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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  • draft-ietf-httpbis/latest/p6-cache.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 Overview" href="#rfc.section.2">
    336       <link rel="Chapter" title="3 Expiration Model" href="#rfc.section.3">
    337       <link rel="Chapter" title="4 Validation Model" href="#rfc.section.4">
    338       <link rel="Chapter" title="5 Response Cacheability" href="#rfc.section.5">
    339       <link rel="Chapter" title="6 Constructing Responses From Caches" href="#rfc.section.6">
    340       <link rel="Chapter" title="7 Caching Negotiated Responses" href="#rfc.section.7">
    341       <link rel="Chapter" title="8 Shared and Non-Shared Caches" href="#rfc.section.8">
    342       <link rel="Chapter" title="9 Errors or Incomplete Response Cache Behavior" href="#rfc.section.9">
    343       <link rel="Chapter" title="10 Side Effects of GET and HEAD" href="#rfc.section.10">
    344       <link rel="Chapter" title="11 Invalidation After Updates or Deletions" href="#rfc.section.11">
    345       <link rel="Chapter" title="12 Write-Through Mandatory" href="#rfc.section.12">
    346       <link rel="Chapter" title="13 Cache Replacement" href="#rfc.section.13">
    347       <link rel="Chapter" title="14 History Lists" href="#rfc.section.14">
    348       <link rel="Chapter" title="15 Header Field Definitions" href="#rfc.section.15">
    349       <link rel="Chapter" title="16 IANA Considerations" href="#rfc.section.16">
    350       <link rel="Chapter" title="17 Security Considerations" href="#rfc.section.17">
    351       <link rel="Chapter" title="18 Acknowledgments" href="#rfc.section.18">
    352       <link rel="Chapter" href="#rfc.section.19" title="19 References">
     335      <link rel="Chapter" title="2 Notational Conventions and Generic Grammar" href="#rfc.section.2">
     336      <link rel="Chapter" title="3 Overview" href="#rfc.section.3">
     337      <link rel="Chapter" title="4 Expiration Model" href="#rfc.section.4">
     338      <link rel="Chapter" title="5 Validation Model" href="#rfc.section.5">
     339      <link rel="Chapter" title="6 Response Cacheability" href="#rfc.section.6">
     340      <link rel="Chapter" title="7 Constructing Responses From Caches" href="#rfc.section.7">
     341      <link rel="Chapter" title="8 Caching Negotiated Responses" href="#rfc.section.8">
     342      <link rel="Chapter" title="9 Shared and Non-Shared Caches" href="#rfc.section.9">
     343      <link rel="Chapter" title="10 Errors or Incomplete Response Cache Behavior" href="#rfc.section.10">
     344      <link rel="Chapter" title="11 Side Effects of GET and HEAD" href="#rfc.section.11">
     345      <link rel="Chapter" title="12 Invalidation After Updates or Deletions" href="#rfc.section.12">
     346      <link rel="Chapter" title="13 Write-Through Mandatory" href="#rfc.section.13">
     347      <link rel="Chapter" title="14 Cache Replacement" href="#rfc.section.14">
     348      <link rel="Chapter" title="15 History Lists" href="#rfc.section.15">
     349      <link rel="Chapter" title="16 Header Field Definitions" href="#rfc.section.16">
     350      <link rel="Chapter" title="17 IANA Considerations" href="#rfc.section.17">
     351      <link rel="Chapter" title="18 Security Considerations" href="#rfc.section.18">
     352      <link rel="Chapter" title="19 Acknowledgments" href="#rfc.section.19">
     353      <link rel="Chapter" href="#rfc.section.20" title="20 References">
    353354      <link rel="Appendix" title="A Compatibility with Previous Versions" href="#rfc.section.A">
    354355      <link rel="Appendix" title="B Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.B">
     
    494495            </ul>
    495496         </li>
    496          <li class="tocline0">2.&nbsp;&nbsp;&nbsp;<a href="#caching.overview">Overview</a><ul class="toc">
    497                <li class="tocline1">2.1&nbsp;&nbsp;&nbsp;<a href="#cache.correctness">Cache Correctness</a></li>
    498                <li class="tocline1">2.2&nbsp;&nbsp;&nbsp;<a href="#warnings">Warnings</a></li>
    499                <li class="tocline1">2.3&nbsp;&nbsp;&nbsp;<a href="#cache-control.mechanisms">Cache-control Mechanisms</a></li>
    500                <li class="tocline1">2.4&nbsp;&nbsp;&nbsp;<a href="#explicit.ua.warnings">Explicit User Agent Warnings</a></li>
    501                <li class="tocline1">2.5&nbsp;&nbsp;&nbsp;<a href="#exceptions.to.the.rules.and.warnings">Exceptions to the Rules and Warnings</a></li>
    502                <li class="tocline1">2.6&nbsp;&nbsp;&nbsp;<a href="#client-controlled.behavior">Client-controlled Behavior</a></li>
     497         <li class="tocline0">2.&nbsp;&nbsp;&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a></li>
     498         <li class="tocline0">3.&nbsp;&nbsp;&nbsp;<a href="#caching.overview">Overview</a><ul class="toc">
     499               <li class="tocline1">3.1&nbsp;&nbsp;&nbsp;<a href="#cache.correctness">Cache Correctness</a></li>
     500               <li class="tocline1">3.2&nbsp;&nbsp;&nbsp;<a href="#warnings">Warnings</a></li>
     501               <li class="tocline1">3.3&nbsp;&nbsp;&nbsp;<a href="#cache-control.mechanisms">Cache-control Mechanisms</a></li>
     502               <li class="tocline1">3.4&nbsp;&nbsp;&nbsp;<a href="#explicit.ua.warnings">Explicit User Agent Warnings</a></li>
     503               <li class="tocline1">3.5&nbsp;&nbsp;&nbsp;<a href="#exceptions.to.the.rules.and.warnings">Exceptions to the Rules and Warnings</a></li>
     504               <li class="tocline1">3.6&nbsp;&nbsp;&nbsp;<a href="#client-controlled.behavior">Client-controlled Behavior</a></li>
    503505            </ul>
    504506         </li>
    505          <li class="tocline0">3.&nbsp;&nbsp;&nbsp;<a href="#expiration.model">Expiration Model</a><ul class="toc">
    506                <li class="tocline1">3.1&nbsp;&nbsp;&nbsp;<a href="#server-specified.expiration">Server-Specified Expiration</a></li>
    507                <li class="tocline1">3.2&nbsp;&nbsp;&nbsp;<a href="#heuristic.expiration">Heuristic Expiration</a></li>
    508                <li class="tocline1">3.3&nbsp;&nbsp;&nbsp;<a href="#age.calculations">Age Calculations</a></li>
    509                <li class="tocline1">3.4&nbsp;&nbsp;&nbsp;<a href="#expiration.calculations">Expiration Calculations</a></li>
    510                <li class="tocline1">3.5&nbsp;&nbsp;&nbsp;<a href="#disambiguating.expiration.values">Disambiguating Expiration Values</a></li>
    511                <li class="tocline1">3.6&nbsp;&nbsp;&nbsp;<a href="#disambiguating.multiple.responses">Disambiguating Multiple Responses</a></li>
     507         <li class="tocline0">4.&nbsp;&nbsp;&nbsp;<a href="#expiration.model">Expiration Model</a><ul class="toc">
     508               <li class="tocline1">4.1&nbsp;&nbsp;&nbsp;<a href="#server-specified.expiration">Server-Specified Expiration</a></li>
     509               <li class="tocline1">4.2&nbsp;&nbsp;&nbsp;<a href="#heuristic.expiration">Heuristic Expiration</a></li>
     510               <li class="tocline1">4.3&nbsp;&nbsp;&nbsp;<a href="#age.calculations">Age Calculations</a></li>
     511               <li class="tocline1">4.4&nbsp;&nbsp;&nbsp;<a href="#expiration.calculations">Expiration Calculations</a></li>
     512               <li class="tocline1">4.5&nbsp;&nbsp;&nbsp;<a href="#disambiguating.expiration.values">Disambiguating Expiration Values</a></li>
     513               <li class="tocline1">4.6&nbsp;&nbsp;&nbsp;<a href="#disambiguating.multiple.responses">Disambiguating Multiple Responses</a></li>
    512514            </ul>
    513515         </li>
    514          <li class="tocline0">4.&nbsp;&nbsp;&nbsp;<a href="#validation.model">Validation Model</a></li>
    515          <li class="tocline0">5.&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Response Cacheability</a></li>
    516          <li class="tocline0">6.&nbsp;&nbsp;&nbsp;<a href="#constructing.responses.from.caches">Constructing Responses From Caches</a><ul class="toc">
    517                <li class="tocline1">6.1&nbsp;&nbsp;&nbsp;<a href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></li>
    518                <li class="tocline1">6.2&nbsp;&nbsp;&nbsp;<a href="#non-modifiable.headers">Non-modifiable Headers</a></li>
    519                <li class="tocline1">6.3&nbsp;&nbsp;&nbsp;<a href="#combining.headers">Combining Headers</a></li>
     516         <li class="tocline0">5.&nbsp;&nbsp;&nbsp;<a href="#validation.model">Validation Model</a></li>
     517         <li class="tocline0">6.&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Response Cacheability</a></li>
     518         <li class="tocline0">7.&nbsp;&nbsp;&nbsp;<a href="#constructing.responses.from.caches">Constructing Responses From Caches</a><ul class="toc">
     519               <li class="tocline1">7.1&nbsp;&nbsp;&nbsp;<a href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></li>
     520               <li class="tocline1">7.2&nbsp;&nbsp;&nbsp;<a href="#non-modifiable.headers">Non-modifiable Headers</a></li>
     521               <li class="tocline1">7.3&nbsp;&nbsp;&nbsp;<a href="#combining.headers">Combining Headers</a></li>
    520522            </ul>
    521523         </li>
    522          <li class="tocline0">7.&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
    523          <li class="tocline0">8.&nbsp;&nbsp;&nbsp;<a href="#shared.and.non-shared.caches">Shared and Non-Shared Caches</a></li>
    524          <li class="tocline0">9.&nbsp;&nbsp;&nbsp;<a href="#errors.or.incomplete.response.cache.behavior">Errors or Incomplete Response Cache Behavior</a></li>
    525          <li class="tocline0">10.&nbsp;&nbsp;&nbsp;<a href="#side.effects.of.get.and.head">Side Effects of GET and HEAD</a></li>
    526          <li class="tocline0">11.&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Invalidation After Updates or Deletions</a></li>
    527          <li class="tocline0">12.&nbsp;&nbsp;&nbsp;<a href="#write-through.mandatory">Write-Through Mandatory</a></li>
    528          <li class="tocline0">13.&nbsp;&nbsp;&nbsp;<a href="#cache.replacement">Cache Replacement</a></li>
    529          <li class="tocline0">14.&nbsp;&nbsp;&nbsp;<a href="#history.lists">History Lists</a></li>
    530          <li class="tocline0">15.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul class="toc">
    531                <li class="tocline1">15.1&nbsp;&nbsp;&nbsp;<a href="#header.age">Age</a></li>
    532                <li class="tocline1">15.2&nbsp;&nbsp;&nbsp;<a href="#header.cache-control">Cache-Control</a><ul class="toc">
    533                      <li class="tocline1">15.2.1&nbsp;&nbsp;&nbsp;<a href="#what.is.cacheable">What is Cacheable</a></li>
    534                      <li class="tocline1">15.2.2&nbsp;&nbsp;&nbsp;<a href="#what.may.be.stored.by.caches">What May be Stored by Caches</a></li>
    535                      <li class="tocline1">15.2.3&nbsp;&nbsp;&nbsp;<a href="#modifications.of.the.basic.expiration.mechanism">Modifications of the Basic Expiration Mechanism</a></li>
    536                      <li class="tocline1">15.2.4&nbsp;&nbsp;&nbsp;<a href="#cache.revalidation.and.reload.controls">Cache Revalidation and Reload Controls</a></li>
    537                      <li class="tocline1">15.2.5&nbsp;&nbsp;&nbsp;<a href="#no-transform.directive">No-Transform Directive</a></li>
    538                      <li class="tocline1">15.2.6&nbsp;&nbsp;&nbsp;<a href="#cache.control.extensions">Cache Control Extensions</a></li>
     524         <li class="tocline0">8.&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
     525         <li class="tocline0">9.&nbsp;&nbsp;&nbsp;<a href="#shared.and.non-shared.caches">Shared and Non-Shared Caches</a></li>
     526         <li class="tocline0">10.&nbsp;&nbsp;&nbsp;<a href="#errors.or.incomplete.response.cache.behavior">Errors or Incomplete Response Cache Behavior</a></li>
     527         <li class="tocline0">11.&nbsp;&nbsp;&nbsp;<a href="#side.effects.of.get.and.head">Side Effects of GET and HEAD</a></li>
     528         <li class="tocline0">12.&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Invalidation After Updates or Deletions</a></li>
     529         <li class="tocline0">13.&nbsp;&nbsp;&nbsp;<a href="#write-through.mandatory">Write-Through Mandatory</a></li>
     530         <li class="tocline0">14.&nbsp;&nbsp;&nbsp;<a href="#cache.replacement">Cache Replacement</a></li>
     531         <li class="tocline0">15.&nbsp;&nbsp;&nbsp;<a href="#history.lists">History Lists</a></li>
     532         <li class="tocline0">16.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul class="toc">
     533               <li class="tocline1">16.1&nbsp;&nbsp;&nbsp;<a href="#header.age">Age</a></li>
     534               <li class="tocline1">16.2&nbsp;&nbsp;&nbsp;<a href="#header.cache-control">Cache-Control</a><ul class="toc">
     535                     <li class="tocline1">16.2.1&nbsp;&nbsp;&nbsp;<a href="#what.is.cacheable">What is Cacheable</a></li>
     536                     <li class="tocline1">16.2.2&nbsp;&nbsp;&nbsp;<a href="#what.may.be.stored.by.caches">What May be Stored by Caches</a></li>
     537                     <li class="tocline1">16.2.3&nbsp;&nbsp;&nbsp;<a href="#modifications.of.the.basic.expiration.mechanism">Modifications of the Basic Expiration Mechanism</a></li>
     538                     <li class="tocline1">16.2.4&nbsp;&nbsp;&nbsp;<a href="#cache.revalidation.and.reload.controls">Cache Revalidation and Reload Controls</a></li>
     539                     <li class="tocline1">16.2.5&nbsp;&nbsp;&nbsp;<a href="#no-transform.directive">No-Transform Directive</a></li>
     540                     <li class="tocline1">16.2.6&nbsp;&nbsp;&nbsp;<a href="#cache.control.extensions">Cache Control Extensions</a></li>
    539541                  </ul>
    540542               </li>
    541                <li class="tocline1">15.3&nbsp;&nbsp;&nbsp;<a href="#header.expires">Expires</a></li>
    542                <li class="tocline1">15.4&nbsp;&nbsp;&nbsp;<a href="#header.pragma">Pragma</a></li>
    543                <li class="tocline1">15.5&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
    544                <li class="tocline1">15.6&nbsp;&nbsp;&nbsp;<a href="#header.warning">Warning</a></li>
     543               <li class="tocline1">16.3&nbsp;&nbsp;&nbsp;<a href="#header.expires">Expires</a></li>
     544               <li class="tocline1">16.4&nbsp;&nbsp;&nbsp;<a href="#header.pragma">Pragma</a></li>
     545               <li class="tocline1">16.5&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
     546               <li class="tocline1">16.6&nbsp;&nbsp;&nbsp;<a href="#header.warning">Warning</a></li>
    545547            </ul>
    546548         </li>
    547          <li class="tocline0">16.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a></li>
    548          <li class="tocline0">17.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a></li>
    549          <li class="tocline0">18.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
    550          <li class="tocline0">19.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul class="toc">
    551                <li class="tocline1">19.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
    552                <li class="tocline1">19.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
     549         <li class="tocline0">17.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a></li>
     550         <li class="tocline0">18.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a></li>
     551         <li class="tocline0">19.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
     552         <li class="tocline0">20.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul class="toc">
     553               <li class="tocline1">20.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
     554               <li class="tocline1">20.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
    553555            </ul>
    554556         </li>
     
    582584      <p id="rfc.section.1.1.p.2">Caching would be useless if it did not significantly improve performance. The goal of caching in HTTP/1.1 is to reuse a prior
    583585         response message to satisfy a current request. In some cases, the existing response can be reused without the need for a network
    584          request, reducing latency and network round-trips; we use an "expiration" mechanism for this purpose (see <a href="#expiration.model" title="Expiration Model">Section&nbsp;3</a>). Even when a new request is required, it is often possible to reuse all or parts of the payload of a prior response to satisfy
    585          the request, thereby reducing network bandwidth usage; we use a "validation" mechanism for this purpose (see <a href="#validation.model" title="Validation Model">Section&nbsp;4</a>).
     586         request, reducing latency and network round-trips; we use an "expiration" mechanism for this purpose (see <a href="#expiration.model" title="Expiration Model">Section&nbsp;4</a>). Even when a new request is required, it is often possible to reuse all or parts of the payload of a prior response to satisfy
     587         the request, thereby reducing network bandwidth usage; we use a "validation" mechanism for this purpose (see <a href="#validation.model" title="Validation Model">Section&nbsp;5</a>).
    586588      </p>
    587589      <div id="rfc.iref.s.1"></div>
     
    675677      <p id="rfc.section.1.3.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."
    676678      </p>
    677       <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="caching.overview" href="#caching.overview">Overview</a></h1>
    678       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="cache.correctness" href="#cache.correctness">Cache Correctness</a></h2>
    679       <p id="rfc.section.2.1.p.1">A correct cache <em class="bcp14">MUST</em> respond to a request with the most up-to-date response held by the cache that is appropriate to the request (see Sections <a href="#disambiguating.expiration.values" title="Disambiguating Expiration Values">3.5</a>, <a href="#disambiguating.multiple.responses" title="Disambiguating Multiple Responses">3.6</a>, and <a href="#cache.replacement" title="Cache Replacement">13</a>) which meets one of the following conditions:
     679      <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>
     680      <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>
     681      </p>
     682      <div id="rfc.figure.u.1"></div><pre class="inline">  DIGIT         = &lt;DIGIT, 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;
     683  DQUOTE        = &lt;DQUOTE, 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#basic.rules" title="Basic Rules">Section 2.2</a>&gt;
     684  SP            = &lt;SP, defined in <a href="#Part1" id="rfc.xref.Part1.5"><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;
     685</pre><div id="rfc.figure.u.2"></div><pre class="inline">  quoted-string = &lt;quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.6"><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;
     686  token         = &lt;token, defined in <a href="#Part1" id="rfc.xref.Part1.7"><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;
     687</pre><p id="rfc.section.2.p.4">The ABNF rules below are defined in other parts:</p>
     688      <div id="rfc.figure.u.3"></div><pre class="inline">  field-name    = &lt;field-name, defined in <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#message.headers" title="Message Headers">Section 4.2</a>&gt;
     689  HTTP-date     = &lt;HTTP-date, defined in <a href="#Part1" id="rfc.xref.Part1.9"><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;
     690  port          = &lt;port, defined in <a href="#Part1" id="rfc.xref.Part1.10"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#general.syntax" title="General Syntax">Section 3.2.1</a>&gt;
     691  pseudonym     = &lt;pseudonym, defined in <a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.via" title="Via">Section 8.9</a>&gt;
     692  uri-host      = &lt;uri-host, defined in <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#general.syntax" title="General Syntax">Section 3.2.1</a>&gt;
     693</pre><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="caching.overview" href="#caching.overview">Overview</a></h1>
     694      <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="cache.correctness" href="#cache.correctness">Cache Correctness</a></h2>
     695      <p id="rfc.section.3.1.p.1">A correct cache <em class="bcp14">MUST</em> respond to a request with the most up-to-date response held by the cache that is appropriate to the request (see Sections <a href="#disambiguating.expiration.values" title="Disambiguating Expiration Values">4.5</a>, <a href="#disambiguating.multiple.responses" title="Disambiguating Multiple Responses">4.6</a>, and <a href="#cache.replacement" title="Cache Replacement">14</a>) which meets one of the following conditions:
    680696      </p>
    681697      <ol>
    682698         <li>It has been checked for equivalence with what the origin server would have returned by revalidating the response with the
    683             origin server (<a href="#validation.model" title="Validation Model">Section&nbsp;4</a>);
    684          </li>
    685          <li>It is "fresh enough" (see <a href="#expiration.model" title="Expiration Model">Section&nbsp;3</a>). In the default case, this means it meets the least restrictive freshness requirement of the client, origin server, and
    686             cache (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section&nbsp;15.2</a>); if the origin server so specifies, it is the freshness requirement of the origin server alone. If a stored response is
     699            origin server (<a href="#validation.model" title="Validation Model">Section&nbsp;5</a>);
     700         </li>
     701         <li>It is "fresh enough" (see <a href="#expiration.model" title="Expiration Model">Section&nbsp;4</a>). In the default case, this means it meets the least restrictive freshness requirement of the client, origin server, and
     702            cache (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section&nbsp;16.2</a>); if the origin server so specifies, it is the freshness requirement of the origin server alone. If a stored response is
    687703            not "fresh enough" by the most restrictive freshness requirement of both the client and the origin server, in carefully considered
    688             circumstances the cache <em class="bcp14">MAY</em> still return the response with the appropriate Warning header (see Sections <a href="#exceptions.to.the.rules.and.warnings" title="Exceptions to the Rules and Warnings">2.5</a> and <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">15.6</a>), unless such a response is prohibited (e.g., by a "no-store" cache-directive, or by a "no-cache" cache-request-directive;
    689             see <a href="#header.cache-control" id="rfc.xref.header.cache-control.2" title="Cache-Control">Section&nbsp;15.2</a>).
     704            circumstances the cache <em class="bcp14">MAY</em> still return the response with the appropriate Warning header (see Sections <a href="#exceptions.to.the.rules.and.warnings" title="Exceptions to the Rules and Warnings">3.5</a> and <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">16.6</a>), unless such a response is prohibited (e.g., by a "no-store" cache-directive, or by a "no-cache" cache-request-directive;
     705            see <a href="#header.cache-control" id="rfc.xref.header.cache-control.2" title="Cache-Control">Section&nbsp;16.2</a>).
    690706         </li>
    691707         <li>It is an appropriate 304 (Not Modified), 305 (Use Proxy), or error (4xx or 5xx) response message.</li>
    692708      </ol>
    693       <p id="rfc.section.2.1.p.2">If the cache can not communicate with the origin server, then a correct cache <em class="bcp14">SHOULD</em> respond as above if the response can be correctly served from the cache; if not it <em class="bcp14">MUST</em> return an error or warning indicating that there was a communication failure.
    694       </p>
    695       <p id="rfc.section.2.1.p.3">If a cache receives a response (either an entire response, or a 304 (Not Modified) response) that it would normally forward
     709      <p id="rfc.section.3.1.p.2">If the cache can not communicate with the origin server, then a correct cache <em class="bcp14">SHOULD</em> respond as above if the response can be correctly served from the cache; if not it <em class="bcp14">MUST</em> return an error or warning indicating that there was a communication failure.
     710      </p>
     711      <p id="rfc.section.3.1.p.3">If a cache receives a response (either an entire response, or a 304 (Not Modified) response) that it would normally forward
    696712         to the requesting client, and the received response is no longer fresh, the cache <em class="bcp14">SHOULD</em> forward it to the requesting client without adding a new Warning (but without removing any existing Warning headers). A cache <em class="bcp14">SHOULD NOT</em> attempt to revalidate a response simply because that response became stale in transit; this might lead to an infinite loop.
    697713         A user agent that receives a stale response without a Warning <em class="bcp14">MAY</em> display a warning indication to the user.
    698714      </p>
    699       <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="warnings" href="#warnings">Warnings</a></h2>
    700       <p id="rfc.section.2.2.p.1">Whenever a cache returns a response that is neither first-hand nor "fresh enough" (in the sense of condition 2 in <a href="#cache.correctness" title="Cache Correctness">Section&nbsp;2.1</a>), it <em class="bcp14">MUST</em> attach a warning to that effect, using a Warning general-header. The Warning header and the currently defined warnings are
    701          described in <a href="#header.warning" id="rfc.xref.header.warning.2" title="Warning">Section&nbsp;15.6</a>. The warning allows clients to take appropriate action.
    702       </p>
    703       <p id="rfc.section.2.2.p.2">Warnings <em class="bcp14">MAY</em> be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status code, distinguish
     715      <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="warnings" href="#warnings">Warnings</a></h2>
     716      <p id="rfc.section.3.2.p.1">Whenever a cache returns a response that is neither first-hand nor "fresh enough" (in the sense of condition 2 in <a href="#cache.correctness" title="Cache Correctness">Section&nbsp;3.1</a>), it <em class="bcp14">MUST</em> attach a warning to that effect, using a Warning general-header. The Warning header and the currently defined warnings are
     717         described in <a href="#header.warning" id="rfc.xref.header.warning.2" title="Warning">Section&nbsp;16.6</a>. The warning allows clients to take appropriate action.
     718      </p>
     719      <p id="rfc.section.3.2.p.2">Warnings <em class="bcp14">MAY</em> be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status code, distinguish
    704720         these responses from true failures.
    705721      </p>
    706       <p id="rfc.section.2.2.p.3">Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning <em class="bcp14">MUST</em> or <em class="bcp14">MUST NOT</em> be deleted from a stored cache entry after a successful revalidation:
    707       </p>
    708       <p id="rfc.section.2.2.p.4"> </p>
     722      <p id="rfc.section.3.2.p.3">Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning <em class="bcp14">MUST</em> or <em class="bcp14">MUST NOT</em> be deleted from a stored cache entry after a successful revalidation:
     723      </p>
     724      <p id="rfc.section.3.2.p.4"> </p>
    709725      <dl>
    710726         <dt>1xx</dt>
     
