Ignore:
Timestamp:
Mar 30, 2012, 8:19:59 AM (8 years ago)
Author:
julian.reschke@…
Message:

Step 5 of p2/p3-merge (see #351)

File:
1 edited

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

    r1642 r1643  
    1616  <!ENTITY ID-YEAR "2012">
    1717  <!ENTITY mdash "&#8212;">
    18   <!ENTITY architecture             "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    19   <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    20   <!ENTITY abnf-extension           "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    21   <!ENTITY acks                     "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    22   <!ENTITY whitespace               "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    23   <!ENTITY field-components         "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    24   <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    25   <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    26   <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    27   <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    28   <!ENTITY header-etag              "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    29   <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    30   <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    31   <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    32   <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    33   <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    34   <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    35   <!ENTITY http-date                "<xref target='Part2' x:rel='#http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    36   <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    37   <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    38   <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    39   <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    40   <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    41   <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    42   <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    43   <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    44   <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4518]>
    4619<?rfc toc="yes" ?>
     
    5629<?rfc-ext allow-markup-in-artwork="yes" ?>
    5730<?rfc-ext include-references-in-index="yes" ?>
    58 <rfc obsoletes="2616" category="std" x:maturity-level="proposed"
     31<rfc category="std" x:maturity-level="proposed"
    5932     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
    6033     xmlns:x='http://purl.org/net/xml2rfc/ext'>
    61 <x:link rel="prev" basename="p2-semantics"/>
    62 <x:link rel="next" basename="p4-conditional"/>
    6334<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
    6435<front>
     
    12697  This part is now obsolete. Please see HTTPbis, Part 2.
    12798</t>
    128 
    129 <section title="Syntax Notation" anchor="notation">
    130   <x:anchor-alias value="ALPHA"/>
    131   <x:anchor-alias value="CR"/>
    132   <x:anchor-alias value="DIGIT"/>
    133   <x:anchor-alias value="LF"/>
    134   <x:anchor-alias value="OCTET"/>
    135   <x:anchor-alias value="VCHAR"/>
    136 
    137 <section title="Core Rules" anchor="core.rules">
    138   <x:anchor-alias value="token"/>
    139   <x:anchor-alias value="word"/>
    140   <x:anchor-alias value="OWS"/>
    14199</section>
    142 
    143 <section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
    144   <x:anchor-alias value="absolute-URI"/>
    145   <x:anchor-alias value="partial-URI"/>
    146   <x:anchor-alias value="qvalue"/>
    147 </section>
    148 
    149 </section>
    150 
    151 </section>
    152 
    153 <section title="Protocol Parameters" anchor="protocol.parameters">
    154 
    155 <section title="Character Encodings (charset)" anchor="character.sets">
    156 <t>
    157    HTTP uses charset names to indicate the character encoding of a
    158    textual representation.
    159 </t>
    160 <t anchor="rule.charset">
    161   <x:anchor-alias value="charset"/>
    162    A character encoding is identified by a case-insensitive token. The
    163    complete set of tokens is defined by the IANA Character Set registry
    164    (<eref target="http://www.iana.org/assignments/character-sets"/>).
    165 </t>
    166 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
    167   <x:ref>charset</x:ref> = <x:ref>token</x:ref>
    168 </artwork></figure>
    169 <t>
    170    Although HTTP allows an arbitrary token to be used as a charset
    171    value, any token that has a predefined value within the IANA
    172    Character Set registry &MUST; represent the character encoding defined
    173    by that registry. Applications &SHOULD; limit their use of character
    174    encodings to those defined within the IANA registry.
    175 </t>
    176 <t>
    177    HTTP uses charset in two contexts: within an Accept-Charset request
    178    header field (in which the charset value is an unquoted token) and as the
    179    value of a parameter in a Content-Type header field (within a request or
    180    response), in which case the parameter value of the charset parameter
    181    can be quoted.
    182 </t>
    183 <t>
    184    Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
    185    <xref target="RFC2277"/>.
    186 </t>
    187 </section>
    188 
    189 <section title="Content Codings" anchor="content.codings">
    190   <x:anchor-alias value="content-coding"/>
    191 <t>
    192    Content coding values indicate an encoding transformation that has
    193    been or can be applied to a representation. Content codings are primarily
    194    used to allow a representation to be compressed or otherwise usefully
    195    transformed without losing the identity of its underlying media type
    196    and without loss of information. Frequently, the representation is stored in
    197    coded form, transmitted directly, and only decoded by the recipient.
    198 </t>
    199 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
    200   <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
    201 </artwork></figure>
    202 <t>
    203    All content-coding values are case-insensitive. HTTP/1.1 uses
    204    content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
    205    Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
    206    describes the content-coding, what is more important is that it
    207    indicates what decoding mechanism will be required to remove the
    208    encoding.
    209 </t>
    210 <t>
    211    compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
    212   <list>
    213     <t>
    214       See &compress-coding;.
    215     </t>
    216   </list>
    217 </t>
    218 <t>
    219    deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
    220   <list>
    221     <t>
    222       See &deflate-coding;.
    223     </t>
    224   </list>
    225 </t>
    226 <t>
    227    gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
    228   <list>
    229     <t>
    230       See &gzip-coding;.
    231     </t>
    232   </list>
    233 </t>
    234 
    235 <section title="Content Coding Registry" anchor="content.coding.registry">
    236 <t>
    237    The HTTP Content Coding Registry defines the name space for the content
    238    coding names.
    239 </t>
    240 <t>
    241    Registrations &MUST; include the following fields:
    242    <list style="symbols">
    243      <t>Name</t>
    244      <t>Description</t>
    245      <t>Pointer to specification text</t>
    246    </list>
    247 </t>
    248 <t>
    249    Names of content codings &MUST-NOT; overlap with names of transfer codings
    250    (&transfer-codings;), unless the encoding transformation is identical (as
    251    is the case for the compression codings defined in
    252    &compression-codings;).
    253 </t>
    254 <t>
    255    Values to be added to this name space require IETF Review
    256    (see <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
    257    conform to the purpose of content coding defined in this section.
    258 </t>
    259 <t>
    260    The registry itself is maintained at
    261    <eref target="http://www.iana.org/assignments/http-parameters"/>.
    262 </t>
    263 </section>
    264 
    265 </section>
    266 
    267 <section title="Media Types" anchor="media.types">
    268   <x:anchor-alias value="media-type"/>
    269   <x:anchor-alias value="type"/>
    270   <x:anchor-alias value="subtype"/>
    271 <t>
    272    HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
    273    and Accept (<xref target="header.accept"/>) header fields in order to provide
    274    open and extensible data typing and type negotiation.
    275 </t>
    276 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/>
    277   <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
    278   <x:ref>type</x:ref>       = <x:ref>token</x:ref>
    279   <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
    280 </artwork></figure>
    281 <t anchor="rule.parameter">
    282   <x:anchor-alias value="attribute"/>
    283   <x:anchor-alias value="parameter"/>
    284   <x:anchor-alias value="value"/>
    285    The type/subtype &MAY; be followed by parameters in the form of
    286    attribute/value pairs.
    287 </t>
    288 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
    289   <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
    290   <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
    291   <x:ref>value</x:ref>          = <x:ref>word</x:ref>
    292 </artwork></figure>
    293 <t>
    294    The type, subtype, and parameter attribute names are case-insensitive.
    295    Parameter values might or might not be case-sensitive, depending on the
    296    semantics of the parameter name.  The presence or absence of a parameter might
    297    be significant to the processing of a media-type, depending on its
    298    definition within the media type registry.
    299 </t>
    300 <t>
    301    A parameter value that matches the <x:ref>token</x:ref> production can be
    302    transmitted as either a token or within a quoted-string. The quoted and
    303    unquoted values are equivalent.
    304 </t>
    305 <t>
    306    Note that some older HTTP applications do not recognize media type
    307    parameters. When sending data to older HTTP applications,
    308    implementations &SHOULD; only use media type parameters when they are
    309    required by that type/subtype definition.
    310 </t>
    311 <t>
    312    Media-type values are registered with the Internet Assigned Number
    313    Authority (IANA). The media type registration process is
    314    outlined in <xref target="RFC4288"/>. Use of non-registered media types is
    315    discouraged.
    316 </t>
    317 
    318 <section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
    319 <t>
    320    Internet media types are registered with a canonical form. A
    321    representation transferred via HTTP messages &MUST; be in the
    322    appropriate canonical form prior to its transmission except for
    323    "text" types, as defined in the next paragraph.
    324 </t>
    325 <t>
    326    When in canonical form, media subtypes of the "text" type use CRLF as
    327    the text line break. HTTP relaxes this requirement and allows the
    328    transport of text media with plain CR or LF alone representing a line
    329    break when it is done consistently for an entire representation. HTTP
    330    applications &MUST; accept CRLF, bare CR, and bare LF as indicating
    331    a line break in text media received via HTTP. In
    332    addition, if the text is in a character encoding that does not
    333    use octets 13 and 10 for CR and LF respectively, as is the case for
    334    some multi-byte character encodings, HTTP allows the use of whatever octet
    335    sequences are defined by that character encoding to represent the
    336    equivalent of CR and LF for line breaks. This flexibility regarding
    337    line breaks applies only to text media in the payload body; a bare CR
    338    or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
    339    structures (such as header fields and multipart boundaries).
    340 </t>
    341 <t>
    342    If a representation is encoded with a content-coding, the underlying
    343    data &MUST; be in a form defined above prior to being encoded.
    344 </t>
    345 </section>
    346 
    347 <section title="Multipart Types" anchor="multipart.types">
    348 <t>
    349    MIME provides for a number of "multipart" types &mdash; encapsulations of
    350    one or more representations within a single message body. All multipart
    351    types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
    352    and &MUST; include a boundary parameter as part of the media type
    353    value. The message body is itself a protocol element and &MUST;
    354    therefore use only CRLF to represent line breaks between body-parts.
    355 </t>
    356 <t>
    357    In general, HTTP treats a multipart message body no differently than
    358    any other media type: strictly as payload.  HTTP does not use the
    359    multipart boundary as an indicator of message body length.
    360    <!-- jre: re-insert removed text pointing to caching? -->
    361    In all other respects, an HTTP user agent &SHOULD; follow the same or similar
    362    behavior as a MIME user agent would upon receipt of a multipart type.
    363    The MIME header fields within each body-part of a multipart message body
    364    do not have any significance to HTTP beyond that defined by
    365    their MIME semantics.
    366 </t>
    367 <t>
    368    If an application receives an unrecognized multipart subtype, the
    369    application &MUST; treat it as being equivalent to "multipart/mixed".
    370 </t>
    371 <x:note>
    372   <t>
    373     <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
    374     for carrying form data suitable for processing via the POST
    375     request method, as described in <xref target="RFC2388"/>.
