30/03/12 15:19:59 (11 years ago)

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

1 edited


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

    r1642 r1643  
    2020  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2121  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    22   <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2322  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2423  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2524  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2625  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    27   <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    28   <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     26  <!ENTITY content-negotiation        "<xref target='content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     27  <!ENTITY agent-driven-negotiation   "<xref target='agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    2928  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    3029  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    3736  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    3837  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    39   <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4038  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    41   <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    42   <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    43   <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    44   <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     39  <!ENTITY header-accept              "<xref target='header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     40  <!ENTITY header-accept-charset      "<xref target='header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     41  <!ENTITY header-accept-encoding     "<xref target='header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     42  <!ENTITY header-accept-language     "<xref target='header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4543  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4644  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4846  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    4947  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    50   <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     48  <!ENTITY header-content-location    "<xref target='header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    5149  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    52   <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     50  <!ENTITY header-content-type        "<xref target='header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    5351  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    5452  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7068  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7169  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    72   <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     70  <!ENTITY media-types                "<xref target='media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7371  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7472  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    7977  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8078  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    81   <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8279  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    8380  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    10097  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    10198  <!ENTITY header-last-modified       "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    102   <!ENTITY header-user-agent          "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     99  <!ENTITY header-user-agent          "<xref target='header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    103100  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    104101  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    105102  <!ENTITY multipart-byteranges       "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    106   <!ENTITY http-date                  "<xref target='Part2' x:rel='#http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     103  <!ENTITY http-date                  "<xref target='http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    107104  <!ENTITY qvalue                     "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    108105  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    113110  <!ENTITY deflate-coding             "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    114111  <!ENTITY gzip-coding                "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    115   <!ENTITY response-representation    "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
     112  <!ENTITY response-representation    "<xref target='identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
    117114<?rfc toc="yes" ?>
    18301827   The resource identified by the request is only capable of generating
    18311828   response representations which have content characteristics not acceptable
    1832    according to the Accept and Accept-* header fields sent in the request
    1833    (see &p3-header-fields;).
     1829   according to the Accept and Accept-* header fields sent in the request.
    21172113   consists of metadata (representation header fields) and data (representation
    21182114   body).  When a complete or partial representation is enclosed in an HTTP message,
    2119    it is referred to as the payload of the message. HTTP representations
    2120    are defined in &payload;.
     2115   it is referred to as the payload of the message.
    30863081   <ttcol>Reference</ttcol>
     3083   <c>Accept</c>
     3084   <c>http</c>
     3085   <c>standard</c>
     3086   <c>
     3087      <xref target="header.accept"/>
     3088   </c>
     3089   <c>Accept-Charset</c>
     3090   <c>http</c>
     3091   <c>standard</c>
     3092   <c>
     3093      <xref target="header.accept-charset"/>
     3094   </c>
     3095   <c>Accept-Encoding</c>
     3096   <c>http</c>
     3097   <c>standard</c>
     3098   <c>
     3099      <xref target="header.accept-encoding"/>
     3100   </c>
     3101   <c>Accept-Language</c>
     3102   <c>http</c>
     3103   <c>standard</c>
     3104   <c>
     3105      <xref target="header.accept-language"/>
     3106   </c>
    30883107   <c>Allow</c>
    30893108   <c>http</c>
    30913110   <c>
    30923111      <xref target="header.allow"/>
     3112   </c>
     3113   <c>Content-Encoding</c>
     3114   <c>http</c>
     3115   <c>standard</c>
     3116   <c>
     3117      <xref target="header.content-encoding"/>
     3118   </c>
     3119   <c>Content-Language</c>
     3120   <c>http</c>
     3121   <c>standard</c>
     3122   <c>
     3123      <xref target="header.content-language"/>
     3124   </c>
     3125   <c>Content-Location</c>
     3126   <c>http</c>
     3127   <c>standard</c>
     3128   <c>
     3129      <xref target="header.content-location"/>
     3130   </c>
     3131   <c>Content-Type</c>
     3132   <c>http</c>
     3133   <c>standard</c>
     3134   <c>
     3135      <xref target="header.content-type"/>
    30933136   </c>
    30943137   <c>Date</c>
    31153158   <c>
    31163159      <xref target="header.location"/>
     3160   </c>
     3161   <c>MIME-Version</c>
     3162   <c>http</c>
     3163   <c>standard</c>
     3164   <c>
     3165      <xref target="mime-version"/>
    31173166   </c>
    31183167   <c>Max-Forwards</c>
    3315 <reference anchor="Part3">
    3316   <front>
    3317     <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
    3318     <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    3319       <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
    3320       <address><email>fielding@gbiv.com</email></address>
    3321     </author>
    3322     <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    3323       <organization abbrev="W3C">World Wide Web Consortium</organization>
    3324       <address><email>ylafon@w3.org</email></address>
    3325     </author>
    3326     <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
    3327       <organization abbrev="greenbytes">greenbytes GmbH</organization>
    3328       <address><email>julian.reschke@greenbytes.de</email></address>
    3329     </author>
    3330     <date month="&ID-MONTH;" year="&ID-YEAR;"/>
    3331   </front>
    3332   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
    3333   <x:source href="p3-payload.xml" basename="p3-payload"/>
    3334 </reference>
    33363364<reference anchor="Part4">
    33373365  <front>
    40874115<artwork type="abnf" name="p2-semantics.parsed-abnf">
     4116<x:ref>Accept</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
     4117 OWS media-range [ accept-params ] ] ) ]
     4118<x:ref>Accept-Charset</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
     4119 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
     4120 qvalue ] ] )
     4121<x:ref>Accept-Encoding</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
     4122 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
     4123<x:ref>Accept-Language</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
     4124 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
     4125 ] )
    40884126<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
    40904128<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
     4130<x:ref>Content-Encoding</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
     4131 content-coding ] )
     4132<x:ref>Content-Language</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
     4133 language-tag ] )
     4134<x:ref>Content-Location</x:ref> = absolute-URI / partial-URI
     4135<x:ref>Content-Type</x:ref> = media-type
    40924137<x:ref>Date</x:ref> = HTTP-date
    41024147<x:ref>Location</x:ref> = URI-reference
     4149<x:ref>MIME-Version</x:ref> = 1*DIGIT "." 1*DIGIT
    41044151<x:ref>Max-Forwards</x:ref> = 1*DIGIT
    41084155<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
    41094157<x:ref>Referer</x:ref> = absolute-URI / partial-URI
    41104158<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
    41144162<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
    41154164<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
    41174166<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
     4168<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
     4169<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
    41184170<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
     4171<x:ref>attribute</x:ref> = token
     4173<x:ref>charset</x:ref> = token
     4175<x:ref>codings</x:ref> = content-coding / "identity" / "*"
    41204176<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
     4177<x:ref>content-coding</x:ref> = token
    41224179<x:ref>date1</x:ref> = day SP month SP year
    41234181<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
    41244182<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
    41424200<x:ref>expect-name</x:ref> = token
    41434202<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
    41444203<x:ref>expect-value</x:ref> = token / quoted-string
    41484207<x:ref>hour</x:ref> = 2DIGIT
     4209<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
     4211<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
    41504213<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
     4215<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
     4216 ";" OWS parameter )
     4217<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
    41514218<x:ref>method</x:ref> = token
    41524219<x:ref>minute</x:ref> = 2DIGIT
    41664233<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
    41674235<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
     4237<x:ref>parameter</x:ref> = attribute "=" value
    41694239<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
    41754245<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
    41764247<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
    41784249<x:ref>second</x:ref> = 2DIGIT
     4251<x:ref>subtype</x:ref> = token
    41804253<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
    41814255<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
    4183 word = &lt;word, defined in [Part1], Section 3.2.4&gt;
     4256<x:ref>type</x:ref> = token
     4258<x:ref>value</x:ref> = word
     4260<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 3.2.4&gt;
    41854262<x:ref>year</x:ref> = 4DIGIT
    41884265<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
     4266; qvalue UNDEFINED
     4267; Accept defined but not used
     4268; Accept-Charset defined but not used
     4269; Accept-Encoding defined but not used
     4270; Accept-Language defined but not used
    41894271; Allow defined but not used
     4272; Content-Encoding defined but not used
     4273; Content-Language defined but not used
     4274; Content-Location defined but not used
     4275; Content-Type defined but not used
    41904276; Date defined but not used
    41914277; Expect defined but not used
    41924278; From defined but not used
    41934279; Location defined but not used
     4280; MIME-Version defined but not used
    41944281; Max-Forwards defined but not used
    41954282; Referer defined but not used
    41984285; User-Agent defined but not used
    41994286; obs-text defined but not used
    4200 ; word defined but not used
    42024288<?ENDINC p2-semantics.abnf-appendix ?>
     4932<section title="THE TEXT FORMERLY KNOWN AS PART3">
     4933<section title="Protocol Parameters" anchor="protocol.parameters">
     4935<section title="Character Encodings (charset)" anchor="character.sets">
     4937   HTTP uses charset names to indicate the character encoding of a
     4938   textual representation.