    716732         </dd>
    717733      </dl>
    718       <p id="rfc.section.2.2.p.5">See <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section&nbsp;15.6</a> for the definitions of the codes themselves.
    719       </p>
    720       <p id="rfc.section.2.2.p.6">HTTP/1.0 caches will cache all Warnings in responses, without deleting the ones in the first category. Warnings in responses
     734      <p id="rfc.section.3.2.p.5">See <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section&nbsp;16.6</a> for the definitions of the codes themselves.
     735      </p>
     736      <p id="rfc.section.3.2.p.6">HTTP/1.0 caches will cache all Warnings in responses, without deleting the ones in the first category. Warnings in responses
    721737         that are passed to HTTP/1.0 caches carry an extra warning-date field, which prevents a future HTTP/1.1 recipient from believing
    722738         an erroneously cached Warning.
    723739      </p>
    724       <p id="rfc.section.2.2.p.7">Warnings also carry a warning text. The text <em class="bcp14">MAY</em> be in any appropriate natural language (perhaps based on the client's Accept headers), and include an <em class="bcp14">OPTIONAL</em> indication of what character set is used.
    725       </p>
    726       <p id="rfc.section.2.2.p.8">Multiple warnings <em class="bcp14">MAY</em> be attached to a response (either by the origin server or by a cache), including multiple warnings with the same code number.
     740      <p id="rfc.section.3.2.p.7">Warnings also carry a warning text. The text <em class="bcp14">MAY</em> be in any appropriate natural language (perhaps based on the client's Accept headers), and include an <em class="bcp14">OPTIONAL</em> indication of what character set is used.
     741      </p>
     742      <p id="rfc.section.3.2.p.8">Multiple warnings <em class="bcp14">MAY</em> be attached to a response (either by the origin server or by a cache), including multiple warnings with the same code number.
    727743         For example, a server might provide the same warning with texts in both English and Basque.
    728744      </p>
    729       <p id="rfc.section.2.2.p.9">When multiple warnings are attached to a response, it might not be practical or reasonable to display all of them to the user.
     745      <p id="rfc.section.3.2.p.9">When multiple warnings are attached to a response, it might not be practical or reasonable to display all of them to the user.
    730746         This version of HTTP does not specify strict priority rules for deciding which warnings to display and in what order, but
    731747         does suggest some heuristics.
    732748      </p>
    733       <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="cache-control.mechanisms" href="#cache-control.mechanisms">Cache-control Mechanisms</a></h2>
    734       <p id="rfc.section.2.3.p.1">The basic cache mechanisms in HTTP/1.1 (server-specified expiration times and validators) are implicit directives to caches.
     749      <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a id="cache-control.mechanisms" href="#cache-control.mechanisms">Cache-control Mechanisms</a></h2>
     750      <p id="rfc.section.3.3.p.1">The basic cache mechanisms in HTTP/1.1 (server-specified expiration times and validators) are implicit directives to caches.
    735751         In some cases, a server or client might need to provide explicit directives to the HTTP caches. We use the Cache-Control header
    736752         for this purpose.
    737753      </p>
    738       <p id="rfc.section.2.3.p.2">The Cache-Control header allows a client or server to transmit a variety of directives in either requests or responses. These
     754      <p id="rfc.section.3.3.p.2">The Cache-Control header allows a client or server to transmit a variety of directives in either requests or responses. These
    739755         directives typically override the default caching algorithms. As a general rule, if there is any apparent conflict between
    740756         header values, the most restrictive interpretation is applied (that is, the one that is most likely to preserve semantic transparency).
     
    742758         (for example, "max-stale" or "public").
    743759      </p>
    744       <p id="rfc.section.2.3.p.3">The cache-control directives are described in detail in <a href="#header.cache-control" id="rfc.xref.header.cache-control.3" title="Cache-Control">Section&nbsp;15.2</a>.
    745       </p>
    746       <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a id="explicit.ua.warnings" href="#explicit.ua.warnings">Explicit User Agent Warnings</a></h2>
    747       <p id="rfc.section.2.4.p.1">Many user agents make it possible for users to override the basic caching mechanisms. For example, the user agent might allow
     760      <p id="rfc.section.3.3.p.3">The cache-control directives are described in detail in <a href="#header.cache-control" id="rfc.xref.header.cache-control.3" title="Cache-Control">Section&nbsp;16.2</a>.
     761      </p>
     762      <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a id="explicit.ua.warnings" href="#explicit.ua.warnings">Explicit User Agent Warnings</a></h2>
     763      <p id="rfc.section.3.4.p.1">Many user agents make it possible for users to override the basic caching mechanisms. For example, the user agent might allow
    748764         the user to specify that cached entities (even explicitly stale ones) are never validated. Or the user agent might habitually
    749765         add "Cache-Control: max-stale=3600" to every request. The user agent <em class="bcp14">SHOULD NOT</em> default to either non-transparent behavior, or behavior that results in abnormally ineffective caching, but <em class="bcp14">MAY</em> be explicitly configured to do so by an explicit action of the user.
    750766      </p>
    751       <p id="rfc.section.2.4.p.2">If the user has overridden the basic caching mechanisms, the user agent <em class="bcp14">SHOULD</em> explicitly indicate to the user whenever this results in the display of information that might not meet the server's transparency
     767      <p id="rfc.section.3.4.p.2">If the user has overridden the basic caching mechanisms, the user agent <em class="bcp14">SHOULD</em> explicitly indicate to the user whenever this results in the display of information that might not meet the server's transparency
    752768         requirements (in particular, if the displayed entity is known to be stale). Since the protocol normally allows the user agent
    753769         to determine if responses are stale or not, this indication need only be displayed when this actually happens. The indication
    754770         need not be a dialog box; it could be an icon (for example, a picture of a rotting fish) or some other indicator.
    755771      </p>
    756       <p id="rfc.section.2.4.p.3">If the user has overridden the caching mechanisms in a way that would abnormally reduce the effectiveness of caches, the user
     772      <p id="rfc.section.3.4.p.3">If the user has overridden the caching mechanisms in a way that would abnormally reduce the effectiveness of caches, the user
    757773         agent <em class="bcp14">SHOULD</em> continually indicate this state to the user (for example, by a display of a picture of currency in flames) so that the user
    758774         does not inadvertently consume excess resources or suffer from excessive latency.
    759775      </p>
    760       <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="exceptions.to.the.rules.and.warnings" href="#exceptions.to.the.rules.and.warnings">Exceptions to the Rules and Warnings</a></h2>
    761       <p id="rfc.section.2.5.p.1">In some cases, the operator of a cache <em class="bcp14">MAY</em> choose to configure it to return stale responses even when not requested by clients. This decision ought not be made lightly,
     776      <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="exceptions.to.the.rules.and.warnings" href="#exceptions.to.the.rules.and.warnings">Exceptions to the Rules and Warnings</a></h2>
     777      <p id="rfc.section.3.5.p.1">In some cases, the operator of a cache <em class="bcp14">MAY</em> choose to configure it to return stale responses even when not requested by clients. This decision ought not be made lightly,
    762778         but may be necessary for reasons of availability or performance, especially when the cache is poorly connected to the origin
    763779         server. Whenever a cache returns a stale response, it <em class="bcp14">MUST</em> mark it as such (using a Warning header) enabling the client software to alert the user that there might be a potential problem.
    764780      </p>
    765       <p id="rfc.section.2.5.p.2">It also allows the user agent to take steps to obtain a first-hand or fresh response. For this reason, a cache <em class="bcp14">SHOULD NOT</em> return a stale response if the client explicitly requests a first-hand or fresh one, unless it is impossible to comply for
     781      <p id="rfc.section.3.5.p.2">It also allows the user agent to take steps to obtain a first-hand or fresh response. For this reason, a cache <em class="bcp14">SHOULD NOT</em> return a stale response if the client explicitly requests a first-hand or fresh one, unless it is impossible to comply for
    766782         technical or policy reasons.
    767783      </p>
    768       <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a>&nbsp;<a id="client-controlled.behavior" href="#client-controlled.behavior">Client-controlled Behavior</a></h2>
    769       <p id="rfc.section.2.6.p.1">While the origin server (and to a lesser extent, intermediate caches, by their contribution to the age of a response) are
     784      <h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6</a>&nbsp;<a id="client-controlled.behavior" href="#client-controlled.behavior">Client-controlled Behavior</a></h2>
     785      <p id="rfc.section.3.6.p.1">While the origin server (and to a lesser extent, intermediate caches, by their contribution to the age of a response) are
    770786         the primary source of expiration information, in some cases the client might need to control a cache's decision about whether
    771787         to return a cached response without validating it. Clients do this using several directives of the Cache-Control header.
    772788      </p>
    773       <p id="rfc.section.2.6.p.2">A client's request <em class="bcp14">MAY</em> specify the maximum age it is willing to accept of an unvalidated response; specifying a value of zero forces the cache(s)
     789      <p id="rfc.section.3.6.p.2">A client's request <em class="bcp14">MAY</em> specify the maximum age it is willing to accept of an unvalidated response; specifying a value of zero forces the cache(s)
    774790         to revalidate all responses. A client <em class="bcp14">MAY</em> also specify the minimum time remaining before a response expires. Both of these options increase constraints on the behavior
    775791         of caches, and so cannot further relax the cache's approximation of semantic transparency.
    776792      </p>
    777       <p id="rfc.section.2.6.p.3">A client <em class="bcp14">MAY</em> also specify that it will accept stale responses, up to some maximum amount of staleness. This loosens the constraints on
     793      <p id="rfc.section.3.6.p.3">A client <em class="bcp14">MAY</em> also specify that it will accept stale responses, up to some maximum amount of staleness. This loosens the constraints on
    778794         the caches, and so might violate the origin server's specified constraints on semantic transparency, but might be necessary
    779795         to support disconnected operation, or high availability in the face of poor connectivity.
    780796      </p>
    781       <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="expiration.model" href="#expiration.model">Expiration Model</a></h1>
    782       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="server-specified.expiration" href="#server-specified.expiration">Server-Specified Expiration</a></h2>
    783       <p id="rfc.section.3.1.p.1">HTTP caching works best when caches can entirely avoid making requests to the origin server. The primary mechanism for avoiding
     797      <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="expiration.model" href="#expiration.model">Expiration Model</a></h1>
     798      <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="server-specified.expiration" href="#server-specified.expiration">Server-Specified Expiration</a></h2>
     799      <p id="rfc.section.4.1.p.1">HTTP caching works best when caches can entirely avoid making requests to the origin server. The primary mechanism for avoiding
    784800         requests is for an origin server to provide an explicit expiration time in the future, indicating that a response <em class="bcp14">MAY</em> be used to satisfy subsequent requests. In other words, a cache can return a fresh response without first contacting the server.
    785801      </p>
    786       <p id="rfc.section.3.1.p.2">Our expectation is that servers will assign future explicit expiration times to responses in the belief that the entity is
     802      <p id="rfc.section.4.1.p.2">Our expectation is that servers will assign future explicit expiration times to responses in the belief that the entity is
    787803         not likely to change, in a semantically significant way, before the expiration time is reached. This normally preserves semantic
    788804         transparency, as long as the server's expiration times are carefully chosen.
    789805      </p>
    790       <p id="rfc.section.3.1.p.3">The expiration mechanism applies only to responses taken from a cache and not to first-hand responses forwarded immediately
     806      <p id="rfc.section.4.1.p.3">The expiration mechanism applies only to responses taken from a cache and not to first-hand responses forwarded immediately
    791807         to the requesting client.
    792808      </p>
    793       <p id="rfc.section.3.1.p.4">If an origin server wishes to force a semantically transparent cache to validate every request, it <em class="bcp14">MAY</em> assign an explicit expiration time in the past. This means that the response is always stale, and so the cache <em class="bcp14">SHOULD</em> validate it before using it for subsequent requests. See <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;15.2.4</a> for a more restrictive way to force revalidation.
    794       </p>
    795       <p id="rfc.section.3.1.p.5">If an origin server wishes to force any HTTP/1.1 cache, no matter how it is configured, to validate every request, it <em class="bcp14">SHOULD</em> use the "must-revalidate" cache-control directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.4" title="Cache-Control">Section&nbsp;15.2</a>).
    796       </p>
    797       <p id="rfc.section.3.1.p.6">Servers specify explicit expiration times using either the Expires header, or the max-age directive of the Cache-Control header.</p>
    798       <p id="rfc.section.3.1.p.7">An expiration time cannot be used to force a user agent to refresh its display or reload a resource; its semantics apply only
     809      <p id="rfc.section.4.1.p.4">If an origin server wishes to force a semantically transparent cache to validate every request, it <em class="bcp14">MAY</em> assign an explicit expiration time in the past. This means that the response is always stale, and so the cache <em class="bcp14">SHOULD</em> validate it before using it for subsequent requests. See <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;16.2.4</a> for a more restrictive way to force revalidation.
     810      </p>
     811      <p id="rfc.section.4.1.p.5">If an origin server wishes to force any HTTP/1.1 cache, no matter how it is configured, to validate every request, it <em class="bcp14">SHOULD</em> use the "must-revalidate" cache-control directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.4" title="Cache-Control">Section&nbsp;16.2</a>).
     812      </p>
     813      <p id="rfc.section.4.1.p.6">Servers specify explicit expiration times using either the Expires header, or the max-age directive of the Cache-Control header.</p>
     814      <p id="rfc.section.4.1.p.7">An expiration time cannot be used to force a user agent to refresh its display or reload a resource; its semantics apply only
    799815         to caching mechanisms, and such mechanisms need only check a resource's expiration status when a new request for that resource
    800          is initiated. See <a href="#history.lists" title="History Lists">Section&nbsp;14</a> for an explanation of the difference between caches and history mechanisms.
    801       </p>
    802       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="heuristic.expiration" href="#heuristic.expiration">Heuristic Expiration</a></h2>
    803       <p id="rfc.section.3.2.p.1">Since origin servers do not always provide explicit expiration times, HTTP caches typically assign heuristic expiration times,
     816         is initiated. See <a href="#history.lists" title="History Lists">Section&nbsp;15</a> for an explanation of the difference between caches and history mechanisms.
     817      </p>
     818      <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="heuristic.expiration" href="#heuristic.expiration">Heuristic Expiration</a></h2>
     819      <p id="rfc.section.4.2.p.1">Since origin servers do not always provide explicit expiration times, HTTP caches typically assign heuristic expiration times,
    804820         employing algorithms that use other header values (such as the Last-Modified time) to estimate a plausible expiration time.
    805821         The HTTP/1.1 specification does not provide specific algorithms, but does impose worst-case constraints on their results.
     
    807823         origin servers to provide explicit expiration times as much as possible.
    808824      </p>
    809       <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a id="age.calculations" href="#age.calculations">Age Calculations</a></h2>
    810       <p id="rfc.section.3.3.p.1">In order to know if a cached entry is fresh, a cache needs to know if its age exceeds its freshness lifetime. We discuss how
    811          to calculate the latter in <a href="#expiration.calculations" title="Expiration Calculations">Section&nbsp;3.4</a>; this section describes how to calculate the age of a response or cache entry.
    812       </p>
    813       <p id="rfc.section.3.3.p.2">In this discussion, we use the term "now" to mean "the current value of the clock at the host performing the calculation."
     825      <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a id="age.calculations" href="#age.calculations">Age Calculations</a></h2>
     826      <p id="rfc.section.4.3.p.1">In order to know if a cached entry is fresh, a cache needs to know if its age exceeds its freshness lifetime. We discuss how
     827         to calculate the latter in <a href="#expiration.calculations" title="Expiration Calculations">Section&nbsp;4.4</a>; this section describes how to calculate the age of a response or cache entry.
     828      </p>
     829      <p id="rfc.section.4.3.p.2">In this discussion, we use the term "now" to mean "the current value of the clock at the host performing the calculation."
    814830         Hosts that use HTTP, but especially hosts running origin servers and caches, <em class="bcp14">SHOULD</em> use NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a> or some similar protocol to synchronize their clocks to a globally accurate time standard.
    815831      </p>
    816       <p id="rfc.section.3.3.p.3">HTTP/1.1 requires origin servers to send a Date header, if possible, with every response, giving the time at which the response
    817          was generated (see <a href="p1-messaging.html#header.date" title="Date">Section 8.3</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>). We use the term "date_value" to denote the value of the Date header, in a form appropriate for arithmetic operations.
    818       </p>
    819       <p id="rfc.section.3.3.p.4">HTTP/1.1 uses the Age response-header to convey the estimated age of the response message when obtained from a cache. The
     832      <p id="rfc.section.4.3.p.3">HTTP/1.1 requires origin servers to send a Date header, if possible, with every response, giving the time at which the response
     833         was generated (see <a href="p1-messaging.html#header.date" title="Date">Section 8.3</a> of <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). We use the term "date_value" to denote the value of the Date header, in a form appropriate for arithmetic operations.
     834      </p>
     835      <p id="rfc.section.4.3.p.4">HTTP/1.1 uses the Age response-header to convey the estimated age of the response message when obtained from a cache. The
    820836         Age field value is the cache's estimate of the amount of time since the response was generated or revalidated by the origin
    821837         server.
    822838      </p>
    823       <p id="rfc.section.3.3.p.5">In essence, the Age value is the sum of the time that the response has been resident in each of the caches along the path
     839      <p id="rfc.section.4.3.p.5">In essence, the Age value is the sum of the time that the response has been resident in each of the caches along the path
    824840         from the origin server, plus the amount of time it has been in transit along network paths.
    825841      </p>
    826       <p id="rfc.section.3.3.p.6">We use the term "age_value" to denote the value of the Age header, in a form appropriate for arithmetic operations.</p>
    827       <p id="rfc.section.3.3.p.7">A response's age can be calculated in two entirely independent ways: </p>
     842      <p id="rfc.section.4.3.p.6">We use the term "age_value" to denote the value of the Age header, in a form appropriate for arithmetic operations.</p>
     843      <p id="rfc.section.4.3.p.7">A response's age can be calculated in two entirely independent ways: </p>
    828844      <ol>
    829845         <li>now minus date_value, if the local clock is reasonably well synchronized to the origin server's clock. If the result is negative,
     
    832848         <li>age_value, if all of the caches along the response path implement HTTP/1.1.</li>
    833849      </ol>
    834       <p id="rfc.section.3.3.p.8">Given that we have two independent ways to compute the age of a response when it is received, we can combine these as</p>
    835       <div id="rfc.figure.u.1"></div><pre class="text">    corrected_received_age = max(now - date_value, age_value)
    836 </pre><p id="rfc.section.3.3.p.10">and as long as we have either nearly synchronized clocks or all-HTTP/1.1 paths, one gets a reliable (conservative) result.</p>
    837       <p id="rfc.section.3.3.p.11">Because of network-imposed delays, some significant interval might pass between the time that a server generates a response
     850      <p id="rfc.section.4.3.p.8">Given that we have two independent ways to compute the age of a response when it is received, we can combine these as</p>
     851      <div id="rfc.figure.u.4"></div><pre class="text">    corrected_received_age = max(now - date_value, age_value)
     852</pre><p id="rfc.section.4.3.p.10">and as long as we have either nearly synchronized clocks or all-HTTP/1.1 paths, one gets a reliable (conservative) result.</p>
     853      <p id="rfc.section.4.3.p.11">Because of network-imposed delays, some significant interval might pass between the time that a server generates a response
    838854         and the time it is received at the next outbound cache or client. If uncorrected, this delay could result in improperly low
    839855         ages.
    840856      </p>
    841       <p id="rfc.section.3.3.p.12">Because the request that resulted in the returned Age value must have been initiated prior to that Age value's generation,
     857      <p id="rfc.section.4.3.p.12">Because the request that resulted in the returned Age value must have been initiated prior to that Age value's generation,
    842858         we can correct for delays imposed by the network by recording the time at which the request was initiated. Then, when an Age
    843859         value is received, it <em class="bcp14">MUST</em> be interpreted relative to the time the request was initiated, not the time that the response was received. This algorithm
    844860         results in conservative behavior no matter how much delay is experienced. So, we compute:
    845861      </p>
    846       <div id="rfc.figure.u.2"></div><pre class="text">   corrected_initial_age = corrected_received_age
     862      <div id="rfc.figure.u.5"></div><pre class="text">   corrected_initial_age = corrected_received_age
    847863                         + (now - request_time)
    848 </pre><p id="rfc.section.3.3.p.14">where "request_time" is the time (according to the local clock) when the request that elicited this response was sent.</p>
    849       <p id="rfc.section.3.3.p.15">Summary of age calculation algorithm, when a cache receives a response:</p>
    850       <div id="rfc.figure.u.3"></div><pre class="text">   /*
     864</pre><p id="rfc.section.4.3.p.14">where "request_time" is the time (according to the local clock) when the request that elicited this response was sent.</p>
     865      <p id="rfc.section.4.3.p.15">Summary of age calculation algorithm, when a cache receives a response:</p>
     866      <div id="rfc.figure.u.6"></div><pre class="text">   /*
    851867    * age_value
    852868    *      is the value of Age: header received by the cache with
     
