Ignore:
Timestamp:
Feb 6, 2008, 11:15:29 AM (12 years ago)
Author:
julian.reschke@…
Message:

Add sections that for now normatively reference the ABNF syntax and basic rules from Part1, also start work on referencing ABNF rules adopted from other parts (ongoing); relates to #36.

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1 edited

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  • draft-ietf-httpbis/latest/p4-conditional.html

    r204 r205  
    333333      <link rel="Index" href="#rfc.index">
    334334      <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
    335       <link rel="Chapter" title="2 Entity Tags" href="#rfc.section.2">
    336       <link rel="Chapter" title="3 Status Code Definitions" href="#rfc.section.3">
    337       <link rel="Chapter" title="4 Weak and Strong Validators" href="#rfc.section.4">
    338       <link rel="Chapter" title="5 Rules for When to Use Entity Tags and Last-Modified Dates" href="#rfc.section.5">
    339       <link rel="Chapter" title="6 Header Field Definitions" href="#rfc.section.6">
    340       <link rel="Chapter" title="7 IANA Considerations" href="#rfc.section.7">
    341       <link rel="Chapter" title="8 Security Considerations" href="#rfc.section.8">
    342       <link rel="Chapter" title="9 Acknowledgments" href="#rfc.section.9">
    343       <link rel="Chapter" href="#rfc.section.10" title="10 References">
     335      <link rel="Chapter" title="2 Notational Conventions and Generic Grammar" href="#rfc.section.2">
     336      <link rel="Chapter" title="3 Entity Tags" href="#rfc.section.3">
     337      <link rel="Chapter" title="4 Status Code Definitions" href="#rfc.section.4">
     338      <link rel="Chapter" title="5 Weak and Strong Validators" href="#rfc.section.5">
     339      <link rel="Chapter" title="6 Rules for When to Use Entity Tags and Last-Modified Dates" href="#rfc.section.6">
     340      <link rel="Chapter" title="7 Header Field Definitions" href="#rfc.section.7">
     341      <link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8">
     342      <link rel="Chapter" title="9 Security Considerations" href="#rfc.section.9">
     343      <link rel="Chapter" title="10 Acknowledgments" href="#rfc.section.10">
     344      <link rel="Chapter" href="#rfc.section.11" title="11 References">
    344345      <link rel="Appendix" title="A Compatibility with Previous Versions" href="#rfc.section.A">
    345346      <link rel="Appendix" title="B Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.B">
     
    482483            </ul>
    483484         </li>
    484          <li class="tocline0">2.&nbsp;&nbsp;&nbsp;<a href="#entity.tags">Entity Tags</a></li>
    485          <li class="tocline0">3.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3">Status Code Definitions</a><ul class="toc">
    486                <li class="tocline1">3.1&nbsp;&nbsp;&nbsp;<a href="#status.304">304 Not Modified</a></li>
    487                <li class="tocline1">3.2&nbsp;&nbsp;&nbsp;<a href="#status.412">412 Precondition Failed</a></li>
     485         <li class="tocline0">2.&nbsp;&nbsp;&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a></li>
     486         <li class="tocline0">3.&nbsp;&nbsp;&nbsp;<a href="#entity.tags">Entity Tags</a></li>
     487         <li class="tocline0">4.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.4">Status Code Definitions</a><ul class="toc">
     488               <li class="tocline1">4.1&nbsp;&nbsp;&nbsp;<a href="#status.304">304 Not Modified</a></li>
     489               <li class="tocline1">4.2&nbsp;&nbsp;&nbsp;<a href="#status.412">412 Precondition Failed</a></li>
    488490            </ul>
    489491         </li>
    490          <li class="tocline0">4.&nbsp;&nbsp;&nbsp;<a href="#weak.and.strong.validators">Weak and Strong Validators</a></li>
    491          <li class="tocline0">5.&nbsp;&nbsp;&nbsp;<a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></li>
    492          <li class="tocline0">6.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul class="toc">
    493                <li class="tocline1">6.1&nbsp;&nbsp;&nbsp;<a href="#header.etag">ETag</a></li>
    494                <li class="tocline1">6.2&nbsp;&nbsp;&nbsp;<a href="#header.if-match">If-Match</a></li>
    495                <li class="tocline1">6.3&nbsp;&nbsp;&nbsp;<a href="#header.if-modified-since">If-Modified-Since</a></li>
    496                <li class="tocline1">6.4&nbsp;&nbsp;&nbsp;<a href="#header.if-none-match">If-None-Match</a></li>
    497                <li class="tocline1">6.5&nbsp;&nbsp;&nbsp;<a href="#header.if-unmodified-since">If-Unmodified-Since</a></li>
    498                <li class="tocline1">6.6&nbsp;&nbsp;&nbsp;<a href="#header.last-modified">Last-Modified</a></li>
     492         <li class="tocline0">5.&nbsp;&nbsp;&nbsp;<a href="#weak.and.strong.validators">Weak and Strong Validators</a></li>
     493         <li class="tocline0">6.&nbsp;&nbsp;&nbsp;<a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></li>
     494         <li class="tocline0">7.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul class="toc">
     495               <li class="tocline1">7.1&nbsp;&nbsp;&nbsp;<a href="#header.etag">ETag</a></li>
     496               <li class="tocline1">7.2&nbsp;&nbsp;&nbsp;<a href="#header.if-match">If-Match</a></li>
     497               <li class="tocline1">7.3&nbsp;&nbsp;&nbsp;<a href="#header.if-modified-since">If-Modified-Since</a></li>
     498               <li class="tocline1">7.4&nbsp;&nbsp;&nbsp;<a href="#header.if-none-match">If-None-Match</a></li>
     499               <li class="tocline1">7.5&nbsp;&nbsp;&nbsp;<a href="#header.if-unmodified-since">If-Unmodified-Since</a></li>
     500               <li class="tocline1">7.6&nbsp;&nbsp;&nbsp;<a href="#header.last-modified">Last-Modified</a></li>
    499501            </ul>
    500502         </li>
    501          <li class="tocline0">7.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a></li>
    502          <li class="tocline0">8.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a></li>
    503          <li class="tocline0">9.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
    504          <li class="tocline0">10.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul class="toc">
    505                <li class="tocline1">10.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
    506                <li class="tocline1">10.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
     503         <li class="tocline0">8.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a></li>
     504         <li class="tocline0">9.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a></li>
     505         <li class="tocline0">10.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
     506         <li class="tocline0">11.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul class="toc">
     507               <li class="tocline1">11.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
     508               <li class="tocline1">11.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
    507509            </ul>
    508510         </li>
     