    376   </t>
    377 </x:note>
    378 </section>
    379 </section>
    380 
    381 <section title="Language Tags" anchor="language.tags">
    382   <x:anchor-alias value="language-tag"/>
    383 <t>
    384    A language tag, as defined in <xref target="RFC5646"/>, identifies a
    385    natural language spoken, written, or otherwise conveyed by human beings for
    386    communication of information to other human beings. Computer languages are
    387    explicitly excluded. HTTP uses language tags within the Accept-Language and
    388    Content-Language fields.
    389 </t>
    390 <t>
    391    In summary, a language tag is composed of one or more parts: A primary
    392    language subtag followed by a possibly empty series of subtags:
    393 </t>
    394 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
    395   <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
    396 </artwork></figure>
    397 <t>
    398    White space is not allowed within the tag and all tags are case-insensitive.
    399    The name space of language subtags is administered by the IANA (see
    400    <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
    401 </t>
    402 <figure>
    403   <preamble>Example tags include:</preamble>
    404 <artwork type="example">
    405   en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
    406 </artwork>
    407 </figure>
    408 <t>
    409    See <xref target="RFC5646"/> for further information.
    410 </t>
    411 </section>
    412 </section>
    413 
    414 <section title="Payload" anchor="payload">
    415 <t>
    416    HTTP messages &MAY; transfer a payload if not otherwise restricted by
    417    the request method or response status code.  The payload consists of
    418    metadata, in the form of header fields, and data, in the form of the
    419    sequence of octets in the message body after any transfer-coding has
    420    been decoded.
    421 </t>
    422 <iref item="payload"/>
    423 <t>   
    424    A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
    425    representation of some resource.  We use separate terms for payload
    426    and representation because some messages contain only the associated
    427    representation's header fields (e.g., responses to HEAD) or only some
    428    part(s) of the representation (e.g., the 206 status code).
    429 </t>
    430 <section title="Payload Header Fields" anchor="payload.header.fields">
    431   <x:anchor-alias value="payload-header"/>
    432 <t>
    433    HTTP header fields that specifically define the payload, rather than the
    434    associated representation, are referred to as "payload header fields".
    435    The following payload header fields are defined by HTTP/1.1:
    436 </t>
    437 <texttable align="left">
    438   <ttcol>Header Field Name</ttcol>
    439   <ttcol>Defined in...</ttcol>
    440 
    441   <c>Content-Length</c> <c>&header-content-length;</c>
    442   <c>Content-Range</c> <c>&header-content-range;</c>
    443 </texttable>
    444 </section>
    445 
    446 <section title="Payload Body" anchor="payload.body">
    447   <x:anchor-alias value="payload-body"/>
    448 <t>
    449    A payload body is only present in a message when a message body is
    450    present, as described in &message-body;. The payload body is obtained
    451    from the message body by decoding any Transfer-Encoding that might
    452    have been applied to ensure safe and proper transfer of the message.
    453 </t>
    454 </section>
    455 </section>
    456 
    457 <section title="Representation" anchor="representation">
    458 <iref item="representation"/>
    459 <t>
    460    A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
    461    communicated from one party to another.  A resource representation
    462    is information that reflects the state of that resource, as observed
    463    at some point in the past (e.g., in a response to GET) or to be
    464    desired at some point in the future (e.g., in a PUT request).
    465 </t>
    466 <t>
    467    Most, but not all, representations transferred via HTTP are intended
    468    to be a representation of the target resource (the resource identified
    469    by the effective request URI).  The precise semantics of a representation
    470    are determined by the type of message (request or response), the request
    471    method, the response status code, and the representation metadata.
    472    For example, the above semantic is true for the representation in any
    473    200 (OK) response to GET and for the representation in any PUT request.
    474    A 200 response to PUT, in contrast, contains either a representation
    475    that describes the successful action or a representation of the target
    476    resource, with the latter indicated by a Content-Location header field
    477    with the same value as the effective request URI.  Likewise, response
    478    messages with an error status code usually contain a representation that
    479    describes the error and what next steps are suggested for resolving it.
    480 </t>
    481 
    482 <section title="Representation Header Fields" anchor="representation.header.fields">
    483   <x:anchor-alias value="representation-header"/>
    484 <t>
    485    Representation header fields define metadata about the representation data
    486    enclosed in the message body or, if no message body is present, about
    487    the representation that would have been transferred in a 200 response
    488    to a simultaneous GET request with the same effective request URI.
    489 </t>
    490 <t>
    491    The following header fields are defined as representation metadata:
    492 </t>
    493 <texttable align="left">
    494   <ttcol>Header Field Name</ttcol>
    495   <ttcol>Defined in...</ttcol>
    496 
    497   <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
    498   <c>Content-Language</c> <c><xref target="header.content-language"/></c>
    499   <c>Content-Location</c> <c><xref target="header.content-location"/></c>
    500   <c>Content-Type</c> <c><xref target="header.content-type"/></c>
    501   <c>Expires</c> <c>&header-expires;</c>
    502 </texttable>
    503 <t>
    504    Additional header fields define metadata about the selected
    505    representation, which might differ from the representation included
    506    in the message for responses to some state-changing methods.
    507    The following header fields are defined as selected representation
    508    metadata:
    509 </t>
    510 <texttable align="left">
    511   <ttcol>Header Field Name</ttcol>
    512   <ttcol>Defined in...</ttcol>
    513 
    514   <c>ETag</c> <c>&header-etag;</c>
    515   <c>Last-Modified</c> <c>&header-last-modified;</c>
    516 </texttable>
    517 </section>
    518 
    519 <section title="Representation Data" anchor="representation.data">
    520   <x:anchor-alias value="representation-data"/>
    521 <t>
    522    The representation body associated with an HTTP message is
    523    either provided as the payload body of the message or
    524    referred to by the message semantics and the effective request
    525    URI.  The representation data is in a format and encoding defined by
    526    the representation metadata header fields.
    527 </t>
    528 <t>
    529    The data type of the representation data
    530    is determined via the header fields Content-Type and Content-Encoding.
    531    These define a two-layer, ordered encoding model:
    532 </t>
    533 <figure><artwork type="example">
    534   representation-data := Content-Encoding( Content-Type( bits ) )
    535 </artwork></figure>
    536 <t>
    537    Content-Type specifies the media type of the underlying data, which
    538    defines both the data format and how that data &SHOULD; be processed
    539    by the recipient (within the scope of the request method semantics).
    540    Any HTTP/1.1 message containing a payload body &SHOULD; include a
    541    Content-Type header field defining the media type of the associated
    542    representation unless that metadata is unknown to the sender.
    543    If the Content-Type header field is not present, it indicates that
    544    the sender does not know the media type of the representation;
    545    recipients &MAY; either assume that the media type is
    546    "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
    547    or examine the content to determine its type.
    548 </t>
    549 <t>
    550    In practice, resource owners do not always properly configure their origin
    551    server to provide the correct Content-Type for a given representation,
    552    with the result that some clients will examine a response body's content
    553    and override the specified type.
    554    Clients that do so risk drawing incorrect conclusions, which might expose
    555    additional security risks (e.g., "privilege escalation").  Furthermore,
    556    it is impossible to determine the sender's intent by examining the data
    557    format: many data formats match multiple media types that differ only in
    558    processing semantics.  Implementers are encouraged to provide a means of
    559    disabling such "content sniffing" when it is used.
    560 </t>
    561 <t>
    562    Content-Encoding is used to indicate any additional content
    563    codings applied to the data, usually for the purpose of data
    564    compression, that are a property of the representation.  If
    565    Content-Encoding is not present, then there is no additional
    566    encoding beyond that defined by the Content-Type.
    567 </t>
    568 </section>
    569 </section>
    570 
    571 <section title="Content Negotiation" anchor="content.negotiation">
    572 <t>
    573    HTTP responses include a representation which contains information for
    574    interpretation, whether by a human user or for further processing.
    575    Often, the server has different ways of representing the
    576    same information; for example, in different formats, languages,
    577    or using different character encodings.
    578 </t>
    579 <t>
    580    HTTP clients and their users might have different or variable
    581    capabilities, characteristics or preferences which would influence
    582    which representation, among those available from the server,
    583    would be best for the server to deliver. For this reason, HTTP
    584    provides mechanisms for "content negotiation" &mdash; a process of
    585    allowing selection of a representation of a given resource,
    586    when more than one is available.
    587 </t>
    588 <t>
    589    This specification defines two patterns of content negotiation;
    590    "server-driven", where the server selects the representation based
    591    upon the client's stated preferences, and "agent-driven" negotiation,
    592    where the server provides a list of representations for the client to
    593    choose from, based upon their metadata. In addition,  there are
    594    other patterns: some applications use an "active content" pattern,
    595    where the server returns active content which runs on the client
    596    and, based on client available parameters, selects additional
    597    resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
    598    has also been proposed.
    599 </t>
    600 <t>
    601    These patterns are all widely used, and have trade-offs in applicability
    602    and practicality. In particular, when the number of preferences or
    603    capabilities to be expressed by a client are large (such as when many
    604    different formats are supported by a user-agent), server-driven
    605    negotiation becomes unwieldy, and might not be appropriate. Conversely,
    606    when the number of representations to choose from is very large,
    607    agent-driven negotiation might not be appropriate.
    608 </t>
    609 <t>
    610    Note that in all cases, the supplier of representations has the
    611    responsibility for determining which representations might be
    612    considered to be the "same information".
    613 </t>
    614 
    615 <section title="Server-driven Negotiation" anchor="server-driven.negotiation">
    616 <t>
    617    If the selection of the best representation for a response is made by
    618    an algorithm located at the server, it is called server-driven
    619    negotiation. Selection is based on the available representations of
    620    the response (the dimensions over which it can vary; e.g., language,
    621    content-coding, etc.) and the contents of particular header fields in
    622    the request message or on other information pertaining to the request
    623    (such as the network address of the client).
    624 </t>
    625 <t>
    626    Server-driven negotiation is advantageous when the algorithm for
    627    selecting from among the available representations is difficult to
    628    describe to the user agent, or when the server desires to send its
    629    "best guess" to the client along with the first response (hoping to
    630    avoid the round-trip delay of a subsequent request if the "best
    631    guess" is good enough for the user). In order to improve the server's
    632    guess, the user agent &MAY; include request header fields (Accept,
    633    Accept-Language, Accept-Encoding, etc.) which describe its
    634    preferences for such a response.
    635 </t>
    636 <t>
    637    Server-driven negotiation has disadvantages:
    638   <list style="numbers">
    639     <t>
    640          It is impossible for the server to accurately determine what
    641          might be "best" for any given user, since that would require
    642          complete knowledge of both the capabilities of the user agent
    643          and the intended use for the response (e.g., does the user want
    644          to view it on screen or print it on paper?).
    645     </t>
    646     <t>
    647          Having the user agent describe its capabilities in every
    648          request can be both very inefficient (given that only a small
    649          percentage of responses have multiple representations) and a
    650          potential violation of the user's privacy.
    651     </t>
    652     <t>
    653          It complicates the implementation of an origin server and the
    654          algorithms for generating responses to a request.
    655     </t>
    656     <t>
    657          It might limit a public cache's ability to use the same response
    658          for multiple user's requests.
    659     </t>
    660   </list>
    661 </t>
    662 <t>
    663    Server-driven negotiation allows the user agent to specify its preferences,
    664    but it cannot expect responses to always honor them. For example, the origin
    665    server might not implement server-driven negotiation, or it might decide that
    666    sending a response that doesn't conform to them is better than sending a 406
    667    (Not Acceptable) response.
    668 </t>
    669 <t>
    670    Many of the mechanisms for expressing preferences use quality values to
    671    declare relative preference. See &qvalue; for more information.