    870886   resident_time = now - response_time;
    871887   current_age   = corrected_initial_age + resident_time;
    872 </pre><p id="rfc.section.3.3.p.17">The current_age of a cache entry is calculated by adding the amount of time (in seconds) since the cache entry was last validated
     888</pre><p id="rfc.section.4.3.p.17">The current_age of a cache entry is calculated by adding the amount of time (in seconds) since the cache entry was last validated
    873889         by the origin server to the corrected_initial_age. When a response is generated from a cache entry, the cache <em class="bcp14">MUST</em> include a single Age header field in the response with a value equal to the cache entry's current_age.
    874890      </p>
    875       <p id="rfc.section.3.3.p.18">The presence of an Age header field in a response implies that a response is not first-hand. However, the converse is not
     891      <p id="rfc.section.4.3.p.18">The presence of an Age header field in a response implies that a response is not first-hand. However, the converse is not
    876892         true, since the lack of an Age header field in a response does not imply that the response is first-hand unless all caches
    877893         along the request path are compliant with HTTP/1.1 (i.e., older HTTP caches did not implement the Age header field).
    878894      </p>
    879       <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a id="expiration.calculations" href="#expiration.calculations">Expiration Calculations</a></h2>
    880       <p id="rfc.section.3.4.p.1">In order to decide whether a response is fresh or stale, we need to compare its freshness lifetime to its age. The age is
    881          calculated as described in <a href="#age.calculations" title="Age Calculations">Section&nbsp;3.3</a>; this section describes how to calculate the freshness lifetime, and to determine if a response has expired. In the discussion
     895      <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a>&nbsp;<a id="expiration.calculations" href="#expiration.calculations">Expiration Calculations</a></h2>
     896      <p id="rfc.section.4.4.p.1">In order to decide whether a response is fresh or stale, we need to compare its freshness lifetime to its age. The age is
     897         calculated as described in <a href="#age.calculations" title="Age Calculations">Section&nbsp;4.3</a>; this section describes how to calculate the freshness lifetime, and to determine if a response has expired. In the discussion
    882898         below, the values can be represented in any form appropriate for arithmetic operations.
    883899      </p>
    884       <p id="rfc.section.3.4.p.2">We use the term "expires_value" to denote the value of the Expires header. We use the term "max_age_value" to denote an appropriate
    885          value of the number of seconds carried by the "max-age" directive of the Cache-Control header in a response (see <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>).
    886       </p>
    887       <p id="rfc.section.3.4.p.3">The max-age directive takes priority over Expires, so if max-age is present in a response, the calculation is simply:</p>
    888       <div id="rfc.figure.u.4"></div><pre class="text">   freshness_lifetime = max_age_value
    889 </pre><p id="rfc.section.3.4.p.5">Otherwise, if Expires is present in the response, the calculation is:</p>
    890       <div id="rfc.figure.u.5"></div><pre class="text">   freshness_lifetime = expires_value - date_value
    891 </pre><p id="rfc.section.3.4.p.7">Note that neither of these calculations is vulnerable to clock skew, since all of the information comes from the origin server.</p>
    892       <p id="rfc.section.3.4.p.8">If none of Expires, Cache-Control: max-age, or Cache-Control: s-maxage (see <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>) appears in the response, and the response does not include other restrictions on caching, the cache <em class="bcp14">MAY</em> compute a freshness lifetime using a heuristic. The cache <em class="bcp14">MUST</em> attach Warning 113 to any response whose age is more than 24 hours if such warning has not already been added.
    893       </p>
    894       <p id="rfc.section.3.4.p.9">Also, if the response does have a Last-Modified time, the heuristic expiration value <em class="bcp14">SHOULD</em> be no more than some fraction of the interval since that time. A typical setting of this fraction might be 10%.
    895       </p>
    896       <p id="rfc.section.3.4.p.10">The calculation to determine if a response has expired is quite simple:</p>
    897       <div id="rfc.figure.u.6"></div><pre class="text">   response_is_fresh = (freshness_lifetime &gt; current_age)
    898 </pre><h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="disambiguating.expiration.values" href="#disambiguating.expiration.values">Disambiguating Expiration Values</a></h2>
    899       <p id="rfc.section.3.5.p.1">Because expiration values are assigned optimistically, it is possible for two caches to contain fresh values for the same
     900      <p id="rfc.section.4.4.p.2">We use the term "expires_value" to denote the value of the Expires header. We use the term "max_age_value" to denote an appropriate
     901         value of the number of seconds carried by the "max-age" directive of the Cache-Control header in a response (see <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>).
     902      </p>
     903      <p id="rfc.section.4.4.p.3">The max-age directive takes priority over Expires, so if max-age is present in a response, the calculation is simply:</p>
     904      <div id="rfc.figure.u.7"></div><pre class="text">   freshness_lifetime = max_age_value
     905</pre><p id="rfc.section.4.4.p.5">Otherwise, if Expires is present in the response, the calculation is:</p>
     906      <div id="rfc.figure.u.8"></div><pre class="text">   freshness_lifetime = expires_value - date_value
     907</pre><p id="rfc.section.4.4.p.7">Note that neither of these calculations is vulnerable to clock skew, since all of the information comes from the origin server.</p>
     908      <p id="rfc.section.4.4.p.8">If none of Expires, Cache-Control: max-age, or Cache-Control: s-maxage (see <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>) appears in the response, and the response does not include other restrictions on caching, the cache <em class="bcp14">MAY</em> compute a freshness lifetime using a heuristic. The cache <em class="bcp14">MUST</em> attach Warning 113 to any response whose age is more than 24 hours if such warning has not already been added.
     909      </p>
     910      <p id="rfc.section.4.4.p.9">Also, if the response does have a Last-Modified time, the heuristic expiration value <em class="bcp14">SHOULD</em> be no more than some fraction of the interval since that time. A typical setting of this fraction might be 10%.
     911      </p>
     912      <p id="rfc.section.4.4.p.10">The calculation to determine if a response has expired is quite simple:</p>
     913      <div id="rfc.figure.u.9"></div><pre class="text">   response_is_fresh = (freshness_lifetime &gt; current_age)
     914</pre><h2 id="rfc.section.4.5"><a href="#rfc.section.4.5">4.5</a>&nbsp;<a id="disambiguating.expiration.values" href="#disambiguating.expiration.values">Disambiguating Expiration Values</a></h2>
     915      <p id="rfc.section.4.5.p.1">Because expiration values are assigned optimistically, it is possible for two caches to contain fresh values for the same
    900916         resource that are different.
    901917      </p>
    902       <p id="rfc.section.3.5.p.2">If a client performing a retrieval receives a non-first-hand response for a request that was already fresh in its own cache,
    903          and the Date header in its existing cache entry is newer than the Date on the new response, then the client <em class="bcp14">MAY</em> ignore the response. If so, it <em class="bcp14">MAY</em> retry the request with a "Cache-Control: max-age=0" directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.5" title="Cache-Control">Section&nbsp;15.2</a>), to force a check with the origin server.
    904       </p>
    905       <p id="rfc.section.3.5.p.3">If a cache has two fresh responses for the same representation with different validators, it <em class="bcp14">MUST</em> use the one with the more recent Date header. This situation might arise because the cache is pooling responses from other
     918      <p id="rfc.section.4.5.p.2">If a client performing a retrieval receives a non-first-hand response for a request that was already fresh in its own cache,
     919         and the Date header in its existing cache entry is newer than the Date on the new response, then the client <em class="bcp14">MAY</em> ignore the response. If so, it <em class="bcp14">MAY</em> retry the request with a "Cache-Control: max-age=0" directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.5" title="Cache-Control">Section&nbsp;16.2</a>), to force a check with the origin server.
     920      </p>
     921      <p id="rfc.section.4.5.p.3">If a cache has two fresh responses for the same representation with different validators, it <em class="bcp14">MUST</em> use the one with the more recent Date header. This situation might arise because the cache is pooling responses from other
    906922         caches, or because a client has asked for a reload or a revalidation of an apparently fresh cache entry.
    907923      </p>
    908       <h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6</a>&nbsp;<a id="disambiguating.multiple.responses" href="#disambiguating.multiple.responses">Disambiguating Multiple Responses</a></h2>
    909       <p id="rfc.section.3.6.p.1">Because a client might be receiving responses via multiple paths, so that some responses flow through one set of caches and
     924      <h2 id="rfc.section.4.6"><a href="#rfc.section.4.6">4.6</a>&nbsp;<a id="disambiguating.multiple.responses" href="#disambiguating.multiple.responses">Disambiguating Multiple Responses</a></h2>
     925      <p id="rfc.section.4.6.p.1">Because a client might be receiving responses via multiple paths, so that some responses flow through one set of caches and
    910926         other responses flow through a different set of caches, a client might receive responses in an order different from that in
    911927         which the origin server sent them. We would like the client to use the most recently generated response, even if older responses
    912928         are still apparently fresh.
    913929      </p>
    914       <p id="rfc.section.3.6.p.2">Neither the entity tag nor the expiration value can impose an ordering on responses, since it is possible that a later response
     930      <p id="rfc.section.4.6.p.2">Neither the entity tag nor the expiration value can impose an ordering on responses, since it is possible that a later response
    915931         intentionally carries an earlier expiration time. The Date values are ordered to a granularity of one second.
    916932      </p>
    917       <p id="rfc.section.3.6.p.3">When a client tries to revalidate a cache entry, and the response it receives contains a Date header that appears to be older
     933      <p id="rfc.section.4.6.p.3">When a client tries to revalidate a cache entry, and the response it receives contains a Date header that appears to be older
    918934         than the one for the existing entry, then the client <em class="bcp14">SHOULD</em> repeat the request unconditionally, and include
    919935      </p>
    920       <div id="rfc.figure.u.7"></div><pre class="text">    Cache-Control: max-age=0
    921 </pre><p id="rfc.section.3.6.p.5">to force any intermediate caches to validate their copies directly with the origin server, or</p>
    922       <div id="rfc.figure.u.8"></div><pre class="text">    Cache-Control: no-cache
    923 </pre><p id="rfc.section.3.6.p.7">to force any intermediate caches to obtain a new copy from the origin server.</p>
    924       <p id="rfc.section.3.6.p.8">If the Date values are equal, then the client <em class="bcp14">MAY</em> use either response (or <em class="bcp14">MAY</em>, if it is being extremely prudent, request a new response). Servers <em class="bcp14">MUST NOT</em> depend on clients being able to choose deterministically between responses generated during the same second, if their expiration
     936      <div id="rfc.figure.u.10"></div><pre class="text">    Cache-Control: max-age=0
     937</pre><p id="rfc.section.4.6.p.5">to force any intermediate caches to validate their copies directly with the origin server, or</p>
     938      <div id="rfc.figure.u.11"></div><pre class="text">    Cache-Control: no-cache
     939</pre><p id="rfc.section.4.6.p.7">to force any intermediate caches to obtain a new copy from the origin server.</p>
     940      <p id="rfc.section.4.6.p.8">If the Date values are equal, then the client <em class="bcp14">MAY</em> use either response (or <em class="bcp14">MAY</em>, if it is being extremely prudent, request a new response). Servers <em class="bcp14">MUST NOT</em> depend on clients being able to choose deterministically between responses generated during the same second, if their expiration
    925941         times overlap.
    926942      </p>
    927       <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="validation.model" href="#validation.model">Validation Model</a></h1>
    928       <p id="rfc.section.4.p.1">When a cache has a stale entry that it would like to use as a response to a client's request, it first has to check with the
     943      <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="validation.model" href="#validation.model">Validation Model</a></h1>
     944      <p id="rfc.section.5.p.1">When a cache has a stale entry that it would like to use as a response to a client's request, it first has to check with the
    929945         origin server (or possibly an intermediate cache with a fresh response) to see if its cached entry is still usable. We call
    930946         this "validating" the cache entry.
    931947      </p>
    932       <p id="rfc.section.4.p.2">HTTP's conditional request mechanism, defined in <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, is used to avoid retransmitting the response payload when the cached entry is valid. When a cached response includes one
     948      <p id="rfc.section.5.p.2">HTTP's conditional request mechanism, defined in <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, is used to avoid retransmitting the response payload when the cached entry is valid. When a cached response includes one
    933949         or more "cache validators," such as the field values of an ETag or Last-Modified header field, then a validating GET request <em class="bcp14">SHOULD</em> be made conditional to those field values. The server checks the conditional request's validator against the current state
    934950         of the requested resource and, if they match, the server responds with a 304 (Not Modified) status code to indicate that the
     
    937953         be satisfied and the cache entry supplanted without the need for an additional network round-trip.
    938954      </p>
    939       <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="response.cacheability" href="#response.cacheability">Response Cacheability</a></h1>
    940       <p id="rfc.section.5.p.1">Unless specifically constrained by a cache-control (<a href="#header.cache-control" id="rfc.xref.header.cache-control.6" title="Cache-Control">Section&nbsp;15.2</a>) directive, a caching system <em class="bcp14">MAY</em> always store a successful response (see <a href="#errors.or.incomplete.response.cache.behavior" title="Errors or Incomplete Response Cache Behavior">Section&nbsp;9</a>) as a cache entry, <em class="bcp14">MAY</em> return it without validation if it is fresh, and <em class="bcp14">MAY</em> return it after successful validation. If there is neither a cache validator nor an explicit expiration time associated with
     955      <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="response.cacheability" href="#response.cacheability">Response Cacheability</a></h1>
     956      <p id="rfc.section.6.p.1">Unless specifically constrained by a cache-control (<a href="#header.cache-control" id="rfc.xref.header.cache-control.6" title="Cache-Control">Section&nbsp;16.2</a>) directive, a caching system <em class="bcp14">MAY</em> always store a successful response (see <a href="#errors.or.incomplete.response.cache.behavior" title="Errors or Incomplete Response Cache Behavior">Section&nbsp;10</a>) as a cache entry, <em class="bcp14">MAY</em> return it without validation if it is fresh, and <em class="bcp14">MAY</em> return it after successful validation. If there is neither a cache validator nor an explicit expiration time associated with
    941957         a response, we do not expect it to be cached, but certain caches <em class="bcp14">MAY</em> violate this expectation (for example, when little or no network connectivity is available). A client can usually detect that
    942958         such a response was taken from a cache by comparing the Date header to the current time.
     
    946962         </dd>
    947963      </dl>
    948       <p id="rfc.section.5.p.2">However, in some cases it might be inappropriate for a cache to retain an entity, or to return it in response to a subsequent
     964      <p id="rfc.section.6.p.2">However, in some cases it might be inappropriate for a cache to retain an entity, or to return it in response to a subsequent
    949965         request. This might be because absolute semantic transparency is deemed necessary by the service author, or because of security
    950966         or privacy considerations. Certain cache-control directives are therefore provided so that the server can indicate that certain
    951967         resource entities, or portions thereof, are not to be cached regardless of other considerations.
    952968      </p>
    953       <p id="rfc.section.5.p.3">Note that <a href="p7-auth.html#header.authorization" title="Authorization">Section 3.1</a> of <a href="#Part7" id="rfc.xref.Part7.1"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a> normally prevents a shared cache from saving and returning a response to a previous request if that request included an Authorization
     969      <p id="rfc.section.6.p.3">Note that <a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.1"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a> normally prevents a shared cache from saving and returning a response to a previous request if that request included an Authorization
    954970         header.
    955971      </p>
    956       <p id="rfc.section.5.p.4">A response received with a status code of 200, 203, 206, 300, 301 or 410 <em class="bcp14">MAY</em> be stored by a cache and used in reply to a subsequent request, subject to the expiration mechanism, unless a cache-control
     972      <p id="rfc.section.6.p.4">A response received with a status code of 200, 203, 206, 300, 301 or 410 <em class="bcp14">MAY</em> be stored by a cache and used in reply to a subsequent request, subject to the expiration mechanism, unless a cache-control
    957973         directive prohibits caching. However, a cache that does not support the Range and Content-Range headers <em class="bcp14">MUST NOT</em> cache 206 (Partial Content) responses.
    958974      </p>
    959       <p id="rfc.section.5.p.5">A response received with any other status code (e.g. status codes 302 and 307) <em class="bcp14">MUST NOT</em> be returned in a reply to a subsequent request unless there are cache-control directives or another header(s) that explicitly
    960          allow it. For example, these include the following: an Expires header (<a href="#header.expires" id="rfc.xref.header.expires.1" title="Expires">Section&nbsp;15.3</a>); a "max-age", "s-maxage", "must-revalidate", "proxy-revalidate", "public" or "private" cache-control directive (<a href="#header.cache-control" id="rfc.xref.header.cache-control.7" title="Cache-Control">Section&nbsp;15.2</a>).
    961       </p>
    962       <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="constructing.responses.from.caches" href="#constructing.responses.from.caches">Constructing Responses From Caches</a></h1>
    963       <p id="rfc.section.6.p.1">The purpose of an HTTP cache is to store information received in response to requests for use in responding to future requests.
     975      <p id="rfc.section.6.p.5">A response received with any other status code (e.g. status codes 302 and 307) <em class="bcp14">MUST NOT</em> be returned in a reply to a subsequent request unless there are cache-control directives or another header(s) that explicitly
     976         allow it. For example, these include the following: an Expires header (<a href="#header.expires" id="rfc.xref.header.expires.1" title="Expires">Section&nbsp;16.3</a>); a "max-age", "s-maxage", "must-revalidate", "proxy-revalidate", "public" or "private" cache-control directive (<a href="#header.cache-control" id="rfc.xref.header.cache-control.7" title="Cache-Control">Section&nbsp;16.2</a>).
     977      </p>
     978      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="constructing.responses.from.caches" href="#constructing.responses.from.caches">Constructing Responses From Caches</a></h1>
     979      <p id="rfc.section.7.p.1">The purpose of an HTTP cache is to store information received in response to requests for use in responding to future requests.
    964980         In many cases, a cache simply returns the appropriate parts of a response to the requester. However, if the cache holds a
    965981         cache entry based on a previous response, it might have to combine parts of a new response with what is held in the cache
    966982         entry.
    967983      </p>
    968       <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="end-to-end.and.hop-by-hop.headers" href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></h2>
    969       <p id="rfc.section.6.1.p.1">For the purpose of defining the behavior of caches and non-caching proxies, we divide HTTP headers into two categories: </p>
     984      <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="end-to-end.and.hop-by-hop.headers" href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></h2>
     985      <p id="rfc.section.7.1.p.1">For the purpose of defining the behavior of caches and non-caching proxies, we divide HTTP headers into two categories: </p>
    970986      <ul>
    971987         <li>End-to-end headers, which are transmitted to the ultimate recipient of a request or response. End-to-end headers in responses <em class="bcp14">MUST</em> be stored as part of a cache entry and <em class="bcp14">MUST</em> be transmitted in any response formed from a cache entry.
     