    541543      <p id="rfc.section.1.1.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant."
    542544      </p>
    543       <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="entity.tags" href="#entity.tags">Entity Tags</a></h1>
    544       <p id="rfc.section.2.p.1">Entity tags are used for comparing two or more entities from the same requested resource. HTTP/1.1 uses entity tags in the
    545          ETag (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;6.1</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section&nbsp;6.2</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section&nbsp;6.4</a>), and If-Range (<a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;4</a>. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.
    546       </p>
    547       <div id="rfc.figure.u.1"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  entity-tag = [ weak ] opaque-tag
     545      <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="notation" href="#notation">Notational Conventions and Generic Grammar</a></h1>
     546      <p id="rfc.section.2.p.1">This specification uses the ABNF syntax defined in <a href="p1-messaging.html#notation.abnf" title="Augmented BNF">Section 2.1</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> and the core rules defined in <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 2.2</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>: <span class="comment">[abnf.dep: ABNF syntax and basic rules will be adopted from RFC 5234, see &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>&gt;.]</span>
     547      </p>
     548      <div id="rfc.figure.u.1"></div><pre class="inline">  quoted-string = &lt;quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 2.2</a>&gt;
     549</pre><p id="rfc.section.2.p.3">The ABNF rules below are defined in other parts:</p>
     550      <div id="rfc.figure.u.2"></div><pre class="inline">  HTTP-date     = &lt;HTTP-date, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#full.date" title="Full Date">Section 3.3.1</a>&gt;
     551</pre><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="entity.tags" href="#entity.tags">Entity Tags</a></h1>
     552      <p id="rfc.section.3.p.1">Entity tags are used for comparing two or more entities from the same requested resource. HTTP/1.1 uses entity tags in the
     553         ETag (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;7.1</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section&nbsp;7.2</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section&nbsp;7.4</a>), and If-Range (<a href="p5-range.html#header.if-range" title="If-Range">Section 6.3</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;5</a>. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.
     554      </p>
     555      <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  entity-tag = [ weak ] opaque-tag
    548556  weak       = "W/"
    549557  opaque-tag = quoted-string
    550 </pre><p id="rfc.section.2.p.3">A "strong entity tag" <em class="bcp14">MAY</em> be shared by two entities of a resource only if they are equivalent by octet equality.
    551       </p>
    552       <p id="rfc.section.2.p.4">A "weak entity tag," indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no
     558</pre><p id="rfc.section.3.p.3">A "strong entity tag" <em class="bcp14">MAY</em> be shared by two entities of a resource only if they are equivalent by octet equality.
     559      </p>
     560      <p id="rfc.section.3.p.4">A "weak entity tag," indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no
    553561         significant change in semantics. A weak entity tag can only be used for weak comparison.
    554562      </p>
    555       <p id="rfc.section.2.p.5">An entity tag <em class="bcp14">MUST</em> be unique across all versions of all entities associated with a particular resource. A given entity tag value <em class="bcp14">MAY</em> be used for entities obtained by requests on different URIs. The use of the same entity tag value in conjunction with entities
     563      <p id="rfc.section.3.p.5">An entity tag <em class="bcp14">MUST</em> be unique across all versions of all entities associated with a particular resource. A given entity tag value <em class="bcp14">MAY</em> be used for entities obtained by requests on different URIs. The use of the same entity tag value in conjunction with entities
    556564         obtained by requests on different URIs does not imply the equivalence of those entities.
    557565      </p>
    558       <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;Status Code Definitions
     566      <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;Status Code Definitions
    559567      </h1>
    560568      <div id="rfc.iref.3"></div>
    561569      <div id="rfc.iref.s.1"></div>
    562       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="status.304" href="#status.304">304 Not Modified</a></h2>
    563       <p id="rfc.section.3.1.p.1">If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server <em class="bcp14">SHOULD</em> respond with this status code. The 304 response <em class="bcp14">MUST NOT</em> contain a message-body, and thus is always terminated by the first empty line after the header fields.
    564       </p>
    565       <p id="rfc.section.3.1.p.2">The response <em class="bcp14">MUST</em> include the following header fields:
     570      <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="status.304" href="#status.304">304 Not Modified</a></h2>
     571      <p id="rfc.section.4.1.p.1">If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server <em class="bcp14">SHOULD</em> respond with this status code. The 304 response <em class="bcp14">MUST NOT</em> contain a message-body, and thus is always terminated by the first empty line after the header fields.
     572      </p>
     573      <p id="rfc.section.4.1.p.2">The response <em class="bcp14">MUST</em> include the following header fields:
    566574      </p>
    567575      <ul>
    568          <li>Date, unless its omission is required by <a href="p1-messaging.html#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 8.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a></li>
     576         <li>Date, unless its omission is required by <a href="p1-messaging.html#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 8.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a></li>
    569577      </ul>
    570       <p id="rfc.section.3.1.p.3">If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without
     578      <p id="rfc.section.4.1.p.3">If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without
    571579         one (as already specified by <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, <a href="http://tools.ietf.org/html/rfc2068#section-14.19">Section 14.19</a>), caches will operate correctly.
    572580      </p>
     
    577585         </li>
    578586      </ul>
    579       <p id="rfc.section.3.1.p.4">If the conditional GET used a strong cache validator (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;4</a>), the response <em class="bcp14">SHOULD NOT</em> include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response <em class="bcp14">MUST NOT</em> include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers.
    580       </p>
    581       <p id="rfc.section.3.1.p.5">If a 304 response indicates an entity not currently cached, then the cache <em class="bcp14">MUST</em> disregard the response and repeat the request without the conditional.
    582       </p>
    583       <p id="rfc.section.3.1.p.6">If a cache uses a received 304 response to update a cache entry, the cache <em class="bcp14">MUST</em> update the entry to reflect any new field values given in the response.
     587      <p id="rfc.section.4.1.p.4">If the conditional GET used a strong cache validator (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;5</a>), the response <em class="bcp14">SHOULD NOT</em> include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response <em class="bcp14">MUST NOT</em> include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers.
     588      </p>
     589      <p id="rfc.section.4.1.p.5">If a 304 response indicates an entity not currently cached, then the cache <em class="bcp14">MUST</em> disregard the response and repeat the request without the conditional.
     590      </p>
     591      <p id="rfc.section.4.1.p.6">If a cache uses a received 304 response to update a cache entry, the cache <em class="bcp14">MUST</em> update the entry to reflect any new field values given in the response.
    584592      </p>
    585593      <div id="rfc.iref.4"></div>
    586594      <div id="rfc.iref.s.2"></div>
    587       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="status.412" href="#status.412">412 Precondition Failed</a></h2>
    588       <p id="rfc.section.3.2.p.1">The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This
     595      <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="status.412" href="#status.412">412 Precondition Failed</a></h2>
     596      <p id="rfc.section.4.2.p.1">The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This
    589597         response code allows the client to place preconditions on the current resource metainformation (header field data) and thus
    590598         prevent the requested method from being applied to a resource other than the one intended.
    591599      </p>
    592       <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak and Strong Validators</a></h1>
    593       <p id="rfc.section.4.p.1">Since both origin servers and caches will compare two validators to decide if they represent the same or different entities,
     600      <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak and Strong Validators</a></h1>
     601      <p id="rfc.section.5.p.1">Since both origin servers and caches will compare two validators to decide if they represent the same or different entities,
    594602         one normally would expect that if the entity (the entity-body or any entity-headers) changes in any way, then the associated
    595603         validator would change as well. If this is true, then we call this validator a "strong validator."
    596604      </p>
    597       <p id="rfc.section.4.p.2">However, there might be cases when a server prefers to change the validator only on semantically significant changes, and
     605      <p id="rfc.section.5.p.2">However, there might be cases when a server prefers to change the validator only on semantically significant changes, and
    598606         not when insignificant aspects of the entity change. A validator that does not always change when the resource changes is
    599607         a "weak validator."
    600608      </p>
    601       <p id="rfc.section.4.p.3">Entity tags are normally "strong validators," but the protocol provides a mechanism to tag an entity tag as "weak." One can
     609      <p id="rfc.section.5.p.3">Entity tags are normally "strong validators," but the protocol provides a mechanism to tag an entity tag as "weak." One can
    602610         think of a strong validator as one that changes whenever the bits of an entity changes, while a weak value changes whenever
    603611         the meaning of an entity changes. Alternatively, one can think of a strong validator as part of an identifier for a specific
     
