percentage of responses have multiple representations) and a
    782          potential violation of the user's privacy.
    783     </t>
    784     <t>
    785          It complicates the implementation of an origin server and the
    786          algorithms for generating responses to a request.
    787     </t>
    788     <t>
    789          It might limit a public cache's ability to use the same response
    790          for multiple user's requests.
    791     </t>
    792   </list>
    793 </t>
    794 <t>
    795    Server-driven negotiation allows the user agent to specify its preferences,
    796    but it cannot expect responses to always honor them. For example, the origin
    797    server might not implement server-driven negotiation, or it might decide that
    798    sending a response that doesn't conform to them is better than sending a 406
    799    (Not Acceptable) response.
    800 </t>
    801 <t>
    802    Many of the mechanisms for expressing preferences use quality values to
    803    declare relative preference. See &qvalue; for more information.
    804 </t>
    805 <t>
    806    HTTP/1.1 includes the following header fields for enabling
    807    server-driven negotiation through description of user agent
    808    capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
    809    (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
    810    (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
    811    However, an origin server is not limited to these dimensions and &MAY; vary
    812    the response based on any aspect of the request, including aspects
    813    of the connection (e.g., IP address) or information within extension
    814    header fields not defined by this specification.
    815 </t>
    816 <x:note>
    817   <t>
    818     <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
    819     because new clients might not be recognized.
    820   </t>
    821 </x:note>
    822 <t>
    823    The Vary header field (&header-vary;) can be used to express the parameters the
    824    server uses to select a representation that is subject to server-driven
    825    negotiation.
    826 </t>
    827 </section>
    828 
    829 <section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
    830 <t>
    831    With agent-driven negotiation, selection of the best representation
    832    for a response is performed by the user agent after receiving an
    833    initial response from the origin server. Selection is based on a list
    834    of the available representations of the response included within the
    835    header fields or body of the initial response, with each
    836    representation identified by its own URI. Selection from among the
    837    representations can be performed automatically (if the user agent is
    838    capable of doing so) or manually by the user selecting from a
    839    generated (possibly hypertext) menu.
    840 </t>
    841 <t>
    842    Agent-driven negotiation is advantageous when the response would vary
    843    over commonly-used dimensions (such as type, language, or encoding),
    844    when the origin server is unable to determine a user agent's
    845    capabilities from examining the request, and generally when public
    846    caches are used to distribute server load and reduce network usage.
    847 </t>
    848 <t>
    849    Agent-driven negotiation suffers from the disadvantage of needing a
    850    second request to obtain the best alternate representation. This
    851    second request is only efficient when caching is used. In addition,
    852    this specification does not define any mechanism for supporting
    853    automatic selection, though it also does not prevent any such
    854    mechanism from being developed as an extension and used within
    855    HTTP/1.1.
    856 </t>
    857 <t>
    858    This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
    859    status codes for enabling agent-driven negotiation when the server is
    860    unwilling or unable to provide a varying response using server-driven
    861    negotiation.
    862 </t>
    863 </section>
    864 </section>
    865 
    866 <section title="Header Field Definitions" anchor="header.field.definitions">
    867 <t>
    868    This section defines the syntax and semantics of HTTP/1.1 header fields
    869    related to the payload of messages.
    870 </t>
    871 
    872 <section title="Accept" anchor="header.accept">
    873   <iref primary="true" item="Accept header field" x:for-anchor=""/>
    874   <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
    875   <x:anchor-alias value="Accept"/>
    876   <x:anchor-alias value="accept-ext"/>
    877   <x:anchor-alias value="accept-params"/>
    878   <x:anchor-alias value="media-range"/>
    879 <t>
    880    The "Accept" header field can be used by user agents to specify
    881    response media types that are acceptable. Accept header fields can be used to
    882    indicate that the request is specifically limited to a small set of desired
    883    types, as in the case of a request for an in-line image.
    884 </t>
    885 <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"/>
    886   <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
    887  
    888   <x:ref>media-range</x:ref>    = ( "*/*"
    889                    / ( <x:ref>type</x:ref> "/" "*" )
    890                    / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
    891                    ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
    892   <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> )
    893   <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> ]
    894 </artwork></figure>
    895 <t>
    896    The asterisk "*" character is used to group media types into ranges,
    897    with "*/*" indicating all media types and "type/*" indicating all
    898    subtypes of that type. The media-range &MAY; include media type
    899    parameters that are applicable to that range.
    900 </t>
    901 <t>
    902    Each media-range &MAY; be followed by one or more accept-params,
    903    beginning with the "q" parameter for indicating a relative quality
    904    factor. The first "q" parameter (if any) separates the media-range
    905    parameter(s) from the accept-params. Quality factors allow the user
    906    or user agent to indicate the relative degree of preference for that
    907    media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
    908    default value is q=1.
    909 </t>
    910 <x:note>
    911   <t>
    912     <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
    913     parameters from Accept extension parameters is due to historical
    914     practice. Although this prevents any media type parameter named
    915     "q" from being used with a media range, such an event is believed
    916     to be unlikely given the lack of any "q" parameters in the IANA
    917     media type registry and the rare usage of any media type
    918     parameters in Accept. Future media types are discouraged from
    919     registering any parameter named "q".
    920   </t>
    921 </x:note>
    922 <t>
    923    The example
    924 </t>
    925 <figure><artwork type="example">
    926   Accept: audio/*; q=0.2, audio/basic
    927 </artwork></figure>
    928 <t>
    929    &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
    930    type if it is the best available after an 80% mark-down in quality".
    931 </t>
    932 <t>
    933    A request without any Accept header field implies that the user agent
    934    will accept any media type in response.
    935    If an Accept header field is present in a request and none of the
    936    available representations for the response have a media type that is
    937    listed as acceptable, the origin server &MAY; either
    938    honor the Accept header field by sending a 406 (Not Acceptable) response
    939    or disregard the Accept header field by treating the response as if
    940    it is not subject to content negotiation.
    941 </t>
    942 <t>
    943    A more elaborate example is
    944 </t>
    945 <figure><artwork type="example">
    946   Accept: text/plain; q=0.5, text/html,
    947           text/x-dvi; q=0.8, text/x-c
    948 </artwork></figure>
    949 <t>
    950    Verbally, this would be interpreted as "text/html and text/x-c are
    951    the preferred media types, but if they do not exist, then send the
    952    text/x-dvi representation, and if that does not exist, send the text/plain
    953    representation".
    954 </t>
    955 <t>
    956    Media ranges can be overridden by more specific media ranges or
    957    specific media types. If more than one media range applies to a given
    958    type, the most specific reference has precedence. For example,
    959 </t>
    960 <figure><artwork type="example">
    961   Accept: text/*, text/plain, text/plain;format=flowed, */*
    962 </artwork></figure>
    963 <t>
    964    have the following precedence:
    965    <list style="numbers">
    966     <t>text/plain;format=flowed</t>
    967     <t>text/plain</t>
    968     <t>text/*</t>
    969     <t>*/*</t>
    970    </list>
    971 </t>
    972 <t>
    973    The media type quality factor associated with a given type is
    974    determined by finding the media range with the highest precedence
    975    which matches that type. For example,
    976 </t>
    977 <figure><artwork type="example">
    978   Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
    979           text/html;level=2;q=0.4, */*;q=0.5
    980 </artwork></figure>
    981 <t>
    982    would cause the following values to be associated:
    983 </t>
    984 <texttable align="left">
    985   <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
    986   <c>text/html;level=1</c>    <c>1</c>
    987   <c>text/html</c>            <c>0.7</c>
    988   <c>text/plain</c>           <c>0.3</c>
    989   <c>image/jpeg</c>           <c>0.5</c>
    990   <c>text/html;level=2</c>    <c>0.4</c>
    991   <c>text/html;level=3</c>    <c>0.7</c>
    992 </texttable>
    993 <t>
    994       <x:h>Note:</x:h> A user agent might be provided with a default set of quality
    995       values for certain media ranges. However, unless the user agent is
    996       a closed system which cannot interact with other rendering agents,
    997       this default set ought to be configurable by the user.