    975991         </li>
    976992      </ul>
    977       <p id="rfc.section.6.1.p.2">The following HTTP/1.1 headers are hop-by-hop headers: </p>
     993      <p id="rfc.section.7.1.p.2">The following HTTP/1.1 headers are hop-by-hop headers: </p>
    978994      <ul>
    979995         <li>Connection</li>
     
    9861002         <li>Upgrade</li>
    9871003      </ul>
    988       <p id="rfc.section.6.1.p.3">All other headers defined by HTTP/1.1 are end-to-end headers.</p>
    989       <p id="rfc.section.6.1.p.4">Other hop-by-hop headers <em class="bcp14">MUST</em> be listed in a Connection header (<a href="p1-messaging.html#header.connection" title="Connection">Section 8.1</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>).
    990       </p>
    991       <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a id="non-modifiable.headers" href="#non-modifiable.headers">Non-modifiable Headers</a></h2>
    992       <p id="rfc.section.6.2.p.1">Some features of HTTP/1.1, such as Digest Authentication, depend on the value of certain end-to-end headers. A transparent
     1004      <p id="rfc.section.7.1.p.3">All other headers defined by HTTP/1.1 are end-to-end headers.</p>
     1005      <p id="rfc.section.7.1.p.4">Other hop-by-hop headers <em class="bcp14">MUST</em> be listed in a Connection header (<a href="p1-messaging.html#header.connection" title="Connection">Section 8.1</a> of <a href="#Part1" id="rfc.xref.Part1.14"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
     1006      </p>
     1007      <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="non-modifiable.headers" href="#non-modifiable.headers">Non-modifiable Headers</a></h2>
     1008      <p id="rfc.section.7.2.p.1">Some features of HTTP/1.1, such as Digest Authentication, depend on the value of certain end-to-end headers. A transparent
    9931009         proxy <em class="bcp14">SHOULD NOT</em> modify an end-to-end header unless the definition of that header requires or specifically allows that.
    9941010      </p>
    995       <p id="rfc.section.6.2.p.2">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a request or response, and it <em class="bcp14">MUST NOT</em> add any of these fields if not already present:
     1011      <p id="rfc.section.7.2.p.2">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a request or response, and it <em class="bcp14">MUST NOT</em> add any of these fields if not already present:
    9961012      </p>
    9971013      <ul>
     
    10011017         <li>Last-Modified</li>
    10021018      </ul>
    1003       <p id="rfc.section.6.2.p.3">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a response:
     1019      <p id="rfc.section.7.2.p.3">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a response:
    10041020      </p>
    10051021      <ul>
    10061022         <li>Expires</li>
    10071023      </ul>
    1008       <p id="rfc.section.6.2.p.4">but it <em class="bcp14">MAY</em> add any of these fields if not already present. If an Expires header is added, it <em class="bcp14">MUST</em> be given a field-value identical to that of the Date header in that response.
    1009       </p>
    1010       <p id="rfc.section.6.2.p.5">A proxy <em class="bcp14">MUST NOT</em> modify or add any of the following fields in a message that contains the no-transform cache-control directive, or in any request:
     1024      <p id="rfc.section.7.2.p.4">but it <em class="bcp14">MAY</em> add any of these fields if not already present. If an Expires header is added, it <em class="bcp14">MUST</em> be given a field-value identical to that of the Date header in that response.
     1025      </p>
     1026      <p id="rfc.section.7.2.p.5">A proxy <em class="bcp14">MUST NOT</em> modify or add any of the following fields in a message that contains the no-transform cache-control directive, or in any request:
    10111027      </p>
    10121028      <ul>
     
    10151031         <li>Content-Type</li>
    10161032      </ul>
    1017       <p id="rfc.section.6.2.p.6">A non-transparent proxy <em class="bcp14">MAY</em> modify or add these fields to a message that does not include no-transform, but if it does so, it <em class="bcp14">MUST</em> add a Warning 214 (Transformation applied) if one does not already appear in the message (see <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;15.6</a>).
     1033      <p id="rfc.section.7.2.p.6">A non-transparent proxy <em class="bcp14">MAY</em> modify or add these fields to a message that does not include no-transform, but if it does so, it <em class="bcp14">MUST</em> add a Warning 214 (Transformation applied) if one does not already appear in the message (see <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;16.6</a>).
    10181034      </p>
    10191035      <dl class="empty">
     
    10221038         </dd>
    10231039      </dl>
    1024       <p id="rfc.section.6.2.p.7">The Content-Length field of a request or response is added or deleted according to the rules in <a href="p1-messaging.html#message.length" title="Message Length">Section 4.4</a> of <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. A transparent proxy <em class="bcp14">MUST</em> preserve the entity-length (<a href="p3-payload.html#entity.length" title="Entity Length">Section 3.2.2</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) of the entity-body, although it <em class="bcp14">MAY</em> change the transfer-length (<a href="p1-messaging.html#message.length" title="Message Length">Section 4.4</a> of <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
    1025       </p>
    1026       <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a id="combining.headers" href="#combining.headers">Combining Headers</a></h2>
    1027       <p id="rfc.section.6.3.p.1">When a cache makes a validating request to a server, and the server provides a 304 (Not Modified) response or a 206 (Partial
     1040      <p id="rfc.section.7.2.p.7">The Content-Length field of a request or response is added or deleted according to the rules in <a href="p1-messaging.html#message.length" title="Message Length">Section 4.4</a> of <a href="#Part1" id="rfc.xref.Part1.15"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. A transparent proxy <em class="bcp14">MUST</em> preserve the entity-length (<a href="p3-payload.html#entity.length" title="Entity Length">Section 4.2.2</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) of the entity-body, although it <em class="bcp14">MAY</em> change the transfer-length (<a href="p1-messaging.html#message.length" title="Message Length">Section 4.4</a> of <a href="#Part1" id="rfc.xref.Part1.16"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
     1041      </p>
     1042      <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a>&nbsp;<a id="combining.headers" href="#combining.headers">Combining Headers</a></h2>
     1043      <p id="rfc.section.7.3.p.1">When a cache makes a validating request to a server, and the server provides a 304 (Not Modified) response or a 206 (Partial
    10281044         Content) response, the cache then constructs a response to send to the requesting client.
    10291045      </p>
    1030       <p id="rfc.section.6.3.p.2">If the status code is 304 (Not Modified), the cache uses the entity-body stored in the cache entry as the entity-body of this
     1046      <p id="rfc.section.7.3.p.2">If the status code is 304 (Not Modified), the cache uses the entity-body stored in the cache entry as the entity-body of this
    10311047         outgoing response. If the status code is 206 (Partial Content) and the ETag or Last-Modified headers match exactly, the cache <em class="bcp14">MAY</em> combine the contents stored in the cache entry with the new contents received in the response and use the result as the entity-body
    1032          of this outgoing response, (see <a href="p5-range.html#combining.byte.ranges" title="Combining Byte Ranges">Section 4</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>).
    1033       </p>
    1034       <p id="rfc.section.6.3.p.3">The end-to-end headers stored in the cache entry are used for the constructed response, except that </p>
     1048         of this outgoing response, (see <a href="p5-range.html#combining.byte.ranges" title="Combining Byte Ranges">Section 5</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>).
     1049      </p>
     1050      <p id="rfc.section.7.3.p.3">The end-to-end headers stored in the cache entry are used for the constructed response, except that </p>
    10351051      <ul>
    1036          <li>any stored Warning headers with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section&nbsp;15.6</a>) <em class="bcp14">MUST</em> be deleted from the cache entry and the forwarded response.
     1052         <li>any stored Warning headers with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section&nbsp;16.6</a>) <em class="bcp14">MUST</em> be deleted from the cache entry and the forwarded response.
    10371053         </li>
    10381054         <li>any stored Warning headers with warn-code 2xx <em class="bcp14">MUST</em> be retained in the cache entry and the forwarded response.
     
    10411057         </li>
    10421058      </ul>
    1043       <p id="rfc.section.6.3.p.4">Unless the cache decides to remove the cache entry, it <em class="bcp14">MUST</em> also replace the end-to-end headers stored with the cache entry with corresponding headers received in the incoming response,
     1059      <p id="rfc.section.7.3.p.4">Unless the cache decides to remove the cache entry, it <em class="bcp14">MUST</em> also replace the end-to-end headers stored with the cache entry with corresponding headers received in the incoming response,
    10441060         except for Warning headers as described immediately above. If a header field-name in the incoming response matches more than
    10451061         one header in the cache entry, all such old headers <em class="bcp14">MUST</em> be replaced.
    10461062      </p>
    1047       <p id="rfc.section.6.3.p.5">In other words, the set of end-to-end headers received in the incoming response overrides all corresponding end-to-end headers
     1063      <p id="rfc.section.7.3.p.5">In other words, the set of end-to-end headers received in the incoming response overrides all corresponding end-to-end headers
    10481064         stored with the cache entry (except for stored Warning headers with warn-code 1xx, which are deleted even if not overridden).
    10491065      </p>
     
    10551071         </dd>
    10561072      </dl>
    1057       <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="caching.negotiated.responses" href="#caching.negotiated.responses">Caching Negotiated Responses</a></h1>
    1058       <p id="rfc.section.7.p.1">Use of server-driven content negotiation (<a href="p3-payload.html#server-driven.negotiation" title="Server-driven Negotiation">Section 4.1</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), as indicated by the presence of a Vary header field in a response, alters the conditions and procedure by which a cache
    1059          can use the response for subsequent requests. See <a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section&nbsp;15.5</a> for use of the Vary header field by servers.
    1060       </p>
    1061       <p id="rfc.section.7.p.2">A server <em class="bcp14">SHOULD</em> use the Vary header field to inform a cache of what request-header fields were used to select among multiple representations
     1073      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="caching.negotiated.responses" href="#caching.negotiated.responses">Caching Negotiated Responses</a></h1>
     1074      <p id="rfc.section.8.p.1">Use of server-driven content negotiation (<a href="p3-payload.html#server-driven.negotiation" title="Server-driven Negotiation">Section 5.1</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), as indicated by the presence of a Vary header field in a response, alters the conditions and procedure by which a cache
     1075         can use the response for subsequent requests. See <a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section&nbsp;16.5</a> for use of the Vary header field by servers.
     1076      </p>
     1077      <p id="rfc.section.8.p.2">A server <em class="bcp14">SHOULD</em> use the Vary header field to inform a cache of what request-header fields were used to select among multiple representations
    10621078         of a cacheable response subject to server-driven negotiation. The set of header fields named by the Vary field value is known
    10631079         as the "selecting" request-headers.
    10641080      </p>
    1065       <p id="rfc.section.7.p.3">When the cache receives a subsequent request whose Request-URI specifies one or more cache entries including a Vary header
     1081      <p id="rfc.section.8.p.3">When the cache receives a subsequent request whose Request-URI specifies one or more cache entries including a Vary header
    10661082         field, the cache <em class="bcp14">MUST NOT</em> use such a cache entry to construct a response to the new request unless all of the selecting request-headers present in the
    10671083         new request match the corresponding stored request-headers in the original request.
    10681084      </p>
    1069       <p id="rfc.section.7.p.4">The selecting request-headers from two requests are defined to match if and only if the selecting request-headers in the first
     1085      <p id="rfc.section.8.p.4">The selecting request-headers from two requests are defined to match if and only if the selecting request-headers in the first
    10701086         request can be transformed to the selecting request-headers in the second request by adding or removing linear white space
    10711087         (LWS) at places where this is allowed by the corresponding BNF, and/or combining multiple message-header fields with the same
    1072          field name following the rules about message headers in <a href="p1-messaging.html#message.headers" title="Message Headers">Section 4.2</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>.
    1073       </p>
    1074       <p id="rfc.section.7.p.5">A Vary header field-value of "*" always fails to match and subsequent requests on that resource can only be properly interpreted
     1088         field name following the rules about message headers in <a href="p1-messaging.html#message.headers" title="Message Headers">Section 4.2</a> of <a href="#Part1" id="rfc.xref.Part1.17"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
     1089      </p>
     1090      <p id="rfc.section.8.p.5">A Vary header field-value of "*" always fails to match and subsequent requests on that resource can only be properly interpreted
    10751091         by the origin server.
    10761092      </p>
    1077       <p id="rfc.section.7.p.6">If the selecting request header fields for the cached entry do not match the selecting request header fields of the new request,
     1093      <p id="rfc.section.8.p.6">If the selecting request header fields for the cached entry do not match the selecting request header fields of the new request,
    10781094         then the cache <em class="bcp14">MUST NOT</em> use a cached entry to satisfy the request unless it first relays the new request to the origin server in a conditional request
    10791095         and the server responds with 304 (Not Modified), including an entity tag or Content-Location that indicates the entity to
    10801096         be used.
    10811097      </p>
    1082       <p id="rfc.section.7.p.7">If an entity tag was assigned to a cached representation, the forwarded request <em class="bcp14">SHOULD</em> be conditional and include the entity tags in an If-None-Match header field from all its cache entries for the resource. This
     1098      <p id="rfc.section.8.p.7">If an entity tag was assigned to a cached representation, the forwarded request <em class="bcp14">SHOULD</em> be conditional and include the entity tags in an If-None-Match header field from all its cache entries for the resource. This
    10831099         conveys to the server the set of entities currently held by the cache, so that if any one of these entities matches the requested
    10841100         entity, the server can use the ETag header field in its 304 (Not Modified) response to tell the cache which entry is appropriate.
    10851101         If the entity-tag of the new response matches that of an existing entry, the new response <em class="bcp14">SHOULD</em> be used to update the header fields of the existing entry, and the result <em class="bcp14">MUST</em> be returned to the client.
    10861102      </p>
    1087       <p id="rfc.section.7.p.8">If any of the existing cache entries contains only partial content for the associated entity, its entity-tag <em class="bcp14">SHOULD NOT</em> be included in the If-None-Match header field unless the request is for a range that would be fully satisfied by that entry.
    1088       </p>
    1089       <p id="rfc.section.7.p.9">If a cache receives a successful response whose Content-Location field matches that of an existing cache entry for the same
     1103      <p id="rfc.section.8.p.8">If any of the existing cache entries contains only partial content for the associated entity, its entity-tag <em class="bcp14">SHOULD NOT</em> be included in the If-None-Match header field unless the request is for a range that would be fully satisfied by that entry.
     1104      </p>
     1105      <p id="rfc.section.8.p.9">If a cache receives a successful response whose Content-Location field matches that of an existing cache entry for the same
    10901106         Request-URI, whose entity-tag differs from that of the existing entry, and whose Date is more recent than that of the existing
    10911107         entry, the existing entry <em class="bcp14">SHOULD NOT</em> be returned in response to future requests and <em class="bcp14">SHOULD</em> be deleted from the cache.
    10921108      </p>
    1093       <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="shared.and.non-shared.caches" href="#shared.and.non-shared.caches">Shared and Non-Shared Caches</a></h1>
    1094       <p id="rfc.section.8.p.1">For reasons of security and privacy, it is necessary to make a distinction between "shared" and "non-shared" caches. A non-shared
     1109      <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="shared.and.non-shared.caches" href="#shared.and.non-shared.caches">Shared and Non-Shared Caches</a></h1>
     1110      <p id="rfc.section.9.p.1">For reasons of security and privacy, it is necessary to make a distinction between "shared" and "non-shared" caches. A non-shared
    10951111         cache is one that is accessible only to a single user. Accessibility in this case <em class="bcp14">SHOULD</em> be enforced by appropriate security mechanisms. All other caches are considered to be "shared." Other sections of this specification
    10961112         place certain constraints on the operation of shared caches in order to prevent loss of privacy or failure of access controls.
    10971113      </p>
    1098       <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="errors.or.incomplete.response.cache.behavior" href="#errors.or.incomplete.response.cache.behavior">Errors or Incomplete Response Cache Behavior</a></h1>
    1099       <p id="rfc.section.9.p.1">A cache that receives an incomplete response (for example, with fewer bytes of data than specified in a Content-Length header) <em class="bcp14">MAY</em> store the response. However, the cache <em class="bcp14">MUST</em> treat this as a partial response. Partial responses <em class="bcp14">MAY</em> be combined as described in <a href="p5-range.html#combining.byte.ranges" title="Combining Byte Ranges">Section 4</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 result might be a full response or might still be partial. A cache <em class="bcp14">MUST NOT</em> return a partial response to a client without explicitly marking it as such, using the 206 (Partial Content) status code.
     1114      <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="errors.or.incomplete.response.cache.behavior" href="#errors.or.incomplete.response.cache.behavior">Errors or Incomplete Response Cache Behavior</a></h1>
     1115      <p id="rfc.section.10.p.1">A cache that receives an incomplete response (for example, with fewer bytes of data than specified in a Content-Length header) <em class="bcp14">MAY</em> store the response. However, the cache <em class="bcp14">MUST</em> treat this as a partial response. Partial responses <em class="bcp14">MAY</em> be combined as described in <a href="p5-range.html#combining.byte.ranges" title="Combining Byte Ranges">Section 5</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 result might be a full response or might still be partial. A cache <em class="bcp14">MUST NOT</em> return a partial response to a client without explicitly marking it as such, using the 206 (Partial Content) status code.
    11001116         A cache <em class="bcp14">MUST NOT</em> return a partial response using a status code of 200 (OK).
    11011117      </p>
    1102       <p id="rfc.section.9.p.2">If a cache receives a 5xx response while attempting to revalidate an entry, it <em class="bcp14">MAY</em> either forward this response to the requesting client, or act as if the server failed to respond. In the latter case, it <em class="bcp14">MAY</em> return a previously received response unless the cached entry includes the "must-revalidate" cache-control directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.8" title="Cache-Control">Section&nbsp;15.2</a>).
    1103       </p>
    1104       <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="side.effects.of.get.and.head" href="#side.effects.of.get.and.head">Side Effects of GET and HEAD</a></h1>
    1105       <p id="rfc.section.10.p.1">Unless the origin server explicitly prohibits the caching of their responses, the application of GET and HEAD methods to any
     1118      <p id="rfc.section.10.p.2">If a cache receives a 5xx response while attempting to revalidate an entry, it <em class="bcp14">MAY</em> either forward this response to the requesting client, or act as if the server failed to respond. In the latter case, it <em class="bcp14">MAY</em> return a previously received response unless the cached entry includes the "must-revalidate" cache-control directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.8" title="Cache-Control">Section&nbsp;16.2</a>).
     1119      </p>
     1120      <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a>&nbsp;<a id="side.effects.of.get.and.head" href="#side.effects.of.get.and.head">Side Effects of GET and HEAD</a></h1>
     1121      <p id="rfc.section.11.p.1">Unless the origin server explicitly prohibits the caching of their responses, the application of GET and HEAD methods to any
    11061122         resources <em class="bcp14">SHOULD NOT</em> have side effects that would lead to erroneous behavior if these responses are taken from a cache. They <em class="bcp14">MAY</em> still have side effects, but a cache is not required to consider such side effects in its caching decisions. Caches are always
    11071123         expected to observe an origin server's explicit restrictions on caching.
    11081124      </p>
    1109       <p id="rfc.section.10.p.2">We note one exception to this rule: since some applications have traditionally used GET and HEAD requests with URLs containing
     1125      <p id="rfc.section.11.p.2">We note one exception to this rule: since some applications have traditionally used GET and HEAD requests with URLs containing
    11101126         a query part to perform operations with significant side effects, caches <em class="bcp14">MUST NOT</em> treat responses to such URIs as fresh unless the server provides an explicit expiration time. This specifically means that
    1111          responses from HTTP/1.0 servers for such URIs <em class="bcp14">SHOULD NOT</em> be taken from a cache. See <a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 7.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a> for related information.
    1112       </p>
    1113       <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a>&nbsp;<a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Invalidation After Updates or Deletions</a></h1>
    1114       <p id="rfc.section.11.p.1">The effect of certain methods performed on a resource at the origin server might cause one or more existing cache entries
     1127         responses from HTTP/1.0 servers for such URIs <em class="bcp14">SHOULD NOT</em> be taken from a cache. See <a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 8.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a> for related information.
     1128      </p>
     1129      <h1 id="rfc.section.12"><a href="#rfc.section.12">12.</a>&nbsp;<a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Invalidation After Updates or Deletions</a></h1>
     1130      <p id="rfc.section.12.p.1">The effect of certain methods performed on a resource at the origin server might cause one or more existing cache entries
    11151131         to become non-transparently invalid. That is, although they might continue to be "fresh," they do not accurately reflect what
    11161132         the origin server would return for a new request on that resource.
    11171133      </p>
    1118       <p id="rfc.section.11.p.2">There is no way for HTTP to guarantee that all such cache entries are marked invalid. For example, the request that caused
     1134      <p id="rfc.section.12.p.2">There is no way for HTTP to guarantee that all such cache entries are marked invalid. For example, the request that caused
    11191135         the change at the origin server might not have gone through the proxy where a cache entry is stored. However, several rules
    11201136         help reduce the likelihood of erroneous behavior.
    11211137      </p>
    1122       <p id="rfc.section.11.p.3">In this section, the phrase "invalidate an entity" means that the cache will either remove all instances of that entity from
     1138      <p id="rfc.section.12.p.3">In this section, the phrase "invalidate an entity" means that the cache will either remove all instances of that entity from
    11231139         its storage, or will mark these as "invalid" and in need of a mandatory revalidation before they can be returned in response
    11241140         to a subsequent request.
    11251141      </p>
    1126       <p id="rfc.section.11.p.4">Some HTTP methods <em class="bcp14">MUST</em> cause a cache to invalidate an entity. This is either the entity referred to by the Request-URI, or by the Location or Content-Location
     1142      <p id="rfc.section.12.p.4">Some HTTP methods <em class="bcp14">MUST</em> cause a cache to invalidate an entity. This is either the entity referred to by the Request-URI, or by the Location or Content-Location
    11271143         headers (if present). These methods are:
    11281144      </p>
     
    11321148         <li>POST</li>
    11331149      </ul>
    1134       <p id="rfc.section.11.p.5">An invalidation based on the URI in a Location or Content-Location header <em class="bcp14">MUST NOT</em> be performed if the host part of that URI differs from the host part in the Request-URI. This helps prevent denial of service
     1150      <p id="rfc.section.12.p.5">An invalidation based on the URI in a Location or Content-Location header <em class="bcp14">MUST NOT</em> be performed if the host part of that URI differs from the host part in the Request-URI. This helps prevent denial of service
    11351151         attacks.
    11361152      </p>
    1137       <p id="rfc.section.11.p.6">A cache that passes through requests for methods it does not understand <em class="bcp14">SHOULD</em> invalidate any entities referred to by the Request-URI.
    1138       </p>
    1139       <h1 id="rfc.section.12"><a href="#rfc.section.12">12.</a>&nbsp;<a id="write-through.mandatory" href="#write-through.mandatory">Write-Through Mandatory</a></h1>
    1140       <p id="rfc.section.12.p.1">All methods that might be expected to cause modifications to the origin server's resources <em class="bcp14">MUST</em> be written through to the origin server. This currently includes all methods except for GET and HEAD. A cache <em class="bcp14">MUST NOT</em> reply to such a request from a client before having transmitted the request to the inbound server, and having received a corresponding
     1153      <p id="rfc.section.12.p.6">A cache that passes through requests for methods it does not understand <em class="bcp14">SHOULD</em> invalidate any entities referred to by the Request-URI.
     1154      </p>
     1155      <h1 id="rfc.section.13"><a href="#rfc.section.13">13.</a>&nbsp;<a id="write-through.mandatory" href="#write-through.mandatory">Write-Through Mandatory</a></h1>
     1156      <p id="rfc.section.13.p.1">All methods that might be expected to cause modifications to the origin server's resources <em class="bcp14">MUST</em> be written through to the origin server. This currently includes all methods except for GET and HEAD. A cache <em class="bcp14">MUST NOT</em> reply to such a request from a client before having transmitted the request to the inbound server, and having received a corresponding
    11411157         response from the inbound server. This does not prevent a proxy cache from sending a 100 (Continue) response before the inbound
    11421158         server has sent its final reply.
    11431159      </p>
    1144       <p id="rfc.section.12.p.2">The alternative (known as "write-back" or "copy-back" caching) is not allowed in HTTP/1.1, due to the difficulty of providing
     1160      <p id="rfc.section.13.p.2">The alternative (known as "write-back" or "copy-back" caching) is not allowed in HTTP/1.1, due to the difficulty of providing
    11451161         consistent updates and the problems arising from server, cache, or network failure prior to write-back.
    11461162      </p>
    1147       <h1 id="rfc.section.13"><a href="#rfc.section.13">13.</a>&nbsp;<a id="cache.replacement" href="#cache.replacement">Cache Replacement</a></h1>
    1148       <p id="rfc.section.13.p.1">If a new cacheable (see Sections <a href="#what.may.be.stored.by.caches" title="What May be Stored by Caches">15.2.2</a>, <a href="#disambiguating.expiration.values" title="Disambiguating Expiration Values">3.5</a>, <a href="#disambiguating.multiple.responses" title="Disambiguating Multiple Responses">3.6</a> and <a href="#errors.or.incomplete.response.cache.behavior" title="Errors or Incomplete Response Cache Behavior">9</a>) response is received from a resource while any existing responses for the same resource are cached, the cache <em class="bcp14">SHOULD</em> use the new response to reply to the current request. It <em class="bcp14">MAY</em> insert it into cache storage and <em class="bcp14">MAY</em>, if it meets all other requirements, use it to respond to any future requests that would previously have caused the old response
    1149          to be returned. If it inserts the new response into cache storage the rules in <a href="#combining.headers" title="Combining Headers">Section&nbsp;6.3</a> apply.
     1163      <h1 id="rfc.section.14"><a href="#rfc.section.14">14.</a>&nbsp;<a id="cache.replacement" href="#cache.replacement">Cache Replacement</a></h1>
     1164      <p id="rfc.section.14.p.1">If a new cacheable (see Sections <a href="#what.may.be.stored.by.caches" title="What May be Stored by Caches">16.2.2</a>, <a href="#disambiguating.expiration.values" title="Disambiguating Expiration Values">4.5</a>, <a href="#disambiguating.multiple.responses" title="Disambiguating Multiple Responses">4.6</a> and <a href="#errors.or.incomplete.response.cache.behavior" title="Errors or Incomplete Response Cache Behavior">10</a>) response is received from a resource while any existing responses for the same resource are cached, the cache <em class="bcp14">SHOULD</em> use the new response to reply to the current request. It <em class="bcp14">MAY</em> insert it into cache storage and <em class="bcp14">MAY</em>, if it meets all other requirements, use it to respond to any future requests that would previously have caused the old response
     1165         to be returned. If it inserts the new response into cache storage the rules in <a href="#combining.headers" title="Combining Headers">Section&nbsp;7.3</a> apply.
    11501166      </p>
    11511167      <dl class="empty">
     