     4940<t anchor="rule.charset">
     4941  <x:anchor-alias value="charset"/>
     4942   A character encoding is identified by a case-insensitive token. The
     4943   complete set of tokens is defined by the IANA Character Set registry
     4944   (<eref target="http://www.iana.org/assignments/character-sets"/>).
     4946<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
     4947  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
     4950   Although HTTP allows an arbitrary token to be used as a charset
     4951   value, any token that has a predefined value within the IANA
     4952   Character Set registry &MUST; represent the character encoding defined
     4953   by that registry. Applications &SHOULD; limit their use of character
     4954   encodings to those defined within the IANA registry.
     4957   HTTP uses charset in two contexts: within an Accept-Charset request
     4958   header field (in which the charset value is an unquoted token) and as the
     4959   value of a parameter in a Content-Type header field (within a request or
     4960   response), in which case the parameter value of the charset parameter
     4961   can be quoted.
     4964   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
     4965   <xref target="RFC2277"/>.
     4969<section title="Content Codings" anchor="content.codings">
     4970  <x:anchor-alias value="content-coding"/>
     4972   Content coding values indicate an encoding transformation that has
     4973   been or can be applied to a representation. Content codings are primarily
     4974   used to allow a representation to be compressed or otherwise usefully
     4975   transformed without losing the identity of its underlying media type
     4976   and without loss of information. Frequently, the representation is stored in
     4977   coded form, transmitted directly, and only decoded by the recipient.
     4979<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
     4980  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
     4983   All content-coding values are case-insensitive. HTTP/1.1 uses
     4984   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
     4985   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
     4986   describes the content-coding, what is more important is that it
     4987   indicates what decoding mechanism will be required to remove the
     4988   encoding.
     4991   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
     4992  <list>
     4993    <t>
     4994      See &compress-coding;.
     4995    </t>
     4996  </list>
     4999   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
     5000  <list>
     5001    <t>
     5002      See &deflate-coding;.
     5003    </t>
     5004  </list>
     5007   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
     5008  <list>
     5009    <t>
     5010      See &gzip-coding;.
     5011    </t>
     5012  </list>
     5015<section title="Content Coding Registry" anchor="content.coding.registry">
     5017   The HTTP Content Coding Registry defines the name space for the content
     5018   coding names.
     5021   Registrations &MUST; include the following fields:
     5022   <list style="symbols">
     5023     <t>Name</t>
     5024     <t>Description</t>
     5025     <t>Pointer to specification text</t>
     5026   </list>
     5029   Names of content codings &MUST-NOT; overlap with names of transfer codings
     5030   (&transfer-codings;), unless the encoding transformation is identical (as
     5031   is the case for the compression codings defined in
     5032   &compression-codings;).
     5035   Values to be added to this name space require IETF Review
     5036   (see <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
     5037   conform to the purpose of content coding defined in this section.
     5040   The registry itself is maintained at
     5041   <eref target="http://www.iana.org/assignments/http-parameters"/>.
     5047<section title="Media Types" anchor="media.types">
     5048  <x:anchor-alias value="media-type"/>
     5049  <x:anchor-alias value="type"/>
     5050  <x:anchor-alias value="subtype"/>
     5052   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
     5053   and Accept (<xref target="header.accept"/>) header fields in order to provide
     5054   open and extensible data typing and type negotiation.
     5056<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"/>
     5057  <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> )
     5058  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
     5059  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
     5061<t anchor="rule.parameter">
     5062  <x:anchor-alias value="attribute"/>
     5063  <x:anchor-alias value="parameter"/>
     5064  <x:anchor-alias value="value"/>
     5065   The type/subtype &MAY; be followed by parameters in the form of
     5066   attribute/value pairs.
     5068<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"/>
     5069  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
     5070  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
     5071  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
     5074   The type, subtype, and parameter attribute names are case-insensitive.
     5075   Parameter values might or might not be case-sensitive, depending on the
     5076   semantics of the parameter name.  The presence or absence of a parameter might
     5077   be significant to the processing of a media-type, depending on its
     5078   definition within the media type registry.
     5081   A parameter value that matches the <x:ref>token</x:ref> production can be
     5082   transmitted as either a token or within a quoted-string. The quoted and
     5083   unquoted values are equivalent.
     5086   Note that some older HTTP applications do not recognize media type
     5087   parameters. When sending data to older HTTP applications,
     5088   implementations &SHOULD; only use media type parameters when they are
     5089   required by that type/subtype definition.
     5092   Media-type values are registered with the Internet Assigned Number
     5093   Authority (IANA). The media type registration process is
     5094   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
     5095   discouraged.
     5098<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
     5100   Internet media types are registered with a canonical form. A
     5101   representation transferred via HTTP messages &MUST; be in the
     5102   appropriate canonical form prior to its transmission except for
     5103   "text" types, as defined in the next paragraph.
     5106   When in canonical form, media subtypes of the "text" type use CRLF as
     5107   the text line break. HTTP relaxes this requirement and allows the
     5108   transport of text media with plain CR or LF alone representing a line
     5109   break when it is done consistently for an entire representation. HTTP
     5110   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
     5111   a line break in text media received via HTTP. In
     5112   addition, if the text is in a character encoding that does not
     5113   use octets 13 and 10 for CR and LF respectively, as is the case for
     5114   some multi-byte character encodings, HTTP allows the use of whatever octet
     5115   sequences are defined by that character encoding to represent the
     5116   equivalent of CR and LF for line breaks. This flexibility regarding
     5117   line breaks applies only to text media in the payload body; a bare CR
     5118   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
     5119   structures (such as header fields and multipart boundaries).
     5122   If a representation is encoded with a content-coding, the underlying
     5123   data &MUST; be in a form defined above prior to being encoded.
     5127<section title="Multipart Types" anchor="multipart.types">
     5129   MIME provides for a number of "multipart" types &mdash; encapsulations of
     5130   one or more representations within a single message body. All multipart
     5131   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
     5132   and &MUST; include a boundary parameter as part of the media type
     5133   value. The message body is itself a protocol element and &MUST;
     5134   therefore use only CRLF to represent line breaks between body-parts.
     5137   In general, HTTP treats a multipart message body no differently than
     5138   any other media type: strictly as payload.  HTTP does not use the
     5139   multipart boundary as an indicator of message body length.
     5140   <!-- jre: re-insert removed text pointing to caching? -->
     5141   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
     5142   behavior as a MIME user agent would upon receipt of a multipart type.
     5143   The MIME header fields within each body-part of a multipart message body
     5144   do not have any significance to HTTP beyond that defined by
     5145   their MIME semantics.
     5148   If an application receives an unrecognized multipart subtype, the
     5149   application &MUST; treat it as being equivalent to "multipart/mixed".
     5152  <t>
     5153    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
     5154    for carrying form data suitable for processing via the POST
     5155    request method, as described in <xref target="RFC2388"/>.
     5156  </t>
     5161<section title="Language Tags" anchor="language.tags">
     5162  <x:anchor-alias value="language-tag"/>
     5164   A language tag, as defined in <xref target="RFC5646"/>, identifies a
     5165   natural language spoken, written, or otherwise conveyed by human beings for
     5166   communication of information to other human beings. Computer languages are
     5167   explicitly excluded. HTTP uses language tags within the Accept-Language and
     5168   Content-Language fields.
     5171   In summary, a language tag is composed of one or more parts: A primary
     5172   language subtag followed by a possibly empty series of subtags:
     5174<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
     5175  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
     5178   White space is not allowed within the tag and all tags are case-insensitive.
     5179   The name space of language subtags is administered by the IANA (see
     5180   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
     5183  <preamble>Example tags include:</preamble>
     5184<artwork type="example">
     5185  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
     5189   See <xref target="RFC5646"/> for further information.
     5194<section title="Payload" anchor="payload">
     5196   HTTP messages &MAY; transfer a payload if not otherwise restricted by
     5197   the request method or response status code.  The payload consists of
     5198   metadata, in the form of header fields, and data, in the form of the
     5199   sequence of octets in the message body after any transfer-coding has
     5200   been decoded.