    998 </t>
    999 </section>
    1000 
    1001 <section title="Accept-Charset" anchor="header.accept-charset">
    1002   <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
    1003   <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
    1004   <x:anchor-alias value="Accept-Charset"/>
    1005 <t>
    1006    The "Accept-Charset" header field can be used by user agents to
    1007    indicate what character encodings are acceptable in a response
    1008    payload. This field allows
    1009    clients capable of understanding more comprehensive or special-purpose
    1010    character encodings to signal that capability to a server which is capable of
    1011    representing documents in those character encodings.
    1012 </t>
    1013 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
    1014   <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
    1015                          [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
    1016 </artwork></figure>
    1017 <t>
    1018    Character encoding values (a.k.a., charsets) are described in
    1019    <xref target="character.sets"/>. Each charset &MAY; be given an
    1020    associated quality value which represents the user's preference
    1021    for that charset. The default value is q=1. An example is
    1022 </t>
    1023 <figure><artwork type="example">
    1024   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
    1025 </artwork></figure>
    1026 <t>
    1027    The special value "*", if present in the Accept-Charset field,
    1028    matches every character encoding which is not mentioned elsewhere in the
    1029    Accept-Charset field. If no "*" is present in an Accept-Charset field, then
    1030    all character encodings not explicitly mentioned get a quality value of 0.
    1031 </t>
    1032 <t>
    1033    A request without any Accept-Charset header field implies that the user
    1034    agent will accept any character encoding in response.
    1035    If an Accept-Charset header field is present in a request and none of the
    1036    available representations for the response have a character encoding that
    1037    is listed as acceptable, the origin server &MAY; either honor the
    1038    Accept-Charset header field by sending a 406 (Not Acceptable) response or
    1039    disregard the Accept-Charset header field by treating the response as if
    1040    it is not subject to content negotiation.
    1041 </t>
    1042 </section>
    1043 
    1044 <section title="Accept-Encoding" anchor="header.accept-encoding">
    1045   <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
    1046   <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
    1047   <x:anchor-alias value="Accept-Encoding"/>
    1048   <x:anchor-alias value="codings"/>
    1049 <t>
    1050    The "Accept-Encoding" header field can be used by user agents to
    1051    indicate what response content-codings (<xref target="content.codings"/>)
    1052    are acceptable in the response.  An "identity" token is used as a synonym
    1053    for "no encoding" in order to communicate when no encoding is preferred.
    1054 </t>
    1055 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
    1056   <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> ] )
    1057   <x:ref>codings</x:ref>          = <x:ref>content-coding</x:ref> / "identity" / "*"
    1058 </artwork></figure>
    1059 <t>
    1060    Each codings value &MAY; be given an associated quality value which
    1061    represents the preference for that encoding. The default value is q=1.
    1062 </t>
    1063 <t>
    1064    For example,
    1065 </t>
    1066 <figure><artwork type="example">
    1067   Accept-Encoding: compress, gzip
    1068   Accept-Encoding:
    1069   Accept-Encoding: *
    1070   Accept-Encoding: compress;q=0.5, gzip;q=1.0
    1071   Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
    1072 </artwork></figure>
    1073 <t>
    1074    A server tests whether a content-coding for a given representation is
    1075    acceptable, according to an Accept-Encoding field, using these rules:
    1076   <list style="numbers">
    1077       <t>The special "*" symbol in an Accept-Encoding field matches any
    1078          available content-coding not explicitly listed in the header
    1079          field.</t>
    1080 
    1081       <t>If the representation has no content-coding, then it is acceptable
    1082          by default unless specifically excluded by the Accept-Encoding field
    1083          stating either "identity;q=0" or "*;q=0" without a more specific
    1084          entry for "identity".</t>
    1085 
    1086       <t>If the representation's content-coding is one of the content-codings
    1087          listed in the Accept-Encoding field, then it is acceptable unless
    1088          it is accompanied by a qvalue of 0. (As defined in &qvalue;, a
    1089          qvalue of 0 means "not acceptable".)</t>
    1090 
    1091       <t>If multiple content-codings are acceptable, then the acceptable
    1092          content-coding with the highest non-zero qvalue is preferred.</t>
    1093   </list>
    1094 </t>
    1095 <t>
    1096    An Accept-Encoding header field with a combined field-value that is empty
    1097    implies that the user agent does not want any content-coding in response.
    1098    If an Accept-Encoding header field is present in a request and none of the
    1099    available representations for the response have a content-coding that
    1100    is listed as acceptable, the origin server &SHOULD; send a response
    1101    without any content-coding.
    1102 </t>
    1103 <t>
    1104    A request without an Accept-Encoding header field implies that the user
    1105    agent will accept any content-coding in response, but a representation
    1106    without content-coding is preferred for compatibility with the widest
    1107    variety of user agents.
    1108 </t>
    1109 <x:note>
    1110   <t>
    1111     <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
    1112     associated with content-codings. This means that qvalues will not
    1113     work and are not permitted with x-gzip or x-compress.
    1114   </t>
    1115 </x:note>
    1116 </section>
    1117 
    1118 <section title="Accept-Language" anchor="header.accept-language">
    1119   <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
    1120   <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
    1121   <x:anchor-alias value="Accept-Language"/>
    1122   <x:anchor-alias value="language-range"/>
    1123 <t>
    1124    The "Accept-Language" header field can be used by user agents to
    1125    indicate the set of natural languages that are preferred in the response.
    1126    Language tags are defined in <xref target="language.tags"/>.
    1127 </t>
    1128 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
    1129   <x:ref>Accept-Language</x:ref> =
    1130                     1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
    1131   <x:ref>language-range</x:ref>  =
    1132             &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
    1133 </artwork></figure>
    1134 <t>
    1135    Each language-range can be given an associated quality value which
    1136    represents an estimate of the user's preference for the languages
    1137    specified by that range. The quality value defaults to "q=1". For
    1138    example,
    1139 </t>
    1140 <figure><artwork type="example">
    1141   Accept-Language: da, en-gb;q=0.8, en;q=0.7
    1142 </artwork></figure>
    1143 <t>
    1144    would mean: "I prefer Danish, but will accept British English and
    1145    other types of English".
    1146    (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
    1147 </t>
    1148 <t>
    1149    For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
    1150    several matching schemes. Implementations can offer the most appropriate
    1151    matching scheme for their requirements.
    1152 </t>
    1153 <x:note>
    1154   <t>
    1155     <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
    1156     x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
    1157     previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
    1158   </t>
    1159 </x:note>
    1160 <t>
    1161    It might be contrary to the privacy expectations of the user to send
    1162    an Accept-Language header field with the complete linguistic preferences of
    1163    the user in every request. For a discussion of this issue, see
    1164    <xref target="privacy.issues.connected.to.accept.header.fields"/>.