    672 </t>
    673 <t>
    674    HTTP/1.1 includes the following header fields for enabling
    675    server-driven negotiation through description of user agent
    676    capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
    677    (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
    678    (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
    679    However, an origin server is not limited to these dimensions and &MAY; vary
    680    the response based on any aspect of the request, including aspects
    681    of the connection (e.g., IP address) or information within extension
    682    header fields not defined by this specification.
    683 </t>
    684 <x:note>
    685   <t>
    686     <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
    687     because new clients might not be recognized.
    688   </t>
    689 </x:note>
    690 <t>
    691    The Vary header field (&header-vary;) can be used to express the parameters the
    692    server uses to select a representation that is subject to server-driven
    693    negotiation.
    694 </t>
    695 </section>
    696 
    697 <section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
    698 <t>
    699    With agent-driven negotiation, selection of the best representation
    700    for a response is performed by the user agent after receiving an
    701    initial response from the origin server. Selection is based on a list
    702    of the available representations of the response included within the
    703    header fields or body of the initial response, with each
    704    representation identified by its own URI. Selection from among the
    705    representations can be performed automatically (if the user agent is
    706    capable of doing so) or manually by the user selecting from a
    707    generated (possibly hypertext) menu.
    708 </t>
    709 <t>
    710    Agent-driven negotiation is advantageous when the response would vary
    711    over commonly-used dimensions (such as type, language, or encoding),
    712    when the origin server is unable to determine a user agent's
    713    capabilities from examining the request, and generally when public
    714    caches are used to distribute server load and reduce network usage.
    715 </t>
    716 <t>
    717    Agent-driven negotiation suffers from the disadvantage of needing a
    718    second request to obtain the best alternate representation. This
    719    second request is only efficient when caching is used. In addition,
    720    this specification does not define any mechanism for supporting
    721    automatic selection, though it also does not prevent any such
    722    mechanism from being developed as an extension and used within
    723    HTTP/1.1.
    724 </t>
    725 <t>
    726    This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
    727    status codes for enabling agent-driven negotiation when the server is
    728    unwilling or unable to provide a varying response using server-driven
    729    negotiation.
    730 </t>
    731 </section>
    732 </section>
    733 
    734 <section title="Header Field Definitions" anchor="header.field.definitions">
    735 <t>
    736    This section defines the syntax and semantics of HTTP/1.1 header fields
    737    related to the payload of messages.
    738 </t>
    739 
    740 <section title="Accept" anchor="header.accept">
    741   <iref primary="true" item="Accept header field" x:for-anchor=""/>
    742   <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
    743   <x:anchor-alias value="Accept"/>
    744   <x:anchor-alias value="accept-ext"/>
    745   <x:anchor-alias value="accept-params"/>
    746   <x:anchor-alias value="media-range"/>
    747 <t>
    748    The "Accept" header field can be used by user agents to specify
    749    response media types that are acceptable. Accept header fields can be used to
    750    indicate that the request is specifically limited to a small set of desired
    751    types, as in the case of a request for an in-line image.
    752 </t>
    753 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
    754   <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
    755  
    756   <x:ref>media-range</x:ref>    = ( "*/*"
    757                    / ( <x:ref>type</x:ref> "/" "*" )
    758                    / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
    759                    ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
    760   <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
    761   <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
    762 </artwork></figure>
    763 <t>
    764    The asterisk "*" character is used to group media types into ranges,
    765    with "*/*" indicating all media types and "type/*" indicating all
    766    subtypes of that type. The media-range &MAY; include media type
    767    parameters that are applicable to that range.
    768 </t>
    769 <t>
    770    Each media-range &MAY; be followed by one or more accept-params,
    771    beginning with the "q" parameter for indicating a relative quality
    772    factor. The first "q" parameter (if any) separates the media-range
    773    parameter(s) from the accept-params. Quality factors allow the user
    774    or user agent to indicate the relative degree of preference for that
    775    media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
    776    default value is q=1.
    777 </t>
    778 <x:note>
    779   <t>
    780     <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
    781     parameters from Accept extension parameters is due to historical
    782     practice. Although this prevents any media type parameter named
    783     "q" from being used with a media range, such an event is believed
    784     to be unlikely given the lack of any "q" parameters in the IANA
    785     media type registry and the rare usage of any media type
    786     parameters in Accept. Future media types are discouraged from
    787     registering any parameter named "q".
    788   </t>
    789 </x:note>
    790 <t>
    791    The example
    792 </t>
    793 <figure><artwork type="example">
    794   Accept: audio/*; q=0.2, audio/basic
    795 </artwork></figure>
    796 <t>
    797    &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
    798    type if it is the best available after an 80% mark-down in quality".
    799 </t>
    800 <t>
    801    A request without any Accept header field implies that the user agent
    802    will accept any media type in response.
    803    If an Accept header field is present in a request and none of the
    804    available representations for the response have a media type that is
    805    listed as acceptable, the origin server &MAY; either
    806    honor the Accept header field by sending a 406 (Not Acceptable) response
    807    or disregard the Accept header field by treating the response as if
    808    it is not subject to content negotiation.
    809 </t>
    810 <t>
    811    A more elaborate example is
    812 </t>
    813 <figure><artwork type="example">
    814   Accept: text/plain; q=0.5, text/html,
    815           text/x-dvi; q=0.8, text/x-c
    816 </artwork></figure>
    817 <t>
    818    Verbally, this would be interpreted as "text/html and text/x-c are
    819    the preferred media types, but if they do not exist, then send the
    820    text/x-dvi representation, and if that does not exist, send the text/plain
    821    representation".
    822 </t>
    823 <t>
    824    Media ranges can be overridden by more specific media ranges or
    825    specific media types. If more than one media range applies to a given
    826    type, the most specific reference has precedence. For example,
    827 </t>
    828 <figure><artwork type="example">
    829   Accept: text/*, text/plain, text/plain;format=flowed, */*
    830 </artwork></figure>
    831 <t>
    832    have the following precedence:
    833    <list style="numbers">
    834     <t>text/plain;format=flowed</t>
    835     <t>text/plain</t>
    836     <t>text/*</t>
    837     <t>*/*</t>
    838    </list>
    839 </t>
    840 <t>
    841    The media type quality factor associated with a given type is
    842    determined by finding the media range with the highest precedence
    843    which matches that type. For example,
    844 </t>
    845 <figure><artwork type="example">
    846   Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
    847           text/html;level=2;q=0.4, */*;q=0.5
    848 </artwork></figure>
    849 <t>
    850    would cause the following values to be associated:
    851 </t>
    852 <texttable align="left">
    853   <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
    854   <c>text/html;level=1</c>    <c>1</c>
    855   <c>text/html</c>            <c>0.7</c>
    856   <c>text/plain</c>           <c>0.3</c>
    857   <c>image/jpeg</c>           <c>0.5</c>
    858   <c>text/html;level=2</c>    <c>0.4</c>
    859   <c>text/html;level=3</c>    <c>0.7</c>
    860 </texttable>
    861 <t>
    862       <x:h>Note:</x:h> A user agent might be provided with a default set of quality
    863       values for certain media ranges. However, unless the user agent is
    864       a closed system which cannot interact with other rendering agents,
    865       this default set ought to be configurable by the user.
    866 </t>
    867 </section>
    868 
    869 <section title="Accept-Charset" anchor="header.accept-charset">
    870   <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
    871   <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
    872   <x:anchor-alias value="Accept-Charset"/>
    873 <t>
    874    The "Accept-Charset" header field can be used by user agents to
    875    indicate what character encodings are acceptable in a response
    876    payload. This field allows
    877    clients capable of understanding more comprehensive or special-purpose
    878    character encodings to signal that capability to a server which is capable of
    879    representing documents in those character encodings.
    880 </t>
    881 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
    882   <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
    883                          [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
    884 </artwork></figure>
    885 <t>
    886    Character encoding values (a.k.a., charsets) are described in
    887    <xref target="character.sets"/>. Each charset &MAY; be given an
    888    associated quality value which represents the user's preference
    889    for that charset. The default value is q=1. An example is
    890 </t>
    891 <figure><artwork type="example">
    892   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
    893 </artwork></figure>
    894 <t>
    895    The special value "*", if present in the Accept-Charset field,
    896    matches every character encoding which is not mentioned elsewhere in the
    897    Accept-Charset field. If no "*" is present in an Accept-Charset field, then
    898    all character encodings not explicitly mentioned get a quality value of 0.
    899 </t>
    900 <t>
    901    A request without any Accept-Charset header field implies that the user
    902    agent will accept any character encoding in response.
    903    If an Accept-Charset header field is present in a request and none of the
    904    available representations for the response have a character encoding that
    905    is listed as acceptable, the origin server &MAY; either honor the
    906    Accept-Charset header field by sending a 406 (Not Acceptable) response or
    907    disregard the Accept-Charset header field by treating the response as if
    908    it is not subject to content negotiation.
    909 </t>
    910 </section>
    911 
    912 <section title="Accept-Encoding" anchor="header.accept-encoding">
    913   <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
    914   <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
    915   <x:anchor-alias value="Accept-Encoding"/>
    916   <x:anchor-alias value="codings"/>
    917 <t>
    918    The "Accept-Encoding" header field can be used by user agents to
    919    indicate what response content-codings (<xref target="content.codings"/>)
    920    are acceptable in the response.  An "identity" token is used as a synonym
    921    for "no encoding" in order to communicate when no encoding is preferred.
    922 </t>
    923 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
    924   <x:ref>Accept-Encoding</x:ref>  = #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
    925   <x:ref>codings</x:ref>          = <x:ref>content-coding</x:ref> / "identity" / "*"
    926 </artwork></figure>
    927 <t>
    928    Each codings value &MAY; be given an associated quality value which
    929    represents the preference for that encoding. The default value is q=1.
    930 </t>
    931 <t>
    932    For example,
    933 </t>
    934 <figure><artwork type="example">
    935   Accept-Encoding: compress, gzip
    936   Accept-Encoding:
    937   Accept-Encoding: *
    938   Accept-Encoding: compress;q=0.5, gzip;q=1.0
    939   Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
    940 </artwork></figure>
    941 <t>
    942    A server tests whether a content-coding for a given representation is
    943    acceptable, according to an Accept-Encoding field, using these rules:
    944   <list style="numbers">
    945       <t>The special "*" symbol in an Accept-Encoding field matches any
    946          available content-coding not explicitly listed in the header
    947          field.</t>
    948 
    949       <t>If the representation has no content-coding, then it is acceptable
    950          by default unless specifically excluded by the Accept-Encoding field
    951          stating either "identity;q=0" or "*;q=0" without a more specific
    952          entry for "identity".</t>
    953 
    954       <t>If the representation's content-coding is one of the content-codings
    955          listed in the Accept-Encoding field, then it is acceptable unless
    956          it is accompanied by a qvalue of 0. (As defined in &qvalue;, a
    957          qvalue of 0 means "not acceptable".)</t>
    958 
    959       <t>If multiple content-codings are acceptable, then the acceptable
    960          content-coding with the highest non-zero qvalue is preferred.</t>
    961   </list>
    962 </t>
    963 <t>
    964    An Accept-Encoding header field with a combined field-value that is empty
    965    implies that the user agent does not want any content-coding in response.