     5202<iref item="payload"/>
     5204   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
     5205   representation of some resource.  We use separate terms for payload
     5206   and representation because some messages contain only the associated
     5207   representation's header fields (e.g., responses to HEAD) or only some
     5208   part(s) of the representation (e.g., the 206 status code).
     5210<section title="Payload Header Fields" anchor="payload.header.fields">
     5211  <x:anchor-alias value="payload-header"/>
     5213   HTTP header fields that specifically define the payload, rather than the
     5214   associated representation, are referred to as "payload header fields".
     5215   The following payload header fields are defined by HTTP/1.1:
     5217<texttable align="left">
     5218  <ttcol>Header Field Name</ttcol>
     5219  <ttcol>Defined in...</ttcol>
     5221  <c>Content-Length</c> <c>&header-content-length;</c>
     5222  <c>Content-Range</c> <c>&header-content-range;</c>
     5226<section title="Payload Body" anchor="payload.body">
     5227  <x:anchor-alias value="payload-body"/>
     5229   A payload body is only present in a message when a message body is
     5230   present, as described in &message-body;. The payload body is obtained
     5231   from the message body by decoding any Transfer-Encoding that might
     5232   have been applied to ensure safe and proper transfer of the message.
     5237<section title="Representation" anchor="representation3">
     5238<iref item="representation"/>
     5240   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
     5241   communicated from one party to another.  A resource representation
     5242   is information that reflects the state of that resource, as observed
     5243   at some point in the past (e.g., in a response to GET) or to be
     5244   desired at some point in the future (e.g., in a PUT request).
     5247   Most, but not all, representations transferred via HTTP are intended
     5248   to be a representation of the target resource (the resource identified
     5249   by the effective request URI).  The precise semantics of a representation
     5250   are determined by the type of message (request or response), the request
     5251   method, the response status code, and the representation metadata.
     5252   For example, the above semantic is true for the representation in any
     5253   200 (OK) response to GET and for the representation in any PUT request.
     5254   A 200 response to PUT, in contrast, contains either a representation
     5255   that describes the successful action or a representation of the target
     5256   resource, with the latter indicated by a Content-Location header field
     5257   with the same value as the effective request URI.  Likewise, response
     5258   messages with an error status code usually contain a representation that
     5259   describes the error and what next steps are suggested for resolving it.
     5262<section title="Representation Header Fields" anchor="representation.header.fields">
     5263  <x:anchor-alias value="representation-header"/>
     5265   Representation header fields define metadata about the representation data
     5266   enclosed in the message body or, if no message body is present, about
     5267   the representation that would have been transferred in a 200 response
     5268   to a simultaneous GET request with the same effective request URI.
     5271   The following header fields are defined as representation metadata:
     5273<texttable align="left">
     5274  <ttcol>Header Field Name</ttcol>
     5275  <ttcol>Defined in...</ttcol>
     5277  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
     5278  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
     5279  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
     5280  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
     5281  <c>Expires</c> <c>&header-expires;</c>
     5284   Additional header fields define metadata about the selected
     5285   representation, which might differ from the representation included
     5286   in the message for responses to some state-changing methods.
     5287   The following header fields are defined as selected representation
     5288   metadata:
     5290<texttable align="left">
     5291  <ttcol>Header Field Name</ttcol>
     5292  <ttcol>Defined in...</ttcol>
     5294  <c>ETag</c> <c>&header-etag;</c>
     5295  <c>Last-Modified</c> <c>&header-last-modified;</c>
     5299<section title="Representation Data" anchor="representation.data">
     5300  <x:anchor-alias value="representation-data"/>
     5302   The representation body associated with an HTTP message is
     5303   either provided as the payload body of the message or
     5304   referred to by the message semantics and the effective request
     5305   URI.  The representation data is in a format and encoding defined by
     5306   the representation metadata header fields.
     5309   The data type of the representation data
     5310   is determined via the header fields Content-Type and Content-Encoding.
     5311   These define a two-layer, ordered encoding model:
     5313<figure><artwork type="example">
     5314  representation-data := Content-Encoding( Content-Type( bits ) )
     5317   Content-Type specifies the media type of the underlying data, which
     5318   defines both the data format and how that data &SHOULD; be processed
     5319   by the recipient (within the scope of the request method semantics).
     5320   Any HTTP/1.1 message containing a payload body &SHOULD; include a
     5321   Content-Type header field defining the media type of the associated
     5322   representation unless that metadata is unknown to the sender.
     5323   If the Content-Type header field is not present, it indicates that
     5324   the sender does not know the media type of the representation;
     5325   recipients &MAY; either assume that the media type is
     5326   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
     5327   or examine the content to determine its type.
     5330   In practice, resource owners do not always properly configure their origin
     5331   server to provide the correct Content-Type for a given representation,
     5332   with the result that some clients will examine a response body's content
     5333   and override the specified type.
     5334   Clients that do so risk drawing incorrect conclusions, which might expose
     5335   additional security risks (e.g., "privilege escalation").  Furthermore,
     5336   it is impossible to determine the sender's intent by examining the data
     5337   format: many data formats match multiple media types that differ only in
     5338   processing semantics.  Implementers are encouraged to provide a means of
     5339   disabling such "content sniffing" when it is used.
     5342   Content-Encoding is used to indicate any additional content
     5343   codings applied to the data, usually for the purpose of data
     5344   compression, that are a property of the representation.  If
     5345   Content-Encoding is not present, then there is no additional
     5346   encoding beyond that defined by the Content-Type.
     5351<section title="Content Negotiation" anchor="content.negotiation">
     5353   HTTP responses include a representation which contains information for
     5354   interpretation, whether by a human user or for further processing.
     5355   Often, the server has different ways of representing the
     5356   same information; for example, in different formats, languages,
     5357   or using different character encodings.
     5360   HTTP clients and their users might have different or variable
     5361   capabilities, characteristics or preferences which would influence
     5362   which representation, among those available from the server,
     5363   would be best for the server to deliver. For this reason, HTTP
     5364   provides mechanisms for "content negotiation" &mdash; a process of
     5365   allowing selection of a representation of a given resource,
     5366   when more than one is available.
     5369   This specification defines two patterns of content negotiation;
     5370   "server-driven", where the server selects the representation based
     5371   upon the client's stated preferences, and "agent-driven" negotiation,
     5372   where the server provides a list of representations for the client to
     5373   choose from, based upon their metadata. In addition,  there are
     5374   other patterns: some applications use an "active content" pattern,
     5375   where the server returns active content which runs on the client
     5376   and, based on client available parameters, selects additional
     5377   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
     5378   has also been proposed.
     5381   These patterns are all widely used, and have trade-offs in applicability
     5382   and practicality. In particular, when the number of preferences or
     5383   capabilities to be expressed by a client are large (such as when many
     5384   different formats are supported by a user-agent), server-driven
     5385   negotiation becomes unwieldy, and might not be appropriate. Conversely,
     5386   when the number of representations to choose from is very large,
     5387   agent-driven negotiation might not be appropriate.
     5390   Note that in all cases, the supplier of representations has the
     5391   responsibility for determining which representations might be
     5392   considered to be the "same information".
     5395<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
     5397   If the selection of the best representation for a response is made by
     5398   an algorithm located at the server, it is called server-driven
     5399   negotiation. Selection is based on the available representations of
     5400   the response (the dimensions over which it can vary; e.g., language,
     5401   content-coding, etc.) and the contents of particular header fields in
     5402   the request message or on other information pertaining to the request
     5403   (such as the network address of the client).
     5406   Server-driven negotiation is advantageous when the algorithm for
     5407   selecting from among the available representations is difficult to
     5408   describe to the user agent, or when the server desires to send its
     5409   "best guess" to the client along with the first response (hoping to
     5410   avoid the round-trip delay of a subsequent request if the "best
     5411   guess" is good enough for the user). In order to improve the server's
     5412   guess, the user agent &MAY; include request header fields (Accept,
     5413   Accept-Language, Accept-Encoding, etc.) which describe its
     5414   preferences for such a response.