    1165 </t>
    1166 <t>
    1167    As intelligibility is highly dependent on the individual user, it is
    1168    recommended that client applications make the choice of linguistic
    1169    preference available to the user. If the choice is not made
    1170    available, then the Accept-Language header field &MUST-NOT; be given in
    1171    the request.
    1172 </t>
    1173 <x:note>
    1174   <t>
    1175     <x:h>Note:</x:h> When making the choice of linguistic preference available to
    1176     the user, we remind implementors of  the fact that users are not
    1177     familiar with the details of language matching as described above,
    1178     and ought to be provided appropriate guidance. As an example, users
    1179     might assume that on selecting "en-gb", they will be served any
    1180     kind of English document if British English is not available. A
    1181     user agent might suggest in such a case to add "en" to get the
    1182     best matching behavior.
    1183   </t>
    1184 </x:note>
    1185 </section>
    1186 
    1187 <section title="Content-Encoding" anchor="header.content-encoding">
    1188   <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
    1189   <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
    1190   <x:anchor-alias value="Content-Encoding"/>
    1191 <t>
    1192    The "Content-Encoding" header field indicates what content-codings
    1193    have been applied to the representation beyond those inherent in the media
    1194    type, and thus what decoding mechanisms have to be applied in order to obtain
    1195    the media-type referenced by the Content-Type header field.
    1196    Content-Encoding is primarily used to allow a representation to be
    1197    compressed without losing the identity of its underlying media type.
    1198 </t>
    1199 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
    1200   <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
    1201 </artwork></figure>
    1202 <t>
    1203    Content codings are defined in <xref target="content.codings"/>. An example of its use is
    1204 </t>
    1205 <figure><artwork type="example">
    1206   Content-Encoding: gzip
    1207 </artwork></figure>
    1208 <t>
    1209    The content-coding is a characteristic of the representation.
    1210    Typically, the representation body is stored with this
    1211    encoding and is only decoded before rendering or analogous usage.
    1212    However, a transforming proxy &MAY; modify the content-coding if the
    1213    new coding is known to be acceptable to the recipient, unless the
    1214    "no-transform" cache-control directive is present in the message.
    1215 </t>
    1216 <t>
    1217    If the media type includes an inherent encoding, such as a data format
    1218    that is always compressed, then that encoding would not be restated as
    1219    a Content-Encoding even if it happens to be the same algorithm as one
    1220    of the content-codings.  Such a content-coding would only be listed if,
    1221    for some bizarre reason, it is applied a second time to form the
    1222    representation.  Likewise, an origin server might choose to publish the
    1223    same payload data as multiple representations that differ only in whether
    1224    the coding is defined as part of Content-Type or Content-Encoding, since
    1225    some user agents will behave differently in their handling of each
    1226    response (e.g., open a "Save as ..." dialog instead of automatic
    1227    decompression and rendering of content).
    1228 </t>
    1229 <t>
    1230    A representation that has a content-coding applied to it &MUST; include
    1231    a Content-Encoding header field (<xref target="header.content-encoding"/>)
    1232    that lists the content-coding(s) applied.
    1233 </t>
    1234 <t>
    1235    If multiple encodings have been applied to a representation, the content
    1236    codings &MUST; be listed in the order in which they were applied.
    1237    Additional information about the encoding parameters &MAY; be provided
    1238    by other header fields not defined by this specification.
    1239 </t>
    1240 <t>
    1241    If the content-coding of a representation in a request message is not
    1242    acceptable to the origin server, the server &SHOULD; respond with a
    1243    status code of 415 (Unsupported Media Type).
    1244 </t>
    1245 </section>
    1246 
    1247 <section title="Content-Language" anchor="header.content-language">
    1248   <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
    1249   <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
    1250   <x:anchor-alias value="Content-Language"/>
    1251 <t>
    1252    The "Content-Language" header field describes the natural
    1253    language(s) of the intended audience for the representation. Note that this might
    1254    not be equivalent to all the languages used within the representation.
    1255 </t>
    1256 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
    1257   <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
    1258 </artwork></figure>
    1259 <t>
    1260    Language tags are defined in <xref target="language.tags"/>. The primary purpose of
    1261    Content-Language is to allow a user to identify and differentiate
    1262    representations according to the user's own preferred language. Thus, if the
    1263    body content is intended only for a Danish-literate audience, the
    1264    appropriate field is
    1265 </t>
    1266 <figure><artwork type="example">
    1267   Content-Language: da
    1268 </artwork></figure>
    1269 <t>
    1270    If no Content-Language is specified, the default is that the content
    1271    is intended for all language audiences. This might mean that the
    1272    sender does not consider it to be specific to any natural language,
    1273    or that the sender does not know for which language it is intended.
    1274 </t>
    1275 <t>
    1276    Multiple languages &MAY; be listed for content that is intended for
    1277    multiple audiences. For example, a rendition of the "Treaty of
    1278    Waitangi", presented simultaneously in the original Maori and English
    1279    versions, would call for
    1280 </t>
    1281 <figure><artwork type="example">
    1282   Content-Language: mi, en
    1283 </artwork></figure>
    1284 <t>
    1285    However, just because multiple languages are present within a representation
    1286    does not mean that it is intended for multiple linguistic audiences.
    1287    An example would be a beginner's language primer, such as "A First
    1288    Lesson in Latin", which is clearly intended to be used by an
    1289    English-literate audience. In this case, the Content-Language would
    1290    properly only include "en".
    1291 </t>
    1292 <t>
    1293    Content-Language &MAY; be applied to any media type &mdash; it is not
    1294    limited to textual documents.
    1295 </t>
    1296 </section>
    1297 
    1298 <section title="Content-Location" anchor="header.content-location">
    1299   <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
    1300   <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
    1301   <x:anchor-alias value="Content-Location"/>
    1302 <t>
    1303    The "Content-Location" header field supplies a URI that can be used
    1304    as a specific identifier for the representation in this message.
    1305    In other words, if one were to perform a GET on this URI at the time
    1306    of this message's generation, then a 200 response would contain the
    1307    same representation that is enclosed as payload in this message.
    1308 </t>
    1309 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
    1310   <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
    1311 </artwork></figure>
    1312 <t>
    1313    The Content-Location value is not a replacement for the effective
    1314    Request URI (&effective-request-uri;).  It is representation metadata.
    1315    It has the same syntax and semantics as the header field of the same name
    1316    defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
    1317    However, its appearance in an HTTP message has some special implications
    1318    for HTTP recipients.
    1319 </t>
    1320 <t>
    1321    If Content-Location is included in a response message and its value
    1322    is the same as the effective request URI, then the response payload
    1323    &SHOULD; be considered a current representation of that resource.
    1324    For a GET or HEAD request, this is the same as the default semantics
    1325    when no Content-Location is provided by the server.  For a state-changing
    1326    request like PUT or POST, it implies that the server's response contains
    1327    the new representation of that resource, thereby distinguishing it from
    1328    representations that might only report about the action (e.g., "It worked!").
    1329    This allows authoring applications to update their local copies without
    1330    the need for a subsequent GET request.
