Changeset 1751


Ignore:
Timestamp:
Jul 9, 2012, 4:44:03 PM (7 years ago)
Author:
mnot@…
Message:

Re-org caching sections

Location:
draft-ietf-httpbis/latest
Files:
2 edited

Legend:

Unmodified
Added
Removed
  • draft-ietf-httpbis/latest/p6-cache.html

    r1745 r1751  
    452452  }
    453453  @bottom-center {
    454        content: "Expires January 10, 2013";
     454       content: "Expires January 11, 2013";
    455455  }
    456456  @bottom-right {
     
    475475      <link rel="Index" href="#rfc.index">
    476476      <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
    477       <link rel="Chapter" title="2 Cache Operation" href="#rfc.section.2">
    478       <link rel="Chapter" title="3 Header Field Definitions" href="#rfc.section.3">
    479       <link rel="Chapter" title="4 History Lists" href="#rfc.section.4">
    480       <link rel="Chapter" title="5 IANA Considerations" href="#rfc.section.5">
    481       <link rel="Chapter" title="6 Security Considerations" href="#rfc.section.6">
    482       <link rel="Chapter" title="7 Acknowledgments" href="#rfc.section.7">
    483       <link rel="Chapter" href="#rfc.section.8" title="8 References">
     477      <link rel="Chapter" title="2 Overview of Cache Operation" href="#rfc.section.2">
     478      <link rel="Chapter" title="3 Storing Responses in Caches" href="#rfc.section.3">
     479      <link rel="Chapter" title="4 Constructing Responses from Caches" href="#rfc.section.4">
     480      <link rel="Chapter" title="5 Updating Caches with HEAD Responses" href="#rfc.section.5">
     481      <link rel="Chapter" title="6 Request Methods that Invalidate" href="#rfc.section.6">
     482      <link rel="Chapter" title="7 Header Field Definitions" href="#rfc.section.7">
     483      <link rel="Chapter" title="8 History Lists" href="#rfc.section.8">
     484      <link rel="Chapter" title="9 IANA Considerations" href="#rfc.section.9">
     485      <link rel="Chapter" title="10 Security Considerations" href="#rfc.section.10">
     486      <link rel="Chapter" title="11 Acknowledgments" href="#rfc.section.11">
     487      <link rel="Chapter" href="#rfc.section.12" title="12 References">
    484488      <link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A">
    485489      <link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B">
     
    494498      <meta name="dct.creator" content="Reschke, J. F.">
    495499      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p6-cache-latest">
    496       <meta name="dct.issued" scheme="ISO8601" content="2012-07-09">
     500      <meta name="dct.issued" scheme="ISO8601" content="2012-07-10">
    497501      <meta name="dct.replaces" content="urn:ietf:rfc:2616">
    498502      <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 6 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 6 defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages.">
     
    520524            </tr>
    521525            <tr>
    522                <td class="left">Expires: January 10, 2013</td>
     526               <td class="left">Expires: January 11, 2013</td>
    523527               <td class="right">M. Nottingham, Editor</td>
    524528            </tr>
     
    537541            <tr>
    538542               <td class="left"></td>
    539                <td class="right">July 9, 2012</td>
     543               <td class="right">July 10, 2012</td>
    540544            </tr>
    541545         </tbody>
     
    567571         in progress”.
    568572      </p>
    569       <p>This Internet-Draft will expire on January 10, 2013.</p>
     573      <p>This Internet-Draft will expire on January 11, 2013.</p>
    570574      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    571575      <p>Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
     