     5417   Server-driven negotiation has disadvantages:
     5418  <list style="numbers">
     5419    <t>
     5420         It is impossible for the server to accurately determine what
     5421         might be "best" for any given user, since that would require
     5422         complete knowledge of both the capabilities of the user agent
     5423         and the intended use for the response (e.g., does the user want
     5424         to view it on screen or print it on paper?).
     5425    </t>
     5426    <t>
     5427         Having the user agent describe its capabilities in every
     5428         request can be both very inefficient (given that only a small
     5429         percentage of responses have multiple representations) and a
     5430         potential violation of the user's privacy.
     5431    </t>
     5432    <t>
     5433         It complicates the implementation of an origin server and the
     5434         algorithms for generating responses to a request.
     5435    </t>
     5436    <t>
     5437         It might limit a public cache's ability to use the same response
     5438         for multiple user's requests.
     5439    </t>
     5440  </list>
     5443   Server-driven negotiation allows the user agent to specify its preferences,
     5444   but it cannot expect responses to always honor them. For example, the origin
     5445   server might not implement server-driven negotiation, or it might decide that
     5446   sending a response that doesn't conform to them is better than sending a 406
     5447   (Not Acceptable) response.
     5450   Many of the mechanisms for expressing preferences use quality values to
     5451   declare relative preference. See &qvalue; for more information.
     5454   HTTP/1.1 includes the following header fields for enabling
     5455   server-driven negotiation through description of user agent
     5456   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
     5457   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
     5458   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
     5459   However, an origin server is not limited to these dimensions and &MAY; vary
     5460   the response based on any aspect of the request, including aspects
     5461   of the connection (e.g., IP address) or information within extension
     5462   header fields not defined by this specification.
     5465  <t>
     5466    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
     5467    because new clients might not be recognized.
     5468  </t>
     5471   The Vary header field (&header-vary;) can be used to express the parameters the
     5472   server uses to select a representation that is subject to server-driven
     5473   negotiation.
     5477<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
     5479   With agent-driven negotiation, selection of the best representation
     5480   for a response is performed by the user agent after receiving an
     5481   initial response from the origin server. Selection is based on a list
     5482   of the available representations of the response included within the
     5483   header fields or body of the initial response, with each
     5484   representation identified by its own URI. Selection from among the
     5485   representations can be performed automatically (if the user agent is
     5486   capable of doing so) or manually by the user selecting from a
     5487   generated (possibly hypertext) menu.
     5490   Agent-driven negotiation is advantageous when the response would vary
     5491   over commonly-used dimensions (such as type, language, or encoding),
     5492   when the origin server is unable to determine a user agent's
     5493   capabilities from examining the request, and generally when public
     5494   caches are used to distribute server load and reduce network usage.
     5497   Agent-driven negotiation suffers from the disadvantage of needing a
     5498   second request to obtain the best alternate representation. This
     5499   second request is only efficient when caching is used. In addition,
     5500   this specification does not define any mechanism for supporting
     5501   automatic selection, though it also does not prevent any such
     5502   mechanism from being developed as an extension and used within
     5503   HTTP/1.1.
     5506   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
     5507   status codes for enabling agent-driven negotiation when the server is
     5508   unwilling or unable to provide a varying response using server-driven
     5509   negotiation.
     5514<section title="Header Field Definitions" anchor="header.field.definitions3">
     5516   This section defines the syntax and semantics of HTTP/1.1 header fields
     5517   related to the payload of messages.
     5520<section title="Accept" anchor="header.accept">
     5521  <iref primary="true" item="Accept header field" x:for-anchor=""/>
     5522  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
     5523  <x:anchor-alias value="Accept"/>
     5524  <x:anchor-alias value="accept-ext"/>
     5525  <x:anchor-alias value="accept-params"/>
     5526  <x:anchor-alias value="media-range"/>
     5528   The "Accept" header field can be used by user agents to specify
     5529   response media types that are acceptable. Accept header fields can be used to
     5530   indicate that the request is specifically limited to a small set of desired
     5531   types, as in the case of a request for an in-line image.
     5533<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"/>
     5534  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
     5536  <x:ref>media-range</x:ref>    = ( "*/*"
     5537                   / ( <x:ref>type</x:ref> "/" "*" )
     5538                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
     5539                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
     5540  <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> )
     5541  <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> ]
     5544   The asterisk "*" character is used to group media types into ranges,
     5545   with "*/*" indicating all media types and "type/*" indicating all
     5546   subtypes of that type. The media-range &MAY; include media type
     5547   parameters that are applicable to that range.
     5550   Each media-range &MAY; be followed by one or more accept-params,
     5551   beginning with the "q" parameter for indicating a relative quality
     5552   factor. The first "q" parameter (if any) separates the media-range
     5553   parameter(s) from the accept-params. Quality factors allow the user
     5554   or user agent to indicate the relative degree of preference for that
     5555   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
     5556   default value is q=1.
     5559  <t>
     5560    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
     5561    parameters from Accept extension parameters is due to historical
     5562    practice. Although this prevents any media type parameter named
     5563    "q" from being used with a media range, such an event is believed
     5564    to be unlikely given the lack of any "q" parameters in the IANA
     5565    media type registry and the rare usage of any media type
     5566    parameters in Accept. Future media types are discouraged from
     5567    registering any parameter named "q".
     5568  </t>
     5571   The example
     5573<figure><artwork type="example">
     5574  Accept: audio/*; q=0.2, audio/basic
     5577   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
     5578   type if it is the best available after an 80% mark-down in quality".
     5581   A request without any Accept header field implies that the user agent
     5582   will accept any media type in response.
     5583   If an Accept header field is present in a request and none of the
     5584   available representations for the response have a media type that is
     5585   listed as acceptable, the origin server &MAY; either
     5586   honor the Accept header field by sending a 406 (Not Acceptable) response
     5587   or disregard the Accept header field by treating the response as if
     5588   it is not subject to content negotiation.
     5591   A more elaborate example is
     5593<figure><artwork type="example">
     5594  Accept: text/plain; q=0.5, text/html,
     5595          text/x-dvi; q=0.8, text/x-c
     5598   Verbally, this would be interpreted as "text/html and text/x-c are
     5599   the preferred media types, but if they do not exist, then send the
     5600   text/x-dvi representation, and if that does not exist, send the text/plain
     5601   representation".
     5604   Media ranges can be overridden by more specific media ranges or
     5605   specific media types. If more than one media range applies to a given
     5606   type, the most specific reference has precedence. For example,
     5608<figure><artwork type="example">
     5609  Accept: text/*, text/plain, text/plain;format=flowed, */*
     5612   have the following precedence:
     5613   <list style="numbers">
     5614    <t>text/plain;format=flowed</t>
     5615    <t>text/plain</t>
     5616    <t>text/*</t>
     5617    <t>*/*</t>
     5618   </list>
     5621   The media type quality factor associated with a given type is
     5622   determined by finding the media range with the highest precedence
     5623   which matches that type. For example,
     5625<figure><artwork type="example">
     5626  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
     5627          text/html;level=2;q=0.4, */*;q=0.5
     5630   would cause the following values to be associated:
     5632<texttable align="left">
     5633  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
     5634  <c>text/html;level=1</c>    <c>1</c>
     5635  <c>text/html</c>            <c>0.7</c>
     5636  <c>text/plain</c>           <c>0.3</c>
     5637  <c>image/jpeg</c>           <c>0.5</c>
     5638  <c>text/html;level=2</c>    <c>0.4</c>
     5639  <c>text/html;level=3</c>    <c>0.7</c>
     5642      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
     5643      values for certain media ranges. However, unless the user agent is
     5644      a closed system which cannot interact with other rendering agents,
     5645      this default set ought to be configurable by the user.
     5649<section title="Accept-Charset" anchor="header.accept-charset">
     5650  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
     5651  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
     5652  <x:anchor-alias value="Accept-Charset"/>
     5654   The "Accept-Charset" header field can be used by user agents to
     5655   indicate what character encodings are acceptable in a response
     5656   payload. This field allows
     5657   clients capable of understanding more comprehensive or special-purpose
     5658   character encodings to signal that capability to a server which is capable of
     5659   representing documents in those character encodings.