    1331 </t>
    1332 <t>
    1333    If Content-Location is included in a response message and its value
    1334    differs from the effective request URI, then the origin server is
    1335    informing recipients that this representation has its own, presumably
    1336    more specific, identifier.  For a GET or HEAD request, this is an
    1337    indication that the effective request URI identifies a resource that
    1338    is subject to content negotiation and the selected representation for
    1339    this response can also be found at the identified URI.  For other
    1340    methods, such a Content-Location indicates that this representation
    1341    contains a report on the action's status and the same report is
    1342    available (for future access with GET) at the given URI.  For
    1343    example, a purchase transaction made via a POST request might
    1344    include a receipt document as the payload of the 200 response;
    1345    the Content-Location value provides an identifier for retrieving
    1346    a copy of that same receipt in the future.
    1347 </t>
    1348 <t>
    1349    If Content-Location is included in a request message, then it &MAY;
    1350    be interpreted by the origin server as an indication of where the
    1351    user agent originally obtained the content of the enclosed
    1352    representation (prior to any subsequent modification of the content
    1353    by that user agent).  In other words, the user agent is providing
    1354    the same representation metadata that it received with the original
    1355    representation.  However, such interpretation &MUST-NOT; be used to
    1356    alter the semantics of the method requested by the client.  For
    1357    example, if a client makes a PUT request on a negotiated resource
    1358    and the origin server accepts that PUT (without redirection), then the
    1359    new set of values for that resource is expected to be consistent with
    1360    the one representation supplied in that PUT; the Content-Location
    1361    cannot be used as a form of reverse content selection that
    1362    identifies only one of the negotiated representations to be updated.
    1363    If the user agent had wanted the latter semantics, it would have applied
    1364    the PUT directly to the Content-Location URI.
    1365 </t>
    1366 <t>
    1367    A Content-Location field received in a request message is transitory
    1368    information that &SHOULD-NOT; be saved with other representation
    1369    metadata for use in later responses.  The Content-Location's value
    1370    might be saved for use in other contexts, such as within source links
    1371    or other metadata.
    1372 </t>
    1373 <t>
    1374    A cache cannot assume that a representation with a Content-Location
    1375    different from the URI used to retrieve it can be used to respond to
    1376    later requests on that Content-Location URI.
    1377 </t>
    1378 <t>
    1379    If the Content-Location value is a partial URI, the partial URI is
    1380    interpreted relative to the effective request URI.
    1381 </t>
    1382 </section>
    1383 
    1384 <section title="Content-Type" anchor="header.content-type">
    1385   <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
    1386   <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
    1387   <x:anchor-alias value="Content-Type"/>
    1388 <t>
    1389    The "Content-Type" header field indicates the media type of the
    1390    representation. In the case of responses to the HEAD method, the media type is
    1391    that which would have been sent had the request been a GET.
    1392 </t>
    1393 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
    1394   <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
    1395 </artwork></figure>
    1396 <t>
    1397    Media types are defined in <xref target="media.types"/>. An example of the field is
    1398 </t>
    1399 <figure><artwork type="example">
    1400   Content-Type: text/html; charset=ISO-8859-4
    1401 </artwork></figure>
    1402 <t>
    1403    Further discussion of Content-Type is provided in <xref target="representation.data"/>.
    1404 </t>
    1405 </section>
    1406 
    1407 </section>
    1408 
    1409 <section title="IANA Considerations" anchor="IANA.considerations">
    1410 <section title="Header Field Registration" anchor="header.field.registration">
    1411 <t>
    1412    The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
    1413    with the permanent registrations below (see <xref target="RFC3864"/>):
    1414 </t>
    1415 <?BEGININC p3-payload.iana-headers ?>
    1416 <!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
    1417 <texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
    1418    <ttcol>Header Field Name</ttcol>
    1419    <ttcol>Protocol</ttcol>
    1420    <ttcol>Status</ttcol>
    1421    <ttcol>Reference</ttcol>
    1422 
    1423    <c>Accept</c>
    1424    <c>http</c>
    1425    <c>standard</c>
    1426    <c>
    1427       <xref target="header.accept"/>
    1428    </c>
    1429    <c>Accept-Charset</c>
    1430    <c>http</c>
    1431    <c>standard</c>
    1432    <c>
    1433       <xref target="header.accept-charset"/>
    1434    </c>
    1435    <c>Accept-Encoding</c>
    1436    <c>http</c>
    1437    <c>standard</c>
    1438    <c>
    1439       <xref target="header.accept-encoding"/>
    1440    </c>
    1441    <c>Accept-Language</c>
    1442    <c>http</c>
    1443    <c>standard</c>
    1444    <c>
    1445       <xref target="header.accept-language"/>
    1446    </c>
    1447    <c>Content-Encoding</c>
    1448    <c>http</c>
    1449    <c>standard</c>
    1450    <c>
    1451       <xref target="header.content-encoding"/>
    1452    </c>
    1453    <c>Content-Language</c>
    1454    <c>http</c>
    1455    <c>standard</c>
    1456    <c>
    1457       <xref target="header.content-language"/>
    1458    </c>
    1459    <c>Content-Location</c>
    1460    <c>http</c>
    1461    <c>standard</c>
    1462    <c>
    1463       <xref target="header.content-location"/>
    1464    </c>
    1465    <c>Content-Type</c>
    1466    <c>http</c>
    1467    <c>standard</c>
    1468    <c>
    1469       <xref target="header.content-type"/>
    1470    </c>
    1471    <c>MIME-Version</c>
    1472    <c>http</c>
    1473    <c>standard</c>
    1474    <c>
    1475       <xref target="mime-version"/>
    1476    </c>
    1477 </texttable>
    1478 <!--(END)-->
    1479 <?ENDINC p3-payload.iana-headers ?>
    1480 <t>
    1481    The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
    1482 </t>
    1483 </section>
    1484 
    1485 <section title="Content Coding Registry" anchor="content.coding.registration">
    1486 <t>
    1487    The registration procedure for HTTP Content Codings is now defined
    1488    by <xref target="content.coding.registry"/> of this document.
    1489 </t>
    1490 <t>
    1491    The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
    1492    shall be updated with the registration below:
    1493 </t>
    1494 <texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
    1495    <ttcol>Name</ttcol>
    1496    <ttcol>Description</ttcol>
    1497    <ttcol>Reference</ttcol>
    1498    <c>compress</c>
    1499    <c>UNIX "compress" program method</c>
    1500    <c>
    1501       &compress-coding;
    1502    </c>
    1503    <c>deflate</c>
    1504    <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
    1505    the "zlib" data format (<xref target="RFC1950"/>)
    1506    </c>
    1507    <c>
    1508       &deflate-coding;
    1509    </c>
    1510    <c>gzip</c>
    1511    <c>Same as GNU zip <xref target="RFC1952"/></c>
    1512    <c>
    1513       &gzip-coding;
    1514    </c>
    1515    <c>identity</c>
    1516    <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
    1517    <c>
    1518       <xref target="header.accept-encoding"/>
    1519    </c>
    1520 </texttable>
    1521 </section>
    1522 
    1523 </section>
    1524 
    1525 <section title="Security Considerations" anchor="security.considerations">
    1526 <t>
    1527    This section is meant to inform application developers, information
    1528    providers, and users of the security limitations in HTTP/1.1 as
    1529    described by this document. The discussion does not include
    1530    definitive solutions to the problems revealed, though it does make
    1531    some suggestions for reducing security risks.
    1532 </t>
    1533 
    1534 <section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
    1535 <t>
    1536    Accept header fields can reveal information about the user to all
    1537    servers which are accessed. The Accept-Language header field in particular
    1538    can reveal information the user would consider to be of a private
    1539    nature, because the understanding of particular languages is often
    1540    strongly correlated to the membership of a particular ethnic group.