    966    If an Accept-Encoding header field is present in a request and none of the
    967    available representations for the response have a content-coding that
    968    is listed as acceptable, the origin server &SHOULD; send a response
    969    without any content-coding.
    970 </t>
    971 <t>
    972    A request without an Accept-Encoding header field implies that the user
    973    agent will accept any content-coding in response, but a representation
    974    without content-coding is preferred for compatibility with the widest
    975    variety of user agents.
    976 </t>
    977 <x:note>
    978   <t>
    979     <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
    980     associated with content-codings. This means that qvalues will not
    981     work and are not permitted with x-gzip or x-compress.
    982   </t>
    983 </x:note>
    984 </section>
    985 
    986 <section title="Accept-Language" anchor="header.accept-language">
    987   <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
    988   <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
    989   <x:anchor-alias value="Accept-Language"/>
    990   <x:anchor-alias value="language-range"/>
    991 <t>
    992    The "Accept-Language" header field can be used by user agents to
    993    indicate the set of natural languages that are preferred in the response.
    994    Language tags are defined in <xref target="language.tags"/>.
    995 </t>
    996 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
    997   <x:ref>Accept-Language</x:ref> =
    998                     1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
    999   <x:ref>language-range</x:ref>  =
    1000             &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
    1001 </artwork></figure>
    1002 <t>
    1003    Each language-range can be given an associated quality value which
    1004    represents an estimate of the user's preference for the languages
    1005    specified by that range. The quality value defaults to "q=1". For
    1006    example,
    1007 </t>
    1008 <figure><artwork type="example">
    1009   Accept-Language: da, en-gb;q=0.8, en;q=0.7
    1010 </artwork></figure>
    1011 <t>
    1012    would mean: "I prefer Danish, but will accept British English and
    1013    other types of English".
    1014    (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
    1015 </t>
    1016 <t>
    1017    For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
    1018    several matching schemes. Implementations can offer the most appropriate
    1019    matching scheme for their requirements.
    1020 </t>
    1021 <x:note>
    1022   <t>
    1023     <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
    1024     x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
    1025     previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
    1026   </t>
    1027 </x:note>
    1028 <t>
    1029    It might be contrary to the privacy expectations of the user to send
    1030    an Accept-Language header field with the complete linguistic preferences of
    1031    the user in every request. For a discussion of this issue, see
    1032    <xref target="privacy.issues.connected.to.accept.header.fields"/>.
    1033 </t>
    1034 <t>
    1035    As intelligibility is highly dependent on the individual user, it is
    1036    recommended that client applications make the choice of linguistic
    1037    preference available to the user. If the choice is not made
    1038    available, then the Accept-Language header field &MUST-NOT; be given in
    1039    the request.
    1040 </t>
    1041 <x:note>
    1042   <t>
    1043     <x:h>Note:</x:h> When making the choice of linguistic preference available to
    1044     the user, we remind implementors of  the fact that users are not
    1045     familiar with the details of language matching as described above,
    1046     and ought to be provided appropriate guidance. As an example, users
    1047     might assume that on selecting "en-gb", they will be served any
    1048     kind of English document if British English is not available. A
    1049     user agent might suggest in such a case to add "en" to get the
    1050     best matching behavior.
    1051   </t>
    1052 </x:note>
    1053 </section>
    1054 
    1055 <section title="Content-Encoding" anchor="header.content-encoding">
    1056   <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
    1057   <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
    1058   <x:anchor-alias value="Content-Encoding"/>
    1059 <t>
    1060    The "Content-Encoding" header field indicates what content-codings
    1061    have been applied to the representation beyond those inherent in the media
    1062    type, and thus what decoding mechanisms have to be applied in order to obtain
    1063    the media-type referenced by the Content-Type header field.
    1064    Content-Encoding is primarily used to allow a representation to be
    1065    compressed without losing the identity of its underlying media type.
    1066 </t>
    1067 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
    1068   <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
    1069 </artwork></figure>
    1070 <t>
    1071    Content codings are defined in <xref target="content.codings"/>. An example of its use is
    1072 </t>
    1073 <figure><artwork type="example">
    1074   Content-Encoding: gzip
    1075 </artwork></figure>
    1076 <t>
    1077    The content-coding is a characteristic of the representation.
    1078    Typically, the representation body is stored with this
    1079    encoding and is only decoded before rendering or analogous usage.
    1080    However, a transforming proxy &MAY; modify the content-coding if the
    1081    new coding is known to be acceptable to the recipient, unless the
    1082    "no-transform" cache-control directive is present in the message.
    1083 </t>
    1084 <t>
    1085    If the media type includes an inherent encoding, such as a data format
    1086    that is always compressed, then that encoding would not be restated as
    1087    a Content-Encoding even if it happens to be the same algorithm as one
    1088    of the content-codings.  Such a content-coding would only be listed if,
    1089    for some bizarre reason, it is applied a second time to form the
    1090    representation.  Likewise, an origin server might choose to publish the
    1091    same payload data as multiple representations that differ only in whether
    1092    the coding is defined as part of Content-Type or Content-Encoding, since
    1093    some user agents will behave differently in their handling of each
    1094    response (e.g., open a "Save as ..." dialog instead of automatic
    1095    decompression and rendering of content).
    1096 </t>
    1097 <t>
    1098    A representation that has a content-coding applied to it &MUST; include
    1099    a Content-Encoding header field (<xref target="header.content-encoding"/>)
    1100    that lists the content-coding(s) applied.
    1101 </t>
    1102 <t>
    1103    If multiple encodings have been applied to a representation, the content
    1104    codings &MUST; be listed in the order in which they were applied.
    1105    Additional information about the encoding parameters &MAY; be provided
    1106    by other header fields not defined by this specification.
    1107 </t>
    1108 <t>
    1109    If the content-coding of a representation in a request message is not
    1110    acceptable to the origin server, the server &SHOULD; respond with a
    1111    status code of 415 (Unsupported Media Type).
    1112 </t>
    1113 </section>
    1114 
    1115 <section title="Content-Language" anchor="header.content-language">
    1116   <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
    1117   <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
    1118   <x:anchor-alias value="Content-Language"/>
    1119 <t>
    1120    The "Content-Language" header field describes the natural
    1121    language(s) of the intended audience for the representation. Note that this might
    1122    not be equivalent to all the languages used within the representation.
    1123 </t>
    1124 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
    1125   <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
    1126 </artwork></figure>
    1127 <t>
    1128    Language tags are defined in <xref target="language.tags"/>. The primary purpose of
    1129    Content-Language is to allow a user to identify and differentiate
    1130    representations according to the user's own preferred language. Thus, if the
    1131    body content is intended only for a Danish-literate audience, the
    1132    appropriate field is
    1133 </t>
    1134 <figure><artwork type="example">
    1135   Content-Language: da
    1136 </artwork></figure>
    1137 <t>
    1138    If no Content-Language is specified, the default is that the content
    1139    is intended for all language audiences. This might mean that the
    1140    sender does not consider it to be specific to any natural language,
    1141    or that the sender does not know for which language it is intended.
    1142 </t>
    1143 <t>
    1144    Multiple languages &MAY; be listed for content that is intended for
    1145    multiple audiences. For example, a rendition of the "Treaty of
    1146    Waitangi", presented simultaneously in the original Maori and English
    1147    versions, would call for
    1148 </t>
    1149 <figure><artwork type="example">
    1150   Content-Language: mi, en
    1151 </artwork></figure>
    1152 <t>
    1153    However, just because multiple languages are present within a representation
    1154    does not mean that it is intended for multiple linguistic audiences.
    1155    An example would be a beginner's language primer, such as "A First
    1156    Lesson in Latin", which is clearly intended to be used by an
    1157    English-literate audience. In this case, the Content-Language would
    1158    properly only include "en".
    1159 </t>
    1160 <t>
    1161    Content-Language &MAY; be applied to any media type &mdash; it is not
    1162    limited to textual documents.
    1163 </t>
    1164 </section>
    1165 
    1166 <section title="Content-Location" anchor="header.content-location">
    1167   <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
    1168   <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
    1169   <x:anchor-alias value="Content-Location"/>
    1170 <t>
    1171    The "Content-Location" header field supplies a URI that can be used
    1172    as a specific identifier for the representation in this message.
    1173    In other words, if one were to perform a GET on this URI at the time
    1174    of this message's generation, then a 200 response would contain the
    1175    same representation that is enclosed as payload in this message.
    1176 </t>
    1177 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
    1178   <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
    1179 </artwork></figure>
    1180 <t>
    1181    The Content-Location value is not a replacement for the effective
    1182    Request URI (&effective-request-uri;).  It is representation metadata.
    1183    It has the same syntax and semantics as the header field of the same name
    1184    defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
    1185    However, its appearance in an HTTP message has some special implications
    1186    for HTTP recipients.
    1187 </t>
    1188 <t>
    1189    If Content-Location is included in a response message and its value
    1190    is the same as the effective request URI, then the response payload
    1191    &SHOULD; be considered a current representation of that resource.
    1192    For a GET or HEAD request, this is the same as the default semantics
    1193    when no Content-Location is provided by the server.  For a state-changing
    1194    request like PUT or POST, it implies that the server's response contains
    1195    the new representation of that resource, thereby distinguishing it from
    1196    representations that might only report about the action (e.g., "It worked!").
    1197    This allows authoring applications to update their local copies without
    1198    the need for a subsequent GET request.
    1199 </t>
    1200 <t>
    1201    If Content-Location is included in a response message and its value
    1202    differs from the effective request URI, then the origin server is
    1203    informing recipients that this representation has its own, presumably
    1204    more specific, identifier.  For a GET or HEAD request, this is an
    1205    indication that the effective request URI identifies a resource that
    1206    is subject to content negotiation and the selected representation for
    1207    this response can also be found at the identified URI.  For other
    1208    methods, such a Content-Location indicates that this representation
    1209    contains a report on the action's status and the same report is
    1210    available (for future access with GET) at the given URI.  For
    1211    example, a purchase transaction made via a POST request might
    1212    include a receipt document as the payload of the 200 response;
    1213    the Content-Location value provides an identifier for retrieving
    1214    a copy of that same receipt in the future.
    1215 </t>
    1216 <t>
    1217    If Content-Location is included in a request message, then it &MAY;
    1218    be interpreted by the origin server as an indication of where the
    1219    user agent originally obtained the content of the enclosed
    1220    representation (prior to any subsequent modification of the content
    1221    by that user agent).  In other words, the user agent is providing
    1222    the same representation metadata that it received with the original
    1223    representation.  However, such interpretation &MUST-NOT; be used to
    1224    alter the semantics of the method requested by the client.  For
    1225    example, if a client makes a PUT request on a negotiated resource
    1226    and the origin server accepts that PUT (without redirection), then the
    1227    new set of values for that resource is expected to be consistent with
    1228    the one representation supplied in that PUT; the Content-Location
    1229    cannot be used as a form of reverse content selection that
    1230    identifies only one of the negotiated representations to be updated.
    1231    If the user agent had wanted the latter semantics, it would have applied
    1232    the PUT directly to the Content-Location URI.
    1233 </t>
    1234 <t>
    1235    A Content-Location field received in a request message is transitory
    1236    information that &SHOULD-NOT; be saved with other representation
    1237    metadata for use in later responses.  The Content-Location's value
    1238    might be saved for use in other contexts, such as within source links
    1239    or other metadata.