     5661<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
     5662  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
     5663                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
     5666   Character encoding values (a.k.a., charsets) are described in
     5667   <xref target="character.sets"/>. Each charset &MAY; be given an
     5668   associated quality value which represents the user's preference
     5669   for that charset. The default value is q=1. An example is
     5671<figure><artwork type="example">
     5672  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
     5675   The special value "*", if present in the Accept-Charset field,
     5676   matches every character encoding which is not mentioned elsewhere in the
     5677   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
     5678   all character encodings not explicitly mentioned get a quality value of 0.
     5681   A request without any Accept-Charset header field implies that the user
     5682   agent will accept any character encoding in response.
     5683   If an Accept-Charset header field is present in a request and none of the
     5684   available representations for the response have a character encoding that
     5685   is listed as acceptable, the origin server &MAY; either honor the
     5686   Accept-Charset header field by sending a 406 (Not Acceptable) response or
     5687   disregard the Accept-Charset header field by treating the response as if
     5688   it is not subject to content negotiation.
     5692<section title="Accept-Encoding" anchor="header.accept-encoding">
     5693  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
     5694  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
     5695  <x:anchor-alias value="Accept-Encoding"/>
     5696  <x:anchor-alias value="codings"/>
     5698   The "Accept-Encoding" header field can be used by user agents to
     5699   indicate what response content-codings (<xref target="content.codings"/>)
     5700   are acceptable in the response.  An "identity" token is used as a synonym
     5701   for "no encoding" in order to communicate when no encoding is preferred.
     5703<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
     5704  <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> ] )
     5705  <x:ref>codings</x:ref>          = <x:ref>content-coding</x:ref> / "identity" / "*"
     5708   Each codings value &MAY; be given an associated quality value which
     5709   represents the preference for that encoding. The default value is q=1.
     5712   For example,
     5714<figure><artwork type="example">
     5715  Accept-Encoding: compress, gzip
     5716  Accept-Encoding:
     5717  Accept-Encoding: *
     5718  Accept-Encoding: compress;q=0.5, gzip;q=1.0
     5719  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
     5722   A server tests whether a content-coding for a given representation is
     5723   acceptable, according to an Accept-Encoding field, using these rules:
     5724  <list style="numbers">
     5725      <t>The special "*" symbol in an Accept-Encoding field matches any
     5726         available content-coding not explicitly listed in the header
     5727         field.</t>
     5729      <t>If the representation has no content-coding, then it is acceptable
     5730         by default unless specifically excluded by the Accept-Encoding field
     5731         stating either "identity;q=0" or "*;q=0" without a more specific
     5732         entry for "identity".</t>
     5734      <t>If the representation's content-coding is one of the content-codings
     5735         listed in the Accept-Encoding field, then it is acceptable unless
     5736         it is accompanied by a qvalue of 0. (As defined in &qvalue;, a
     5737         qvalue of 0 means "not acceptable".)</t>
     5739      <t>If multiple content-codings are acceptable, then the acceptable
     5740         content-coding with the highest non-zero qvalue is preferred.</t>
     5741  </list>
     5744   An Accept-Encoding header field with a combined field-value that is empty
     5745   implies that the user agent does not want any content-coding in response.
     5746   If an Accept-Encoding header field is present in a request and none of the
     5747   available representations for the response have a content-coding that
     5748   is listed as acceptable, the origin server &SHOULD; send a response
     5749   without any content-coding.
     5752   A request without an Accept-Encoding header field implies that the user
     5753   agent will accept any content-coding in response, but a representation
     5754   without content-coding is preferred for compatibility with the widest
     5755   variety of user agents.
     5758  <t>
     5759    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
     5760    associated with content-codings. This means that qvalues will not
     5761    work and are not permitted with x-gzip or x-compress.
     5762  </t>
     5766<section title="Accept-Language" anchor="header.accept-language">
     5767  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
     5768  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
     5769  <x:anchor-alias value="Accept-Language"/>
     5770  <x:anchor-alias value="language-range"/>
     5772   The "Accept-Language" header field can be used by user agents to
     5773   indicate the set of natural languages that are preferred in the response.
     5774   Language tags are defined in <xref target="language.tags"/>.
     5776<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
     5777  <x:ref>Accept-Language</x:ref> =
     5778                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
     5779  <x:ref>language-range</x:ref>  =
     5780            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
     5783   Each language-range can be given an associated quality value which
     5784   represents an estimate of the user's preference for the languages
     5785   specified by that range. The quality value defaults to "q=1". For
     5786   example,
     5788<figure><artwork type="example">
     5789  Accept-Language: da, en-gb;q=0.8, en;q=0.7
     5792   would mean: "I prefer Danish, but will accept British English and
     5793   other types of English".
     5794   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
     5797   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
     5798   several matching schemes. Implementations can offer the most appropriate
     5799   matching scheme for their requirements.
     5802  <t>
     5803    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
     5804    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
     5805    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
     5806  </t>
     5809   It might be contrary to the privacy expectations of the user to send
     5810   an Accept-Language header field with the complete linguistic preferences of
     5811   the user in every request. For a discussion of this issue, see
     5812   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
     5815   As intelligibility is highly dependent on the individual user, it is
     5816   recommended that client applications make the choice of linguistic
     5817   preference available to the user. If the choice is not made
     5818   available, then the Accept-Language header field &MUST-NOT; be given in
     5819   the request.
     5822  <t>
     5823    <x:h>Note:</x:h> When making the choice of linguistic preference available to
     5824    the user, we remind implementors of  the fact that users are not
     5825    familiar with the details of language matching as described above,
     5826    and ought to be provided appropriate guidance. As an example, users
     5827    might assume that on selecting "en-gb", they will be served any
     5828    kind of English document if British English is not available. A
     5829    user agent might suggest in such a case to add "en" to get the
     5830    best matching behavior.
     5831  </t>
     5835<section title="Content-Encoding" anchor="header.content-encoding">
     5836  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
     5837  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
     5838  <x:anchor-alias value="Content-Encoding"/>
     5840   The "Content-Encoding" header field indicates what content-codings
     5841   have been applied to the representation beyond those inherent in the media
     5842   type, and thus what decoding mechanisms have to be applied in order to obtain
     5843   the media-type referenced by the Content-Type header field.
     5844   Content-Encoding is primarily used to allow a representation to be
     5845   compressed without losing the identity of its underlying media type.
     5847<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
     5848  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
     5851   Content codings are defined in <xref target="content.codings"/>. An example of its use is
     5853<figure><artwork type="example">
     5854  Content-Encoding: gzip
     5857   The content-coding is a characteristic of the representation.
     5858   Typically, the representation body is stored with this
     5859   encoding and is only decoded before rendering or analogous usage.
     5860   However, a transforming proxy &MAY; modify the content-coding if the
     5861   new coding is known to be acceptable to the recipient, unless the
     5862   "no-transform" cache-control directive is present in the message.
     5865   If the media type includes an inherent encoding, such as a data format
     5866   that is always compressed, then that encoding would not be restated as
     5867   a Content-Encoding even if it happens to be the same algorithm as one
     5868   of the content-codings.  Such a content-coding would only be listed if,
     5869   for some bizarre reason, it is applied a second time to form the
     5870   representation.  Likewise, an origin server might choose to publish the
     5871   same payload data as multiple representations that differ only in whether
     5872   the coding is defined as part of Content-Type or Content-Encoding, since
     5873   some user agents will behave differently in their handling of each
     5874   response (e.g., open a "Save as ..." dialog instead of automatic
     5875   decompression and rendering of content).
     5878   A representation that has a content-coding applied to it &MUST; include
     5879   a Content-Encoding header field (<xref target="header.content-encoding"/>)
     5880   that lists the content-coding(s) applied.
     5883   If multiple encodings have been applied to a representation, the content
     5884   codings &MUST; be listed in the order in which they were applied.
     5885   Additional information about the encoding parameters &MAY; be provided
     5886   by other header fields not defined by this specification.
     5889   If the content-coding of a representation in a request message is not
     5890   acceptable to the origin server, the server &SHOULD; respond with a
     5891   status code of 415 (Unsupported Media Type).
     5895<section title="Content-Language" anchor="header.content-language">
     5896  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
     5897  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
     5898  <x:anchor-alias value="Content-Language"/>
     5900   The "Content-Language" header field describes the natural
     5901   language(s) of the intended audience for the representation. Note that this might
     5902   not be equivalent to all the languages used within the representation.