    1541    User agents which offer the option to configure the contents of an
    1542    Accept-Language header field to be sent in every request are strongly
    1543    encouraged to let the configuration process include a message which
    1544    makes the user aware of the loss of privacy involved.
    1545 </t>
    1546 <t>
    1547    An approach that limits the loss of privacy would be for a user agent
    1548    to omit the sending of Accept-Language header fields by default, and to ask
    1549    the user whether or not to start sending Accept-Language header fields to a
    1550    server if it detects, by looking for any Vary header fields
    1551    generated by the server, that such sending could improve the quality
    1552    of service.
    1553 </t>
    1554 <t>
    1555    Elaborate user-customized accept header fields sent in every request,
    1556    in particular if these include quality values, can be used by servers
    1557    as relatively reliable and long-lived user identifiers. Such user
    1558    identifiers would allow content providers to do click-trail tracking,
    1559    and would allow collaborating content providers to match cross-server
    1560    click-trails or form submissions of individual users. Note that for
    1561    many users not behind a proxy, the network address of the host
    1562    running the user agent will also serve as a long-lived user
    1563    identifier. In environments where proxies are used to enhance
    1564    privacy, user agents ought to be conservative in offering accept
    1565    header configuration options to end users. As an extreme privacy
    1566    measure, proxies could filter the accept header fields in relayed requests.
    1567    General purpose user agents which provide a high degree of header
    1568    configurability &SHOULD; warn users about the loss of privacy which can
    1569    be involved.
    1570 </t>
    1571 </section>
    1572 
    1573 </section>
    1574 
    1575 <section title="Acknowledgments" anchor="acks">
    1576 <t>
    1577   See &acks;.
    1578 </t>
    1579127</section>
    1580128</middle>
     
    1762310</reference>
    1763311
    1764 <reference anchor="RFC2045">
    1765   <front>
    1766     <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
    1767     <author initials="N." surname="Freed" fullname="Ned Freed">
    1768       <organization>Innosoft International, Inc.</organization>
    1769       <address><email>ned@innosoft.com</email></address>
    1770     </author>
    1771     <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
    1772       <organization>First Virtual Holdings</organization>
    1773       <address><email>nsb@nsb.fv.com</email></address>
    1774     </author>
    1775     <date month="November" year="1996"/>
    1776   </front>
    1777   <seriesInfo name="RFC" value="2045"/>
    1778 </reference>
    1779 
    1780 <reference anchor="RFC2046">
    1781   <front>
    1782     <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
    1783     <author initials="N." surname="Freed" fullname="Ned Freed">
    1784       <organization>Innosoft International, Inc.</organization>
    1785       <address><email>ned@innosoft.com</email></address>
    1786     </author>
    1787     <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
    1788       <organization>First Virtual Holdings</organization>
    1789       <address><email>nsb@nsb.fv.com</email></address>
    1790     </author>
    1791     <date month="November" year="1996"/>
    1792   </front>
    1793   <seriesInfo name="RFC" value="2046"/>
    1794 </reference>
    1795 
    1796 <reference anchor="RFC2119">
    1797   <front>
    1798     <title>Key words for use in RFCs to Indicate Requirement Levels</title>
    1799     <author initials="S." surname="Bradner" fullname="Scott Bradner">
    1800       <organization>Harvard University</organization>
    1801       <address><email>sob@harvard.edu</email></address>
    1802     </author>
    1803     <date month="March" year="1997"/>
    1804   </front>
    1805   <seriesInfo name="BCP" value="14"/>
    1806   <seriesInfo name="RFC" value="2119"/>
    1807 </reference>
    1808 
    1809312<reference anchor='RFC4647'>
    1810313  <front>
     
    1886389</reference>
    1887390
    1888 <reference anchor="RFC2049">
    1889   <front>
    1890     <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
    1891     <author initials="N." surname="Freed" fullname="Ned Freed">
    1892       <organization>Innosoft International, Inc.</organization>
    1893       <address><email>ned@innosoft.com</email></address>
    1894     </author>
    1895     <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
    1896       <organization>First Virtual Holdings</organization>
    1897       <address><email>nsb@nsb.fv.com</email></address>
    1898     </author>
    1899     <date month="November" year="1996"/>
    1900   </front>
    1901   <seriesInfo name="RFC" value="2049"/>
    1902 </reference>
    1903 
    1904391<reference anchor="RFC2068">
    1905392  <front>
     
    1930417</reference>
    1931418
    1932 <reference anchor="RFC2076">
    1933   <front>
    1934     <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
    1935     <author initials="J." surname="Palme" fullname="Jacob Palme">
    1936       <organization>Stockholm University/KTH</organization>
    1937       <address><email>jpalme@dsv.su.se</email></address>
    1938     </author>
    1939     <date month="February" year="1997"/>
    1940   </front>
    1941   <seriesInfo name="RFC" value="2076"/>
    1942 </reference>
    1943 
    1944419<reference anchor="RFC2277">
    1945420  <front>
     
    1987462</reference>
    1988463
    1989 <reference anchor="RFC2557">
    1990   <front>
    1991     <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
    1992     <author initials="F." surname="Palme" fullname="Jacob Palme">
    1993       <organization>Stockholm University and KTH</organization>
    1994       <address><email>jpalme@dsv.su.se</email></address>
    1995     </author>
    1996     <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
    1997       <organization>Microsoft Corporation</organization>
    1998       <address><email>alexhop@microsoft.com</email></address>
    1999     </author>
    2000     <author initials="N." surname="Shelness" fullname="Nick Shelness">
    2001       <organization>Lotus Development Corporation</organization>
    2002       <address><email>Shelness@lotus.com</email></address>
    2003     </author>
    2004     <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
    2005       <address><email>stef@nma.com</email></address>
    2006     </author>
    2007     <date year="1999" month="March"/>
    2008   </front>
    2009   <seriesInfo name="RFC" value="2557"/>
    2010 </reference>
    2011 
    2012464<reference anchor="RFC2616">
    2013465  <front>
     
    2128580</reference>
    2129581
    2130 <reference anchor="RFC6151">
    2131   <front>
    2132     <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
    2133     <author initials="S." surname="Turner" fullname="S. Turner"/>
    2134     <author initials="L." surname="Chen" fullname="L. Chen"/>
    2135     <date year="2011" month="March" />
    2136   </front>
    2137   <seriesInfo name="RFC" value="6151" />
    2138 </reference>
    2139 
    2140582<!--<reference anchor='BCP97'>
    2141583  <front>
     
    2158600</reference>-->
    2159601
    2160 <reference anchor="RFC6266">
    2161   <front>
    2162     <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
    2163     in the Hypertext Transfer Protocol (HTTP)</title>
    2164     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
    2165       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    2166       <address>
    2167         <email>julian.reschke@greenbytes.de</email>
    2168       </address>
    2169     </author>
    2170     <date month="June" year="2011"/>
    2171   </front>
    2172   <seriesInfo name='RFC' value='6266' />
    2173 </reference>
    2174602
    2175603</references>
    2176604
    2177 <section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
    2178 <t>
    2179    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
    2180    allow a message body to be transmitted in an open variety of
    2181    representations and with extensible mechanisms. However, RFC 2045
    2182    discusses mail, and HTTP has a few features that are different from
    2183    those described in MIME. These differences were carefully chosen
    2184    to optimize performance over binary connections, to allow greater
    2185    freedom in the use of new media types, to make date comparisons
    2186    easier, and to acknowledge the practice of some early HTTP servers
    2187    and clients.