    1240 </t>
    1241 <t>
    1242    A cache cannot assume that a representation with a Content-Location
    1243    different from the URI used to retrieve it can be used to respond to
    1244    later requests on that Content-Location URI.
    1245 </t>
    1246 <t>
    1247    If the Content-Location value is a partial URI, the partial URI is
    1248    interpreted relative to the effective request URI.
    1249 </t>
    1250 </section>
    1251 
    1252 <section title="Content-Type" anchor="header.content-type">
    1253   <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
    1254   <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
    1255   <x:anchor-alias value="Content-Type"/>
    1256 <t>
    1257    The "Content-Type" header field indicates the media type of the
    1258    representation. In the case of responses to the HEAD method, the media type is
    1259    that which would have been sent had the request been a GET.
    1260 </t>
    1261 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
    1262   <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
    1263 </artwork></figure>
    1264 <t>
    1265    Media types are defined in <xref target="media.types"/>. An example of the field is
    1266 </t>
    1267 <figure><artwork type="example">
    1268   Content-Type: text/html; charset=ISO-8859-4
    1269 </artwork></figure>
    1270 <t>
    1271    Further discussion of Content-Type is provided in <xref target="representation.data"/>.
    1272 </t>
    1273 </section>
    1274 
    1275 </section>
    1276 
    1277 <section title="IANA Considerations" anchor="IANA.considerations">
    1278 
    1279 <section title="Content Coding Registry" anchor="content.coding.registration">
    1280 <t>
    1281    The registration procedure for HTTP Content Codings is now defined
    1282    by <xref target="content.coding.registry"/> of this document.
    1283 </t>
    1284 <t>
    1285    The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
    1286    shall be updated with the registration below:
    1287 </t>
    1288 <texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
    1289    <ttcol>Name</ttcol>
    1290    <ttcol>Description</ttcol>
    1291    <ttcol>Reference</ttcol>
    1292    <c>compress</c>
    1293    <c>UNIX "compress" program method</c>
    1294    <c>
    1295       &compress-coding;
    1296    </c>
    1297    <c>deflate</c>
    1298    <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
    1299    the "zlib" data format (<xref target="RFC1950"/>)
    1300    </c>
    1301    <c>
    1302       &deflate-coding;
    1303    </c>
    1304    <c>gzip</c>
    1305    <c>Same as GNU zip <xref target="RFC1952"/></c>
    1306    <c>
    1307       &gzip-coding;
    1308    </c>
    1309    <c>identity</c>
    1310    <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
    1311    <c>
    1312       <xref target="header.accept-encoding"/>
    1313    </c>
    1314 </texttable>
    1315 </section>
    1316 
    1317 </section>
    1318 
    1319 <section title="Security Considerations" anchor="security.considerations">
    1320 <t>
    1321    This section is meant to inform application developers, information
    1322    providers, and users of the security limitations in HTTP/1.1 as
    1323    described by this document. The discussion does not include
    1324    definitive solutions to the problems revealed, though it does make
    1325    some suggestions for reducing security risks.
    1326 </t>
    1327 
    1328 <section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
    1329 <t>
    1330    Accept header fields can reveal information about the user to all
    1331    servers which are accessed. The Accept-Language header field in particular
    1332    can reveal information the user would consider to be of a private
    1333    nature, because the understanding of particular languages is often
    1334    strongly correlated to the membership of a particular ethnic group.
    1335    User agents which offer the option to configure the contents of an
    1336    Accept-Language header field to be sent in every request are strongly
    1337    encouraged to let the configuration process include a message which
    1338    makes the user aware of the loss of privacy involved.
    1339 </t>
    1340 <t>
    1341    An approach that limits the loss of privacy would be for a user agent
    1342    to omit the sending of Accept-Language header fields by default, and to ask
    1343    the user whether or not to start sending Accept-Language header fields to a
    1344    server if it detects, by looking for any Vary header fields
    1345    generated by the server, that such sending could improve the quality
    1346    of service.
    1347 </t>
    1348 <t>
    1349    Elaborate user-customized accept header fields sent in every request,
    1350    in particular if these include quality values, can be used by servers
    1351    as relatively reliable and long-lived user identifiers. Such user
    1352    identifiers would allow content providers to do click-trail tracking,
    1353    and would allow collaborating content providers to match cross-server
    1354    click-trails or form submissions of individual users. Note that for
    1355    many users not behind a proxy, the network address of the host
    1356    running the user agent will also serve as a long-lived user
    1357    identifier. In environments where proxies are used to enhance
    1358    privacy, user agents ought to be conservative in offering accept
    1359    header configuration options to end users. As an extreme privacy
    1360    measure, proxies could filter the accept header fields in relayed requests.
    1361    General purpose user agents which provide a high degree of header
    1362    configurability &SHOULD; warn users about the loss of privacy which can
    1363    be involved.
    1364 </t>
    1365 </section>
    1366 
    1367 </section>
    1368 
    1369100</middle>
    1370 <back>
    1371 
    1372 <references title="Normative References">
    1373 
    1374 <reference anchor="Part1">
    1375   <front>
    1376     <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
    1377     <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    1378       <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    1379       <address><email>fielding@gbiv.com</email></address>
    1380     </author>
    1381     <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    1382       <organization abbrev="W3C">World Wide Web Consortium</organization>
    1383       <address><email>ylafon@w3.org</email></address>
    1384     </author>
    1385     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    1386       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    1387       <address><email>julian.reschke@greenbytes.de</email></address>
    1388     </author>
    1389     <date month="&ID-MONTH;" year="&ID-YEAR;"/>
    1390   </front>
    1391   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
    1392   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
    1393 </reference>
    1394 
    1395 <reference anchor="Part2">
    1396   <front>
    1397     <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
    1398     <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    1399       <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    1400       <address><email>fielding@gbiv.com</email></address>
    1401     </author>
    1402     <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    1403       <organization abbrev="W3C">World Wide Web Consortium</organization>
    1404       <address><email>ylafon@w3.org</email></address>
    1405     </author>
    1406     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    1407       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    1408       <address><email>julian.reschke@greenbytes.de</email></address>
    1409     </author>
    1410     <date month="&ID-MONTH;" year="&ID-YEAR;"/>
    1411   </front>
    1412   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
    1413   <x:source href="p2-semantics.xml" basename="p2-semantics"/>
    1414 </reference>
    1415 
    1416 <reference anchor="Part4">
    1417   <front>
    1418     <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
    1419     <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    1420       <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    1421       <address><email>fielding@gbiv.com</email></address>
    1422     </author>
    1423     <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    1424       <organization abbrev="W3C">World Wide Web Consortium</organization>
    1425       <address><email>ylafon@w3.org</email></address>
    1426     </author>
    1427     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    1428       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    1429       <address><email>julian.reschke@greenbytes.de</email></address>
    1430     </author>
    1431     <date month="&ID-MONTH;" year="&ID-YEAR;"/>
    1432   </front>
    1433   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
    1434   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
    1435 </reference>
    1436 
    1437 <reference anchor="Part5">
    1438   <front>
    1439     <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
    1440     <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    1441       <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    1442       <address><email>fielding@gbiv.com</email></address>
    1443     </author>
    1444     <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    1445       <organization abbrev="W3C">World Wide Web Consortium</organization>
    1446       <address><email>ylafon@w3.org</email></address>
    1447     </author>
    1448     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    1449       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    1450       <address><email>julian.reschke@greenbytes.de</email></address>
    1451     </author>
    1452     <date month="&ID-MONTH;" year="&ID-YEAR;"/>
    1453   </front>
    1454   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
    1455   <x:source href="p5-range.xml" basename="p5-range"/>
    1456 </reference>
    1457 
    1458 <reference anchor="Part6">
    1459   <front>
    1460     <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
    1461     <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    1462       <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    1463       <address><email>fielding@gbiv.com</email></address>
    1464     </author>
    1465     <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    1466       <organization abbrev="W3C">World Wide Web Consortium</organization>
    1467       <address><email>ylafon@w3.org</email></address>
    1468     </author>
    1469     <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
    1470       <organization>Rackspace</organization>
    1471       <address><email>mnot@mnot.net</email></address>
    1472     </author>
    1473     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    1474       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    1475       <address><email>julian.reschke@greenbytes.de</email></address>
    1476     </author>
    1477     <date month="&ID-MONTH;" year="&ID-YEAR;"/>
    1478   </front>
    1479   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
    1480   <x:source href="p6-cache.xml" basename="p6-cache"/>
    1481 </reference>
    1482 
    1483 <reference anchor="RFC1950">
    1484   <front>
    1485     <title>ZLIB Compressed Data Format Specification version 3.3</title>
    1486     <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
    1487       <organization>Aladdin Enterprises</organization>
    1488       <address><email>ghost@aladdin.com</email></address>
    1489     </author>
    1490     <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
    1491     <date month="May" year="1996"/>
    1492   </front>
    1493   <seriesInfo name="RFC" value="1950"/>
    1494   <!--<annotation>
    1495     RFC 1950 is an Informational RFC, thus it might be less stable than
    1496     this specification. On the other hand, this downward reference was
    1497     present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
    1498     therefore it is unlikely to cause problems in practice. See also
    1499     <xref target="BCP97"/>.
    1500   </annotation>-->
    1501 </reference>
    1502 
    1503 <reference anchor="RFC1951">
    1504   <front>
    1505     <title>DEFLATE Compressed Data Format Specification version 1.3</title>
    1506     <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
    1507       <organization>Aladdin Enterprises</organization>
    1508       <address><email>ghost@aladdin.com</email></address>
    1509     </author>
    1510     <date month="May" year="1996"/>
    1511   </front>
    1512   <seriesInfo name="RFC" value="1951"/>
    1513   <!--<annotation>
    1514     RFC 1951 is an Informational RFC, thus it might be less stable than
    1515     this specification. On the other hand, this downward reference was
    1516     present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
    1517     therefore it is unlikely to cause problems in practice. See also
    1518     <xref target="BCP97"/>.
    1519   </annotation>-->
    1520 </reference>
    1521 
    1522 <reference anchor="RFC1952">
    1523   <front>
    1524     <title>GZIP file format specification version 4.3</title>
    1525     <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
    1526       <organization>Aladdin Enterprises</organization>
    1527       <address><email>ghost@aladdin.com</email></address>
    1528     </author>
    1529     <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
    1530       <address><email>gzip@prep.ai.mit.edu</email></address>
    1531     </author>
    1532     <author initials="M." surname="Adler" fullname="Mark Adler">
    1533       <address><email>madler@alumni.caltech.edu</email></address>
    1534     </author>
    1535     <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
    1536       <address><email>ghost@aladdin.com</email></address>
    1537     </author>
    1538     <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
    1539       <address><email>randeg@alumni.rpi.edu</email></address>
    1540     </author>
    1541     <date month="May" year="1996"/>
    1542   </front>
    1543   <seriesInfo name="RFC" value="1952"/>
    1544   <!--<annotation>
    1545     RFC 1952 is an Informational RFC, thus it might be less stable than
    1546     this specification. On the other hand, this downward reference was
    1547     present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
    1548     therefore it is unlikely to cause problems in practice. See also
    1549     <xref target="BCP97"/>.