    615623         </dd>
    616624      </dl>
    617       <p id="rfc.section.4.p.4">A "use" of a validator is either when a client generates a request and includes the validator in a validating header field,
     625      <p id="rfc.section.5.p.4">A "use" of a validator is either when a client generates a request and includes the validator in a validating header field,
    618626         or when a server compares two validators.
    619627      </p>
    620       <p id="rfc.section.4.p.5">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality
     628      <p id="rfc.section.5.p.5">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality
    621629         of an entity. For example, either kind is usable for a conditional GET of a full entity. However, only a strong validator
    622630         is usable for a sub-range retrieval, since otherwise the client might end up with an internally inconsistent entity.
    623631      </p>
    624       <p id="rfc.section.4.p.6">Clients <em class="bcp14">MAY</em> issue simple (non-subrange) GET requests with either weak validators or strong validators. Clients <em class="bcp14">MUST NOT</em> use weak validators in other forms of request.
    625       </p>
    626       <p id="rfc.section.4.p.7">The only function that HTTP/1.1 defines on validators is comparison. There are two validator comparison functions, depending
     632      <p id="rfc.section.5.p.6">Clients <em class="bcp14">MAY</em> issue simple (non-subrange) GET requests with either weak validators or strong validators. Clients <em class="bcp14">MUST NOT</em> use weak validators in other forms of request.
     633      </p>
     634      <p id="rfc.section.5.p.7">The only function that HTTP/1.1 defines on validators is comparison. There are two validator comparison functions, depending
    627635         on whether the comparison context allows the use of weak validators or not:
    628636      </p>
     
    633641         </li>
    634642      </ul>
    635       <p id="rfc.section.4.p.8">An entity tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity Tags">Section&nbsp;2</a> gives the syntax for entity tags.
    636       </p>
    637       <p id="rfc.section.4.p.9">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is
     643      <p id="rfc.section.5.p.8">An entity tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity Tags">Section&nbsp;3</a> gives the syntax for entity tags.
     644      </p>
     645      <p id="rfc.section.5.p.9">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is
    638646         strong, using the following rules:
    639647      </p>
     
    644652         </li>
    645653      </ul>
    646       <p id="rfc.section.4.p.10">or </p>
     654      <p id="rfc.section.5.p.10">or </p>
    647655      <ul>
    648656         <li>The validator is about to be used by a client in an If-Modified-Since or If-Unmodified-Since header, because the client has
     
    652660         <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li>
    653661      </ul>
    654       <p id="rfc.section.4.p.11">or </p>
     662      <p id="rfc.section.5.p.11">or </p>
    655663      <ul>
    656664         <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the entity, and</li>
     
    658666         <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li>
    659667      </ul>
    660       <p id="rfc.section.4.p.12">This method relies on the fact that if two different responses were sent by the origin server during the same second, but
     668      <p id="rfc.section.5.p.12">This method relies on the fact that if two different responses were sent by the origin server during the same second, but
    661669         both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified
    662670         time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from
    663671         different clocks, or at somewhat different times during the preparation of the response. An implementation <em class="bcp14">MAY</em> use a value larger than 60 seconds, if it is believed that 60 seconds is too short.
    664672      </p>
    665       <p id="rfc.section.4.p.13">If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator,
     673      <p id="rfc.section.5.p.13">If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator,
    666674         it <em class="bcp14">MAY</em> do this only if the Last-Modified time is strong in the sense described here.
    667675      </p>
    668       <p id="rfc.section.4.p.14">A cache or origin server receiving a conditional request, other than a full-body GET request, <em class="bcp14">MUST</em> use the strong comparison function to evaluate the condition.
    669       </p>
    670       <p id="rfc.section.4.p.15">These rules allow HTTP/1.1 caches and clients to safely perform sub-range retrievals on values that have been obtained from
     676      <p id="rfc.section.5.p.14">A cache or origin server receiving a conditional request, other than a full-body GET request, <em class="bcp14">MUST</em> use the strong comparison function to evaluate the condition.
     677      </p>
     678      <p id="rfc.section.5.p.15">These rules allow HTTP/1.1 caches and clients to safely perform sub-range retrievals on values that have been obtained from
    671679         HTTP/1.0 servers.
    672680      </p>
    673       <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></h1>
    674       <p id="rfc.section.5.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types
     681      <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></h1>
     682      <p id="rfc.section.6.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types
    675683         ought to be used, and for what purposes.
    676684      </p>
    677       <p id="rfc.section.5.p.2">HTTP/1.1 origin servers: </p>
     685      <p id="rfc.section.6.p.2">HTTP/1.1 origin servers: </p>
    678686      <ul>
    679687         <li><em class="bcp14">SHOULD</em> send an entity tag validator unless it is not feasible to generate one.
     
    686694         </li>
    687695      </ul>
    688       <p id="rfc.section.5.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity tag and a Last-Modified
     696      <p id="rfc.section.6.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity tag and a Last-Modified
    689697         value.
    690698      </p>
    691       <p id="rfc.section.5.p.4">In order to be legal, a strong entity tag <em class="bcp14">MUST</em> change whenever the associated entity value changes in any way. A weak entity tag <em class="bcp14">SHOULD</em> change whenever the associated entity changes in a semantically significant way.
     699      <p id="rfc.section.6.p.4">In order to be legal, a strong entity tag <em class="bcp14">MUST</em> change whenever the associated entity value changes in any way. A weak entity tag <em class="bcp14">SHOULD</em> change whenever the associated entity changes in a semantically significant way.
    692700      </p>
    693701      <dl class="empty">
     
    698706         </dd>
    699707      </dl>
    700       <p id="rfc.section.5.p.5">HTTP/1.1 clients: </p>
     708      <p id="rfc.section.6.p.5">HTTP/1.1 clients: </p>
    701709      <ul>
    702710         <li>If an entity tag has been provided by the origin server, <em class="bcp14">MUST</em> use that entity tag in any cache-conditional request (using If-Match or If-None-Match).
     