     5904<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
     5905  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
     5908   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
     5909   Content-Language is to allow a user to identify and differentiate
     5910   representations according to the user's own preferred language. Thus, if the
     5911   body content is intended only for a Danish-literate audience, the
     5912   appropriate field is
     5914<figure><artwork type="example">
     5915  Content-Language: da
     5918   If no Content-Language is specified, the default is that the content
     5919   is intended for all language audiences. This might mean that the
     5920   sender does not consider it to be specific to any natural language,
     5921   or that the sender does not know for which language it is intended.
     5924   Multiple languages &MAY; be listed for content that is intended for
     5925   multiple audiences. For example, a rendition of the "Treaty of
     5926   Waitangi", presented simultaneously in the original Maori and English
     5927   versions, would call for
     5929<figure><artwork type="example">
     5930  Content-Language: mi, en
     5933   However, just because multiple languages are present within a representation
     5934   does not mean that it is intended for multiple linguistic audiences.
     5935   An example would be a beginner's language primer, such as "A First
     5936   Lesson in Latin", which is clearly intended to be used by an
     5937   English-literate audience. In this case, the Content-Language would
     5938   properly only include "en".
     5941   Content-Language &MAY; be applied to any media type &mdash; it is not
     5942   limited to textual documents.
     5946<section title="Content-Location" anchor="header.content-location">
     5947  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
     5948  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
     5949  <x:anchor-alias value="Content-Location"/>
     5951   The "Content-Location" header field supplies a URI that can be used
     5952   as a specific identifier for the representation in this message.
     5953   In other words, if one were to perform a GET on this URI at the time
     5954   of this message's generation, then a 200 response would contain the
     5955   same representation that is enclosed as payload in this message.
     5957<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
     5958  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
     5961   The Content-Location value is not a replacement for the effective
     5962   Request URI (&effective-request-uri;).  It is representation metadata.
     5963   It has the same syntax and semantics as the header field of the same name
     5964   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
     5965   However, its appearance in an HTTP message has some special implications
     5966   for HTTP recipients.
     5969   If Content-Location is included in a response message and its value
     5970   is the same as the effective request URI, then the response payload
     5971   &SHOULD; be considered a current representation of that resource.
     5972   For a GET or HEAD request, this is the same as the default semantics
     5973   when no Content-Location is provided by the server.  For a state-changing
     5974   request like PUT or POST, it implies that the server's response contains
     5975   the new representation of that resource, thereby distinguishing it from
     5976   representations that might only report about the action (e.g., "It worked!").
     5977   This allows authoring applications to update their local copies without
     5978   the need for a subsequent GET request.
     5981   If Content-Location is included in a response message and its value
     5982   differs from the effective request URI, then the origin server is
     5983   informing recipients that this representation has its own, presumably
     5984   more specific, identifier.  For a GET or HEAD request, this is an
     5985   indication that the effective request URI identifies a resource that
     5986   is subject to content negotiation and the selected representation for
     5987   this response can also be found at the identified URI.  For other
     5988   methods, such a Content-Location indicates that this representation
     5989   contains a report on the action's status and the same report is
     5990   available (for future access with GET) at the given URI.  For
     5991   example, a purchase transaction made via a POST request might
     5992   include a receipt document as the payload of the 200 response;
     5993   the Content-Location value provides an identifier for retrieving
     5994   a copy of that same receipt in the future.
     5997   If Content-Location is included in a request message, then it &MAY;
     5998   be interpreted by the origin server as an indication of where the
     5999   user agent originally obtained the content of the enclosed
     6000   representation (prior to any subsequent modification of the content
     6001   by that user agent).  In other words, the user agent is providing
     6002   the same representation metadata that it received with the original
     6003   representation.  However, such interpretation &MUST-NOT; be used to
     6004   alter the semantics of the method requested by the client.  For
     6005   example, if a client makes a PUT request on a negotiated resource
     6006   and the origin server accepts that PUT (without redirection), then the
     6007   new set of values for that resource is expected to be consistent with
     6008   the one representation supplied in that PUT; the Content-Location
     6009   cannot be used as a form of reverse content selection that
     6010   identifies only one of the negotiated representations to be updated.
     6011   If the user agent had wanted the latter semantics, it would have applied
     6012   the PUT directly to the Content-Location URI.
     6015   A Content-Location field received in a request message is transitory
     6016   information that &SHOULD-NOT; be saved with other representation
     6017   metadata for use in later responses.  The Content-Location's value
     6018   might be saved for use in other contexts, such as within source links
     6019   or other metadata.
     6022   A cache cannot assume that a representation with a Content-Location
     6023   different from the URI used to retrieve it can be used to respond to
     6024   later requests on that Content-Location URI.
     6027   If the Content-Location value is a partial URI, the partial URI is
     6028   interpreted relative to the effective request URI.
     6032<section title="Content-Type" anchor="header.content-type">
     6033  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
     6034  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
     6035  <x:anchor-alias value="Content-Type"/>
     6037   The "Content-Type" header field indicates the media type of the
     6038   representation. In the case of responses to the HEAD method, the media type is
     6039   that which would have been sent had the request been a GET.
     6041<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
     6042  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
     6045   Media types are defined in <xref target="media.types"/>. An example of the field is
     6047<figure><artwork type="example">
     6048  Content-Type: text/html; charset=ISO-8859-4
     6051   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
     6057<section title="IANA Considerations" anchor="IANA.considerations3">
     6059<section title="Content Coding Registry" anchor="content.coding.registration">
     6061   The registration procedure for HTTP Content Codings is now defined
     6062   by <xref target="content.coding.registry"/> of this document.
     6065   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
     6066   shall be updated with the registration below:
     6068<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
     6069   <ttcol>Name</ttcol>
     6070   <ttcol>Description</ttcol>
     6071   <ttcol>Reference</ttcol>
     6072   <c>compress</c>
     6073   <c>UNIX "compress" program method</c>
     6074   <c>
     6075      &compress-coding;
     6076   </c>
     6077   <c>deflate</c>
     6078   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
     6079   the "zlib" data format (<xref target="RFC1950"/>)
     6080   </c>
     6081   <c>
     6082      &deflate-coding;
     6083   </c>
     6084   <c>gzip</c>
     6085   <c>Same as GNU zip <xref target="RFC1952"/></c>
     6086   <c>
     6087      &gzip-coding;
     6088   </c>
     6089   <c>identity</c>
     6090   <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
     6091   <c>
     6092      <xref target="header.accept-encoding"/>
     6093   </c>
     6099<section title="Security Considerations" anchor="security.considerations3">
     6101   This section is meant to inform application developers, information
     6102   providers, and users of the security limitations in HTTP/1.1 as
     6103   described by this document. The discussion does not include
     6104   definitive solutions to the problems revealed, though it does make
     6105   some suggestions for reducing security risks.
     6108<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
     6110   Accept header fields can reveal information about the user to all
     6111   servers which are accessed. The Accept-Language header field in particular
     6112   can reveal information the user would consider to be of a private
     6113   nature, because the understanding of particular languages is often
     6114   strongly correlated to the membership of a particular ethnic group.
     6115   User agents which offer the option to configure the contents of an
     6116   Accept-Language header field to be sent in every request are strongly
     6117   encouraged to let the configuration process include a message which
     6118   makes the user aware of the loss of privacy involved.
     6121   An approach that limits the loss of privacy would be for a user agent
     6122   to omit the sending of Accept-Language header fields by default, and to ask
     6123   the user whether or not to start sending Accept-Language header fields to a
     6124   server if it detects, by looking for any Vary header fields
     6125   generated by the server, that such sending could improve the quality
     6126   of service.
     6129   Elaborate user-customized accept header fields sent in every request,
     6130   in particular if these include quality values, can be used by servers
     6131   as relatively reliable and long-lived user identifiers. Such user
     6132   identifiers would allow content providers to do click-trail tracking,
     6133   and would allow collaborating content providers to match cross-server
     6134   click-trails or form submissions of individual users. Note that for
     6135   many users not behind a proxy, the network address of the host
     6136   running the user agent will also serve as a long-lived user
     6137   identifier. In environments where proxies are used to enhance
     6138   privacy, user agents ought to be conservative in offering accept
     6139   header configuration options to end users. As an extreme privacy
     6140   measure, proxies could filter the accept header fields in relayed requests.
     6141   General purpose user agents which provide a high degree of header
     6142   configurability &SHOULD; warn users about the loss of privacy which can
     6143   be involved.