    2188 </t>
    2189 <t>
    2190    This appendix describes specific areas where HTTP differs from MIME.
    2191    Proxies and gateways to strict MIME environments &SHOULD; be
    2192    aware of these differences and provide the appropriate conversions
    2193    where necessary. Proxies and gateways from MIME environments to HTTP
    2194    also need to be aware of the differences because some conversions
    2195    might be required.
    2196 </t>
    2197 
    2198 <section title="MIME-Version" anchor="mime-version">
    2199   <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
    2200   <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
    2201   <x:anchor-alias value="MIME-Version"/>
    2202 <t>
    2203    HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
    2204    include a single MIME-Version header field to indicate what
    2205    version of the MIME protocol was used to construct the message. Use
    2206    of the MIME-Version header field indicates that the message is in
    2207    full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
    2208    Proxies/gateways are responsible for ensuring full conformance (where
    2209    possible) when exporting HTTP messages to strict MIME environments.
    2210 </t>
    2211 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
    2212   <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
    2213 </artwork></figure>
    2214 <t>
    2215    MIME version "1.0" is the default for use in HTTP/1.1. However,
    2216    HTTP/1.1 message parsing and semantics are defined by this document
    2217    and not the MIME specification.
    2218 </t>
    2219 </section>
    2220 
    2221 <section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
    2222 <t>
    2223    MIME requires that an Internet mail body-part be converted to
    2224    canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
    2225    <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
    2226    allowed for subtypes of the "text" media type when transmitted over
    2227    HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
    2228    line breaks as CRLF and forbids the use of CR or LF outside of line
    2229    break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
    2230    line break within text content when a message is transmitted over
    2231    HTTP.
    2232 </t>
    2233 <t>
    2234    Where it is possible, a proxy or gateway from HTTP to a strict MIME
    2235    environment &SHOULD; translate all line breaks within the text media
    2236    types described in <xref target="canonicalization.and.text.defaults"/>
    2237    of this document to the RFC 2049
    2238    canonical form of CRLF. Note, however, that this might be complicated
    2239    by the presence of a Content-Encoding and by the fact that HTTP
    2240    allows the use of some character encodings which do not use octets 13 and
    2241    10 to represent CR and LF, respectively, as is the case for some multi-byte
    2242    character encodings.
    2243 </t>
    2244 <t>
    2245    Conversion will break any cryptographic
    2246    checksums applied to the original content unless the original content
    2247    is already in canonical form. Therefore, the canonical form is
    2248    recommended for any content that uses such checksums in HTTP.
    2249 </t>
    2250 </section>
    2251 
    2252 
    2253 <section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
    2254 <t>
    2255    HTTP/1.1 uses a restricted set of date formats (&http-date;) to
    2256    simplify the process of date comparison. Proxies and gateways from
    2257    other protocols &SHOULD; ensure that any Date header field present in a
    2258    message conforms to one of the HTTP/1.1 formats and rewrite the date
    2259    if necessary.
    2260 </t>
    2261 </section>
    2262 
    2263 <section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
    2264 <t>
    2265    MIME does not include any concept equivalent to HTTP/1.1's
    2266    Content-Encoding header field. Since this acts as a modifier on the
    2267    media type, proxies and gateways from HTTP to MIME-compliant
    2268    protocols &MUST; either change the value of the Content-Type header
    2269    field or decode the representation before forwarding the message. (Some
    2270    experimental applications of Content-Type for Internet mail have used
    2271    a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
    2272    a function equivalent to Content-Encoding. However, this parameter is
    2273    not part of the MIME standards).
    2274 </t>
    2275 </section>
    2276 
    2277 <section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
    2278   <iref item="Content-Transfer-Encoding header field" x:for-anchor=""/>
    2279   <iref item="Header Fields" subitem="Content-Transfer-Encoding" x:for-anchor=""/>
    2280 <t>
    2281    HTTP does not use the Content-Transfer-Encoding field of MIME.
    2282    Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
    2283    remove any Content-Transfer-Encoding
    2284    prior to delivering the response message to an HTTP client.
    2285 </t>
    2286 <t>
    2287    Proxies and gateways from HTTP to MIME-compliant protocols are
    2288    responsible for ensuring that the message is in the correct format
    2289    and encoding for safe transport on that protocol, where "safe
    2290    transport" is defined by the limitations of the protocol being used.
    2291    Such a proxy or gateway &SHOULD; label the data with an appropriate
    2292    Content-Transfer-Encoding if doing so will improve the likelihood of
    2293    safe transport over the destination protocol.
    2294 </t>
    2295 </section>
    2296 
    2297 <section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
    2298 <t>
    2299    HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
    2300    Proxies/gateways &MUST; remove any transfer-coding prior to
    2301    forwarding a message via a MIME-compliant protocol.
    2302 </t>
    2303 </section>
    2304 
    2305 <section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
    2306 <t>
    2307    HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
    2308    need to be aware of MIME line length limitations. Since HTTP does not
    2309    have this limitation, HTTP does not fold long lines. MHTML messages
    2310    being transported by HTTP follow all conventions of MHTML, including
    2311    line length limitations and folding, canonicalization, etc., since
    2312    HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
    2313    does not interpret the content or any MIME header lines that might be
    2314    contained therein.
    2315 </t>
    2316 </section>
    2317 </section>
    2318 
    2319 <section title="Additional Features" anchor="additional.features">
    2320 <t>
    2321    <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
    2322    existing HTTP implementations, but not consistently and correctly
    2323    across most HTTP/1.1 applications. Implementors are advised to be
    2324    aware of these features, but cannot rely upon their presence in, or
    2325    interoperability with, other HTTP/1.1 applications. Some of these
    2326    describe proposed experimental features, and some describe features
    2327    that experimental deployment found lacking that are now addressed in
    2328    the base HTTP/1.1 specification.
    2329 </t>
    2330 <t>
    2331    A number of other header fields, such as Content-Disposition and Title,
    2332    from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
    2333    and <xref target="RFC2076"/>).
    2334 </t>
    2335 </section>
    2336 
    2337605<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
    2338 <t>
    2339   Clarify contexts that charset is used in.
    2340   (<xref target="character.sets"/>)
    2341 </t>
    2342 <t>
    2343   Registration of Content Codings now requires IETF Review
    2344   (<xref target="content.coding.registry"/>)
    2345 </t>
    2346 <t>
    2347   Remove the default character encoding for text media types; the default
    2348   now is whatever the media type definition says.
    2349   (<xref target="canonicalization.and.text.defaults"/>)
    2350 </t>
    2351 <t>
    2352   Change ABNF productions for header fields to only define the field value.
    2353   (<xref target="header.field.definitions"/>)
    2354 </t>
    2355 <t>
    2356   Remove definition of Content-MD5 header field because it was inconsistently
    2357   implemented with respect to partial responses, and also because of known
    2358   deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
    2359   (<xref target="header.field.definitions"/>)
    2360 </t>
    2361 <t>
    2362   Remove ISO-8859-1 special-casing in Accept-Charset.
    2363   (<xref target="header.accept-charset"/>)
    2364 </t>
    2365 <t>
    2366   Remove base URI setting semantics for Content-Location due to poor
    2367   implementation support, which was caused by too many broken servers emitting
    2368   bogus Content-Location header fields, and also the potentially undesirable effect
    2369   of potentially breaking relative links in content-negotiated resources.