    11531169         </dd>
    11541170      </dl>
    1155       <h1 id="rfc.section.14"><a href="#rfc.section.14">14.</a>&nbsp;<a id="history.lists" href="#history.lists">History Lists</a></h1>
    1156       <p id="rfc.section.14.p.1">User agents often have history mechanisms, such as "Back" buttons and history lists, which can be used to redisplay an entity
     1171      <h1 id="rfc.section.15"><a href="#rfc.section.15">15.</a>&nbsp;<a id="history.lists" href="#history.lists">History Lists</a></h1>
     1172      <p id="rfc.section.15.p.1">User agents often have history mechanisms, such as "Back" buttons and history lists, which can be used to redisplay an entity
    11571173         retrieved earlier in a session.
    11581174      </p>
    1159       <p id="rfc.section.14.p.2">History mechanisms and caches are different. In particular history mechanisms <em class="bcp14">SHOULD NOT</em> try to show a semantically transparent view of the current state of a resource. Rather, a history mechanism is meant to show
     1175      <p id="rfc.section.15.p.2">History mechanisms and caches are different. In particular history mechanisms <em class="bcp14">SHOULD NOT</em> try to show a semantically transparent view of the current state of a resource. Rather, a history mechanism is meant to show
    11601176         exactly what the user saw at the time when the resource was retrieved.
    11611177      </p>
    1162       <p id="rfc.section.14.p.3">By default, an expiration time does not apply to history mechanisms. If the entity is still in storage, a history mechanism <em class="bcp14">SHOULD</em> display it even if the entity has expired, unless the user has specifically configured the agent to refresh expired history
     1178      <p id="rfc.section.15.p.3">By default, an expiration time does not apply to history mechanisms. If the entity is still in storage, a history mechanism <em class="bcp14">SHOULD</em> display it even if the entity has expired, unless the user has specifically configured the agent to refresh expired history
    11631179         documents.
    11641180      </p>
    1165       <p id="rfc.section.14.p.4">This is not to be construed to prohibit the history mechanism from telling the user that a view might be stale. </p>
     1181      <p id="rfc.section.15.p.4">This is not to be construed to prohibit the history mechanism from telling the user that a view might be stale. </p>
    11661182      <dl class="empty">
    11671183         <dd> <b>Note:</b> if history list mechanisms unnecessarily prevent users from viewing stale resources, this will tend to force service authors
     
    11731189         </dd>
    11741190      </dl>
    1175       <h1 id="rfc.section.15"><a href="#rfc.section.15">15.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
    1176       <p id="rfc.section.15.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p>
    1177       <p id="rfc.section.15.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who
     1191      <h1 id="rfc.section.16"><a href="#rfc.section.16">16.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
     1192      <p id="rfc.section.16.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p>
     1193      <p id="rfc.section.16.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who
    11781194         receives the entity.
    11791195      </p>
    11801196      <div id="rfc.iref.a.2"></div>
    11811197      <div id="rfc.iref.h.2"></div>
    1182       <h2 id="rfc.section.15.1"><a href="#rfc.section.15.1">15.1</a>&nbsp;<a id="header.age" href="#header.age">Age</a></h2>
    1183       <p id="rfc.section.15.1.p.1">The Age response-header field conveys the sender's estimate of the amount of time since the response (or its revalidation)
     1198      <h2 id="rfc.section.16.1"><a href="#rfc.section.16.1">16.1</a>&nbsp;<a id="header.age" href="#header.age">Age</a></h2>
     1199      <p id="rfc.section.16.1.p.1">The Age response-header field conveys the sender's estimate of the amount of time since the response (or its revalidation)
    11841200         was generated at the origin server. A cached response is "fresh" if its age does not exceed its freshness lifetime. Age values
    1185          are calculated as specified in <a href="#age.calculations" title="Age Calculations">Section&nbsp;3.3</a>.
    1186       </p>
    1187       <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span>  Age = "Age" ":" age-value
     1201         are calculated as specified in <a href="#age.calculations" title="Age Calculations">Section&nbsp;4.3</a>.
     1202      </p>
     1203      <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span>  Age = "Age" ":" age-value
    11881204  age-value = delta-seconds
    1189 </pre><p id="rfc.section.15.1.p.3">Age values are non-negative decimal integers, representing time in seconds.</p>
    1190       <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.3"></span>  delta-seconds  = 1*DIGIT
    1191 </pre><p id="rfc.section.15.1.p.5">If a cache receives a value larger than the largest positive integer it can represent, or if any of its age calculations overflows,
     1205</pre><p id="rfc.section.16.1.p.3">Age values are non-negative decimal integers, representing time in seconds.</p>
     1206      <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.3"></span>  delta-seconds  = 1*DIGIT
     1207</pre><p id="rfc.section.16.1.p.5">If a cache receives a value larger than the largest positive integer it can represent, or if any of its age calculations overflows,
    11921208         it <em class="bcp14">MUST</em> transmit an Age header with a value of 2147483648 (2^31). An HTTP/1.1 server that includes a cache <em class="bcp14">MUST</em> include an Age header field in every response generated from its own cache. Caches <em class="bcp14">SHOULD</em> use an arithmetic type of at least 31 bits of range.
    11931209      </p>
    11941210      <div id="rfc.iref.c.3"></div>
    11951211      <div id="rfc.iref.h.3"></div>
    1196       <h2 id="rfc.section.15.2"><a href="#rfc.section.15.2">15.2</a>&nbsp;<a id="header.cache-control" href="#header.cache-control">Cache-Control</a></h2>
    1197       <p id="rfc.section.15.2.p.1">The Cache-Control general-header field is used to specify directives that <em class="bcp14">MUST</em> be obeyed by all caching mechanisms along the request/response chain. The directives specify behavior intended to prevent
     1212      <h2 id="rfc.section.16.2"><a href="#rfc.section.16.2">16.2</a>&nbsp;<a id="header.cache-control" href="#header.cache-control">Cache-Control</a></h2>
     1213      <p id="rfc.section.16.2.p.1">The Cache-Control general-header field is used to specify directives that <em class="bcp14">MUST</em> be obeyed by all caching mechanisms along the request/response chain. The directives specify behavior intended to prevent
    11981214         caches from adversely interfering with the request or response. These directives typically override the default caching algorithms.
    11991215         Cache directives are unidirectional in that the presence of a directive in a request does not imply that the same directive
     
    12011217      </p>
    12021218      <dl class="empty">
    1203          <dd>Note that HTTP/1.0 caches might not implement Cache-Control and might only implement Pragma: no-cache (see <a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section&nbsp;15.4</a>).
    1204          </dd>
    1205       </dl>
    1206       <p id="rfc.section.15.2.p.2">Cache directives <em class="bcp14">MUST</em> be passed through by a proxy or gateway application, regardless of their significance to that application, since the directives
     1219         <dd>Note that HTTP/1.0 caches might not implement Cache-Control and might only implement Pragma: no-cache (see <a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section&nbsp;16.4</a>).
     1220         </dd>
     1221      </dl>
     1222      <p id="rfc.section.16.2.p.2">Cache directives <em class="bcp14">MUST</em> be passed through by a proxy or gateway application, regardless of their significance to that application, since the directives
    12071223         might be applicable to all recipients along the request/response chain. It is not possible to specify a cache-directive for
    12081224         a specific cache.
    12091225      </p>
    1210       <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span>  Cache-Control   = "Cache-Control" ":" 1#cache-directive
     1226      <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span>  Cache-Control   = "Cache-Control" ":" 1#cache-directive
    12111227
    12121228  cache-directive = cache-request-directive
     
    12141230
    12151231  cache-request-directive =
    1216          "no-cache"                          ; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;15.2.1</a>
    1217        | "no-store"                          ; <a href="#what.may.be.stored.by.caches" title="What May be Stored by Caches">Section&nbsp;15.2.2</a>
    1218        | "max-age" "=" delta-seconds         ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>, <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">15.2.4</a>
    1219        | "max-stale" [ "=" delta-seconds ]   ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>
    1220        | "min-fresh" "=" delta-seconds       ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>
    1221        | "no-transform"                      ; <a href="#no-transform.directive" title="No-Transform Directive">Section&nbsp;15.2.5</a>
    1222        | "only-if-cached"                    ; <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;15.2.4</a>
    1223        | cache-extension                     ; <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;15.2.6</a>
     1232         "no-cache"                          ; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;16.2.1</a>
     1233       | "no-store"                          ; <a href="#what.may.be.stored.by.caches" title="What May be Stored by Caches">Section&nbsp;16.2.2</a>
     1234       | "max-age" "=" delta-seconds         ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>, <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">16.2.4</a>
     1235       | "max-stale" [ "=" delta-seconds ]   ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>
     1236       | "min-fresh" "=" delta-seconds       ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>
     1237       | "no-transform"                      ; <a href="#no-transform.directive" title="No-Transform Directive">Section&nbsp;16.2.5</a>
     1238       | "only-if-cached"                    ; <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;16.2.4</a>
     1239       | cache-extension                     ; <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;16.2.6</a>
    12241240
    12251241  cache-response-directive =
    1226          "public"                               ; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;15.2.1</a>
    1227        | "private" [ "=" DQUOTE 1#field-name DQUOTE ] ; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;15.2.1</a>
    1228        | "no-cache" [ "=" DQUOTE 1#field-name DQUOTE ]; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;15.2.1</a>
    1229        | "no-store"                             ; <a href="#what.may.be.stored.by.caches" title="What May be Stored by Caches">Section&nbsp;15.2.2</a>
    1230        | "no-transform"                         ; <a href="#no-transform.directive" title="No-Transform Directive">Section&nbsp;15.2.5</a>
    1231        | "must-revalidate"                      ; <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;15.2.4</a>
    1232        | "proxy-revalidate"                     ; <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;15.2.4</a>
    1233        | "max-age" "=" delta-seconds            ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>
    1234        | "s-maxage" "=" delta-seconds           ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>
    1235        | cache-extension                        ; <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;15.2.6</a>
     1242         "public"                               ; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;16.2.1</a>
     1243       | "private" [ "=" DQUOTE 1#field-name DQUOTE ] ; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;16.2.1</a>
     1244       | "no-cache" [ "=" DQUOTE 1#field-name DQUOTE ]; <a href="#what.is.cacheable" title="What is Cacheable">Section&nbsp;16.2.1</a>
     1245       | "no-store"                             ; <a href="#what.may.be.stored.by.caches" title="What May be Stored by Caches">Section&nbsp;16.2.2</a>
     1246       | "no-transform"                         ; <a href="#no-transform.directive" title="No-Transform Directive">Section&nbsp;16.2.5</a>
     1247       | "must-revalidate"                      ; <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;16.2.4</a>
     1248       | "proxy-revalidate"                     ; <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;16.2.4</a>
     1249       | "max-age" "=" delta-seconds            ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>
     1250       | "s-maxage" "=" delta-seconds           ; <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>
     1251       | cache-extension                        ; <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;16.2.6</a>
    12361252
    12371253  cache-extension = token [ "=" ( token | quoted-string ) ]
    1238 </pre><p id="rfc.section.15.2.p.4">When a directive appears without any 1#field-name parameter, the directive applies to the entire request or response. When
     1254</pre><p id="rfc.section.16.2.p.4">When a directive appears without any 1#field-name parameter, the directive applies to the entire request or response. When
    12391255         such a directive appears with a 1#field-name parameter, it applies only to the named field or fields, and not to the rest
    12401256         of the request or response. This mechanism supports extensibility; implementations of future versions of HTTP might apply
    12411257         these directives to header fields not defined in HTTP/1.1.
    12421258      </p>
    1243       <p id="rfc.section.15.2.p.5">The cache-control directives can be broken down into these general categories: </p>
     1259      <p id="rfc.section.16.2.p.5">The cache-control directives can be broken down into these general categories: </p>
    12441260      <ul>
    12451261         <li>Restrictions on what are cacheable; these may only be imposed by the origin server.</li>
     
    12501266         <li>Extensions to the caching system.</li>
    12511267      </ul>
    1252       <h3 id="rfc.section.15.2.1"><a href="#rfc.section.15.2.1">15.2.1</a>&nbsp;<a id="what.is.cacheable" href="#what.is.cacheable">What is Cacheable</a></h3>
    1253       <p id="rfc.section.15.2.1.p.1">By default, a response is cacheable if the requirements of the request method, request header fields, and the response status
    1254          indicate that it is cacheable. <a href="#response.cacheability" title="Response Cacheability">Section&nbsp;5</a> summarizes these defaults for cacheability. The following Cache-Control response directives allow an origin server to override
     1268      <h3 id="rfc.section.16.2.1"><a href="#rfc.section.16.2.1">16.2.1</a>&nbsp;<a id="what.is.cacheable" href="#what.is.cacheable">What is Cacheable</a></h3>
     1269      <p id="rfc.section.16.2.1.p.1">By default, a response is cacheable if the requirements of the request method, request header fields, and the response status
     1270         indicate that it is cacheable. <a href="#response.cacheability" title="Response Cacheability">Section&nbsp;6</a> summarizes these defaults for cacheability. The following Cache-Control response directives allow an origin server to override
    12551271         the default cacheability of a response:
    12561272      </p>
    1257       <p id="rfc.section.15.2.1.p.2"> <span id="rfc.iref.c.4"></span>  <span id="rfc.iref.p.1"></span> public
     1273      <p id="rfc.section.16.2.1.p.2"> <span id="rfc.iref.c.4"></span>  <span id="rfc.iref.p.1"></span> public
    12581274      </p>
    12591275      <dl class="empty">
    12601276         <dd>Indicates that the response <em class="bcp14">MAY</em> be cached by any cache, even if it would normally be non-cacheable or cacheable only within a non-shared cache. (See also
    1261             Authorization, <a href="p7-auth.html#header.authorization" title="Authorization">Section 3.1</a> of <a href="#Part7" id="rfc.xref.Part7.2"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>, for additional details.)
    1262          </dd>
    1263       </dl>
    1264       <p id="rfc.section.15.2.1.p.3"> <span id="rfc.iref.c.5"></span>  <span id="rfc.iref.p.2"></span> private
     1277            Authorization, <a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.2"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>, for additional details.)
     1278         </dd>
     1279      </dl>
     1280      <p id="rfc.section.16.2.1.p.3"> <span id="rfc.iref.c.5"></span>  <span id="rfc.iref.p.2"></span> private
    12651281      </p>
    12661282      <dl class="empty">
     
    12721288         </dd>
    12731289      </dl>
    1274       <p id="rfc.section.15.2.1.p.4"> <span id="rfc.iref.c.6"></span>  <span id="rfc.iref.n.1"></span> no-cache
     1290      <p id="rfc.section.16.2.1.p.4"> <span id="rfc.iref.c.6"></span>  <span id="rfc.iref.n.1"></span> no-cache
    12751291      </p>
    12761292      <dl class="empty">
     
    12861302         </dd>
    12871303      </dl>
    1288       <h3 id="rfc.section.15.2.2"><a href="#rfc.section.15.2.2">15.2.2</a>&nbsp;<a id="what.may.be.stored.by.caches" href="#what.may.be.stored.by.caches">What May be Stored by Caches</a></h3>
    1289       <p id="rfc.section.15.2.2.p.1"> <span id="rfc.iref.c.7"></span>  <span id="rfc.iref.n.2"></span> no-store
     1304      <h3 id="rfc.section.16.2.2"><a href="#rfc.section.16.2.2">16.2.2</a>&nbsp;<a id="what.may.be.stored.by.caches" href="#what.may.be.stored.by.caches">What May be Stored by Caches</a></h3>
     1305      <p id="rfc.section.16.2.2.p.1"> <span id="rfc.iref.c.7"></span>  <span id="rfc.iref.n.2"></span> no-store
    12901306      </p>
    12911307      <dl class="empty">
     
    13041320         </dd>
    13051321      </dl>
    1306       <h3 id="rfc.section.15.2.3"><a href="#rfc.section.15.2.3">15.2.3</a>&nbsp;<a id="modifications.of.the.basic.expiration.mechanism" href="#modifications.of.the.basic.expiration.mechanism">Modifications of the Basic Expiration Mechanism</a></h3>
    1307       <p id="rfc.section.15.2.3.p.1">The expiration time of an entity <em class="bcp14">MAY</em> be specified by the origin server using the Expires header (see <a href="#header.expires" id="rfc.xref.header.expires.2" title="Expires">Section&nbsp;15.3</a>). Alternatively, it <em class="bcp14">MAY</em> be specified using the max-age directive in a response. When the max-age cache-control directive is present in a cached response,
     1322      <h3 id="rfc.section.16.2.3"><a href="#rfc.section.16.2.3">16.2.3</a>&nbsp;<a id="modifications.of.the.basic.expiration.mechanism" href="#modifications.of.the.basic.expiration.mechanism">Modifications of the Basic Expiration Mechanism</a></h3>
     1323      <p id="rfc.section.16.2.3.p.1">The expiration time of an entity <em class="bcp14">MAY</em> be specified by the origin server using the Expires header (see <a href="#header.expires" id="rfc.xref.header.expires.2" title="Expires">Section&nbsp;16.3</a>). Alternatively, it <em class="bcp14">MAY</em> be specified using the max-age directive in a response. When the max-age cache-control directive is present in a cached response,
    13081324         the response is stale if its current age is greater than the age value given (in seconds) at the time of a new request for
    13091325         that resource. The max-age directive on a response implies that the response is cacheable (i.e., "public") unless some other,
    13101326         more restrictive cache directive is also present.
    13111327      </p>
    1312       <p id="rfc.section.15.2.3.p.2">If a response includes both an Expires header and a max-age directive, the max-age directive overrides the Expires header,
     1328      <p id="rfc.section.16.2.3.p.2">If a response includes both an Expires header and a max-age directive, the max-age directive overrides the Expires header,
    13131329         even if the Expires header is more restrictive. This rule allows an origin server to provide, for a given response, a longer
    13141330         expiration time to an HTTP/1.1 (or later) cache than to an HTTP/1.0 cache. This might be useful if certain HTTP/1.0 caches
    13151331         improperly calculate ages or expiration times, perhaps due to desynchronized clocks.
    13161332      </p>
    1317       <p id="rfc.section.15.2.3.p.3">Many HTTP/1.0 cache implementations will treat an Expires value that is less than or equal to the response Date value as being
     1333      <p id="rfc.section.16.2.3.p.3">Many HTTP/1.0 cache implementations will treat an Expires value that is less than or equal to the response Date value as being
    13181334         equivalent to the Cache-Control response directive "no-cache". If an HTTP/1.1 cache receives such a response, and the response
    13191335         does not include a Cache-Control header field, it <em class="bcp14">SHOULD</em> consider the response to be non-cacheable in order to retain compatibility with HTTP/1.0 servers.
     
    13261342         </dd>
    13271343      </dl>
    1328       <p id="rfc.section.15.2.3.p.4"> <span id="rfc.iref.c.8"></span>  <span id="rfc.iref.s.3"></span> s-maxage
     1344      <p id="rfc.section.16.2.3.p.4"> <span id="rfc.iref.c.8"></span>  <span id="rfc.iref.s.3"></span> s-maxage
    13291345      </p>
    13301346      <dl class="empty">
    13311347         <dd>If a response includes an s-maxage directive, then for a shared cache (but not for a private cache), the maximum age specified
    13321348            by this directive overrides the maximum age specified by either the max-age directive or the Expires header. The s-maxage
    1333             directive also implies the semantics of the proxy-revalidate directive (see <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;15.2.4</a>), i.e., that the shared cache must not use the entry after it becomes stale to respond to a subsequent request without first
     1349            directive also implies the semantics of the proxy-revalidate directive (see <a href="#cache.revalidation.and.reload.controls" title="Cache Revalidation and Reload Controls">Section&nbsp;16.2.4</a>), i.e., that the shared cache must not use the entry after it becomes stale to respond to a subsequent request without first
    13341350            revalidating it with the origin server. The s-maxage directive is always ignored by a private cache.
    13351351         </dd>
    13361352      </dl>
    1337       <p id="rfc.section.15.2.3.p.5">Note that most older caches, not compliant with this specification, do not implement any cache-control directives. An origin
     1353      <p id="rfc.section.16.2.3.p.5">Note that most older caches, not compliant with this specification, do not implement any cache-control directives. An origin
    13381354         server wishing to use a cache-control directive that restricts, but does not prevent, caching by an HTTP/1.1-compliant cache <em class="bcp14">MAY</em> exploit the requirement that the max-age directive overrides the Expires header, and the fact that pre-HTTP/1.1-compliant
    13391355         caches do not observe the max-age directive.
    13401356      </p>
    1341       <p id="rfc.section.15.2.3.p.6">Other directives allow a user agent to modify the basic expiration mechanism. These directives <em class="bcp14">MAY</em> be specified on a request:
    1342       </p>
    1343       <p id="rfc.section.15.2.3.p.7"> <span id="rfc.iref.c.9"></span>  <span id="rfc.iref.m.1"></span> max-age
     1357      <p id="rfc.section.16.2.3.p.6">Other directives allow a user agent to modify the basic expiration mechanism. These directives <em class="bcp14">MAY</em> be specified on a request:
     1358      </p>
     1359      <p id="rfc.section.16.2.3.p.7"> <span id="rfc.iref.c.9"></span>  <span id="rfc.iref.m.1"></span> max-age
    13441360      </p>
    13451361      <dl class="empty">
     
    13481364         </dd>
    13491365      </dl>
    1350       <p id="rfc.section.15.2.3.p.8"> <span id="rfc.iref.c.10"></span>  <span id="rfc.iref.m.2"></span> min-fresh
     1366      <p id="rfc.section.16.2.3.p.8"> <span id="rfc.iref.c.10"></span>  <span id="rfc.iref.m.2"></span> min-fresh
    13511367      </p>
    13521368      <dl class="empty">
     
    13561372         </dd>
    13571373      </dl>
    1358       <p id="rfc.section.15.2.3.p.9"> <span id="rfc.iref.c.11"></span>  <span id="rfc.iref.m.3"></span> max-stale
     1374      <p id="rfc.section.16.2.3.p.9"> <span id="rfc.iref.c.11"></span>  <span id="rfc.iref.m.3"></span> max-stale
    13591375      </p>
    13601376      <dl class="empty">
     
    13641380         </dd>
    13651381      </dl>
    1366       <p id="rfc.section.15.2.3.p.10">If a cache returns a stale response, either because of a max-stale directive on a request, or because the cache is configured
     1382      <p id="rfc.section.16.2.3.p.10">If a cache returns a stale response, either because of a max-stale directive on a request, or because the cache is configured
    13671383         to override the expiration time of a response, the cache <em class="bcp14">MUST</em> attach a Warning header to the stale response, using Warning 110 (Response is stale).
    13681384      </p>
    1369       <p id="rfc.section.15.2.3.p.11">A cache <em class="bcp14">MAY</em> be configured to return stale responses without validation, but only if this does not conflict with any "MUST"-level requirements
     1385      <p id="rfc.section.16.2.3.p.11">A cache <em class="bcp14">MAY</em> be configured to return stale responses without validation, but only if this does not conflict with any "MUST"-level requirements
    13701386         concerning cache validation (e.g., a "must-revalidate" cache-control directive).
    13711387      </p>
    1372       <p id="rfc.section.15.2.3.p.12">If both the new request and the cached entry include "max-age" directives, then the lesser of the two values is used for determining
     1388      <p id="rfc.section.16.2.3.p.12">If both the new request and the cached entry include "max-age" directives, then the lesser of the two values is used for determining
    13731389         the freshness of the cached entry for that request.
    13741390      </p>
    1375       <h3 id="rfc.section.15.2.4"><a href="#rfc.section.15.2.4">15.2.4</a>&nbsp;<a id="cache.revalidation.and.reload.controls" href="#cache.revalidation.and.reload.controls">Cache Revalidation and Reload Controls</a></h3>
    1376       <p id="rfc.section.15.2.4.p.1">Sometimes a user agent might want or need to insist that a cache revalidate its cache entry with the origin server (and not
     1391      <h3 id="rfc.section.16.2.4"><a href="#rfc.section.16.2.4">16.2.4</a>&nbsp;<a id="cache.revalidation.and.reload.controls" href="#cache.revalidation.and.reload.controls">Cache Revalidation and Reload Controls</a></h3>
     1392      <p id="rfc.section.16.2.4.p.1">Sometimes a user agent might want or need to insist that a cache revalidate its cache entry with the origin server (and not
    13771393         just with the next cache along the path to the origin server), or to reload its cache entry from the origin server. End-to-end
    13781394         revalidation might be necessary if either the cache or the origin server has overestimated the expiration time of the cached
    13791395         response. End-to-end reload may be necessary if the cache entry has become corrupted for some reason.
    13801396      </p>
    1381       <p id="rfc.section.15.2.4.p.2">End-to-end revalidation may be requested either when the client does not have its own local cached copy, in which case we
     1397      <p id="rfc.section.16.2.4.p.2">End-to-end revalidation may be requested either when the client does not have its own local cached copy, in which case we
    13821398         call it "unspecified end-to-end revalidation", or when the client does have a local cached copy, in which case we call it
    13831399         "specific end-to-end revalidation."
    13841400      </p>
    1385       <p id="rfc.section.15.2.4.p.3">The client can specify these three kinds of action using Cache-Control request directives:</p>
    1386       <p id="rfc.section.15.2.4.p.4">End-to-end reload </p>
     1401      <p id="rfc.section.16.2.4.p.3">The client can specify these three kinds of action using Cache-Control request directives:</p>
     1402      <p id="rfc.section.16.2.4.p.4">End-to-end reload </p>
    13871403      <dl class="empty">
    13881404         <dd>The request includes a "no-cache" cache-control directive or, for compatibility with HTTP/1.0 clients, "Pragma: no-cache".
     