    709717         </li>
    710718      </ul>
    711       <p id="rfc.section.5.p.6">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since
     719      <p id="rfc.section.6.p.6">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since
    712720         or If-Unmodified-Since header field) and one or more entity tags (e.g., in an If-Match, If-None-Match, or If-Range header
    713721         field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields in
    714722         the request.
    715723      </p>
    716       <p id="rfc.section.5.p.7">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity
     724      <p id="rfc.section.6.p.7">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity
    717725         tags as cache validators, <em class="bcp14">MUST NOT</em> return a locally cached response to the client unless that cached response is consistent with all of the conditional header
    718726         fields in the request.
     
    729737         </dd>
    730738      </dl>
    731       <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
    732       <p id="rfc.section.6.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to conditional requests.</p>
    733       <p id="rfc.section.6.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who
     739      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
     740      <p id="rfc.section.7.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to conditional requests.</p>
     741      <p id="rfc.section.7.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who
    734742         receives the entity.
    735743      </p>
    736744      <div id="rfc.iref.e.1"></div>
    737745      <div id="rfc.iref.h.1"></div>
    738       <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="header.etag" href="#header.etag">ETag</a></h2>
    739       <p id="rfc.section.6.1.p.1">The ETag response-header field provides the current value of the entity tag for the requested variant. The headers used with
    740          entity tags are described in Sections <a href="#header.if-match" id="rfc.xref.header.if-match.2" title="If-Match">6.2</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">6.4</a> of this document, and in <a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. The entity tag <em class="bcp14">MAY</em> be used for comparison with other entities from the same resource (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;4</a>).
    741       </p>
    742       <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.4"></span>  ETag = "ETag" ":" entity-tag
    743 </pre><div id="rfc.figure.u.3"></div>
     746      <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="header.etag" href="#header.etag">ETag</a></h2>
     747      <p id="rfc.section.7.1.p.1">The ETag response-header field provides the current value of the entity tag for the requested variant. The headers used with
     748         entity tags are described in Sections <a href="#header.if-match" id="rfc.xref.header.if-match.2" title="If-Match">7.2</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">7.4</a> of this document, and in <a href="p5-range.html#header.if-range" title="If-Range">Section 6.3</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. The entity tag <em class="bcp14">MAY</em> be used for comparison with other entities from the same resource (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;5</a>).
     749      </p>
     750      <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.4"></span>  ETag = "ETag" ":" entity-tag
     751</pre><div id="rfc.figure.u.5"></div>
    744752      <p>Examples:</p>  <pre class="text">   ETag: "xyzzy"
    745753   ETag: W/"xyzzy"
    746754   ETag: ""
    747 </pre><p id="rfc.section.6.1.p.4">The ETag response-header field value, an entity tag, provides for an "opaque" cache validator. This might allow more reliable
     755</pre><p id="rfc.section.7.1.p.4">The ETag response-header field value, an entity tag, provides for an "opaque" cache validator. This might allow more reliable
    748756         validation in situations where it is inconvenient to store modification dates, where the one-second resolution of HTTP date
    749757         values is not sufficient, or where the origin server wishes to avoid certain paradoxes that might arise from the use of modification
    750758         dates.
    751759      </p>
    752       <p id="rfc.section.6.1.p.5">The principle behind entity tags is that only the service author knows the semantics of a resource well enough to select an
     760      <p id="rfc.section.7.1.p.5">The principle behind entity tags is that only the service author knows the semantics of a resource well enough to select an
    753761         appropriate cache validation mechanism, and the specification of any validator comparison function more complex than byte-equality
    754762         would open up a can of worms. Thus, comparisons of any other headers (except Last-Modified, for compatibility with HTTP/1.0)
     
    757765      <div id="rfc.iref.i.1"></div>
    758766      <div id="rfc.iref.h.2"></div>
    759       <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a id="header.if-match" href="#header.if-match">If-Match</a></h2>
    760       <p id="rfc.section.6.2.p.1">The If-Match request-header field is used with a method to make it conditional. A client that has one or more entities previously
     767      <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="header.if-match" href="#header.if-match">If-Match</a></h2>
     768      <p id="rfc.section.7.2.p.1">The If-Match request-header field is used with a method to make it conditional. A client that has one or more entities previously
    761769         obtained from the resource can verify that one of those entities is current by including a list of their associated entity
    762          tags in the If-Match header field. Entity tags are defined in <a href="#entity.tags" title="Entity Tags">Section&nbsp;2</a>. The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead.
     770         tags in the If-Match header field. Entity tags are defined in <a href="#entity.tags" title="Entity Tags">Section&nbsp;3</a>. The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead.
    763771         It is also used, on updating requests, to prevent inadvertent modification of the wrong version of a resource. As a special
    764772         case, the value "*" matches any current entity of the resource.
    765773      </p>
    766       <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.5"></span>  If-Match = "If-Match" ":" ( "*" | 1#entity-tag )
    767 </pre><p id="rfc.section.6.2.p.3">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET
     774      <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.5"></span>  If-Match = "If-Match" ":" ( "*" | 1#entity-tag )
     775</pre><p id="rfc.section.7.2.p.3">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET
    768776         request (without the If-Match header) on that resource, or if "*" is given and any current entity exists for that resource,
    769777         then the server <em class="bcp14">MAY</em> perform the requested method as if the If-Match header field did not exist.
    770778      </p>
    771       <p id="rfc.section.6.2.p.4">A server <em class="bcp14">MUST</em> use the strong comparison function (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;4</a>) to compare the entity tags in If-Match.
    772       </p>
    773       <p id="rfc.section.6.2.p.5">If none of the entity tags match, or if "*" is given and no current entity exists, the server <em class="bcp14">MUST NOT</em> perform the requested method, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed) response. This behavior is most useful when the client wants to prevent an updating method,
     779      <p id="rfc.section.7.2.p.4">A server <em class="bcp14">MUST</em> use the strong comparison function (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;5</a>) to compare the entity tags in If-Match.
     780      </p>
     781      <p id="rfc.section.7.2.p.5">If none of the entity tags match, or if "*" is given and no current entity exists, the server <em class="bcp14">MUST NOT</em> perform the requested method, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed) response. This behavior is most useful when the client wants to prevent an updating method,
    774782         such as PUT, from modifying a resource that has changed since the client last retrieved it.
    775783      </p>
    776       <p id="rfc.section.6.2.p.6">If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status, then the If-Match
     784      <p id="rfc.section.7.2.p.6">If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status, then the If-Match
    777785         header <em class="bcp14">MUST</em> be ignored.
    778786      </p>
    779       <p id="rfc.section.6.2.p.7">The meaning of "If-Match: *" is that the method <em class="bcp14">SHOULD</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 15.5</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">MUST NOT</em> be performed if the representation does not exist.
    780       </p>
    781       <p id="rfc.section.6.2.p.8">A request intended to update a resource (e.g., a PUT) <em class="bcp14">MAY</em> include an If-Match header field to signal that the request method <em class="bcp14">MUST NOT</em> be applied if the entity corresponding to the If-Match value (a single entity tag) is no longer a representation of that resource.
     787      <p id="rfc.section.7.2.p.7">The meaning of "If-Match: *" is that the method <em class="bcp14">SHOULD</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 16.5</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">MUST NOT</em> be performed if the representation does not exist.
     788      </p>
     789      <p id="rfc.section.7.2.p.8">A request intended to update a resource (e.g., a PUT) <em class="bcp14">MAY</em> include an If-Match header field to signal that the request method <em class="bcp14">MUST NOT</em> be applied if the entity corresponding to the If-Match value (a single entity tag) is no longer a representation of that resource.
    782790         This allows the user to indicate that they do not wish the request to be successful if the resource has been changed without
    783791         their knowledge. Examples:
    784792      </p>
    785       <div id="rfc.figure.u.5"></div><pre class="text">    If-Match: "xyzzy"
     793      <div id="rfc.figure.u.7"></div><pre class="text">    If-Match: "xyzzy"
    786794    If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
    787795    If-Match: *
    788 </pre><p id="rfc.section.6.2.p.10">The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since header fields
     796</pre><p id="rfc.section.7.2.p.10">The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since header fields
    789797         is undefined by this specification.
    790798      </p>
    791799      <div id="rfc.iref.i.2"></div>
    792800      <div id="rfc.iref.h.3"></div>
    793       <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a id="header.if-modified-since" href="#header.if-modified-since">If-Modified-Since</a></h2>
    794       <p id="rfc.section.6.3.p.1">The If-Modified-Since request-header field is used with a method to make it conditional: if the requested variant has not
     801      <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a>&nbsp;<a id="header.if-modified-since" href="#header.if-modified-since">If-Modified-Since</a></h2>
     802      <p id="rfc.section.7.3.p.1">The If-Modified-Since request-header field is used with a method to make it conditional: if the requested variant has not
    795803         been modified since the time specified in this field, an entity will not be returned from the server; instead, a 304 (Not
    796804         Modified) response will be returned without any message-body.
    797805      </p>
    798       <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  If-Modified-Since = "If-Modified-Since" ":" HTTP-date
    799 </pre><p id="rfc.section.6.3.p.3">An example of the field is:</p>
    800       <div id="rfc.figure.u.7"></div><pre class="text">    If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
    801 </pre><p id="rfc.section.6.3.p.5">A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred only
     806      <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  If-Modified-Since = "If-Modified-Since" ":" HTTP-date
     807</pre><p id="rfc.section.7.3.p.3">An example of the field is:</p>
     808      <div id="rfc.figure.u.9"></div><pre class="text">    If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
     809</pre><p id="rfc.section.7.3.p.5">A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred only
    802810         if it has been modified since the date given by the If-Modified-Since header. The algorithm for determining this includes
    803811         the following cases:
     