    2370   (<xref target="header.content-location"/>)
    2371 </t>
    2372 <t>
    2373   Remove reference to non-existant identity transfer-coding value tokens.
    2374   (<xref target="no.content-transfer-encoding"/>)
    2375 </t>
    2376 <t>
    2377   Remove discussion of Content-Disposition header field, it is now defined
    2378   by <xref target="RFC6266"/>.
    2379   (<xref target="additional.features"/>)
    2380 </t>
    2381606</section>
    2382607
     
    2385610<figure>
    2386611<artwork type="abnf" name="p3-payload.parsed-abnf">
    2387 <x:ref>Accept</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
    2388  OWS media-range [ accept-params ] ] ) ]
    2389 <x:ref>Accept-Charset</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
    2390  qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
    2391  qvalue ] ] )
    2392 <x:ref>Accept-Encoding</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
    2393  *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
    2394 <x:ref>Accept-Language</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
    2395  qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
    2396  ] )
    2397 
    2398 <x:ref>Content-Encoding</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
    2399  content-coding ] )
    2400 <x:ref>Content-Language</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
    2401  language-tag ] )
    2402 <x:ref>Content-Location</x:ref> = absolute-URI / partial-URI
    2403 <x:ref>Content-Type</x:ref> = media-type
    2404 
    2405 <x:ref>MIME-Version</x:ref> = 1*DIGIT "." 1*DIGIT
    2406 
    2407 <x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
    2408 
    2409 <x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
    2410 <x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
    2411 <x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
    2412 <x:ref>attribute</x:ref> = token
    2413 
    2414 <x:ref>charset</x:ref> = token
    2415 <x:ref>codings</x:ref> = content-coding / "identity" / "*"
    2416 <x:ref>content-coding</x:ref> = token
    2417 
    2418 <x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
    2419 <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
    2420 
    2421 <x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
    2422  ";" OWS parameter )
    2423 <x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
    2424 
    2425 <x:ref>parameter</x:ref> = attribute "=" value
    2426 <x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
    2427 
    2428 <x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 4.3.1&gt;
    2429 
    2430 <x:ref>subtype</x:ref> = token
    2431 
    2432 <x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
    2433 <x:ref>type</x:ref> = token
    2434 
    2435 <x:ref>value</x:ref> = word
    2436 
    2437 <x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 3.2.4&gt;
     612foo = bar
    2438613</artwork>
    2439614</figure>
    2440615<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
    2441 ; Accept defined but not used
    2442 ; Accept-Charset defined but not used
    2443 ; Accept-Encoding defined but not used
    2444 ; Accept-Language defined but not used
    2445 ; Content-Encoding defined but not used
    2446 ; Content-Language defined but not used
    2447 ; Content-Location defined but not used
    2448 ; Content-Type defined but not used
    2449 ; MIME-Version defined but not used
     616; bar UNDEFINED
     617; foo defined but not used
    2450618</artwork></figure></section>
    2451619<?ENDINC p3-payload.abnf-appendix ?>
    2452620
    2453 <section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
    2454 
    2455 <section title="Since RFC 2616">
    2456 <t>
    2457   Extracted relevant partitions from <xref target="RFC2616"/>.
    2458 </t>
    2459 </section>
    2460 
    2461 <section title="Since draft-ietf-httpbis-p3-payload-00">
    2462 <t>
    2463   Closed issues:
    2464   <list style="symbols">
    2465     <t>
    2466       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
    2467       "Media Type Registrations"
    2468       (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
    2469     </t>
    2470     <t>
    2471       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
    2472       "Clarification regarding quoting of charset values"
    2473       (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
    2474     </t>
    2475     <t>
    2476       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
    2477       "Remove 'identity' token references"
    2478       (<eref target="http://purl.org/NET/http-errata#identity"/>)
    2479     </t>
    2480     <t>
    2481       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
    2482       "Accept-Encoding BNF"
    2483     </t>
    2484     <t>
    2485       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
    2486       "Normative and Informative references"
    2487     </t>
    2488     <t>
    2489       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
    2490       "RFC1700 references"
    2491     </t>
    2492     <t>
    2493       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
    2494       "Updating to RFC4288"
    2495     </t>
    2496     <t>
    2497       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
    2498       "Informative references"
    2499     </t>
    2500     <t>
    2501       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
    2502       "ISO-8859-1 Reference"
    2503     </t>
    2504     <t>
    2505       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
    2506       "Encoding References Normative"
    2507     </t>
    2508     <t>
    2509       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
    2510       "Normative up-to-date references"
    2511     </t>
    2512   </list>
    2513 </t>
    2514 </section>
    2515 
    2516 <section title="Since draft-ietf-httpbis-p3-payload-01">
    2517 <t>
    2518   Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
    2519   <list style="symbols">
    2520     <t>
    2521       Add explicit references to BNF syntax and rules imported from other parts of the specification.
    2522     </t>
    2523   </list>
    2524 </t>
    2525 </section>
    2526 
    2527 <section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
    2528 <t>
    2529   Closed issues:
    2530   <list style="symbols">
    2531     <t>
    2532       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
    2533       "Quoting Charsets"
    2534     </t>
    2535     <t>
    2536       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
    2537       "Classification for Allow header"
    2538     </t>
    2539     <t>
    2540       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
    2541       "missing default for qvalue in description of Accept-Encoding"
    2542     </t>
    2543   </list>
    2544 </t>
    2545 <t>
    2546   Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
    2547   <list style="symbols">
    2548     <t>
    2549       Reference RFC 3984, and update header field registrations for headers defined
    2550       in this document.
    2551     </t>
    2552   </list>
    2553 </t>
    2554 </section>
    2555 
    2556 <section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
    2557 <t>
    2558   Closed issues:
    2559   <list style="symbols">
    2560     <t>
    2561       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
    2562       "Quoting Charsets"
    2563     </t>
    2564     <t>
    2565       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
    2566       "language tag matching (Accept-Language) vs RFC4647"
    2567     </t>
    2568     <t>
    2569       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
    2570       "RFC 1806 has been replaced by RFC2183"
    2571     </t>
    2572   </list>
    2573 </t>
    2574 <t>
    2575   Other changes:
    2576   <list style="symbols">
    2577     <t>
    2578       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
    2579       "Encoding References Normative" &mdash; rephrase the annotation and reference
    2580       BCP97.
    2581     </t>
    2582   </list>
    2583 </t>
    2584  </section>
    2585 
    2586 <section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
    2587 <t>
    2588   Closed issues:
    2589   <list style="symbols">
    2590     <t>
    2591       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
    2592       "RFC 2822 is updated by RFC 5322"
    2593     </t>
    2594   </list>
    2595 </t>
    2596 <t>
    2597   Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
    2598   <list style="symbols">
    2599     <t>
    2600       Use "/" instead of "|" for alternatives.
    2601     </t>
    2602     <t>
    2603       Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
    2604       whitespace ("OWS") and required whitespace ("RWS").
    2605     </t>
    2606     <t>
    2607       Rewrite ABNFs to spell out whitespace rules, factor out
    2608       header field value format definitions.