    1550   </annotation>-->
    1551 </reference>
    1552 
    1553 <reference anchor="RFC2045">
    1554   <front>
    1555     <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
    1556     <author initials="N." surname="Freed" fullname="Ned Freed">
    1557       <organization>Innosoft International, Inc.</organization>
    1558       <address><email>ned@innosoft.com</email></address>
    1559     </author>
    1560     <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
    1561       <organization>First Virtual Holdings</organization>
    1562       <address><email>nsb@nsb.fv.com</email></address>
    1563     </author>
    1564     <date month="November" year="1996"/>
    1565   </front>
    1566   <seriesInfo name="RFC" value="2045"/>
    1567 </reference>
    1568 
    1569 <reference anchor="RFC2046">
    1570   <front>
    1571     <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
    1572     <author initials="N." surname="Freed" fullname="Ned Freed">
    1573       <organization>Innosoft International, Inc.</organization>
    1574       <address><email>ned@innosoft.com</email></address>
    1575     </author>
    1576     <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
    1577       <organization>First Virtual Holdings</organization>
    1578       <address><email>nsb@nsb.fv.com</email></address>
    1579     </author>
    1580     <date month="November" year="1996"/>
    1581   </front>
    1582   <seriesInfo name="RFC" value="2046"/>
    1583 </reference>
    1584 
    1585 <reference anchor='RFC4647'>
    1586   <front>
    1587     <title>Matching of Language Tags</title>
    1588     <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
    1589       <organization>Yahoo! Inc.</organization>
    1590       <address><email>addison@inter-locale.com</email></address>
    1591     </author>
    1592     <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
    1593       <organization>Google</organization>
    1594       <address><email>mark.davis@macchiato.com</email></address>
    1595     </author>
    1596     <date year='2006' month='September' />
    1597   </front>
    1598   <seriesInfo name='BCP' value='47' />
    1599   <seriesInfo name='RFC' value='4647' />
    1600 </reference>
    1601 
    1602 <reference anchor='RFC5646'>
    1603   <front>
    1604     <title>Tags for Identifying Languages</title>
    1605     <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
    1606       <organization>Lab126</organization>
    1607       <address><email>addison@inter-locale.com</email></address>
    1608     </author>
    1609     <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
    1610       <organization>Google</organization>
    1611       <address><email>mark.davis@google.com</email></address>
    1612     </author>
    1613     <date month='September' year='2009' />
    1614   </front>
    1615   <seriesInfo name='BCP' value='47' />
    1616   <seriesInfo name='RFC' value='5646' />
    1617 </reference>
    1618 
    1619 </references>
    1620 
    1621 <references title="Informative References">
    1622 
    1623 <reference anchor="RFC1945">
    1624   <front>
    1625     <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
    1626     <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
    1627       <organization>MIT, Laboratory for Computer Science</organization>
    1628       <address><email>timbl@w3.org</email></address>
    1629     </author>
    1630     <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
    1631       <organization>University of California, Irvine, Department of Information and Computer Science</organization>
    1632       <address><email>fielding@ics.uci.edu</email></address>
    1633     </author>
    1634     <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
    1635       <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
    1636       <address><email>frystyk@w3.org</email></address>
    1637     </author>
    1638     <date month="May" year="1996"/>
    1639   </front>
    1640   <seriesInfo name="RFC" value="1945"/>
    1641 </reference>
    1642 
    1643 <reference anchor="RFC2049">
    1644   <front>
    1645     <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
    1646     <author initials="N." surname="Freed" fullname="Ned Freed">
    1647       <organization>Innosoft International, Inc.</organization>
    1648       <address><email>ned@innosoft.com</email></address>
    1649     </author>
    1650     <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
    1651       <organization>First Virtual Holdings</organization>
    1652       <address><email>nsb@nsb.fv.com</email></address>
    1653     </author>
    1654     <date month="November" year="1996"/>
    1655   </front>
    1656   <seriesInfo name="RFC" value="2049"/>
    1657 </reference>
    1658 
    1659 <reference anchor="RFC2068">
    1660   <front>
    1661     <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
    1662     <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
    1663       <organization>University of California, Irvine, Department of Information and Computer Science</organization>
    1664       <address><email>fielding@ics.uci.edu</email></address>
    1665     </author>
    1666     <author initials="J." surname="Gettys" fullname="Jim Gettys">
    1667       <organization>MIT Laboratory for Computer Science</organization>
    1668       <address><email>jg@w3.org</email></address>
    1669     </author>
    1670     <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
    1671       <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
    1672       <address><email>mogul@wrl.dec.com</email></address>
    1673     </author>
    1674     <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
    1675       <organization>MIT Laboratory for Computer Science</organization>
    1676       <address><email>frystyk@w3.org</email></address>
    1677     </author>
    1678     <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
    1679       <organization>MIT Laboratory for Computer Science</organization>
    1680       <address><email>timbl@w3.org</email></address>
    1681     </author>
    1682     <date month="January" year="1997"/>
    1683   </front>
    1684   <seriesInfo name="RFC" value="2068"/>
    1685 </reference>
    1686 
    1687 <reference anchor="RFC2076">
    1688   <front>
    1689     <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
    1690     <author initials="J." surname="Palme" fullname="Jacob Palme">
    1691       <organization>Stockholm University/KTH</organization>
    1692       <address><email>jpalme@dsv.su.se</email></address>
    1693     </author>
    1694     <date month="February" year="1997"/>
    1695   </front>
    1696   <seriesInfo name="RFC" value="2076"/>
    1697 </reference>
    1698 
    1699 <reference anchor="RFC2277">
    1700   <front>
    1701     <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
    1702     <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
    1703       <organization>UNINETT</organization>
    1704       <address><email>Harald.T.Alvestrand@uninett.no</email></address>
    1705     </author>
    1706     <date month="January" year="1998"/>
    1707   </front>
    1708   <seriesInfo name="BCP" value="18"/>
    1709   <seriesInfo name="RFC" value="2277"/>
    1710 </reference>
    1711 
    1712 <reference anchor='RFC2295'>
    1713   <front>
    1714     <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
    1715     <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
    1716       <organization>Technische Universiteit Eindhoven</organization>
    1717       <address>
    1718         <email>koen@win.tue.nl</email>
    1719       </address>
    1720     </author>
    1721     <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
    1722       <organization>Hewlett-Packard Company</organization>
    1723       <address>
    1724         <email>mutz@hpl.hp.com</email>
    1725       </address>
    1726     </author>
    1727     <date year='1998' month='March'/>
    1728   </front>
    1729   <seriesInfo name='RFC' value='2295'/>
    1730 </reference>
    1731 
    1732 <reference anchor="RFC2388">
    1733   <front>
    1734     <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
    1735     <author initials="L." surname="Masinter" fullname="Larry Masinter">
    1736       <organization>Xerox Palo Alto Research Center</organization>
    1737       <address><email>masinter@parc.xerox.com</email></address>
    1738     </author>
    1739     <date year="1998" month="August"/>
    1740   </front>
    1741   <seriesInfo name="RFC" value="2388"/>
    1742 </reference>
    1743 
    1744 <reference anchor="RFC2557">
    1745   <front>
    1746     <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
    1747     <author initials="F." surname="Palme" fullname="Jacob Palme">
    1748       <organization>Stockholm University and KTH</organization>
    1749       <address><email>jpalme@dsv.su.se</email></address>
    1750     </author>
    1751     <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
    1752       <organization>Microsoft Corporation</organization>
    1753       <address><email>alexhop@microsoft.com</email></address>
    1754     </author>
    1755     <author initials="N." surname="Shelness" fullname="Nick Shelness">
    1756       <organization>Lotus Development Corporation</organization>
    1757       <address><email>Shelness@lotus.com</email></address>
    1758     </author>
    1759     <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
    1760       <address><email>stef@nma.com</email></address>
    1761     </author>
    1762     <date year="1999" month="March"/>
    1763   </front>
    1764   <seriesInfo name="RFC" value="2557"/>
    1765 </reference>
    1766 
    1767 <reference anchor="RFC2616">
    1768   <front>
    1769     <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
    1770     <author initials="R." surname="Fielding" fullname="R. Fielding">
    1771       <organization>University of California, Irvine</organization>
    1772       <address><email>fielding@ics.uci.edu</email></address>
    1773     </author>
    1774     <author initials="J." surname="Gettys" fullname="J. Gettys">
    1775       <organization>W3C</organization>
    1776       <address><email>jg@w3.org</email></address>
    1777     </author>
    1778     <author initials="J." surname="Mogul" fullname="J. Mogul">
    1779       <organization>Compaq Computer Corporation</organization>
    1780       <address><email>mogul@wrl.dec.com</email></address>
    1781     </author>
    1782     <author initials="H." surname="Frystyk" fullname="H. Frystyk">
    1783       <organization>MIT Laboratory for Computer Science</organization>
    1784       <address><email>frystyk@w3.org</email></address>
    1785     </author>
    1786     <author initials="L." surname="Masinter" fullname="L. Masinter">
    1787       <organization>Xerox Corporation</organization>
    1788       <address><email>masinter@parc.xerox.com</email></address>
    1789     </author>
    1790     <author initials="P." surname="Leach" fullname="P. Leach">
    1791       <organization>Microsoft Corporation</organization>
    1792       <address><email>paulle@microsoft.com</email></address>
    1793     </author>
    1794     <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
    1795       <organization>W3C</organization>
    1796       <address><email>timbl@w3.org</email></address>
    1797     </author>
    1798     <date month="June" year="1999"/>
    1799   </front>
    1800   <seriesInfo name="RFC" value="2616"/>
    1801 </reference>
    1802 
    1803 <reference anchor="RFC3629">
    1804   <front>
    1805     <title>UTF-8, a transformation format of ISO 10646</title>
    1806     <author initials="F." surname="Yergeau" fullname="F. Yergeau">
    1807       <organization>Alis Technologies</organization>
    1808       <address><email>fyergeau@alis.com</email></address>
    1809     </author>
    1810     <date month="November" year="2003"/>
    1811   </front>
    1812   <seriesInfo name="STD" value="63"/>
    1813   <seriesInfo name="RFC" value="3629"/>
    1814 </reference>
    1815 
    1816 <reference anchor="RFC4288">
    1817   <front>
    1818     <title>Media Type Specifications and Registration Procedures</title>
    1819     <author initials="N." surname="Freed" fullname="N. Freed">
    1820       <organization>Sun Microsystems</organization>
    1821       <address>
    1822         <email>ned.freed@mrochek.com</email>
    1823       </address>
    1824     </author>
    1825     <author initials="J." surname="Klensin" fullname="J. Klensin">
    1826       <address>
    1827         <email>klensin+ietf@jck.com</email>
    1828       </address>
    1829     </author>
    1830     <date year="2005" month="December"/>
    1831   </front>
    1832   <seriesInfo name="BCP" value="13"/>
    1833   <seriesInfo name="RFC" value="4288"/>
    1834 </reference>
    1835 
    1836 <reference anchor='RFC5226'>
    1837   <front>
    1838     <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
    1839     <author initials='T.' surname='Narten' fullname='T. Narten'>
    1840       <organization>IBM</organization>
    1841       <address><email>narten@us.ibm.com</email></address>
    1842     </author>
    1843     <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
    1844       <organization>Google</organization>
    1845       <address><email>Harald@Alvestrand.no</email></address>
    1846     </author>
    1847     <date year='2008' month='May' />
    1848   </front>
    1849   <seriesInfo name='BCP' value='26' />
    1850   <seriesInfo name='RFC' value='5226' />
    1851 </reference>
    1852 
    1853 <reference anchor="RFC5322">
    1854   <front>
    1855     <title>Internet Message Format</title>
    1856     <author initials="P." surname="Resnick" fullname="P. Resnick">
    1857       <organization>Qualcomm Incorporated</organization>
    1858     </author>
    1859     <date year="2008" month="October"/>
    1860   </front>
    1861   <seriesInfo name="RFC" value="5322"/>
    1862 </reference>
    1863 
    1864 <reference anchor="RFC6151">
    1865   <front>
    1866     <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
    1867     <author initials="S." surname="Turner" fullname="S. Turner"/>
    1868     <author initials="L." surname="Chen" fullname="L. Chen"/>
    1869     <date year="2011" month="March" />
    1870   </front>
    1871   <seriesInfo name="RFC" value="6151" />
    1872 </reference>
    1873 
    1874 <!--<reference anchor='BCP97'>
    1875   <front>
    1876     <title>Handling Normative References to Standards-Track Documents</title>
    1877     <author initials='J.' surname='Klensin' fullname='J. Klensin'>
    1878       <address>
    1879         <email>klensin+ietf@jck.com</email>
    1880       </address>
    1881     </author>
    1882     <author initials='S.' surname='Hartman' fullname='S. Hartman'>
    1883       <organization>MIT</organization>
    1884       <address>
    1885         <email>hartmans-ietf@mit.edu</email>
    1886       </address>
    1887     </author>
    1888     <date year='2007' month='June' />
    1889   </front>
    1890   <seriesInfo name='BCP' value='97' />
    1891   <seriesInfo name='RFC' value='4897' />
    1892 </reference>-->
    1893 
    1894 <reference anchor="RFC6266">
    1895   <front>
    1896     <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
    1897     in the Hypertext Transfer Protocol (HTTP)</title>
    1898     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
    1899       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    1900       <address>
    1901         <email>julian.reschke@greenbytes.de</email>
    1902       </address>
    1903     </author>
    1904     <date month="June" year="2011"/>
    1905   </front>
    1906   <seriesInfo name='RFC' value='6266' />
    1907 </reference>
    1908 
    1909 </references>
    1910 
    1911 <section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
    1912 <t>
    1913    HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC5322"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
    1914    allow a message body to be transmitted in an open variety of
    1915    representations and with extensible mechanisms. However, RFC 2045
    1916    discusses mail, and HTTP has a few features that are different from
    1917    those described in MIME. These differences were carefully chosen
    1918    to optimize performance over binary connections, to allow greater
    1919    freedom in the use of new media types, to make date comparisons
    1920    easier, and to acknowledge the practice of some early HTTP servers
    1921    and clients.