    811819         </li>
    812820      </ol>
    813       <p id="rfc.section.6.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p>
     821      <p id="rfc.section.7.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p>
    814822      <dl class="empty">
    815          <dd> <b>Note:</b> The Range request-header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details.
     823         <dd> <b>Note:</b> The Range request-header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 6.4</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details.
    816824         </dd>
    817825         <dd> <b>Note:</b> If-Modified-Since times are interpreted by the server, whose clock might not be synchronized with the client.
     
    831839         </dd>
    832840      </dl>
    833       <p id="rfc.section.6.3.p.7">The result of a request having both an If-Modified-Since header field and either an If-Match or an If-Unmodified-Since header
     841      <p id="rfc.section.7.3.p.7">The result of a request having both an If-Modified-Since header field and either an If-Match or an If-Unmodified-Since header
    834842         fields is undefined by this specification.
    835843      </p>
    836844      <div id="rfc.iref.i.3"></div>
    837845      <div id="rfc.iref.h.4"></div>
    838       <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a id="header.if-none-match" href="#header.if-none-match">If-None-Match</a></h2>
    839       <p id="rfc.section.6.4.p.1">The If-None-Match request-header field is used with a method to make it conditional. A client that has one or more entities
     846      <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a>&nbsp;<a id="header.if-none-match" href="#header.if-none-match">If-None-Match</a></h2>
     847      <p id="rfc.section.7.4.p.1">The If-None-Match request-header field is used with a method to make it conditional. A client that has one or more entities
    840848         previously obtained from the resource can verify that none of those entities is current by including a list of their associated
    841849         entity tags in the If-None-Match header field. The purpose of this feature is to allow efficient updates of cached information
     
    843851         an existing resource when the client believes that the resource does not exist.
    844852      </p>
    845       <p id="rfc.section.6.4.p.2">As a special case, the value "*" matches any current entity of the resource.</p>
    846       <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.7"></span>  If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag )
    847 </pre><p id="rfc.section.6.4.p.4">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET
     853      <p id="rfc.section.7.4.p.2">As a special case, the value "*" matches any current entity of the resource.</p>
     854      <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.7"></span>  If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag )
     855</pre><p id="rfc.section.7.4.p.4">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET
    848856         request (without the If-None-Match header) on that resource, or if "*" is given and any current entity exists for that resource,
    849857         then the server <em class="bcp14">MUST NOT</em> perform the requested method, unless required to do so because the resource's modification date fails to match that supplied
     