    597601            </ul>
    598602         </li>
    599          <li>2.&nbsp;&nbsp;&nbsp;<a href="#caching.overview">Cache Operation</a><ul>
    600                <li>2.1&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Response Cacheability</a></li>
    601                <li>2.2&nbsp;&nbsp;&nbsp;<a href="#constructing.responses.from.caches">Constructing Responses from Caches</a></li>
    602                <li>2.3&nbsp;&nbsp;&nbsp;<a href="#expiration.model">Freshness Model</a><ul>
    603                      <li>2.3.1&nbsp;&nbsp;&nbsp;<a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a><ul>
    604                            <li>2.3.1.1&nbsp;&nbsp;&nbsp;<a href="#heuristic.freshness">Calculating Heuristic Freshness</a></li>
     603         <li>2.&nbsp;&nbsp;&nbsp;<a href="#caching.overview">Overview of Cache Operation</a></li>
     604         <li>3.&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Storing Responses in Caches</a><ul>
     605               <li>3.1&nbsp;&nbsp;&nbsp;<a href="#incomplete.responses">Storing Incomplete Responses</a></li>
     606               <li>3.2&nbsp;&nbsp;&nbsp;<a href="#caching.authenticated.responses">Storing Responses to Authenticated Requests</a></li>
     607            </ul>
     608         </li>
     609         <li>4.&nbsp;&nbsp;&nbsp;<a href="#constructing.responses.from.caches">Constructing Responses from Caches</a><ul>
     610               <li>4.1&nbsp;&nbsp;&nbsp;<a href="#expiration.model">Freshness Model</a><ul>
     611                     <li>4.1.1&nbsp;&nbsp;&nbsp;<a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></li>
     612                     <li>4.1.2&nbsp;&nbsp;&nbsp;<a href="#heuristic.freshness">Calculating Heuristic Freshness</a></li>
     613                     <li>4.1.3&nbsp;&nbsp;&nbsp;<a href="#age.calculations">Calculating Age</a></li>
     614                     <li>4.1.4&nbsp;&nbsp;&nbsp;<a href="#serving.stale.responses">Serving Stale Responses</a></li>
     615                  </ul>
     616               </li>
     617               <li>4.2&nbsp;&nbsp;&nbsp;<a href="#validation.model">Validation Model</a><ul>
     618                     <li>4.2.1&nbsp;&nbsp;&nbsp;<a href="#freshening.responses">Freshening Responses with 304 Not Modified</a></li>
     619                  </ul>
     620               </li>
     621               <li>4.3&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Using Negotiated Responses</a></li>
     622               <li>4.4&nbsp;&nbsp;&nbsp;<a href="#combining.responses">Combining Partial Content</a></li>
     623            </ul>
     624         </li>
     625         <li>5.&nbsp;&nbsp;&nbsp;<a href="#head.effects">Updating Caches with HEAD Responses</a></li>
     626         <li>6.&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></li>
     627         <li>7.&nbsp;&nbsp;&nbsp;<a href="#header.field.definitions">Header Field Definitions</a><ul>
     628               <li>7.1&nbsp;&nbsp;&nbsp;<a href="#header.age">Age</a></li>
     629               <li>7.2&nbsp;&nbsp;&nbsp;<a href="#header.cache-control">Cache-Control</a><ul>
     630                     <li>7.2.1&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive">Request Cache-Control Directives</a><ul>
     631                           <li>7.2.1.1&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.no-cache">no-cache</a></li>
     632                           <li>7.2.1.2&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.no-store">no-store</a></li>
     633                           <li>7.2.1.3&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.max-age">max-age</a></li>
     634                           <li>7.2.1.4&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.max-stale">max-stale</a></li>
     635                           <li>7.2.1.5&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.min-fresh">min-fresh</a></li>
     636                           <li>7.2.1.6&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.no-transform">no-transform</a></li>
     637                           <li>7.2.1.7&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.only-if-cached">only-if-cached</a></li>
    605638                        </ul>
    606639                     </li>
    607                      <li>2.3.2&nbsp;&nbsp;&nbsp;<a href="#age.calculations">Calculating Age</a></li>
    608                      <li>2.3.3&nbsp;&nbsp;&nbsp;<a href="#serving.stale.responses">Serving Stale Responses</a></li>
     640                     <li>7.2.2&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive">Response Cache-Control Directives</a><ul>
     641                           <li>7.2.2.1&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.only-if-cached">public</a></li>
     642                           <li>7.2.2.2&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.private">private</a></li>
     643                           <li>7.2.2.3&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.no-cache">no-cache</a></li>
     644                           <li>7.2.2.4&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.no-store">no-store</a></li>
     645                           <li>7.2.2.5&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.must-revalidate">must-revalidate</a></li>
     646                           <li>7.2.2.6&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></li>
     647                           <li>7.2.2.7&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.max-age">max-age</a></li>
     648                           <li>7.2.2.8&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.s-maxage">s-maxage</a></li>
     649                           <li>7.2.2.9&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.no-transform">no-transform</a></li>
     650                        </ul>
     651                     </li>
     652                     <li>7.2.3&nbsp;&nbsp;&nbsp;<a href="#cache.control.extensions">Cache Control Extensions</a></li>