    1922 </t>
    1923 <t>
    1924    This appendix describes specific areas where HTTP differs from MIME.
    1925    Proxies and gateways to strict MIME environments &SHOULD; be
    1926    aware of these differences and provide the appropriate conversions
    1927    where necessary. Proxies and gateways from MIME environments to HTTP
    1928    also need to be aware of the differences because some conversions
    1929    might be required.
    1930 </t>
    1931 
    1932 <section title="MIME-Version" anchor="mime-version">
    1933   <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
    1934   <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
    1935   <x:anchor-alias value="MIME-Version"/>
    1936 <t>
    1937    HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
    1938    include a single MIME-Version header field to indicate what
    1939    version of the MIME protocol was used to construct the message. Use
    1940    of the MIME-Version header field indicates that the message is in
    1941    full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
    1942    Proxies/gateways are responsible for ensuring full conformance (where
    1943    possible) when exporting HTTP messages to strict MIME environments.
    1944 </t>
    1945 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
    1946   <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
    1947 </artwork></figure>
    1948 <t>
    1949    MIME version "1.0" is the default for use in HTTP/1.1. However,
    1950    HTTP/1.1 message parsing and semantics are defined by this document
    1951    and not the MIME specification.
    1952 </t>
    1953 </section>
    1954 
    1955 <section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
    1956 <t>
    1957    MIME requires that an Internet mail body-part be converted to
    1958    canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
    1959    <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
    1960    allowed for subtypes of the "text" media type when transmitted over
    1961    HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
    1962    line breaks as CRLF and forbids the use of CR or LF outside of line
    1963    break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
    1964    line break within text content when a message is transmitted over
    1965    HTTP.
    1966 </t>
    1967 <t>
    1968    Where it is possible, a proxy or gateway from HTTP to a strict MIME
    1969    environment &SHOULD; translate all line breaks within the text media
    1970    types described in <xref target="canonicalization.and.text.defaults"/>
    1971    of this document to the RFC 2049
    1972    canonical form of CRLF. Note, however, that this might be complicated
    1973    by the presence of a Content-Encoding and by the fact that HTTP
    1974    allows the use of some character encodings which do not use octets 13 and
    1975    10 to represent CR and LF, respectively, as is the case for some multi-byte
    1976    character encodings.
    1977 </t>
    1978 <t>
    1979    Conversion will break any cryptographic
    1980    checksums applied to the original content unless the original content
    1981    is already in canonical form. Therefore, the canonical form is
    1982    recommended for any content that uses such checksums in HTTP.
    1983 </t>
    1984 </section>
    1985 
    1986 
    1987 <section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
    1988 <t>
    1989    HTTP/1.1 uses a restricted set of date formats (&http-date;) to
    1990    simplify the process of date comparison. Proxies and gateways from
    1991    other protocols &SHOULD; ensure that any Date header field present in a
    1992    message conforms to one of the HTTP/1.1 formats and rewrite the date
    1993    if necessary.
    1994 </t>
    1995 </section>
    1996 
    1997 <section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
    1998 <t>
    1999    MIME does not include any concept equivalent to HTTP/1.1's
    2000    Content-Encoding header field. Since this acts as a modifier on the
    2001    media type, proxies and gateways from HTTP to MIME-compliant
    2002    protocols &MUST; either change the value of the Content-Type header
    2003    field or decode the representation before forwarding the message. (Some
    2004    experimental applications of Content-Type for Internet mail have used
    2005    a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
    2006    a function equivalent to Content-Encoding. However, this parameter is
    2007    not part of the MIME standards).
    2008 </t>
    2009 </section>
    2010 
    2011 <section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
    2012   <iref item="Content-Transfer-Encoding header field" x:for-anchor=""/>
    2013   <iref item="Header Fields" subitem="Content-Transfer-Encoding" x:for-anchor=""/>
    2014 <t>
    2015    HTTP does not use the Content-Transfer-Encoding field of MIME.
    2016    Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
    2017    remove any Content-Transfer-Encoding
    2018    prior to delivering the response message to an HTTP client.
    2019 </t>
    2020 <t>
    2021    Proxies and gateways from HTTP to MIME-compliant protocols are
    2022    responsible for ensuring that the message is in the correct format
    2023    and encoding for safe transport on that protocol, where "safe
    2024    transport" is defined by the limitations of the protocol being used.
    2025    Such a proxy or gateway &SHOULD; label the data with an appropriate
    2026    Content-Transfer-Encoding if doing so will improve the likelihood of
    2027    safe transport over the destination protocol.
    2028 </t>
    2029 </section>
    2030 
    2031 <section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
    2032 <t>
    2033    HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
    2034    Proxies/gateways &MUST; remove any transfer-coding prior to
    2035    forwarding a message via a MIME-compliant protocol.
    2036 </t>
    2037 </section>
    2038 
    2039 <section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
    2040 <t>
    2041    HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
    2042    need to be aware of MIME line length limitations. Since HTTP does not
    2043    have this limitation, HTTP does not fold long lines. MHTML messages
    2044    being transported by HTTP follow all conventions of MHTML, including
    2045    line length limitations and folding, canonicalization, etc., since
    2046    HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
    2047    does not interpret the content or any MIME header lines that might be
    2048    contained therein.
    2049 </t>
    2050 </section>
    2051 </section>
    2052 
    2053 <section title="Additional Features" anchor="additional.features">
    2054 <t>
    2055    <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
    2056    existing HTTP implementations, but not consistently and correctly
    2057    across most HTTP/1.1 applications. Implementors are advised to be
    2058    aware of these features, but cannot rely upon their presence in, or
    2059    interoperability with, other HTTP/1.1 applications. Some of these
    2060    describe proposed experimental features, and some describe features
    2061    that experimental deployment found lacking that are now addressed in
    2062    the base HTTP/1.1 specification.
    2063 </t>
    2064 <t>
    2065    A number of other header fields, such as Content-Disposition and Title,
    2066    from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
    2067    and <xref target="RFC2076"/>).
    2068 </t>
    2069 </section>
    2070 
    2071 <section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
    2072 <t>
    2073   Clarify contexts that charset is used in.
    2074   (<xref target="character.sets"/>)
    2075 </t>
    2076 <t>
    2077   Registration of Content Codings now requires IETF Review
    2078   (<xref target="content.coding.registry"/>)
    2079 </t>
    2080 <t>
    2081   Remove the default character encoding for text media types; the default
    2082   now is whatever the media type definition says.
    2083   (<xref target="canonicalization.and.text.defaults"/>)
    2084 </t>
    2085 <t>
    2086   Change ABNF productions for header fields to only define the field value.
    2087   (<xref target="header.field.definitions"/>)
    2088 </t>
    2089 <t>
    2090   Remove definition of Content-MD5 header field because it was inconsistently
    2091   implemented with respect to partial responses, and also because of known
    2092   deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
    2093   (<xref target="header.field.definitions"/>)
    2094 </t>
    2095 <t>
    2096   Remove ISO-8859-1 special-casing in Accept-Charset.
    2097   (<xref target="header.accept-charset"/>)
    2098 </t>
    2099 <t>
    2100   Remove base URI setting semantics for Content-Location due to poor
    2101   implementation support, which was caused by too many broken servers emitting
    2102   bogus Content-Location header fields, and also the potentially undesirable effect
    2103   of potentially breaking relative links in content-negotiated resources.
    2104   (<xref target="header.content-location"/>)
    2105 </t>
    2106 <t>
    2107   Remove reference to non-existant identity transfer-coding value tokens.
    2108   (<xref target="no.content-transfer-encoding"/>)
    2109 </t>
    2110 <t>
    2111   Remove discussion of Content-Disposition header field, it is now defined
    2112   by <xref target="RFC6266"/>.