    851859         that matched. For all other request methods, the server <em class="bcp14">MUST</em> respond with a status of 412 (Precondition Failed).
    852860      </p>
    853       <p id="rfc.section.6.4.p.5">See <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;4</a> for rules on how to determine if two entities tags match. The weak comparison function can only be used with GET or HEAD requests.
    854       </p>
    855       <p id="rfc.section.6.4.p.6">If none of the entity tags match, then the server <em class="bcp14">MAY</em> perform the requested method as if the If-None-Match header field did not exist, but <em class="bcp14">MUST</em> also ignore any If-Modified-Since header field(s) in the request. That is, if no entity tags match, then the server <em class="bcp14">MUST NOT</em> return a 304 (Not Modified) response.
    856       </p>
    857       <p id="rfc.section.6.4.p.7">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status, then the
    858          If-None-Match header <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity Tags and Last-Modified Dates">Section&nbsp;5</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.)
    859       </p>
    860       <p id="rfc.section.6.4.p.8">The meaning of "If-None-Match: *" is that the method <em class="bcp14">MUST NOT</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 15.5</a> of <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">SHOULD</em> be performed if the representation does not exist. This feature is intended to be useful in preventing races between PUT operations.
    861       </p>
    862       <p id="rfc.section.6.4.p.9">Examples:</p>
    863       <div id="rfc.figure.u.9"></div><pre class="text">    If-None-Match: "xyzzy"
     861      <p id="rfc.section.7.4.p.5">See <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;5</a> for rules on how to determine if two entities tags match. The weak comparison function can only be used with GET or HEAD requests.
     862      </p>
     863      <p id="rfc.section.7.4.p.6">If none of the entity tags match, then the server <em class="bcp14">MAY</em> perform the requested method as if the If-None-Match header field did not exist, but <em class="bcp14">MUST</em> also ignore any If-Modified-Since header field(s) in the request. That is, if no entity tags match, then the server <em class="bcp14">MUST NOT</em> return a 304 (Not Modified) response.
     864      </p>
     865      <p id="rfc.section.7.4.p.7">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status, then the
     866         If-None-Match header <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity Tags and Last-Modified Dates">Section&nbsp;6</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.)
     867      </p>
     868      <p id="rfc.section.7.4.p.8">The meaning of "If-None-Match: *" is that the method <em class="bcp14">MUST NOT</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 16.5</a> of <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">SHOULD</em> be performed if the representation does not exist. This feature is intended to be useful in preventing races between PUT operations.
     869      </p>
     870      <p id="rfc.section.7.4.p.9">Examples:</p>
     871      <div id="rfc.figure.u.11"></div><pre class="text">    If-None-Match: "xyzzy"
    864872    If-None-Match: W/"xyzzy"
    865873    If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
    866874    If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
    867875    If-None-Match: *
    868 </pre><p id="rfc.section.6.4.p.11">The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since header
     876</pre><p id="rfc.section.7.4.p.11">The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since header
    869877         fields is undefined by this specification.
    870878      </p>
    871879      <div id="rfc.iref.i.4"></div>
    872880      <div id="rfc.iref.h.5"></div>
    873       <h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a>&nbsp;<a id="header.if-unmodified-since" href="#header.if-unmodified-since">If-Unmodified-Since</a></h2>
    874       <p id="rfc.section.6.5.p.1">The If-Unmodified-Since request-header field is used with a method to make it conditional. If the requested resource has not
     881      <h2 id="rfc.section.7.5"><a href="#rfc.section.7.5">7.5</a>&nbsp;<a id="header.if-unmodified-since" href="#header.if-unmodified-since">If-Unmodified-Since</a></h2>
     882      <p id="rfc.section.7.5.p.1">The If-Unmodified-Since request-header field is used with a method to make it conditional. If the requested resource has not
    875883         been modified since the time specified in this field, the server <em class="bcp14">SHOULD</em> perform the requested operation as if the If-Unmodified-Since header were not present.
    876884      </p>
    877       <p id="rfc.section.6.5.p.2">If the requested variant has been modified since the specified time, the server <em class="bcp14">MUST NOT</em> perform the requested operation, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed).
    878       </p>
    879       <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.8"></span>  If-Unmodified-Since = "If-Unmodified-Since" ":" HTTP-date
    880 </pre><p id="rfc.section.6.5.p.4">An example of the field is:</p>
    881       <div id="rfc.figure.u.11"></div><pre class="text">    If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
    882 </pre><p id="rfc.section.6.5.p.6">If the request normally (i.e., without the If-Unmodified-Since header) would result in anything other than a 2xx or 412 status,
     885      <p id="rfc.section.7.5.p.2">If the requested variant has been modified since the specified time, the server <em class="bcp14">MUST NOT</em> perform the requested operation, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed).
     886      </p>
     887      <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.8"></span>  If-Unmodified-Since = "If-Unmodified-Since" ":" HTTP-date
     888</pre><p id="rfc.section.7.5.p.4">An example of the field is:</p>
     889      <div id="rfc.figure.u.13"></div><pre class="text">    If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
     890</pre><p id="rfc.section.7.5.p.6">If the request normally (i.e., without the If-Unmodified-Since header) would result in anything other than a 2xx or 412 status,
    883891         the If-Unmodified-Since header <em class="bcp14">SHOULD</em> be ignored.
    884892      </p>
    885       <p id="rfc.section.6.5.p.7">If the specified date is invalid, the header is ignored.</p>
    886       <p id="rfc.section.6.5.p.8">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since
     893      <p id="rfc.section.7.5.p.7">If the specified date is invalid, the header is ignored.</p>
     894      <p id="rfc.section.7.5.p.8">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since
    887895         header fields is undefined by this specification.
    888896      </p>
    889897      <div id="rfc.iref.l.1"></div>
    890898      <div id="rfc.iref.h.6"></div>
    891       <h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a>&nbsp;<a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2>
    892       <p id="rfc.section.6.6.p.1">The Last-Modified entity-header field indicates the date and time at which the origin server believes the variant was last
     899      <h2 id="rfc.section.7.6"><a href="#rfc.section.7.6">7.6</a>&nbsp;<a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2>
     900      <p id="rfc.section.7.6.p.1">The Last-Modified entity-header field indicates the date and time at which the origin server believes the variant was last
    893901         modified.
    894902      </p>
    895       <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  Last-Modified  = "Last-Modified" ":" HTTP-date
    896 </pre><p id="rfc.section.6.6.p.3">An example of its use is</p>
    897       <div id="rfc.figure.u.13"></div><pre class="text">    Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
    898 </pre><p id="rfc.section.6.6.p.5">The exact meaning of this header field depends on the implementation of the origin server and the nature of the original resource.
     903      <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  Last-Modified  = "Last-Modified" ":" HTTP-date
     904</pre><p id="rfc.section.7.6.p.3">An example of its use is</p>
     905      <div id="rfc.figure.u.15"></div><pre class="text">    Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
     906</pre><p id="rfc.section.7.6.p.5">The exact meaning of this header field depends on the implementation of the origin server and the nature of the original resource.
    899907         For files, it may be just the file system last-modified time. For entities with dynamically included parts, it may be the
    900908         most recent of the set of last-modify times for its component parts. For database gateways, it may be the last-update time
    901909         stamp of the record. For virtual objects, it may be the last time the internal state changed.
    902910      </p>
    903       <p id="rfc.section.6.6.p.6">An origin server <em class="bcp14">MUST NOT</em> send a Last-Modified date which is later than the server's time of message origination. In such cases, where the resource's
     911      <p id="rfc.section.7.6.p.6">An origin server <em class="bcp14">MUST NOT</em> send a Last-Modified date which is later than the server's time of message origination. In such cases, where the resource's
    904912         last modification would indicate some time in the future, the server <em class="bcp14">MUST</em> replace that date with the message origination date.
    905913      </p>
    906       <p id="rfc.section.6.6.p.7">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the entity as close as possible to the time that it generates the Date value of its response.
     914      <p id="rfc.section.7.6.p.7">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the entity as close as possible to the time that it generates the Date value of its response.
    907915         This allows a recipient to make an accurate assessment of the entity's modification time, especially if the entity changes
    908916         near the time that the response is generated.
    909917      </p>
    910       <p id="rfc.section.6.6.p.8">HTTP/1.1 servers <em class="bcp14">SHOULD</em> send Last-Modified whenever feasible.
    911       </p>
    912       <p id="rfc.section.6.6.p.9">The Last-Modified entity-header field value is often used as a cache validator. In simple terms, a cache entry is considered
     918      <p id="rfc.section.7.6.p.8">HTTP/1.1 servers <em class="bcp14">SHOULD</em> send Last-Modified whenever feasible.
     919      </p>
     920      <p id="rfc.section.7.6.p.9">The Last-Modified entity-header field value is often used as a cache validator. In simple terms, a cache entry is considered
    913921         to be valid if the entity has not been modified since the Last-Modified value.
    914922      </p>
    915       <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
    916       <p id="rfc.section.7.p.1"> <span class="comment">[rfc.comment.1: TBD.]</span>
    917       </p>
    918       <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
    919       <p id="rfc.section.8.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
    920       </p>
    921       <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
    922       <h1 id="rfc.references"><a id="rfc.section.10" href="#rfc.section.10">10.</a> References
     923      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
     924      <p id="rfc.section.8.p.1"> <span class="comment">[rfc.comment.1: TBD.]</span>
     925      </p>
     926      <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
     927      <p id="rfc.section.9.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
     928      </p>
     929      <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
     930      <h1 id="rfc.references"><a id="rfc.section.11" href="#rfc.section.11">11.</a> References
    923931      </h1>
    924       <h2 id="rfc.references.1"><a href="#rfc.section.10.1" id="rfc.section.10.1">10.1</a> Normative References
     932      <h2 id="rfc.references.1"><a href="#rfc.section.11.1" id="rfc.section.11.1">11.1</a> Normative References
    925933      </h2>
    926934      <table summary="Normative References">       
     