    13901406         </dd>
    13911407      </dl>
    1392       <p id="rfc.section.15.2.4.p.5">Specific end-to-end revalidation </p>
     1408      <p id="rfc.section.16.2.4.p.5">Specific end-to-end revalidation </p>
    13931409      <dl class="empty">
    13941410         <dd>The request includes a "max-age=0" cache-control directive, which forces each cache along the path to the origin server to
     
    13971413         </dd>
    13981414      </dl>
    1399       <p id="rfc.section.15.2.4.p.6">Unspecified end-to-end revalidation </p>
     1415      <p id="rfc.section.16.2.4.p.6">Unspecified end-to-end revalidation </p>
    14001416      <dl class="empty">
    14011417         <dd>The request includes "max-age=0" cache-control directive, which forces each cache along the path to the origin server to revalidate
     
    14051421         </dd>
    14061422      </dl>
    1407       <p id="rfc.section.15.2.4.p.7"> <span id="rfc.iref.c.12"></span>  <span id="rfc.iref.m.4"></span> max-age
     1423      <p id="rfc.section.16.2.4.p.7"> <span id="rfc.iref.c.12"></span>  <span id="rfc.iref.m.4"></span> max-age
    14081424      </p>
    14091425      <dl class="empty">
     
    14221438         </dd>
    14231439      </dl>
    1424       <p id="rfc.section.15.2.4.p.8"> <span id="rfc.iref.c.13"></span>  <span id="rfc.iref.o.1"></span> only-if-cached
     1440      <p id="rfc.section.16.2.4.p.8"> <span id="rfc.iref.c.13"></span>  <span id="rfc.iref.o.1"></span> only-if-cached
    14251441      </p>
    14261442      <dl class="empty">
     
    14321448         </dd>
    14331449      </dl>
    1434       <p id="rfc.section.15.2.4.p.9"> <span id="rfc.iref.c.14"></span>  <span id="rfc.iref.m.5"></span> must-revalidate
     1450      <p id="rfc.section.16.2.4.p.9"> <span id="rfc.iref.c.14"></span>  <span id="rfc.iref.m.5"></span> must-revalidate
    14351451      </p>
    14361452      <dl class="empty">
     
    14501466         </dd>
    14511467      </dl>
    1452       <p id="rfc.section.15.2.4.p.10"> <span id="rfc.iref.c.15"></span>  <span id="rfc.iref.p.3"></span> proxy-revalidate
     1468      <p id="rfc.section.16.2.4.p.10"> <span id="rfc.iref.c.15"></span>  <span id="rfc.iref.p.3"></span> proxy-revalidate
    14531469      </p>
    14541470      <dl class="empty">
     
    14611477         </dd>
    14621478      </dl>
    1463       <h3 id="rfc.section.15.2.5"><a href="#rfc.section.15.2.5">15.2.5</a>&nbsp;<a id="no-transform.directive" href="#no-transform.directive">No-Transform Directive</a></h3>
    1464       <p id="rfc.section.15.2.5.p.1"> <span id="rfc.iref.c.16"></span>  <span id="rfc.iref.n.3"></span> no-transform
     1479      <h3 id="rfc.section.16.2.5"><a href="#rfc.section.16.2.5">16.2.5</a>&nbsp;<a id="no-transform.directive" href="#no-transform.directive">No-Transform Directive</a></h3>
     1480      <p id="rfc.section.16.2.5.p.1"> <span id="rfc.iref.c.16"></span>  <span id="rfc.iref.n.3"></span> no-transform
    14651481      </p>
    14661482      <dl class="empty">
     
    14731489            authentication, all depend on receiving an entity body that is bit for bit identical to the original entity-body.
    14741490         </dd>
    1475          <dd>Therefore, if a message includes the no-transform directive, an intermediate cache or proxy <em class="bcp14">MUST NOT</em> change those headers that are listed in <a href="#non-modifiable.headers" title="Non-modifiable Headers">Section&nbsp;6.2</a> as being subject to the no-transform directive. This implies that the cache or proxy <em class="bcp14">MUST NOT</em> change any aspect of the entity-body that is specified by these headers, including the value of the entity-body itself.
    1476          </dd>
    1477       </dl>
    1478       <h3 id="rfc.section.15.2.6"><a href="#rfc.section.15.2.6">15.2.6</a>&nbsp;<a id="cache.control.extensions" href="#cache.control.extensions">Cache Control Extensions</a></h3>
    1479       <p id="rfc.section.15.2.6.p.1">The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional
     1491         <dd>Therefore, if a message includes the no-transform directive, an intermediate cache or proxy <em class="bcp14">MUST NOT</em> change those headers that are listed in <a href="#non-modifiable.headers" title="Non-modifiable Headers">Section&nbsp;7.2</a> as being subject to the no-transform directive. This implies that the cache or proxy <em class="bcp14">MUST NOT</em> change any aspect of the entity-body that is specified by these headers, including the value of the entity-body itself.
     1492         </dd>
     1493      </dl>
     1494      <h3 id="rfc.section.16.2.6"><a href="#rfc.section.16.2.6">16.2.6</a>&nbsp;<a id="cache.control.extensions" href="#cache.control.extensions">Cache Control Extensions</a></h3>
     1495      <p id="rfc.section.16.2.6.p.1">The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional
    14801496         assigned value. Informational extensions (those which do not require a change in cache behavior) <em class="bcp14">MAY</em> be added without changing the semantics of other directives. Behavioral extensions are designed to work by acting as modifiers
    14811497         to the existing base of cache directives. Both the new directive and the standard directive are supplied, such that applications
     
    14841500         way, extensions to the cache-control directives can be made without requiring changes to the base protocol.
    14851501      </p>
    1486       <p id="rfc.section.15.2.6.p.2">This extension mechanism depends on an HTTP cache obeying all of the cache-control directives defined for its native HTTP-version,
     1502      <p id="rfc.section.16.2.6.p.2">This extension mechanism depends on an HTTP cache obeying all of the cache-control directives defined for its native HTTP-version,
    14871503         obeying certain extensions, and ignoring all directives that it does not understand.
    14881504      </p>
    1489       <p id="rfc.section.15.2.6.p.3">For example, consider a hypothetical new response directive called community which acts as a modifier to the private directive.
     1505      <p id="rfc.section.16.2.6.p.3">For example, consider a hypothetical new response directive called community which acts as a modifier to the private directive.
    14901506         We define this new directive to mean that, in addition to any non-shared cache, any cache which is shared only by members
    14911507         of the community named within its value may cache the response. An origin server wishing to allow the UCI community to use
    14921508         an otherwise private response in their shared cache(s) could do so by including
    14931509      </p>
    1494       <div id="rfc.figure.u.12"></div><pre class="text">    Cache-Control: private, community="UCI"
    1495 </pre><p id="rfc.section.15.2.6.p.5">A cache seeing this header field will act correctly even if the cache does not understand the community cache-extension, since
     1510      <div id="rfc.figure.u.15"></div><pre class="text">    Cache-Control: private, community="UCI"
     1511</pre><p id="rfc.section.16.2.6.p.5">A cache seeing this header field will act correctly even if the cache does not understand the community cache-extension, since
    14961512         it will also see and understand the private directive and thus default to the safe behavior.
    14971513      </p>
    1498       <p id="rfc.section.15.2.6.p.6">Unrecognized cache-directives <em class="bcp14">MUST</em> be ignored; it is assumed that any cache-directive likely to be unrecognized by an HTTP/1.1 cache will be combined with standard
     1514      <p id="rfc.section.16.2.6.p.6">Unrecognized cache-directives <em class="bcp14">MUST</em> be ignored; it is assumed that any cache-directive likely to be unrecognized by an HTTP/1.1 cache will be combined with standard
    14991515         directives (or the response's default cacheability) such that the cache behavior will remain minimally correct even if the
    15001516         cache does not understand the extension(s).
     
    15021518      <div id="rfc.iref.e.2"></div>
    15031519      <div id="rfc.iref.h.4"></div>
    1504       <h2 id="rfc.section.15.3"><a href="#rfc.section.15.3">15.3</a>&nbsp;<a id="header.expires" href="#header.expires">Expires</a></h2>
    1505       <p id="rfc.section.15.3.p.1">The Expires entity-header field gives the date/time after which the response is considered stale. A stale cache entry may
     1520      <h2 id="rfc.section.16.3"><a href="#rfc.section.16.3">16.3</a>&nbsp;<a id="header.expires" href="#header.expires">Expires</a></h2>
     1521      <p id="rfc.section.16.3.p.1">The Expires entity-header field gives the date/time after which the response is considered stale. A stale cache entry may
    15061522         not normally be returned by a cache (either a proxy cache or a user agent cache) unless it is first validated with the origin
    1507          server (or with an intermediate cache that has a fresh copy of the entity). See <a href="#expiration.model" title="Expiration Model">Section&nbsp;3</a> for further discussion of the expiration model.
    1508       </p>
    1509       <p id="rfc.section.15.3.p.2">The presence of an Expires field does not imply that the original resource will change or cease to exist at, before, or after
     1523         server (or with an intermediate cache that has a fresh copy of the entity). See <a href="#expiration.model" title="Expiration Model">Section&nbsp;4</a> for further discussion of the expiration model.
     1524      </p>
     1525      <p id="rfc.section.16.3.p.2">The presence of an Expires field does not imply that the original resource will change or cease to exist at, before, or after
    15101526         that time.
    15111527      </p>
    1512       <p id="rfc.section.15.3.p.3">The format is an absolute date and time as defined by HTTP-date in <a href="p1-messaging.html#full.date" title="Full Date">Section 3.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format.
    1513       </p>
    1514       <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  Expires = "Expires" ":" HTTP-date
    1515 </pre><p id="rfc.section.15.3.p.5">An example of its use is</p>
    1516       <div id="rfc.figure.u.14"></div><pre class="text">   Expires: Thu, 01 Dec 1994 16:00:00 GMT
    1517 </pre><p id="rfc.section.15.3.p.7"> </p>
    1518       <dl class="empty">
    1519          <dd> <b>Note:</b> if a response includes a Cache-Control field with the max-age directive (see <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>), that directive overrides the Expires field.
    1520          </dd>
    1521       </dl>
    1522       <p id="rfc.section.15.3.p.8">HTTP/1.1 clients and caches <em class="bcp14">MUST</em> treat other invalid date formats, especially including the value "0", as in the past (i.e., "already expired").
    1523       </p>
    1524       <p id="rfc.section.15.3.p.9">To mark a response as "already expired," an origin server sends an Expires date that is equal to the Date header value. (See
    1525          the rules for expiration calculations in <a href="#expiration.calculations" title="Expiration Calculations">Section&nbsp;3.4</a>.)
    1526       </p>
    1527       <p id="rfc.section.15.3.p.10">To mark a response as "never expires," an origin server sends an Expires date approximately one year from the time the response
     1528      <p id="rfc.section.16.3.p.3">The format is an absolute date and time as defined by HTTP-date in <a href="p1-messaging.html#full.date" title="Full Date">Section 3.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.18"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format.
     1529      </p>
     1530      <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  Expires = "Expires" ":" HTTP-date
     1531</pre><p id="rfc.section.16.3.p.5">An example of its use is</p>
     1532      <div id="rfc.figure.u.17"></div><pre class="text">   Expires: Thu, 01 Dec 1994 16:00:00 GMT
     1533</pre><p id="rfc.section.16.3.p.7"> </p>
     1534      <dl class="empty">
     1535         <dd> <b>Note:</b> if a response includes a Cache-Control field with the max-age directive (see <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>), that directive overrides the Expires field.
     1536         </dd>
     1537      </dl>
     1538      <p id="rfc.section.16.3.p.8">HTTP/1.1 clients and caches <em class="bcp14">MUST</em> treat other invalid date formats, especially including the value "0", as in the past (i.e., "already expired").
     1539      </p>
     1540      <p id="rfc.section.16.3.p.9">To mark a response as "already expired," an origin server sends an Expires date that is equal to the Date header value. (See
     1541         the rules for expiration calculations in <a href="#expiration.calculations" title="Expiration Calculations">Section&nbsp;4.4</a>.)
     1542      </p>
     1543      <p id="rfc.section.16.3.p.10">To mark a response as "never expires," an origin server sends an Expires date approximately one year from the time the response
    15281544         is sent. HTTP/1.1 servers <em class="bcp14">SHOULD NOT</em> send Expires dates more than one year in the future.
    15291545      </p>
    1530       <p id="rfc.section.15.3.p.11">The presence of an Expires header field with a date value of some time in the future on a response that otherwise would by
     1546      <p id="rfc.section.16.3.p.11">The presence of an Expires header field with a date value of some time in the future on a response that otherwise would by
    15311547         default be non-cacheable indicates that the response is cacheable, unless indicated otherwise by a Cache-Control header field
    1532          (<a href="#header.cache-control" id="rfc.xref.header.cache-control.9" title="Cache-Control">Section&nbsp;15.2</a>).
     1548         (<a href="#header.cache-control" id="rfc.xref.header.cache-control.9" title="Cache-Control">Section&nbsp;16.2</a>).
    15331549      </p>
    15341550      <div id="rfc.iref.p.4"></div>
    15351551      <div id="rfc.iref.h.5"></div>
    1536       <h2 id="rfc.section.15.4"><a href="#rfc.section.15.4">15.4</a>&nbsp;<a id="header.pragma" href="#header.pragma">Pragma</a></h2>
    1537       <p id="rfc.section.15.4.p.1">The Pragma general-header field is used to include implementation-specific directives that might apply to any recipient along
     1552      <h2 id="rfc.section.16.4"><a href="#rfc.section.16.4">16.4</a>&nbsp;<a id="header.pragma" href="#header.pragma">Pragma</a></h2>
     1553      <p id="rfc.section.16.4.p.1">The Pragma general-header field is used to include implementation-specific directives that might apply to any recipient along
    15381554         the request/response chain. All pragma directives specify optional behavior from the viewpoint of the protocol; however, some
    15391555         systems <em class="bcp14">MAY</em> require that behavior be consistent with the directives.
    15401556      </p>
    1541       <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span>  Pragma            = "Pragma" ":" 1#pragma-directive
     1557      <div id="rfc.figure.u.18"></div><pre class="inline"><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span>  Pragma            = "Pragma" ":" 1#pragma-directive
    15421558  pragma-directive  = "no-cache" | extension-pragma
    15431559  extension-pragma  = token [ "=" ( token | quoted-string ) ]
    1544 </pre><p id="rfc.section.15.4.p.3">When the no-cache directive is present in a request message, an application <em class="bcp14">SHOULD</em> forward the request toward the origin server even if it has a cached copy of what is being requested. This pragma directive
    1545          has the same semantics as the no-cache cache-directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.10" title="Cache-Control">Section&nbsp;15.2</a>) and is defined here for backward compatibility with HTTP/1.0. Clients <em class="bcp14">SHOULD</em> include both header fields when a no-cache request is sent to a server not known to be HTTP/1.1 compliant.
    1546       </p>
    1547       <p id="rfc.section.15.4.p.4">Pragma directives <em class="bcp14">MUST</em> be passed through by a proxy or gateway application, regardless of their significance to that application, since the directives
     1560</pre><p id="rfc.section.16.4.p.3">When the no-cache directive is present in a request message, an application <em class="bcp14">SHOULD</em> forward the request toward the origin server even if it has a cached copy of what is being requested. This pragma directive
     1561         has the same semantics as the no-cache cache-directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.10" title="Cache-Control">Section&nbsp;16.2</a>) and is defined here for backward compatibility with HTTP/1.0. Clients <em class="bcp14">SHOULD</em> include both header fields when a no-cache request is sent to a server not known to be HTTP/1.1 compliant.
     1562      </p>
     1563      <p id="rfc.section.16.4.p.4">Pragma directives <em class="bcp14">MUST</em> be passed through by a proxy or gateway application, regardless of their significance to that application, since the directives
    15481564         might be applicable to all recipients along the request/response chain. It is not possible to specify a pragma for a specific
    15491565         recipient; however, any pragma directive not relevant to a recipient <em class="bcp14">SHOULD</em> be ignored by that recipient.
    15501566      </p>
    1551       <p id="rfc.section.15.4.p.5">HTTP/1.1 caches <em class="bcp14">SHOULD</em> treat "Pragma: no-cache" as if the client had sent "Cache-Control: no-cache". No new Pragma directives will be defined in
     1567      <p id="rfc.section.16.4.p.5">HTTP/1.1 caches <em class="bcp14">SHOULD</em> treat "Pragma: no-cache" as if the client had sent "Cache-Control: no-cache". No new Pragma directives will be defined in
    15521568         HTTP.
    15531569      </p>
     
    15591575      <div id="rfc.iref.v.2"></div>
    15601576      <div id="rfc.iref.h.6"></div>
    1561       <h2 id="rfc.section.15.5"><a href="#rfc.section.15.5">15.5</a>&nbsp;<a id="header.vary" href="#header.vary">Vary</a></h2>
    1562       <p id="rfc.section.15.5.p.1">The Vary field value indicates the set of request-header fields that fully determines, while the response is fresh, whether
     1577      <h2 id="rfc.section.16.5"><a href="#rfc.section.16.5">16.5</a>&nbsp;<a id="header.vary" href="#header.vary">Vary</a></h2>
     1578      <p id="rfc.section.16.5.p.1">The Vary field value indicates the set of request-header fields that fully determines, while the response is fresh, whether
    15631579         a cache is permitted to use the response to reply to a subsequent request without revalidation. For uncacheable or stale responses,
    15641580         the Vary field value advises the user agent about the criteria that were used to select the representation. A Vary field value
    15651581         of "*" implies that a cache cannot determine from the request headers of a subsequent request whether this response is the
    1566          appropriate representation. See <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;7</a> for use of the Vary header field by caches.
    1567       </p>
    1568       <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.13"></span>  Vary  = "Vary" ":" ( "*" | 1#field-name )
    1569 </pre><p id="rfc.section.15.5.p.3">An HTTP/1.1 server <em class="bcp14">SHOULD</em> include a Vary header field with any cacheable response that is subject to server-driven negotiation. Doing so allows a cache
     1582         appropriate representation. See <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;8</a> for use of the Vary header field by caches.
     1583      </p>
     1584      <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.13"></span>  Vary  = "Vary" ":" ( "*" | 1#field-name )
     1585</pre><p id="rfc.section.16.5.p.3">An HTTP/1.1 server <em class="bcp14">SHOULD</em> include a Vary header field with any cacheable response that is subject to server-driven negotiation. Doing so allows a cache
    15701586         to properly interpret future requests on that resource and informs the user agent about the presence of negotiation on that
    15711587         resource. A server <em class="bcp14">MAY</em> include a Vary header field with a non-cacheable response that is subject to server-driven negotiation, since this might provide
    15721588         the user agent with useful information about the dimensions over which the response varies at the time of the response.
    15731589      </p>
    1574       <p id="rfc.section.15.5.p.4">A Vary field value consisting of a list of field-names signals that the representation selected for the response is based
     1590      <p id="rfc.section.16.5.p.4">A Vary field value consisting of a list of field-names signals that the representation selected for the response is based
    15751591         on a selection algorithm which considers ONLY the listed request-header field values in selecting the most appropriate representation.
    15761592         A cache <em class="bcp14">MAY</em> assume that the same selection will be made for future requests with the same values for the listed field names, for the duration
    15771593         of time for which the response is fresh.
    15781594      </p>
    1579       <p id="rfc.section.15.5.p.5">The field-names given are not limited to the set of standard request-header fields defined by this specification. Field names
     1595      <p id="rfc.section.16.5.p.5">The field-names given are not limited to the set of standard request-header fields defined by this specification. Field names
    15801596         are case-insensitive.
    15811597      </p>
    1582       <p id="rfc.section.15.5.p.6">A Vary field value of "*" signals that unspecified parameters not limited to the request-headers (e.g., the network address
     1598      <p id="rfc.section.16.5.p.6">A Vary field value of "*" signals that unspecified parameters not limited to the request-headers (e.g., the network address
    15831599         of the client), play a role in the selection of the response representation. The "*" value <em class="bcp14">MUST NOT</em> be generated by a proxy server; it may only be generated by an origin server.
    15841600      </p>
    15851601      <div id="rfc.iref.w.1"></div>
    15861602      <div id="rfc.iref.h.7"></div>
    1587       <h2 id="rfc.section.15.6"><a href="#rfc.section.15.6">15.6</a>&nbsp;<a id="header.warning" href="#header.warning">Warning</a></h2>
    1588       <p id="rfc.section.15.6.p.1">The Warning general-header field is used to carry additional information about the status or transformation of a message which
     1603      <h2 id="rfc.section.16.6"><a href="#rfc.section.16.6">16.6</a>&nbsp;<a id="header.warning" href="#header.warning">Warning</a></h2>
     1604      <p id="rfc.section.16.6.p.1">The Warning general-header field is used to carry additional information about the status or transformation of a message which
    15891605         might not be reflected in the message. This information is typically used to warn about a possible lack of semantic transparency
    15901606         from caching operations or transformations applied to the entity body of the message.
    15911607      </p>
    1592       <p id="rfc.section.15.6.p.2">Warning headers are sent with responses using:</p>
    1593       <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span>  Warning    = "Warning" ":" 1#warning-value
     1608      <p id="rfc.section.16.6.p.2">Warning headers are sent with responses using:</p>
     1609      <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span>  Warning    = "Warning" ":" 1#warning-value
    15941610 
    15951611  warning-value = warn-code SP warn-agent SP warn-text
     