     6150<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
     6152   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
     6153   allow a message body to be transmitted in an open variety of
     6154   representations and with extensible mechanisms. However, RFC 2045
     6155   discusses mail, and HTTP has a few features that are different from
     6156   those described in MIME. These differences were carefully chosen
     6157   to optimize performance over binary connections, to allow greater
     6158   freedom in the use of new media types, to make date comparisons
     6159   easier, and to acknowledge the practice of some early HTTP servers
     6160   and clients.
     6163   This appendix describes specific areas where HTTP differs from MIME.
     6164   Proxies and gateways to strict MIME environments &SHOULD; be
     6165   aware of these differences and provide the appropriate conversions
     6166   where necessary. Proxies and gateways from MIME environments to HTTP
     6167   also need to be aware of the differences because some conversions
     6168   might be required.
     6171<section title="MIME-Version" anchor="mime-version">
     6172  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
     6173  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
     6174  <x:anchor-alias value="MIME-Version"/>
     6176   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
     6177   include a single MIME-Version header field to indicate what
     6178   version of the MIME protocol was used to construct the message. Use
     6179   of the MIME-Version header field indicates that the message is in
     6180   full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
     6181   Proxies/gateways are responsible for ensuring full conformance (where
     6182   possible) when exporting HTTP messages to strict MIME environments.
     6184<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
     6185  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
     6188   MIME version "1.0" is the default for use in HTTP/1.1. However,
     6189   HTTP/1.1 message parsing and semantics are defined by this document
     6190   and not the MIME specification.
     6194<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
     6196   MIME requires that an Internet mail body-part be converted to
     6197   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
     6198   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
     6199   allowed for subtypes of the "text" media type when transmitted over
     6200   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
     6201   line breaks as CRLF and forbids the use of CR or LF outside of line
     6202   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
     6203   line break within text content when a message is transmitted over
     6204   HTTP.
     6207   Where it is possible, a proxy or gateway from HTTP to a strict MIME
     6208   environment &SHOULD; translate all line breaks within the text media
     6209   types described in <xref target="canonicalization.and.text.defaults"/>
     6210   of this document to the RFC 2049
     6211   canonical form of CRLF. Note, however, that this might be complicated
     6212   by the presence of a Content-Encoding and by the fact that HTTP
     6213   allows the use of some character encodings which do not use octets 13 and
     6214   10 to represent CR and LF, respectively, as is the case for some multi-byte
     6215   character encodings.
     6218   Conversion will break any cryptographic
     6219   checksums applied to the original content unless the original content
     6220   is already in canonical form. Therefore, the canonical form is
     6221   recommended for any content that uses such checksums in HTTP.
     6226<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
     6228   HTTP/1.1 uses a restricted set of date formats (&http-date;) to
     6229   simplify the process of date comparison. Proxies and gateways from
     6230   other protocols &SHOULD; ensure that any Date header field present in a
     6231   message conforms to one of the HTTP/1.1 formats and rewrite the date
     6232   if necessary.
     6236<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
     6238   MIME does not include any concept equivalent to HTTP/1.1's
     6239   Content-Encoding header field. Since this acts as a modifier on the
     6240   media type, proxies and gateways from HTTP to MIME-compliant
     6241   protocols &MUST; either change the value of the Content-Type header
     6242   field or decode the representation before forwarding the message. (Some
     6243   experimental applications of Content-Type for Internet mail have used
     6244   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
     6245   a function equivalent to Content-Encoding. However, this parameter is
     6246   not part of the MIME standards).
     6250<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
     6251  <iref item="Content-Transfer-Encoding header field" x:for-anchor=""/>
     6252  <iref item="Header Fields" subitem="Content-Transfer-Encoding" x:for-anchor=""/>
     6254   HTTP does not use the Content-Transfer-Encoding field of MIME.
     6255   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
     6256   remove any Content-Transfer-Encoding
     6257   prior to delivering the response message to an HTTP client.
     6260   Proxies and gateways from HTTP to MIME-compliant protocols are
     6261   responsible for ensuring that the message is in the correct format
     6262   and encoding for safe transport on that protocol, where "safe
     6263   transport" is defined by the limitations of the protocol being used.
     6264   Such a proxy or gateway &SHOULD; label the data with an appropriate
     6265   Content-Transfer-Encoding if doing so will improve the likelihood of
     6266   safe transport over the destination protocol.
     6270<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
     6272   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
     6273   Proxies/gateways &MUST; remove any transfer-coding prior to
     6274   forwarding a message via a MIME-compliant protocol.
     6278<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
     6280   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
     6281   need to be aware of MIME line length limitations. Since HTTP does not
     6282   have this limitation, HTTP does not fold long lines. MHTML messages
     6283   being transported by HTTP follow all conventions of MHTML, including
     6284   line length limitations and folding, canonicalization, etc., since
     6285   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
     6286   does not interpret the content or any MIME header lines that might be
     6287   contained therein.
     6292<section title="Additional Features" anchor="additional.features">
     6294   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
     6295   existing HTTP implementations, but not consistently and correctly
     6296   across most HTTP/1.1 applications. Implementors are advised to be
     6297   aware of these features, but cannot rely upon their presence in, or
     6298   interoperability with, other HTTP/1.1 applications. Some of these
     6299   describe proposed experimental features, and some describe features
     6300   that experimental deployment found lacking that are now addressed in
     6301   the base HTTP/1.1 specification.
     6304   A number of other header fields, such as Content-Disposition and Title,
     6305   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
     6306   and <xref target="RFC2076"/>).
     6310<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616-3">
     6312  Clarify contexts that charset is used in.
     6313  (<xref target="character.sets"/>)
     6316  Registration of Content Codings now requires IETF Review
     6317  (<xref target="content.coding.registry"/>)
     6320  Remove the default character encoding for text media types; the default
     6321  now is whatever the media type definition says.
     6322  (<xref target="canonicalization.and.text.defaults"/>)
     6325  Change ABNF productions for header fields to only define the field value.
     6326  (<xref target="header.field.definitions"/>)
     6329  Remove definition of Content-MD5 header field because it was inconsistently
     6330  implemented with respect to partial responses, and also because of known
     6331  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
     6332  (<xref target="header.field.definitions"/>)
     6335  Remove ISO-8859-1 special-casing in Accept-Charset.
     6336  (<xref target="header.accept-charset"/>)
     6339  Remove base URI setting semantics for Content-Location due to poor
     6340  implementation support, which was caused by too many broken servers emitting
     6341  bogus Content-Location header fields, and also the potentially undesirable effect
     6342  of potentially breaking relative links in content-negotiated resources.
     6343  (<xref target="header.content-location"/>)
     6346  Remove reference to non-existant identity transfer-coding value tokens.
     6347  (<xref target="no.content-transfer-encoding"/>)
     6350  Remove discussion of Content-Disposition header field, it is now defined
     6351  by <xref target="RFC6266"/>.
     6352  (<xref target="additional.features"/>)
     6356<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log3">
     6358<section title="Since RFC 2616">
     6360  Extracted relevant partitions from <xref target="RFC2616"/>.
     6364<section title="Since draft-ietf-httpbis-p3-payload-00">
     6366  Closed issues:
     6367  <list style="symbols">
     6368    <t>
     6369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
     6370      "Media Type Registrations"
     6371      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
     6372    </t>
     6373    <t>
     6374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
     6375      "Clarification regarding quoting of charset values"
     6376      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
     6377    </t>
     6378    <t>
     6379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
     6380      "Remove 'identity' token references"
     6381      (<eref target="http://purl.org/NET/http-errata#identity"/>)
     6382    </t>
     6383    <t>
     6384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
     6385      "Accept-Encoding BNF"
     6386    </t>
     6387    <t>
     6388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
     6389      "Normative and Informative references"
     6390    </t>
     6391    <t>
     6392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
     6393      "RFC1700 references"
     6394    </t>
     6395    <t>
     6396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
     6397      "Updating to RFC4288"
     6398    </t>
     6399    <t>
     6400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
     6401      "Informative references"
     6402    </t>
     6403    <t>
     6404      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
     6405      "ISO-8859-1 Reference"
     6406    </t>
     6407    <t>
     6408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
     6409      "Encoding References Normative"
     6410    </t>
     6411    <t>
     6412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
     6413      "Normative up-to-date references"
     6414    </t>
     6415  </list>
     6419<section title="Since draft-ietf-httpbis-p3-payload-01">
     6421  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
     6422  <list style="symbols">
     6423    <t>
     6424      Add explicit references to BNF syntax and rules imported from other parts of the specification.
     6425    </t>
     6426  </list>
     6430<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.3.since.02">
     6432  Closed issues:
     6433  <list style="symbols">
     6434    <t>
     6435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
     6436      "Quoting Charsets"
     6437    </t>
     6438    <t>
     6439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
     6440      "Classification for Allow header"
     6441    </t>
     6442    <t>
     6443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
     6444      "missing default for qvalue in description of Accept-Encoding"
     6445    </t>
     6446  </list>
     6449  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
     6450  <list style="symbols">
     6451    <t>
     6452      Reference RFC 3984, and update header field registrations for headers defined
     6453      in this document.