    946954         </tr>
    947955      </table>
    948       <h2 id="rfc.references.2"><a href="#rfc.section.10.2" id="rfc.section.10.2">10.2</a> Informative References
     956      <h2 id="rfc.references.2"><a href="#rfc.section.11.2" id="rfc.section.11.2">11.2</a> Informative References
    949957      </h2>
    950958      <table summary="Informative References">   
     
    9971005      <h2 id="rfc.section.B.3"><a href="#rfc.section.B.3">B.3</a>&nbsp;Since draft-ietf-httpbis-p4-conditional-01
    9981006      </h2>
     1007      <p id="rfc.section.B.3.p.1">Ongoing work on ABNF conversion (&lt;<a href="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36">http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36</a>&gt;):
     1008      </p>
     1009      <ul>
     1010         <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li>
     1011      </ul>
    9991012      <h1><a id="rfc.copyright" href="#rfc.copyright">Full Copyright Statement</a></h1>
    10001013      <p>Copyright © The IETF Trust (2008).</p>
     
    10301043         <ul class="ind">
    10311044            <li class="indline0"><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul class="ind">
    1032                   <li class="indline1">304 Not Modified (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.iref.3"><b>3.1</b></a></li>
     1045                  <li class="indline1">304 Not Modified (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.iref.3"><b>4.1</b></a></li>
    10331046               </ul>
    10341047            </li>
    10351048            <li class="indline0"><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul class="ind">
    1036                   <li class="indline1">412 Precondition Failed (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.iref.4"><b>3.2</b></a></li>
     1049                  <li class="indline1">412 Precondition Failed (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.iref.4"><b>4.2</b></a></li>
    10371050               </ul>
    10381051            </li>
    10391052            <li class="indline0"><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul class="ind">
    1040                   <li class="indline1">ETag header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.etag.1">2</a>, <a class="iref" href="#rfc.iref.e.1"><b>6.1</b></a></li>
     1053                  <li class="indline1">ETag header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.etag.1">3</a>, <a class="iref" href="#rfc.iref.e.1"><b>7.1</b></a></li>
    10411054               </ul>
    10421055            </li>
     
    10441057                  <li class="indline1"><tt>Grammar</tt>&nbsp;&nbsp;
    10451058                     <ul class="ind">
    1046                         <li class="indline1"><tt>entity-tag</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.1"><b>2</b></a></li>
    1047                         <li class="indline1"><tt>ETag</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.4"><b>6.1</b></a></li>
    1048                         <li class="indline1"><tt>If-Match</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.5"><b>6.2</b></a></li>
    1049                         <li class="indline1"><tt>If-Modified-Since</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.6"><b>6.3</b></a></li>
    1050                         <li class="indline1"><tt>If-None-Match</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.7"><b>6.4</b></a></li>
    1051                         <li class="indline1"><tt>If-Unmodified-Since</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.8"><b>6.5</b></a></li>
    1052                         <li class="indline1"><tt>Last-Modified</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.9"><b>6.6</b></a></li>
    1053                         <li class="indline1"><tt>opaque-tag</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.3"><b>2</b></a></li>
    1054                         <li class="indline1"><tt>weak</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.2"><b>2</b></a></li>
     1059                        <li class="indline1"><tt>entity-tag</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.1"><b>3</b></a></li>
     1060                        <li class="indline1"><tt>ETag</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.4"><b>7.1</b></a></li>
     1061                        <li class="indline1"><tt>If-Match</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.5"><b>7.2</b></a></li>
     1062                        <li class="indline1"><tt>If-Modified-Since</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.6"><b>7.3</b></a></li>
     1063                        <li class="indline1"><tt>If-None-Match</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.7"><b>7.4</b></a></li>
     1064                        <li class="indline1"><tt>If-Unmodified-Since</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.8"><b>7.5</b></a></li>
     1065                        <li class="indline1"><tt>Last-Modified</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.9"><b>7.6</b></a></li>
     1066                        <li class="indline1"><tt>opaque-tag</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.3"><b>3</b></a></li>
     1067                        <li class="indline1"><tt>weak</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.2"><b>3</b></a></li>
    10551068                     </ul>
    10561069                  </li>
     
    10601073                  <li class="indline1">Headers&nbsp;&nbsp;
    10611074                     <ul class="ind">
    1062                         <li class="indline1">ETag&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.etag.1">2</a>, <a class="iref" href="#rfc.iref.h.1"><b>6.1</b></a></li>
    1063                         <li class="indline1">If-Match&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-match.2">6.1</a>, <a class="iref" href="#rfc.iref.h.2"><b>6.2</b></a></li>
    1064                         <li class="indline1">If-Modified-Since&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.3"><b>6.3</b></a></li>
    1065                         <li class="indline1">If-None-Match&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-none-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">6.1</a>, <a class="iref" href="#rfc.iref.h.4"><b>6.4</b></a></li>
    1066                         <li class="indline1">If-Unmodified-Since&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.5"><b>6.5</b></a></li>
    1067                         <li class="indline1">Last-Modified&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.6"><b>6.6</b></a></li>
     1075                        <li class="indline1">ETag&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.etag.1">3</a>, <a class="iref" href="#rfc.iref.h.1"><b>7.1</b></a></li>
     1076                        <li class="indline1">If-Match&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-match.2">7.1</a>, <a class="iref" href="#rfc.iref.h.2"><b>7.2</b></a></li>
     1077                        <li class="indline1">If-Modified-Since&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.3"><b>7.3</b></a></li>
     1078                        <li class="indline1">If-None-Match&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-none-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">7.1</a>, <a class="iref" href="#rfc.iref.h.4"><b>7.4</b></a></li>
     1079                        <li class="indline1">If-Unmodified-Since&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.5"><b>7.5</b></a></li>
     1080                        <li class="indline1">Last-Modified&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.6"><b>7.6</b></a></li>
    10681081                     </ul>
    10691082                  </li>
     