    16021618  warn-text  = quoted-string
    16031619  warn-date  = DQUOTE HTTP-date DQUOTE
    1604 </pre><p id="rfc.section.15.6.p.4">A response <em class="bcp14">MAY</em> carry more than one Warning header.
    1605       </p>
    1606       <p id="rfc.section.15.6.p.5">The warn-text <em class="bcp14">SHOULD</em> be in a natural language and character set that is most likely to be intelligible to the human user receiving the response.
     1620</pre><p id="rfc.section.16.6.p.4">A response <em class="bcp14">MAY</em> carry more than one Warning header.
     1621      </p>
     1622      <p id="rfc.section.16.6.p.5">The warn-text <em class="bcp14">SHOULD</em> be in a natural language and character set that is most likely to be intelligible to the human user receiving the response.
    16071623         This decision <em class="bcp14">MAY</em> be based on any available knowledge, such as the location of the cache or user, the Accept-Language field in a request, the
    16081624         Content-Language field in a response, etc. The default language is English and the default character set is ISO-8859-1 (<a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a>).
    16091625      </p>
    1610       <p id="rfc.section.15.6.p.6">If a character set other than ISO-8859-1 is used, it <em class="bcp14">MUST</em> be encoded in the warn-text using the method described in <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a>.
    1611       </p>
    1612       <p id="rfc.section.15.6.p.7">Warning headers can in general be applied to any message, however some specific warn-codes are specific to caches and can
     1626      <p id="rfc.section.16.6.p.6">If a character set other than ISO-8859-1 is used, it <em class="bcp14">MUST</em> be encoded in the warn-text using the method described in <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a>.
     1627      </p>
     1628      <p id="rfc.section.16.6.p.7">Warning headers can in general be applied to any message, however some specific warn-codes are specific to caches and can
    16131629         only be applied to response messages. New Warning headers <em class="bcp14">SHOULD</em> be added after any existing Warning headers. A cache <em class="bcp14">MUST NOT</em> delete any Warning header that it received with a message. However, if a cache successfully validates a cache entry, it <em class="bcp14">SHOULD</em> remove any Warning headers previously attached to that entry except as specified for specific Warning codes. It <em class="bcp14">MUST</em> then add any Warning headers received in the validating response. In other words, Warning headers are those that would be
    16141630         attached to the most recent relevant response.
    16151631      </p>
    1616       <p id="rfc.section.15.6.p.8">When multiple Warning headers are attached to a response, the user agent ought to inform the user of as many of them as possible,
     1632      <p id="rfc.section.16.6.p.8">When multiple Warning headers are attached to a response, the user agent ought to inform the user of as many of them as possible,
    16171633         in the order that they appear in the response. If it is not possible to inform the user of all of the warnings, the user agent <em class="bcp14">SHOULD</em> follow these heuristics:
    16181634      </p>
     
    16231639         </li>
    16241640      </ul>
    1625       <p id="rfc.section.15.6.p.9">Systems that generate multiple Warning headers <em class="bcp14">SHOULD</em> order them with this user agent behavior in mind.
    1626       </p>
    1627       <p id="rfc.section.15.6.p.10">Requirements for the behavior of caches with respect to Warnings are stated in <a href="#warnings" title="Warnings">Section&nbsp;2.2</a>.
    1628       </p>
    1629       <p id="rfc.section.15.6.p.11">This is a list of the currently-defined warn-codes, each with a recommended warn-text in English, and a description of its
     1641      <p id="rfc.section.16.6.p.9">Systems that generate multiple Warning headers <em class="bcp14">SHOULD</em> order them with this user agent behavior in mind.
     1642      </p>
     1643      <p id="rfc.section.16.6.p.10">Requirements for the behavior of caches with respect to Warnings are stated in <a href="#warnings" title="Warnings">Section&nbsp;3.2</a>.
     1644      </p>
     1645      <p id="rfc.section.16.6.p.11">This is a list of the currently-defined warn-codes, each with a recommended warn-text in English, and a description of its
    16301646         meaning.
    16311647      </p>
    1632       <p id="rfc.section.15.6.p.12">110 Response is stale </p>
     1648      <p id="rfc.section.16.6.p.12">110 Response is stale </p>
    16331649      <dl class="empty">
    16341650         <dd> <em class="bcp14">MUST</em> be included whenever the returned response is stale.
    16351651         </dd>
    16361652      </dl>
    1637       <p id="rfc.section.15.6.p.13">111 Revalidation failed </p>
     1653      <p id="rfc.section.16.6.p.13">111 Revalidation failed </p>
    16381654      <dl class="empty">
    16391655         <dd> <em class="bcp14">MUST</em> be included if a cache returns a stale response because an attempt to revalidate the response failed, due to an inability
     
    16411657         </dd>
    16421658      </dl>
    1643       <p id="rfc.section.15.6.p.14">112 Disconnected operation </p>
     1659      <p id="rfc.section.16.6.p.14">112 Disconnected operation </p>
    16441660      <dl class="empty">
    16451661         <dd> <em class="bcp14">SHOULD</em> be included if the cache is intentionally disconnected from the rest of the network for a period of time.
    16461662         </dd>
    16471663      </dl>
    1648       <p id="rfc.section.15.6.p.15">113 Heuristic expiration </p>
     1664      <p id="rfc.section.16.6.p.15">113 Heuristic expiration </p>
    16491665      <dl class="empty">
    16501666         <dd> <em class="bcp14">MUST</em> be included if the cache heuristically chose a freshness lifetime greater than 24 hours and the response's age is greater
     
    16521668         </dd>
    16531669      </dl>
    1654       <p id="rfc.section.15.6.p.16">199 Miscellaneous warning </p>
     1670      <p id="rfc.section.16.6.p.16">199 Miscellaneous warning </p>
    16551671      <dl class="empty">
    16561672         <dd>The warning text <em class="bcp14">MAY</em> include arbitrary information to be presented to a human user, or logged. A system receiving this warning <em class="bcp14">MUST NOT</em> take any automated action, besides presenting the warning to the user.
    16571673         </dd>
    16581674      </dl>
    1659       <p id="rfc.section.15.6.p.17">214 Transformation applied </p>
     1675      <p id="rfc.section.16.6.p.17">214 Transformation applied </p>
    16601676      <dl class="empty">
    16611677         <dd> <em class="bcp14">MUST</em> be added by an intermediate cache or proxy if it applies any transformation changing the content-coding (as specified in the
     
    16641680         </dd>
    16651681      </dl>
    1666       <p id="rfc.section.15.6.p.18">299 Miscellaneous persistent warning </p>
     1682      <p id="rfc.section.16.6.p.18">299 Miscellaneous persistent warning </p>
    16671683      <dl class="empty">
    16681684         <dd>The warning text <em class="bcp14">MAY</em> include arbitrary information to be presented to a human user, or logged. A system receiving this warning <em class="bcp14">MUST NOT</em> take any automated action.
    16691685         </dd>
    16701686      </dl>
    1671       <p id="rfc.section.15.6.p.19">If an implementation sends a message with one or more Warning headers whose version is HTTP/1.0 or lower, then the sender <em class="bcp14">MUST</em> include in each warning-value a warn-date that matches the date in the response.
    1672       </p>
    1673       <p id="rfc.section.15.6.p.20">If an implementation receives a message with a warning-value that includes a warn-date, and that warn-date is different from
     1687      <p id="rfc.section.16.6.p.19">If an implementation sends a message with one or more Warning headers whose version is HTTP/1.0 or lower, then the sender <em class="bcp14">MUST</em> include in each warning-value a warn-date that matches the date in the response.
     1688      </p>
     1689      <p id="rfc.section.16.6.p.20">If an implementation receives a message with a warning-value that includes a warn-date, and that warn-date is different from
    16741690         the Date value in the response, then that warning-value <em class="bcp14">MUST</em> be deleted from the message before storing, forwarding, or using it. (This prevents bad consequences of naive caching of Warning
    16751691         header fields.) If all of the warning-values are deleted for this reason, the Warning header <em class="bcp14">MUST</em> be deleted as well.
    16761692      </p>
    1677       <h1 id="rfc.section.16"><a href="#rfc.section.16">16.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
    1678       <p id="rfc.section.16.p.1"> <span class="comment">[rfc.comment.1: TBD.]</span>
    1679       </p>
    1680       <h1 id="rfc.section.17"><a href="#rfc.section.17">17.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
    1681       <p id="rfc.section.17.p.1">Caching proxies provide additional potential vulnerabilities, since the contents of the cache represent an attractive target
     1693      <h1 id="rfc.section.17"><a href="#rfc.section.17">17.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
     1694      <p id="rfc.section.17.p.1"> <span class="comment">[rfc.comment.1: TBD.]</span>
     1695      </p>
     1696      <h1 id="rfc.section.18"><a href="#rfc.section.18">18.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
     1697      <p id="rfc.section.18.p.1">Caching proxies provide additional potential vulnerabilities, since the contents of the cache represent an attractive target
    16821698         for malicious exploitation. Because cache contents persist after an HTTP request is complete, an attack on the cache can reveal
    16831699         information long after a user believes that the information has been removed from the network. Therefore, cache contents should
    16841700         be protected as sensitive information.
    16851701      </p>
    1686       <h1 id="rfc.section.18"><a href="#rfc.section.18">18.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
    1687       <p id="rfc.section.18.p.1">Much of the content and presentation of the caching design is due to suggestions and comments from individuals including:
     1702      <h1 id="rfc.section.19"><a href="#rfc.section.19">19.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
     1703      <p id="rfc.section.19.p.1">Much of the content and presentation of the caching design is due to suggestions and comments from individuals including:
    16881704         Shel Kaphan, Paul Leach, Koen Holtman, David Morris, and Larry Masinter.
    16891705      </p>
    1690       <h1 id="rfc.references"><a id="rfc.section.19" href="#rfc.section.19">19.</a> References
     1706      <h1 id="rfc.references"><a id="rfc.section.20" href="#rfc.section.20">20.</a> References
    16911707      </h1>
    1692       <h2 id="rfc.references.1"><a href="#rfc.section.19.1" id="rfc.section.19.1">19.1</a> Normative References
     1708      <h2 id="rfc.references.1"><a href="#rfc.section.20.1" id="rfc.section.20.1">20.1</a> Normative References
    16931709      </h2>
    16941710      <table summary="Normative References">                 
     
    17411757         </tr>
    17421758      </table>
    1743       <h2 id="rfc.references.2"><a href="#rfc.section.19.2" id="rfc.section.19.2">19.2</a> Informative References
     1759      <h2 id="rfc.references.2"><a href="#rfc.section.20.2" id="rfc.section.20.2">20.2</a> Informative References
    17441760      </h2>
    17451761      <table summary="Informative References">   
     
    17731789      <h1 id="rfc.section.A"><a href="#rfc.section.A">A.</a>&nbsp;<a id="compatibility" href="#compatibility">Compatibility with Previous Versions</a></h1>
    17741790      <h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a>&nbsp;<a id="changes.from.rfc.2068" href="#changes.from.rfc.2068">Changes from RFC 2068</a></h2>
    1775       <p id="rfc.section.A.1.p.1">A case was missed in the Cache-Control model of HTTP/1.1; s-maxage was introduced to add this missing case. (Sections <a href="#response.cacheability" title="Response Cacheability">5</a>, <a href="#header.cache-control" id="rfc.xref.header.cache-control.11" title="Cache-Control">15.2</a>, <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">15.2.3</a>)
     1791      <p id="rfc.section.A.1.p.1">A case was missed in the Cache-Control model of HTTP/1.1; s-maxage was introduced to add this missing case. (Sections <a href="#response.cacheability" title="Response Cacheability">6</a>, <a href="#header.cache-control" id="rfc.xref.header.cache-control.11" title="Cache-Control">16.2</a>, <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">16.2.3</a>)
    17761792      </p>
    17771793      <p id="rfc.section.A.1.p.2">Transfer-coding and message lengths all interact in ways that required fixing exactly when chunked encoding is used (to allow
    17781794         for transfer encoding that may not be self delimiting); it was important to straighten out exactly how message lengths are
    1779          computed. (<a href="#non-modifiable.headers" title="Non-modifiable Headers">Section&nbsp;6.2</a>, see also <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a> and <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>)
    1780       </p>
    1781       <p id="rfc.section.A.1.p.3">Proxies should be able to add Content-Length when appropriate. (<a href="#non-modifiable.headers" title="Non-modifiable Headers">Section&nbsp;6.2</a>)
     1795         computed. (<a href="#non-modifiable.headers" title="Non-modifiable Headers">Section&nbsp;7.2</a>, see also <a href="#Part1" id="rfc.xref.Part1.19"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a> and <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>)
     1796      </p>
     1797      <p id="rfc.section.A.1.p.3">Proxies should be able to add Content-Length when appropriate. (<a href="#non-modifiable.headers" title="Non-modifiable Headers">Section&nbsp;7.2</a>)
    17821798      </p>
    17831799      <p id="rfc.section.A.1.p.4">Range request responses would become very verbose if all meta-data were always returned; by allowing the server to only send
    1784          needed headers in a 206 response, this problem can be avoided. (<a href="#combining.headers" title="Combining Headers">Section&nbsp;6.3</a>)
    1785       </p>
    1786       <p id="rfc.section.A.1.p.5">The Cache-Control: max-age directive was not properly defined for responses. (<a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;15.2.3</a>)
    1787       </p>
    1788       <p id="rfc.section.A.1.p.6">Warnings could be cached incorrectly, or not updated appropriately. (Section <a href="#warnings" title="Warnings">2.2</a>, <a href="#expiration.calculations" title="Expiration Calculations">3.4</a>, <a href="#non-modifiable.headers" title="Non-modifiable Headers">6.2</a>, <a href="#combining.headers" title="Combining Headers">6.3</a>, <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">15.2.3</a>, and <a href="#header.warning" id="rfc.xref.header.warning.6" title="Warning">15.6</a>) Warning also needed to be a general header, as PUT or other methods may have need for it in requests.
     1800         needed headers in a 206 response, this problem can be avoided. (<a href="#combining.headers" title="Combining Headers">Section&nbsp;7.3</a>)
     1801      </p>
     1802      <p id="rfc.section.A.1.p.5">The Cache-Control: max-age directive was not properly defined for responses. (<a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">Section&nbsp;16.2.3</a>)
     1803      </p>
     1804      <p id="rfc.section.A.1.p.6">Warnings could be cached incorrectly, or not updated appropriately. (Section <a href="#warnings" title="Warnings">3.2</a>, <a href="#expiration.calculations" title="Expiration Calculations">4.4</a>, <a href="#non-modifiable.headers" title="Non-modifiable Headers">7.2</a>, <a href="#combining.headers" title="Combining Headers">7.3</a>, <a href="#modifications.of.the.basic.expiration.mechanism" title="Modifications of the Basic Expiration Mechanism">16.2.3</a>, and <a href="#header.warning" id="rfc.xref.header.warning.6" title="Warning">16.6</a>) Warning also needed to be a general header, as PUT or other methods may have need for it in requests.
    17891805      </p>
    17901806      <h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h2>
    1791       <p id="rfc.section.A.2.p.1">Clarify denial of service attack avoidance requirement. (<a href="#invalidation.after.updates.or.deletions" title="Invalidation After Updates or Deletions">Section&nbsp;11</a>)
     1807      <p id="rfc.section.A.2.p.1">Clarify denial of service attack avoidance requirement. (<a href="#invalidation.after.updates.or.deletions" title="Invalidation After Updates or Deletions">Section&nbsp;12</a>)
    17921808      </p>
    17931809      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;Change Log (to be removed by RFC Editor before publication)
     
    18361852         <li>Get rid of duplicate BNF rule names ("host" -&gt; "uri-host") (work in progress on &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;)
    18371853         </li>
     1854         <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li>
    18381855      </ul>
    18391856      <h1><a id="rfc.copyright" href="#rfc.copyright">Full Copyright Statement</a></h1>
     
    18711888            <li class="indline0"><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul class="ind">
    18721889                  <li class="indline1">age&nbsp;&nbsp;<a class="iref" href="#rfc.iref.a.1">1.2</a></li>
    1873                   <li class="indline1">Age header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.a.2"><b>15.1</b></a></li>
     1890                  <li class="indline1">Age header&nbsp;&nbsp;<a class="iref" href="#rfc.iref.a.2"><b>16.1</b></a></li>
    18741891               </ul>
    18751892            </li>
     
    18781895                  <li class="indline1">Cache Directives&nbsp;&nbsp;
    18791896                     <ul class="ind">
    1880                         <li class="indline1">max-age&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.9"><b>15.2.3</b></a>, <a class="iref" href="#rfc.iref.c.12"><b>15.2.4</b></a></li>
    1881                         <li class="indline1">max-stale&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.11"><b>15.2.3</b></a></li>
    1882                         <li class="indline1">min-fresh&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.10"><b>15.2.3</b></a></li>
    1883                         <li class="indline1">must-revalidate&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.14"><b>15.2.4</b></a></li>
    1884                         <li class="indline1">no-cache&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.6"><b>15.2.1</b></a></li>
    1885                         <li class="indline1">no-store&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.7"><b>15.2.2</b></a></li>
    1886                         <li class="indline1">no-transform&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.16"><b>15.2.5</b></a></li>
    1887                         <li class="indline1">only-if-cached&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.13"><b>15.2.4</b></a></li>
    1888                         <li class="indline1">private&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.5"><b>15.2.1</b></a></li>
    1889                         <li class="indline1">proxy-revalidate&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.15"><b>15.2.4</b></a></li>
    1890                         <li class="indline1">public&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.4"><b>15.2.1</b></a></li>
    1891                         <li class="indline1">s-maxage&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.8"><b>15.2.3</b></a></li>
     1897                        <li class="indline1">max-age&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.9"><b>16.2.3</b></a>, <a class="iref" href="#rfc.iref.c.12"><b>16.2.4</b></a></li>
     1898                        <li class="indline1">max-stale&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.11"><b>16.2.3</b></a></li>
     1899                        <li class="indline1">min-fresh&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.10"><b>16.2.3</b></a></li>
     1900                        <li class="indline1">must-revalidate&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.14"><b>16.2.4</b></a></li>
     1901                        <li class="indline1">no-cache&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.6"><b>16.2.1</b></a></li>
     1902                        <li class="indline1">no-store&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.7"><b>16.2.2</b></a></li>
     1903                        <li class="indline1">no-transform&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.16"><b>16.2.5</b></a></li>
     1904                        <li class="indline1">only-if-cached&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.13"><b>16.2.4</b></a></li>
     1905                        <li class="indline1">private&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.5"><b>16.2.1</b></a></li>
     1906                        <li class="indline1">proxy-revalidate&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.15"><b>16.2.4</b></a></li>
     1907                        <li class="indline1">public&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.4"><b>16.2.1</b></a></li>
     1908                        <li class="indline1">s-maxage&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.8"><b>16.2.3</b></a></li>
    18921909                     </ul>
    18931910                  </li>
    1894                   <li class="indline1">Cache-Control header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.cache-control.1">2.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.2">2.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.3">2.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.4">3.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.5">3.5</a>, <a class="iref" href="#rfc.xref.header.cache-control.6">5</a>, <a class="iref" href="#rfc.xref.header.cache-control.7">5</a>, <a class="iref" href="#rfc.xref.header.cache-control.8">9</a>, <a class="iref" href="#rfc.iref.c.3"><b>15.2</b></a>, <a class="iref" href="#rfc.xref.header.cache-control.9">15.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.10">15.4</a>, <a class="iref" href="#rfc.xref.header.cache-control.11">A.1</a></li>
     1911                  <li class="indline1">Cache-Control header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.cache-control.1">3.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.2">3.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.3">3.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.4">4.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.5">4.5</a>, <a class="iref" href="#rfc.xref.header.cache-control.6">6</a>, <a class="iref" href="#rfc.xref.header.cache-control.7">6</a>, <a class="iref" href="#rfc.xref.header.cache-control.8">10</a>, <a class="iref" href="#rfc.iref.c.3"><b>16.2</b></a>, <a class="iref" href="#rfc.xref.header.cache-control.9">16.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.10">16.4</a>, <a class="iref" href="#rfc.xref.header.cache-control.11">A.1</a></li>
    18951912                  <li class="indline1">cacheable&nbsp;&nbsp;<a class="iref" href="#rfc.iref.c.2">1.2</a></li>
    18961913               </ul>
    18971914            </li>
    18981915            <li class="indline0"><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul class="ind">
    1899                   <li class="indline1">Expires header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.expires.1">5</a>, <a class="iref" href="#rfc.xref.header.expires.2">15.2.3</a>, <a class="iref" href="#rfc.iref.e.2"><b>15.3</b></a></li>
     1916                  <li class="indline1">Expires header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.expires.1">6</a>, <a class="iref" href="#rfc.xref.header.expires.2">16.2.3</a>, <a class="iref" href="#rfc.iref.e.2"><b>16.3</b></a></li>
    19001917                  <li class="indline1">explicit expiration time&nbsp;&nbsp;<a class="iref" href="#rfc.iref.e.1">1.2</a></li>
    19011918               </ul>
     