     6454    </t>
     6455  </list>
     6459<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.3.since.03">
     6461  Closed issues:
     6462  <list style="symbols">
     6463    <t>
     6464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
     6465      "Quoting Charsets"
     6466    </t>
     6467    <t>
     6468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
     6469      "language tag matching (Accept-Language) vs RFC4647"
     6470    </t>
     6471    <t>
     6472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
     6473      "RFC 1806 has been replaced by RFC2183"
     6474    </t>
     6475  </list>
     6478  Other changes:
     6479  <list style="symbols">
     6480    <t>
     6481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
     6482      "Encoding References Normative" &mdash; rephrase the annotation and reference
     6483      BCP97.
     6484    </t>
     6485  </list>
     6487 </section>
     6489<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.3.since.04">
     6491  Closed issues:
     6492  <list style="symbols">
     6493    <t>
     6494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
     6495      "RFC 2822 is updated by RFC 5322"
     6496    </t>
     6497  </list>
     6500  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
     6501  <list style="symbols">
     6502    <t>
     6503      Use "/" instead of "|" for alternatives.
     6504    </t>
     6505    <t>
     6506      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
     6507      whitespace ("OWS") and required whitespace ("RWS").
     6508    </t>
     6509    <t>
     6510      Rewrite ABNFs to spell out whitespace rules, factor out
     6511      header field value format definitions.
     6512    </t>
     6513  </list>
     6517<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.3.since.05">
     6519  Closed issues:
     6520  <list style="symbols">
     6521    <t>
     6522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
     6523      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
     6524    </t>
     6525  </list>
     6528  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
     6529  <list style="symbols">
     6530    <t>
     6531      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
     6532    </t>
     6533  </list>
     6536  Other changes:
     6537  <list style="symbols">
     6538    <t>
     6539      Move definition of quality values into Part 1.
     6540    </t>
     6541  </list>
     6545<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.3.since.06">
     6547  Closed issues:
     6548  <list style="symbols">
     6549    <t>
     6550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
     6551      "Content-Location isn't special"
     6552    </t>
     6553    <t>
     6554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
     6555      "Content Sniffing"
     6556    </t>
     6557  </list>
     6561<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.3.since.07">
     6563  Closed issues:
     6564  <list style="symbols">
     6565    <t>
     6566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
     6567      "Updated reference for language tags"
     6568    </t>
     6569    <t>
     6570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
     6571      "Clarify rules for determining what entities a response carries"
     6572    </t>
     6573    <t>
     6574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
     6575      "Content-Location base-setting problems"
     6576    </t>
     6577    <t>
     6578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
     6579      "Content Sniffing"
     6580    </t>
     6581    <t>
     6582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
     6583      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
     6584    </t>
     6585    <t>
     6586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
     6587      "move definitions of gzip/deflate/compress to part 1"
     6588    </t>
     6589  </list>
     6592  Partly resolved issues:
     6593  <list style="symbols">
     6594    <t>
     6595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
     6596      "update IANA requirements wrt Transfer-Coding values" (add the
     6597      IANA Considerations subsection)
     6598    </t>
     6599    <t>
     6600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
     6601      "update IANA requirements wrt Content-Coding values" (add the
     6602      IANA Considerations subsection)
     6603    </t>
     6604  </list>
     6608<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.3.since.08">
     6610  Closed issues:
     6611  <list style="symbols">
     6612    <t>
     6613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
     6614      "Content Negotiation for media types"
     6615    </t>
     6616    <t>
     6617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
     6618      "Accept-Language: which RFC4647 filtering?"
     6619    </t>
     6620  </list>
     6624<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.3.since.09">
     6626  Closed issues:
     6627  <list style="symbols">
     6628    <t>
     6629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
     6630      "MIME-Version not listed in P1, general header fields"
     6631    </t>
     6632    <t>
     6633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
     6634      "IANA registry for content/transfer encodings"
     6635    </t>
     6636    <t>
     6637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
     6638      "Content Sniffing"
     6639    </t>
     6640    <t>
     6641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
     6642      "use of term "word" when talking about header structure"
     6643    </t>
     6644  </list>
     6647  Partly resolved issues:
     6648  <list style="symbols">
     6649    <t>
     6650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
     6651      "Term for the requested resource's URI"
     6652    </t>
     6653  </list>
     6657<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.3.since.10">
     6659  Closed issues:
     6660  <list style="symbols">
     6661    <t>
     6662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
     6663      "Clarify 'Requested Variant'"
     6664    </t>
     6665    <t>
     6666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
     6667      "Content-Location isn't special"
     6668    </t>
     6669    <t>
     6670      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
     6671      "Delimiting messages with multipart/byteranges"
     6672    </t>
     6673    <t>
     6674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
     6675      "Clarify entity / representation / variant terminology"
     6676    </t>
     6677    <t>
     6678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
     6679      "confusing req. language for Content-Location"
     6680    </t>
     6681    <t>
     6682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
     6683      "Content-Location on 304 responses"
     6684    </t>
     6685    <t>
     6686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
     6687      "'requested resource' in content-encoding definition"
     6688    </t>
     6689    <t>
     6690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
     6691      "consider removing the 'changes from 2068' sections"
     6692    </t>
     6693  </list>
     6696  Partly resolved issues:
     6697  <list style="symbols">
     6698    <t>
     6699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
     6700      "Content-MD5 and partial responses"
     6701    </t>
     6702  </list>
     6706<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.3.since.11">
     6708  Closed issues:
     6709  <list style="symbols">
     6710    <t>
     6711      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
     6712      "Factor out Content-Disposition"
     6713    </t>
     6714  </list>
     6718<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.3.since.12">
     6720  Closed issues:
     6721  <list style="symbols">
     6722    <t>
     6723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
     6724      "Header Classification"
     6725    </t>
     6726    <t>
     6727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
     6728      "untangle ABNFs for header fields"
     6729    </t>
     6730    <t>
     6731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
     6732      "potentially misleading MAY in media-type def"
     6733    </t>
     6734  </list>
     6738<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.3.since.13">
     6740  Closed issues:
     6741  <list style="symbols">
     6742    <t>
     6743      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
     6744      "Default charsets for text media types"
     6745    </t>
     6746    <t>
     6747      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
     6748      "Content-MD5 and partial responses"
     6749    </t>
     6750    <t>
     6751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
     6752      "untangle ABNFs for header fields"
     6753    </t>
     6754    <t>
     6755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
     6756      "confusing undefined parameter in media range example"
     6757    </t>
     6758  </list>
     6762<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.3.since.14">
     6764  None.
     6768<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.3.since.15">
     6770  Closed issues:
     6771  <list style="symbols">
     6772    <t>
     6773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
     6774      "Strength of requirements on Accept re: 406"
     6775    </t>
     6776  </list>
     6780<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.3.since.16">
     6782  Closed issues:
     6783  <list style="symbols">
     6784    <t>
     6785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
     6786      "Document HTTP's error-handling philosophy"
     6787    </t>
     6788  </list>
     6792<section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.3.since.17">
     6794  Closed issues:
     6795  <list style="symbols">
     6796    <t>
     6797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
     6798      "intended maturity level vs normative references"
     6799    </t>
     6800  </list>
     6804<section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.3.since.18">
     6806  Closed issues:
     6807  <list style="symbols">
     6808    <t>
     6809      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
     6810      "is ETag a representation header field?"
     6811    </t>
     6812    <t>
     6813      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/338"/>:
     6814      "Content-Location doesn't constrain the cardinality of representations"
     6815    </t>
     6816    <t>
     6817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
     6818      "make IANA policy definitions consistent"
     6819    </t>
     6820  </list>
     6824<section title="Since draft-ietf-httpbis-p3-payload-19" anchor="changes.3.since.19">
     6826  None yet.
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