    10711084            </li>
    10721085            <li class="indline0"><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul class="ind">
    1073                   <li class="indline1">If-Match header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-match.2">6.1</a>, <a class="iref" href="#rfc.iref.i.1"><b>6.2</b></a></li>
    1074                   <li class="indline1">If-Modified-Since header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.i.2"><b>6.3</b></a></li>
    1075                   <li class="indline1">If-None-Match header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-none-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">6.1</a>, <a class="iref" href="#rfc.iref.i.3"><b>6.4</b></a></li>
    1076                   <li class="indline1">If-Unmodified-Since header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.i.4"><b>6.5</b></a></li>
     1086                  <li class="indline1">If-Match header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-match.2">7.1</a>, <a class="iref" href="#rfc.iref.i.1"><b>7.2</b></a></li>
     1087                  <li class="indline1">If-Modified-Since header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.i.2"><b>7.3</b></a></li>
     1088                  <li class="indline1">If-None-Match header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.if-none-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">7.1</a>, <a class="iref" href="#rfc.iref.i.3"><b>7.4</b></a></li>
     1089                  <li class="indline1">If-Unmodified-Since header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.i.4"><b>7.5</b></a></li>
    10771090               </ul>
    10781091            </li>
    10791092            <li class="indline0"><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul class="ind">
    1080                   <li class="indline1">Last-Modified header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.l.1"><b>6.6</b></a></li>
     1093                  <li class="indline1">Last-Modified header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.l.1"><b>7.6</b></a></li>
    10811094               </ul>
    10821095            </li>
    10831096            <li class="indline0"><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul class="ind">
    1084                   <li class="indline1"><em>Part1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">3.1</a>, <a class="iref" href="#rfc.xref.Part1.2">8</a>, <a class="iref" href="#Part1"><b>10.1</b></a><ul class="ind">
    1085                         <li class="indline1"><em>Section 8.3.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">3.1</a></li>
     1097                  <li class="indline1"><em>Part1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">2</a>, <a class="iref" href="#rfc.xref.Part1.2">2</a>, <a class="iref" href="#rfc.xref.Part1.3">2</a>, <a class="iref" href="#rfc.xref.Part1.4">2</a>, <a class="iref" href="#rfc.xref.Part1.5">4.1</a>, <a class="iref" href="#rfc.xref.Part1.6">9</a>, <a class="iref" href="#Part1"><b>11.1</b></a><ul class="ind">
     1098                        <li class="indline1"><em>Section 2.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">2</a></li>
     1099                        <li class="indline1"><em>Section 2.2</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.2">2</a>, <a class="iref" href="#rfc.xref.Part1.3">2</a></li>
     1100                        <li class="indline1"><em>Section 3.3.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.4">2</a></li>
     1101                        <li class="indline1"><em>Section 8.3.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.5">4.1</a></li>
    10861102                     </ul>
    10871103                  </li>
    1088                   <li class="indline1"><em>Part5</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">2</a>, <a class="iref" href="#rfc.xref.Part5.2">6.1</a>, <a class="iref" href="#rfc.xref.Part5.3">6.3</a>, <a class="iref" href="#Part5"><b>10.1</b></a><ul class="ind">
    1089                         <li class="indline1"><em>Section 5.3</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">2</a>, <a class="iref" href="#rfc.xref.Part5.2">6.1</a></li>
    1090                         <li class="indline1"><em>Section 5.4</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.3">6.3</a></li>
     1104                  <li class="indline1"><em>Part5</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">3</a>, <a class="iref" href="#rfc.xref.Part5.2">7.1</a>, <a class="iref" href="#rfc.xref.Part5.3">7.3</a>, <a class="iref" href="#Part5"><b>11.1</b></a><ul class="ind">
     1105                        <li class="indline1"><em>Section 6.3</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">3</a>, <a class="iref" href="#rfc.xref.Part5.2">7.1</a></li>
     1106                        <li class="indline1"><em>Section 6.4</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.3">7.3</a></li>
    10911107                     </ul>
    10921108                  </li>
    1093                   <li class="indline1"><em>Part6</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part6.1">1</a>, <a class="iref" href="#rfc.xref.Part6.2">6.2</a>, <a class="iref" href="#rfc.xref.Part6.3">6.4</a>, <a class="iref" href="#Part6"><b>10.1</b></a><ul class="ind">
    1094                         <li class="indline1"><em>Section 15.5</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part6.2">6.2</a>, <a class="iref" href="#rfc.xref.Part6.3">6.4</a></li>
     1109                  <li class="indline1"><em>Part6</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part6.1">1</a>, <a class="iref" href="#rfc.xref.Part6.2">7.2</a>, <a class="iref" href="#rfc.xref.Part6.3">7.4</a>, <a class="iref" href="#Part6"><b>11.1</b></a><ul class="ind">
     1110                        <li class="indline1"><em>Section 16.5</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part6.2">7.2</a>, <a class="iref" href="#rfc.xref.Part6.3">7.4</a></li>
    10951111                     </ul>
    10961112                  </li>
     
    10981114            </li>
    10991115            <li class="indline0"><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul class="ind">
    1100                   <li class="indline1"><em>RFC2068</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2068.1">3.1</a>, <a class="iref" href="#RFC2068"><b>10.2</b></a><ul class="ind">
    1101                         <li class="indline1"><em>Section 14.19</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2068.1">3.1</a></li>
     1116                  <li class="indline1"><em>RFC2068</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2068.1">4.1</a>, <a class="iref" href="#RFC2068"><b>11.2</b></a><ul class="ind">
     1117                        <li class="indline1"><em>Section 14.19</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2068.1">4.1</a></li>
    11021118                     </ul>
    11031119                  </li>
    1104                   <li class="indline1"><em>RFC2119</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2119.1">1.1</a>, <a class="iref" href="#RFC2119"><b>10.1</b></a></li>
    1105                   <li class="indline1"><em>RFC2616</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2616.1">1</a>, <a class="iref" href="#RFC2616"><b>10.2</b></a>, <a class="iref" href="#rfc.xref.RFC2616.2">B.1</a></li>
     1120                  <li class="indline1"><em>RFC2119</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2119.1">1.1</a>, <a class="iref" href="#RFC2119"><b>11.1</b></a></li>
     1121                  <li class="indline1"><em>RFC2616</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2616.1">1</a>, <a class="iref" href="#RFC2616"><b>11.2</b></a>, <a class="iref" href="#rfc.xref.RFC2616.2">B.1</a></li>
    11061122               </ul>
    11071123            </li>
     
    11091125                  <li class="indline1">Status Codes&nbsp;&nbsp;
    11101126                     <ul class="ind">
    1111                         <li class="indline1">304 Not Modified&nbsp;&nbsp;<a class="iref" href="#rfc.iref.s.1"><b>3.1</b></a></li>
    1112                         <li class="indline1">412 Precondition Failed&nbsp;&nbsp;<a class="iref" href="#rfc.iref.s.2"><b>3.2</b></a></li>
     1127                        <li class="indline1">304 Not Modified&nbsp;&nbsp;<a class="iref" href="#rfc.iref.s.1"><b>4.1</b></a></li>
     1128                        <li class="indline1">412 Precondition Failed&nbsp;&nbsp;<a class="iref" href="#rfc.iref.s.2"><b>4.2</b></a></li>
    11131129                     </ul>
    11141130                  </li>
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