    2113   (<xref target="additional.features"/>)
    2114 </t>
    2115 </section>
    2116 
    2117 <section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
    2118 
    2119 <section title="Since RFC 2616">
    2120 <t>
    2121   Extracted relevant partitions from <xref target="RFC2616"/>.
    2122 </t>
    2123 </section>
    2124 
    2125 <section title="Since draft-ietf-httpbis-p3-payload-00">
    2126 <t>
    2127   Closed issues:
    2128   <list style="symbols">
    2129     <t>
    2130       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
    2131       "Media Type Registrations"
    2132       (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
    2133     </t>
    2134     <t>
    2135       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
    2136       "Clarification regarding quoting of charset values"
    2137       (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
    2138     </t>
    2139     <t>
    2140       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
    2141       "Remove 'identity' token references"
    2142       (<eref target="http://purl.org/NET/http-errata#identity"/>)
    2143     </t>
    2144     <t>
    2145       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
    2146       "Accept-Encoding BNF"
    2147     </t>
    2148     <t>
    2149       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
    2150       "Normative and Informative references"
    2151     </t>
    2152     <t>
    2153       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
    2154       "RFC1700 references"
    2155     </t>
    2156     <t>
    2157       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
    2158       "Updating to RFC4288"
    2159     </t>
    2160     <t>
    2161       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
    2162       "Informative references"
    2163     </t>
    2164     <t>
    2165       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
    2166       "ISO-8859-1 Reference"
    2167     </t>
    2168     <t>
    2169       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
    2170       "Encoding References Normative"
    2171     </t>
    2172     <t>
    2173       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
    2174       "Normative up-to-date references"
    2175     </t>
    2176   </list>
    2177 </t>
    2178 </section>
    2179 
    2180 <section title="Since draft-ietf-httpbis-p3-payload-01">
    2181 <t>
    2182   Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
    2183   <list style="symbols">
    2184     <t>
    2185       Add explicit references to BNF syntax and rules imported from other parts of the specification.
    2186     </t>
    2187   </list>
    2188 </t>
    2189 </section>
    2190 
    2191 <section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
    2192 <t>
    2193   Closed issues:
    2194   <list style="symbols">
    2195     <t>
    2196       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
    2197       "Quoting Charsets"
    2198     </t>
    2199     <t>
    2200       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
    2201       "Classification for Allow header"
    2202     </t>
    2203     <t>
    2204       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
    2205       "missing default for qvalue in description of Accept-Encoding"
    2206     </t>
    2207   </list>
    2208 </t>
    2209 <t>
    2210   Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
    2211   <list style="symbols">
    2212     <t>
    2213       Reference RFC 3984, and update header field registrations for headers defined
    2214       in this document.
    2215     </t>
    2216   </list>
    2217 </t>
    2218 </section>
    2219 
    2220 <section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
    2221 <t>
    2222   Closed issues:
    2223   <list style="symbols">
    2224     <t>
    2225       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
    2226       "Quoting Charsets"
    2227     </t>
    2228     <t>
    2229       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
    2230       "language tag matching (Accept-Language) vs RFC4647"
    2231     </t>
    2232     <t>
    2233       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
    2234       "RFC 1806 has been replaced by RFC2183"
    2235     </t>
    2236   </list>
    2237 </t>
    2238 <t>
    2239   Other changes:
    2240   <list style="symbols">
    2241     <t>
    2242       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
    2243       "Encoding References Normative" &mdash; rephrase the annotation and reference
    2244       BCP97.
    2245     </t>
    2246   </list>
    2247 </t>
    2248  </section>
    2249 
    2250 <section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
    2251 <t>
    2252   Closed issues:
    2253   <list style="symbols">
    2254     <t>
    2255       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
    2256       "RFC 2822 is updated by RFC 5322"
    2257     </t>
    2258   </list>
    2259 </t>
    2260 <t>
    2261   Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
    2262   <list style="symbols">
    2263     <t>
    2264       Use "/" instead of "|" for alternatives.
    2265     </t>
    2266     <t>
    2267       Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
    2268       whitespace ("OWS") and required whitespace ("RWS").
    2269     </t>
    2270     <t>
    2271       Rewrite ABNFs to spell out whitespace rules, factor out
    2272       header field value format definitions.
    2273     </t>
    2274   </list>
    2275 </t>
    2276 </section>
    2277 
    2278 <section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
    2279 <t>
    2280   Closed issues:
    2281   <list style="symbols">
    2282     <t>
    2283       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
    2284       "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
    2285     </t>
    2286   </list>
    2287 </t>
    2288 <t>
    2289   Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
    2290   <list style="symbols">
    2291     <t>
    2292       Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
    2293     </t>
    2294   </list>
    2295 </t>
    2296 <t>
    2297   Other changes:
    2298   <list style="symbols">
    2299     <t>
    2300       Move definition of quality values into Part 1.
    2301     </t>
    2302   </list>
    2303 </t>
    2304 </section>
    2305 
    2306 <section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
    2307 <t>
    2308   Closed issues:
    2309   <list style="symbols">
    2310     <t>
    2311       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
    2312       "Content-Location isn't special"
    2313     </t>
    2314     <t>
    2315       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
    2316       "Content Sniffing"
    2317     </t>
    2318   </list>
    2319 </t>
    2320 </section>
    2321 
    2322 <section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
    2323 <t>
    2324   Closed issues:
    2325   <list style="symbols">
    2326     <t>
    2327       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
    2328       "Updated reference for language tags"
    2329     </t>
    2330     <t>
    2331       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
    2332       "Clarify rules for determining what entities a response carries"
    2333     </t>
    2334     <t>
    2335       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
    2336       "Content-Location base-setting problems"
    2337     </t>
    2338     <t>
    2339       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
    2340       "Content Sniffing"
    2341     </t>
    2342     <t>
    2343       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
    2344       "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
    2345     </t>
    2346     <t>
    2347       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
    2348       "move definitions of gzip/deflate/compress to part 1"
    2349     </t>
    2350   </list>
    2351 </t>
    2352 <t>
    2353   Partly resolved issues:
    2354   <list style="symbols">
    2355     <t>
    2356       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
    2357       "update IANA requirements wrt Transfer-Coding values" (add the
    2358       IANA Considerations subsection)
    2359     </t>
    2360     <t>
    2361       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
    2362       "update IANA requirements wrt Content-Coding values" (add the
    2363       IANA Considerations subsection)
    2364     </t>
    2365   </list>
    2366 </t>
    2367 </section>
    2368 
    2369 <section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
    2370 <t>
    2371   Closed issues:
    2372   <list style="symbols">
    2373     <t>
    2374       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
    2375       "Content Negotiation for media types"
    2376     </t>
    2377     <t>
    2378       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
    2379       "Accept-Language: which RFC4647 filtering?"
    2380     </t>
    2381   </list>
    2382 </t>
    2383 </section>
    2384 
    2385 <section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
    2386 <t>
    2387   Closed issues:
    2388   <list style="symbols">
    2389     <t>
    2390       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
    2391       "MIME-Version not listed in P1, general header fields"
    2392     </t>
    2393     <t>
    2394       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
    2395       "IANA registry for content/transfer encodings"
    2396     </t>
    2397     <t>
    2398       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
    2399       "Content Sniffing"
    2400     </t>
    2401     <t>
    2402       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
    2403       "use of term "word" when talking about header structure"
    2404     </t>
    2405   </list>
    2406 </t>
    2407 <t>
    2408   Partly resolved issues:
    2409   <list style="symbols">
    2410     <t>
    2411       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
    2412       "Term for the requested resource's URI"
    2413     </t>
    2414   </list>
    2415 </t>
    2416 </section>
    2417 
    2418 <section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
    2419 <t>
    2420   Closed issues:
    2421   <list style="symbols">
    2422     <t>
    2423       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
    2424       "Clarify 'Requested Variant'"
    2425     </t>
    2426     <t>
    2427       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
    2428       "Content-Location isn't special"
    2429     </t>
    2430     <t>
    2431       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
    2432       "Delimiting messages with multipart/byteranges"
    2433     </t>
    2434     <t>
    2435       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
    2436       "Clarify entity / representation / variant terminology"
    2437     </t>
    2438     <t>
    2439       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
    2440       "confusing req. language for Content-Location"
    2441     </t>
    2442     <t>
    2443       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
    2444       "Content-Location on 304 responses"
    2445     </t>
    2446     <t>
    2447       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
    2448       "'requested resource' in content-encoding definition"
    2449     </t>
    2450     <t>
    2451       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
    2452       "consider removing the 'changes from 2068' sections"
    2453     </t>
    2454   </list>
    2455 </t>
    2456 <t>
    2457   Partly resolved issues:
    2458   <list style="symbols">
    2459     <t>
    2460       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
    2461       "Content-MD5 and partial responses"
    2462     </t>
    2463   </list>
    2464 </t>
    2465 </section>
    2466 
    2467 <section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
    2468 <t>
    2469   Closed issues:
    2470   <list style="symbols">
    2471     <t>
    2472       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
    2473       "Factor out Content-Disposition"
    2474     </t>
    2475   </list>
    2476 </t>
    2477 </section>
    2478 
    2479 <section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
    2480 <t>
    2481   Closed issues:
    2482   <list style="symbols">
    2483     <t>
    2484       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
    2485       "Header Classification"
    2486     </t>
    2487     <t>
    2488       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
    2489       "untangle ABNFs for header fields"
    2490     </t>
    2491     <t>
    2492       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
    2493       "potentially misleading MAY in media-type def"
    2494     </t>
    2495   </list>
    2496 </t>
    2497 </section>
    2498 
    2499 <section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
    2500 <t>
    2501   Closed issues:
    2502   <list style="symbols">
    2503     <t>
    2504       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
    2505       "Default charsets for text media types"
    2506     </t>
    2507     <t>
    2508       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
    2509       "Content-MD5 and partial responses"
    2510     </t>
    2511     <t>
    2512       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
    2513       "untangle ABNFs for header fields"
    2514     </t>
    2515     <t>
    2516       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
    2517       "confusing undefined parameter in media range example"
    2518     </t>
    2519   </list>
    2520 </t>
    2521 </section>
    2522 
    2523 <section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
    2524 <t>
    2525   None.
    2526 </t>
    2527 </section>
    2528 
    2529 <section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
    2530 <t>
    2531   Closed issues:
    2532   <list style="symbols">
    2533     <t>
    2534       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
    2535       "Strength of requirements on Accept re: 406"
    2536     </t>
    2537   </list>
    2538 </t>
    2539 </section>
    2540 
    2541 <section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
    2542 <t>
    2543   Closed issues:
    2544   <list style="symbols">
    2545     <t>
    2546       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
    2547       "Document HTTP's error-handling philosophy"
    2548     </t>
    2549   </list>
    2550 </t>
    2551 </section>
    2552 
    2553 <section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.since.17">
    2554 <t>
    2555   Closed issues:
    2556   <list style="symbols">
    2557     <t>
    2558       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
    2559       "intended maturity level vs normative references"
    2560     </t>
    2561   </list>
    2562 </t>
    2563 </section>
    2564 
    2565 <section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.since.18">
    2566 <t>
    2567   Closed issues:
    2568   <list style="symbols">
    2569     <t>
    2570       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
    2571       "is ETag a representation header field?"
    2572     </t>
    2573     <t>
    2574       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/338"/>:
    2575       "Content-Location doesn't constrain the cardinality of representations"
    2576     </t>
    2577     <t>
    2578       <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
    2579       "make IANA policy definitions consistent"
    2580     </t>
    2581   </list>
    2582 </t>
    2583 </section>
    2584 
    2585 <section title="Since draft-ietf-httpbis-p3-payload-19" anchor="changes.since.19">
    2586 <t>
    2587   None yet.
    2588 </t>
    2589 </section>
    2590 
    2591 </section>
    2592 
    2593 </back>
    2594101</rfc>
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