    2609     </t>
    2610   </list>
    2611 </t>
    2612 </section>
    2613 
    2614 <section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
    2615 <t>
    2616   Closed issues:
    2617   <list style="symbols">
    2618     <t>
    2619       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
    2620       "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
    2621     </t>
    2622   </list>
    2623 </t>
    2624 <t>
    2625   Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
    2626   <list style="symbols">
    2627     <t>
    2628       Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
    2629     </t>
    2630   </list>
    2631 </t>
    2632 <t>
    2633   Other changes:
    2634   <list style="symbols">
    2635     <t>
    2636       Move definition of quality values into Part 1.
    2637     </t>
    2638   </list>
    2639 </t>
    2640 </section>
    2641 
    2642 <section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
    2643 <t>
    2644   Closed issues:
    2645   <list style="symbols">
    2646     <t>
    2647       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
    2648       "Content-Location isn't special"
    2649     </t>
    2650     <t>
    2651       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
    2652       "Content Sniffing"
    2653     </t>
    2654   </list>
    2655 </t>
    2656 </section>
    2657 
    2658 <section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
    2659 <t>
    2660   Closed issues:
    2661   <list style="symbols">
    2662     <t>
    2663       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
    2664       "Updated reference for language tags"
    2665     </t>
    2666     <t>
    2667       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
    2668       "Clarify rules for determining what entities a response carries"
    2669     </t>
    2670     <t>
    2671       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
    2672       "Content-Location base-setting problems"
    2673     </t>
    2674     <t>
    2675       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
    2676       "Content Sniffing"
    2677     </t>
    2678     <t>
    2679       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
    2680       "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
    2681     </t>
    2682     <t>
    2683       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
    2684       "move definitions of gzip/deflate/compress to part 1"
    2685     </t>
    2686   </list>
    2687 </t>
    2688 <t>
    2689   Partly resolved issues:
    2690   <list style="symbols">
    2691     <t>
    2692       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
    2693       "update IANA requirements wrt Transfer-Coding values" (add the
    2694       IANA Considerations subsection)
    2695     </t>
    2696     <t>
    2697       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
    2698       "update IANA requirements wrt Content-Coding values" (add the
    2699       IANA Considerations subsection)
    2700     </t>
    2701   </list>
    2702 </t>
    2703 </section>
    2704 
    2705 <section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
    2706 <t>
    2707   Closed issues:
    2708   <list style="symbols">
    2709     <t>
    2710       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
    2711       "Content Negotiation for media types"
    2712     </t>
    2713     <t>
    2714       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
    2715       "Accept-Language: which RFC4647 filtering?"
    2716     </t>
    2717   </list>
    2718 </t>
    2719 </section>
    2720 
    2721 <section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
    2722 <t>
    2723   Closed issues:
    2724   <list style="symbols">
    2725     <t>
    2726       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
    2727       "MIME-Version not listed in P1, general header fields"
    2728     </t>
    2729     <t>
    2730       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
    2731       "IANA registry for content/transfer encodings"
    2732     </t>
    2733     <t>
    2734       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
    2735       "Content Sniffing"
    2736     </t>
    2737     <t>
    2738       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
    2739       "use of term "word" when talking about header structure"
    2740     </t>
    2741   </list>
    2742 </t>
    2743 <t>
    2744   Partly resolved issues:
    2745   <list style="symbols">
    2746     <t>
    2747       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
    2748       "Term for the requested resource's URI"
    2749     </t>
    2750   </list>
    2751 </t>
    2752 </section>
    2753 
    2754 <section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
    2755 <t>
    2756   Closed issues:
    2757   <list style="symbols">
    2758     <t>
    2759       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
    2760       "Clarify 'Requested Variant'"
    2761     </t>
    2762     <t>
    2763       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
    2764       "Content-Location isn't special"
    2765     </t>
    2766     <t>
    2767       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
    2768       "Delimiting messages with multipart/byteranges"
    2769     </t>
    2770     <t>
    2771       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
    2772       "Clarify entity / representation / variant terminology"
    2773     </t>
    2774     <t>
    2775       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
    2776       "confusing req. language for Content-Location"
    2777     </t>
    2778     <t>
    2779       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
    2780       "Content-Location on 304 responses"
    2781     </t>
    2782     <t>
    2783       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
    2784       "'requested resource' in content-encoding definition"
    2785     </t>
    2786     <t>
    2787       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
    2788       "consider removing the 'changes from 2068' sections"
    2789     </t>
    2790   </list>
    2791 </t>
    2792 <t>
    2793   Partly resolved issues:
    2794   <list style="symbols">
    2795     <t>
    2796       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
    2797       "Content-MD5 and partial responses"
    2798     </t>
    2799   </list>
    2800 </t>
    2801 </section>
    2802 
    2803 <section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
    2804 <t>
    2805   Closed issues:
    2806   <list style="symbols">
    2807     <t>
    2808       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
    2809       "Factor out Content-Disposition"
    2810     </t>
    2811   </list>
    2812 </t>
    2813 </section>
    2814 
    2815 <section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
    2816 <t>
    2817   Closed issues:
    2818   <list style="symbols">
    2819     <t>
    2820       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
    2821       "Header Classification"
    2822     </t>
    2823     <t>
    2824       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
    2825       "untangle ABNFs for header fields"
    2826     </t>
    2827     <t>
    2828       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
    2829       "potentially misleading MAY in media-type def"
    2830     </t>
    2831   </list>
    2832 </t>
    2833 </section>
    2834 
    2835 <section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
    2836 <t>
    2837   Closed issues:
    2838   <list style="symbols">
    2839     <t>
    2840       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
    2841       "Default charsets for text media types"
    2842     </t>
    2843     <t>
    2844       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
    2845       "Content-MD5 and partial responses"
    2846     </t>
    2847     <t>
    2848       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
    2849       "untangle ABNFs for header fields"
    2850     </t>
    2851     <t>
    2852       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
    2853       "confusing undefined parameter in media range example"
    2854     </t>
    2855   </list>
    2856 </t>
    2857 </section>
    2858 
    2859 <section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
    2860 <t>
    2861   None.
    2862 </t>
    2863 </section>
    2864 
    2865 <section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
    2866 <t>
    2867   Closed issues:
    2868   <list style="symbols">
    2869     <t>
    2870       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
    2871       "Strength of requirements on Accept re: 406"
    2872     </t>
    2873   </list>
    2874 </t>
    2875 </section>
    2876 
    2877 <section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
    2878 <t>
    2879   Closed issues:
    2880   <list style="symbols">
    2881     <t>
    2882       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
    2883       "Document HTTP's error-handling philosophy"
    2884     </t>
    2885   </list>
    2886 </t>
    2887 </section>
    2888 
    2889 <section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.since.17">
    2890 <t>
    2891   Closed issues:
    2892   <list style="symbols">
    2893     <t>
    2894       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
    2895       "intended maturity level vs normative references"
    2896     </t>
    2897   </list>
    2898 </t>
    2899 </section>
    2900 
    2901 <section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.since.18">
    2902 <t>
    2903   Closed issues:
    2904   <list style="symbols">
    2905     <t>
    2906       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
    2907       "is ETag a representation header field?"
    2908     </t>
    2909     <t>
    2910       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/338"/>:
    2911       "Content-Location doesn't constrain the cardinality of representations"
    2912     </t>
    2913     <t>
    2914       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
    2915       "make IANA policy definitions consistent"
    2916     </t>
    2917   </list>
    2918 </t>
    2919 </section>
    2920 
    2921 <section title="Since draft-ietf-httpbis-p3-payload-19" anchor="changes.since.19">
    2922 <t>
    2923   None yet.
    2924 </t>
    2925 </section>
    2926 
    2927 </section>
    2928621
    2929622</back>
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