    19101927                  <li class="indline1"><tt>Grammar</tt>&nbsp;&nbsp;
    19111928                     <ul class="ind">
    1912                         <li class="indline1"><tt>Age</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.1"><b>15.1</b></a></li>
    1913                         <li class="indline1"><tt>age-value</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.2"><b>15.1</b></a></li>
    1914                         <li class="indline1"><tt>Cache-Control</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.4"><b>15.2</b></a></li>
    1915                         <li class="indline1"><tt>cache-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.5"><b>15.2</b></a></li>
    1916                         <li class="indline1"><tt>cache-extension</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.8"><b>15.2</b></a></li>
    1917                         <li class="indline1"><tt>cache-request-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.6"><b>15.2</b></a></li>
    1918                         <li class="indline1"><tt>cache-response-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.7"><b>15.2</b></a></li>
    1919                         <li class="indline1"><tt>delta-seconds</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.3"><b>15.1</b></a></li>
    1920                         <li class="indline1"><tt>Expires</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.9"><b>15.3</b></a></li>
    1921                         <li class="indline1"><tt>extension-pragma</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.12"><b>15.4</b></a></li>
    1922                         <li class="indline1"><tt>Pragma</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.10"><b>15.4</b></a></li>
    1923                         <li class="indline1"><tt>pragma-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.11"><b>15.4</b></a></li>
    1924                         <li class="indline1"><tt>Vary</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.13"><b>15.5</b></a></li>
    1925                         <li class="indline1"><tt>warn-agent</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.17"><b>15.6</b></a></li>
    1926                         <li class="indline1"><tt>warn-code</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.16"><b>15.6</b></a></li>
    1927                         <li class="indline1"><tt>warn-date</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.19"><b>15.6</b></a></li>
    1928                         <li class="indline1"><tt>warn-text</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.18"><b>15.6</b></a></li>
    1929                         <li class="indline1"><tt>Warning</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.14"><b>15.6</b></a></li>
    1930                         <li class="indline1"><tt>warning-value</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.15"><b>15.6</b></a></li>
     1929                        <li class="indline1"><tt>Age</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.1"><b>16.1</b></a></li>
     1930                        <li class="indline1"><tt>age-value</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.2"><b>16.1</b></a></li>
     1931                        <li class="indline1"><tt>Cache-Control</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.4"><b>16.2</b></a></li>
     1932                        <li class="indline1"><tt>cache-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.5"><b>16.2</b></a></li>
     1933                        <li class="indline1"><tt>cache-extension</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.8"><b>16.2</b></a></li>
     1934                        <li class="indline1"><tt>cache-request-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.6"><b>16.2</b></a></li>
     1935                        <li class="indline1"><tt>cache-response-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.7"><b>16.2</b></a></li>
     1936                        <li class="indline1"><tt>delta-seconds</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.3"><b>16.1</b></a></li>
     1937                        <li class="indline1"><tt>Expires</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.9"><b>16.3</b></a></li>
     1938                        <li class="indline1"><tt>extension-pragma</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.12"><b>16.4</b></a></li>
     1939                        <li class="indline1"><tt>Pragma</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.10"><b>16.4</b></a></li>
     1940                        <li class="indline1"><tt>pragma-directive</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.11"><b>16.4</b></a></li>
     1941                        <li class="indline1"><tt>Vary</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.13"><b>16.5</b></a></li>
     1942                        <li class="indline1"><tt>warn-agent</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.17"><b>16.6</b></a></li>
     1943                        <li class="indline1"><tt>warn-code</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.16"><b>16.6</b></a></li>
     1944                        <li class="indline1"><tt>warn-date</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.19"><b>16.6</b></a></li>
     1945                        <li class="indline1"><tt>warn-text</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.18"><b>16.6</b></a></li>
     1946                        <li class="indline1"><tt>Warning</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.14"><b>16.6</b></a></li>
     1947                        <li class="indline1"><tt>warning-value</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.15"><b>16.6</b></a></li>
    19311948                     </ul>
    19321949                  </li>
     
    19361953                  <li class="indline1">Headers&nbsp;&nbsp;
    19371954                     <ul class="ind">
    1938                         <li class="indline1">Age&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.2"><b>15.1</b></a></li>
    1939                         <li class="indline1">Cache-Control&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.cache-control.1">2.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.2">2.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.3">2.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.4">3.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.5">3.5</a>, <a class="iref" href="#rfc.xref.header.cache-control.6">5</a>, <a class="iref" href="#rfc.xref.header.cache-control.7">5</a>, <a class="iref" href="#rfc.xref.header.cache-control.8">9</a>, <a class="iref" href="#rfc.iref.h.3"><b>15.2</b></a>, <a class="iref" href="#rfc.xref.header.cache-control.9">15.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.10">15.4</a>, <a class="iref" href="#rfc.xref.header.cache-control.11">A.1</a></li>
    1940                         <li class="indline1">Expires&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.expires.1">5</a>, <a class="iref" href="#rfc.xref.header.expires.2">15.2.3</a>, <a class="iref" href="#rfc.iref.h.4"><b>15.3</b></a></li>
    1941                         <li class="indline1">Pragma&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.pragma.1">15.2</a>, <a class="iref" href="#rfc.iref.h.5"><b>15.4</b></a></li>
    1942                         <li class="indline1">Vary&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.vary.1">7</a>, <a class="iref" href="#rfc.iref.h.6"><b>15.5</b></a></li>
    1943                         <li class="indline1">Warning&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.warning.1">2.1</a>, <a class="iref" href="#rfc.xref.header.warning.2">2.2</a>, <a class="iref" href="#rfc.xref.header.warning.3">2.2</a>, <a class="iref" href="#rfc.xref.header.warning.4">6.2</a>, <a class="iref" href="#rfc.xref.header.warning.5">6.3</a>, <a class="iref" href="#rfc.iref.h.7"><b>15.6</b></a>, <a class="iref" href="#rfc.xref.header.warning.6">A.1</a></li>
     1955                        <li class="indline1">Age&nbsp;&nbsp;<a class="iref" href="#rfc.iref.h.2"><b>16.1</b></a></li>
     1956                        <li class="indline1">Cache-Control&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.cache-control.1">3.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.2">3.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.3">3.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.4">4.1</a>, <a class="iref" href="#rfc.xref.header.cache-control.5">4.5</a>, <a class="iref" href="#rfc.xref.header.cache-control.6">6</a>, <a class="iref" href="#rfc.xref.header.cache-control.7">6</a>, <a class="iref" href="#rfc.xref.header.cache-control.8">10</a>, <a class="iref" href="#rfc.iref.h.3"><b>16.2</b></a>, <a class="iref" href="#rfc.xref.header.cache-control.9">16.3</a>, <a class="iref" href="#rfc.xref.header.cache-control.10">16.4</a>, <a class="iref" href="#rfc.xref.header.cache-control.11">A.1</a></li>
     1957                        <li class="indline1">Expires&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.expires.1">6</a>, <a class="iref" href="#rfc.xref.header.expires.2">16.2.3</a>, <a class="iref" href="#rfc.iref.h.4"><b>16.3</b></a></li>
     1958                        <li class="indline1">Pragma&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.pragma.1">16.2</a>, <a class="iref" href="#rfc.iref.h.5"><b>16.4</b></a></li>
     1959                        <li class="indline1">Vary&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.vary.1">8</a>, <a class="iref" href="#rfc.iref.h.6"><b>16.5</b></a></li>
     1960                        <li class="indline1">Warning&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.warning.1">3.1</a>, <a class="iref" href="#rfc.xref.header.warning.2">3.2</a>, <a class="iref" href="#rfc.xref.header.warning.3">3.2</a>, <a class="iref" href="#rfc.xref.header.warning.4">7.2</a>, <a class="iref" href="#rfc.xref.header.warning.5">7.3</a>, <a class="iref" href="#rfc.iref.h.7"><b>16.6</b></a>, <a class="iref" href="#rfc.xref.header.warning.6">A.1</a></li>
    19441961                     </ul>
    19451962                  </li>
     
    19481965            </li>
    19491966            <li class="indline0"><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul class="ind">
    1950                   <li class="indline1"><em>ISO-8859-1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.ISO-8859-1.1">15.6</a>, <a class="iref" href="#ISO-8859-1"><b>19.1</b></a></li>
     1967                  <li class="indline1"><em>ISO-8859-1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.ISO-8859-1.1">16.6</a>, <a class="iref" href="#ISO-8859-1"><b>20.1</b></a></li>
    19511968               </ul>
    19521969            </li>
     
    19541971                  <li class="indline1">max-age&nbsp;&nbsp;
    19551972                     <ul class="ind">
    1956                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.1"><b>15.2.3</b></a>, <a class="iref" href="#rfc.iref.m.4"><b>15.2.4</b></a></li>
     1973                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.1"><b>16.2.3</b></a>, <a class="iref" href="#rfc.iref.m.4"><b>16.2.4</b></a></li>
    19571974                     </ul>
    19581975                  </li>
    19591976                  <li class="indline1">max-stale&nbsp;&nbsp;
    19601977                     <ul class="ind">
    1961                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.3"><b>15.2.3</b></a></li>
     1978                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.3"><b>16.2.3</b></a></li>
    19621979                     </ul>
    19631980                  </li>
    19641981                  <li class="indline1">min-fresh&nbsp;&nbsp;
    19651982                     <ul class="ind">
    1966                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.2"><b>15.2.3</b></a></li>
     1983                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.2"><b>16.2.3</b></a></li>
    19671984                     </ul>
    19681985                  </li>
    19691986                  <li class="indline1">must-revalidate&nbsp;&nbsp;
    19701987                     <ul class="ind">
    1971                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.5"><b>15.2.4</b></a></li>
     1988                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.5"><b>16.2.4</b></a></li>
    19721989                     </ul>
    19731990                  </li>
     
    19771994                  <li class="indline1">no-cache&nbsp;&nbsp;
    19781995                     <ul class="ind">
    1979                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.n.1"><b>15.2.1</b></a></li>
     1996                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.n.1"><b>16.2.1</b></a></li>
    19801997                     </ul>
    19811998                  </li>
    19821999                  <li class="indline1">no-store&nbsp;&nbsp;
    19832000                     <ul class="ind">
    1984                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.n.2"><b>15.2.2</b></a></li>
     2001                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.n.2"><b>16.2.2</b></a></li>
    19852002                     </ul>
    19862003                  </li>
    19872004                  <li class="indline1">no-transform&nbsp;&nbsp;
    19882005                     <ul class="ind">
    1989                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.n.3"><b>15.2.5</b></a></li>
     2006                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.n.3"><b>16.2.5</b></a></li>
    19902007                     </ul>
    19912008                  </li>
     
    19952012                  <li class="indline1">only-if-cached&nbsp;&nbsp;
    19962013                     <ul class="ind">
    1997                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.o.1"><b>15.2.4</b></a></li>
     2014                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.o.1"><b>16.2.4</b></a></li>
    19982015                     </ul>
    19992016                  </li>
     
    20012018            </li>
    20022019            <li class="indline0"><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul class="ind">
    2003                   <li class="indline1"><em>Part1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">3.3</a>, <a class="iref" href="#rfc.xref.Part1.2">6.1</a>, <a class="iref" href="#rfc.xref.Part1.3">6.2</a>, <a class="iref" href="#rfc.xref.Part1.4">6.2</a>, <a class="iref" href="#rfc.xref.Part1.5">7</a>, <a class="iref" href="#rfc.xref.Part1.6">15.3</a>, <a class="iref" href="#Part1"><b>19.1</b></a>, <a class="iref" href="#rfc.xref.Part1.7">A.1</a><ul class="ind">
    2004                         <li class="indline1"><em>Section 3.3.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.6">15.3</a></li>
    2005                         <li class="indline1"><em>Section 4.2</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.5">7</a></li>
    2006                         <li class="indline1"><em>Section 4.4</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.3">6.2</a>, <a class="iref" href="#rfc.xref.Part1.4">6.2</a></li>
    2007                         <li class="indline1"><em>Section 8.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.2">6.1</a></li>
    2008                         <li class="indline1"><em>Section 8.3</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">3.3</a></li>
     2020                  <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">2</a>, <a class="iref" href="#rfc.xref.Part1.6">2</a>, <a class="iref" href="#rfc.xref.Part1.7">2</a>, <a class="iref" href="#rfc.xref.Part1.8">2</a>, <a class="iref" href="#rfc.xref.Part1.9">2</a>, <a class="iref" href="#rfc.xref.Part1.10">2</a>, <a class="iref" href="#rfc.xref.Part1.11">2</a>, <a class="iref" href="#rfc.xref.Part1.12">2</a>, <a class="iref" href="#rfc.xref.Part1.13">4.3</a>, <a class="iref" href="#rfc.xref.Part1.14">7.1</a>, <a class="iref" href="#rfc.xref.Part1.15">7.2</a>, <a class="iref" href="#rfc.xref.Part1.16">7.2</a>, <a class="iref" href="#rfc.xref.Part1.17">8</a>, <a class="iref" href="#rfc.xref.Part1.18">16.3</a>, <a class="iref" href="#Part1"><b>20.1</b></a>, <a class="iref" href="#rfc.xref.Part1.19">A.1</a><ul class="ind">
     2021                        <li class="indline1"><em>Section 2.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">2</a></li>
     2022                        <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>, <a class="iref" href="#rfc.xref.Part1.4">2</a>, <a class="iref" href="#rfc.xref.Part1.5">2</a>, <a class="iref" href="#rfc.xref.Part1.6">2</a>, <a class="iref" href="#rfc.xref.Part1.7">2</a></li>
     2023                        <li class="indline1"><em>Section 3.2.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.10">2</a>, <a class="iref" href="#rfc.xref.Part1.12">2</a></li>
     2024                        <li class="indline1"><em>Section 3.3.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.9">2</a>, <a class="iref" href="#rfc.xref.Part1.18">16.3</a></li>
     2025                        <li class="indline1"><em>Section 4.2</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.8">2</a>, <a class="iref" href="#rfc.xref.Part1.17">8</a></li>
     2026                        <li class="indline1"><em>Section 4.4</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.15">7.2</a>, <a class="iref" href="#rfc.xref.Part1.16">7.2</a></li>
     2027                        <li class="indline1"><em>Section 8.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.14">7.1</a></li>
     2028                        <li class="indline1"><em>Section 8.3</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.13">4.3</a></li>
     2029                        <li class="indline1"><em>Section 8.9</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.11">2</a></li>
    20092030                     </ul>
    20102031                  </li>
    2011                   <li class="indline1"><em>Part2</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part2.1">10</a>, <a class="iref" href="#Part2"><b>19.1</b></a><ul class="ind">
    2012                         <li class="indline1"><em>Section 7.1.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part2.1">10</a></li>
     2032                  <li class="indline1"><em>Part2</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part2.1">11</a>, <a class="iref" href="#Part2"><b>20.1</b></a><ul class="ind">
     2033                        <li class="indline1"><em>Section 8.1.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part2.1">11</a></li>
    20132034                     </ul>
    20142035                  </li>
    2015                   <li class="indline1"><em>Part3</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part3.1">6.2</a>, <a class="iref" href="#rfc.xref.Part3.2">7</a>, <a class="iref" href="#Part3"><b>19.1</b></a>, <a class="iref" href="#rfc.xref.Part3.3">A.1</a><ul class="ind">
    2016                         <li class="indline1"><em>Section 3.2.2</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part3.1">6.2</a></li>
    2017                         <li class="indline1"><em>Section 4.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part3.2">7</a></li>
     2036                  <li class="indline1"><em>Part3</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part3.1">7.2</a>, <a class="iref" href="#rfc.xref.Part3.2">8</a>, <a class="iref" href="#Part3"><b>20.1</b></a>, <a class="iref" href="#rfc.xref.Part3.3">A.1</a><ul class="ind">
     2037                        <li class="indline1"><em>Section 4.2.2</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part3.1">7.2</a></li>
     2038                        <li class="indline1"><em>Section 5.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part3.2">8</a></li>
    20182039                     </ul>
    20192040                  </li>
    2020                   <li class="indline1"><em>Part4</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part4.1">4</a>, <a class="iref" href="#Part4"><b>19.1</b></a></li>
    2021                   <li class="indline1"><em>Part5</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">6.3</a>, <a class="iref" href="#rfc.xref.Part5.2">9</a>, <a class="iref" href="#Part5"><b>19.1</b></a>, <a class="iref" href="#rfc.xref.Part5.3">A.1</a><ul class="ind">
    2022                         <li class="indline1"><em>Section 4</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">6.3</a>, <a class="iref" href="#rfc.xref.Part5.2">9</a></li>
     2041                  <li class="indline1"><em>Part4</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part4.1">5</a>, <a class="iref" href="#Part4"><b>20.1</b></a></li>
     2042                  <li class="indline1"><em>Part5</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">7.3</a>, <a class="iref" href="#rfc.xref.Part5.2">10</a>, <a class="iref" href="#Part5"><b>20.1</b></a>, <a class="iref" href="#rfc.xref.Part5.3">A.1</a><ul class="ind">
     2043                        <li class="indline1"><em>Section 5</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part5.1">7.3</a>, <a class="iref" href="#rfc.xref.Part5.2">10</a></li>
    20232044                     </ul>
    20242045                  </li>
    2025                   <li class="indline1"><em>Part7</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part7.1">5</a>, <a class="iref" href="#rfc.xref.Part7.2">15.2.1</a>, <a class="iref" href="#Part7"><b>19.1</b></a><ul class="ind">
    2026                         <li class="indline1"><em>Section 3.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part7.1">5</a>, <a class="iref" href="#rfc.xref.Part7.2">15.2.1</a></li>
     2046                  <li class="indline1"><em>Part7</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part7.1">6</a>, <a class="iref" href="#rfc.xref.Part7.2">16.2.1</a>, <a class="iref" href="#Part7"><b>20.1</b></a><ul class="ind">
     2047                        <li class="indline1"><em>Section 4.1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part7.1">6</a>, <a class="iref" href="#rfc.xref.Part7.2">16.2.1</a></li>
    20272048                     </ul>
    20282049                  </li>
    2029                   <li class="indline1">Pragma header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.pragma.1">15.2</a>, <a class="iref" href="#rfc.iref.p.4"><b>15.4</b></a></li>
     2050                  <li class="indline1">Pragma header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.pragma.1">16.2</a>, <a class="iref" href="#rfc.iref.p.4"><b>16.4</b></a></li>
    20302051                  <li class="indline1">private&nbsp;&nbsp;
    20312052                     <ul class="ind">
    2032                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.p.2"><b>15.2.1</b></a></li>
     2053                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.p.2"><b>16.2.1</b></a></li>
    20332054                     </ul>
    20342055                  </li>
    20352056                  <li class="indline1">proxy-revalidate&nbsp;&nbsp;
    20362057                     <ul class="ind">
    2037                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.p.3"><b>15.2.4</b></a></li>
     2058                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.p.3"><b>16.2.4</b></a></li>
    20382059                     </ul>
    20392060                  </li>
    20402061                  <li class="indline1">public&nbsp;&nbsp;
    20412062                     <ul class="ind">
    2042                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.p.1"><b>15.2.1</b></a></li>
     2063                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.p.1"><b>16.2.1</b></a></li>
    20432064                     </ul>
    20442065                  </li>
     
    20462067            </li>
    20472068            <li class="indline0"><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul class="ind">
    2048                   <li class="indline1"><em>RFC1305</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC1305.1">3.3</a>, <a class="iref" href="#RFC1305"><b>19.2</b></a></li>
    2049                   <li class="indline1"><em>RFC2047</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2047.1">15.6</a>, <a class="iref" href="#RFC2047"><b>19.1</b></a></li>
    2050                   <li class="indline1"><em>RFC2119</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2119.1">1.3</a>, <a class="iref" href="#RFC2119"><b>19.1</b></a></li>
    2051                   <li class="indline1"><em>RFC2616</em>&nbsp;&nbsp;<a class="iref" href="#RFC2616"><b>19.2</b></a>, <a class="iref" href="#rfc.xref.RFC2616.1">B.1</a></li>
     2069                  <li class="indline1"><em>RFC1305</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC1305.1">4.3</a>, <a class="iref" href="#RFC1305"><b>20.2</b></a></li>
     2070                  <li class="indline1"><em>RFC2047</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2047.1">16.6</a>, <a class="iref" href="#RFC2047"><b>20.1</b></a></li>
     2071                  <li class="indline1"><em>RFC2119</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.RFC2119.1">1.3</a>, <a class="iref" href="#RFC2119"><b>20.1</b></a></li>
     2072                  <li class="indline1"><em>RFC2616</em>&nbsp;&nbsp;<a class="iref" href="#RFC2616"><b>20.2</b></a>, <a class="iref" href="#rfc.xref.RFC2616.1">B.1</a></li>
    20522073               </ul>
    20532074            </li>
     
    20552076                  <li class="indline1">s-maxage&nbsp;&nbsp;
    20562077                     <ul class="ind">
    2057                         <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.s.3"><b>15.2.3</b></a></li>
     2078                        <li class="indline1">Cache Directive&nbsp;&nbsp;<a class="iref" href="#rfc.iref.s.3"><b>16.2.3</b></a></li>
    20582079                     </ul>
    20592080                  </li>
     
    20642085            <li class="indline0"><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul class="ind">
    20652086                  <li class="indline1">validator&nbsp;&nbsp;<a class="iref" href="#rfc.iref.v.1">1.2</a></li>
    2066                   <li class="indline1">Vary header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.vary.1">7</a>, <a class="iref" href="#rfc.iref.v.2"><b>15.5</b></a></li>
     2087                  <li class="indline1">Vary header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.vary.1">8</a>, <a class="iref" href="#rfc.iref.v.2"><b>16.5</b></a></li>
    20672088               </ul>
    20682089            </li>
    20692090            <li class="indline0"><a id="rfc.index.W" href="#rfc.index.W"><b>W</b></a><ul class="ind">
    2070                   <li class="indline1">Warning header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.warning.1">2.1</a>, <a class="iref" href="#rfc.xref.header.warning.2">2.2</a>, <a class="iref" href="#rfc.xref.header.warning.3">2.2</a>, <a class="iref" href="#rfc.xref.header.warning.4">6.2</a>, <a class="iref" href="#rfc.xref.header.warning.5">6.3</a>, <a class="iref" href="#rfc.iref.w.1"><b>15.6</b></a>, <a class="iref" href="#rfc.xref.header.warning.6">A.1</a></li>
     2091                  <li class="indline1">Warning header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.warning.1">3.1</a>, <a class="iref" href="#rfc.xref.header.warning.2">3.2</a>, <a class="iref" href="#rfc.xref.header.warning.3">3.2</a>, <a class="iref" href="#rfc.xref.header.warning.4">7.2</a>, <a class="iref" href="#rfc.xref.header.warning.5">7.3</a>, <a class="iref" href="#rfc.iref.w.1"><b>16.6</b></a>, <a class="iref" href="#rfc.xref.header.warning.6">A.1</a></li>
    20712092               </ul>
    20722093            </li>
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