    609653                  </ul>
    610654               </li>
    611                <li>2.4&nbsp;&nbsp;&nbsp;<a href="#validation.model">Validation Model</a><ul>
    612                      <li>2.4.1&nbsp;&nbsp;&nbsp;<a href="#freshening.responses">Freshening Responses with 304 Not Modified</a></li>
    613                   </ul>
    614                </li>
    615                <li>2.5&nbsp;&nbsp;&nbsp;<a href="#head.effects">Updating Caches with HEAD Responses</a></li>
    616                <li>2.6&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></li>
    617                <li>2.7&nbsp;&nbsp;&nbsp;<a href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></li>
    618                <li>2.8&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
    619                <li>2.9&nbsp;&nbsp;&nbsp;<a href="#combining.responses">Combining Partial Content</a></li>
    620             </ul>
    621          </li>
    622          <li>3.&nbsp;&nbsp;&nbsp;<a href="#header.field.definitions">Header Field Definitions</a><ul>
    623                <li>3.1&nbsp;&nbsp;&nbsp;<a href="#header.age">Age</a></li>
    624                <li>3.2&nbsp;&nbsp;&nbsp;<a href="#header.cache-control">Cache-Control</a><ul>
    625                      <li>3.2.1&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive">Request Cache-Control Directives</a><ul>
    626                            <li>3.2.1.1&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.no-cache">no-cache</a></li>
    627                            <li>3.2.1.2&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.no-store">no-store</a></li>
    628                            <li>3.2.1.3&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.max-age">max-age</a></li>
    629                            <li>3.2.1.4&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.max-stale">max-stale</a></li>
    630                            <li>3.2.1.5&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.min-fresh">min-fresh</a></li>
    631                            <li>3.2.1.6&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.no-transform">no-transform</a></li>
    632                            <li>3.2.1.7&nbsp;&nbsp;&nbsp;<a href="#cache-request-directive.only-if-cached">only-if-cached</a></li>
    633                         </ul>
    634                      </li>
    635                      <li>3.2.2&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive">Response Cache-Control Directives</a><ul>
    636                            <li>3.2.2.1&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.only-if-cached">public</a></li>
    637                            <li>3.2.2.2&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.private">private</a></li>
    638                            <li>3.2.2.3&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.no-cache">no-cache</a></li>
    639                            <li>3.2.2.4&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.no-store">no-store</a></li>
    640                            <li>3.2.2.5&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.must-revalidate">must-revalidate</a></li>
    641                            <li>3.2.2.6&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></li>
    642                            <li>3.2.2.7&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.max-age">max-age</a></li>
    643                            <li>3.2.2.8&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.s-maxage">s-maxage</a></li>
    644                            <li>3.2.2.9&nbsp;&nbsp;&nbsp;<a href="#cache-response-directive.no-transform">no-transform</a></li>
    645                         </ul>
    646                      </li>
    647                      <li>3.2.3&nbsp;&nbsp;&nbsp;<a href="#cache.control.extensions">Cache Control Extensions</a></li>
    648                   </ul>
    649                </li>
    650                <li>3.3&nbsp;&nbsp;&nbsp;<a href="#header.expires">Expires</a></li>
    651                <li>3.4&nbsp;&nbsp;&nbsp;<a href="#header.pragma">Pragma</a></li>
    652                <li>3.5&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
    653                <li>3.6&nbsp;&nbsp;&nbsp;<a href="#header.warning">Warning</a><ul>
    654                      <li>3.6.1&nbsp;&nbsp;&nbsp;<a href="#warn.110">110 Response is Stale</a></li>
    655                      <li>3.6.2&nbsp;&nbsp;&nbsp;<a href="#warn.111">111 Revalidation Failed</a></li>
    656                      <li>3.6.3&nbsp;&nbsp;&nbsp;<a href="#warn.112">112 Disconnected Operation</a></li>
    657                      <li>3.6.4&nbsp;&nbsp;&nbsp;<a href="#warn.113">113 Heuristic Expiration</a></li>
    658                      <li>3.6.5&nbsp;&nbsp;&nbsp;<a href="#warn.199">199 Miscellaneous Warning</a></li>
    659                      <li>3.6.6&nbsp;&nbsp;&nbsp;<a href="#warn.214">214 Transformation Applied</a></li>
    660                      <li>3.6.7&nbsp;&nbsp;&nbsp;<a href="#warn.299">299 Miscellaneous Persistent Warning</a></li>
    661                      <li>3.6.8&nbsp;&nbsp;&nbsp;<a href="#warn.code.extensions">Warn Code Extensions</a></li>
     655               <li>7.3&nbsp;&nbsp;&nbsp;<a href="#header.expires">Expires</a></li>
     656               <li>7.4&nbsp;&nbsp;&nbsp;<a href="#header.pragma">Pragma</a></li>
     657               <li>7.5&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
     658               <li>7.6&nbsp;&nbsp;&nbsp;<a href="#header.warning">Warning</a><ul>
     659                     <li>7.6.1&nbsp;&nbsp;&nbsp;<a href="#warn.110">110 Response is Stale</a></li>
     660                     <li>7.6.2&nbsp;&nbsp;&nbsp;<a href="#warn.111">111 Revalidation Failed</a></li>
     661                     <li>7.6.3&nbsp;&nbsp;&nbsp;<a href="#warn.112">112 Disconnected Operation</a></li>
     662                     <li>7.6.4&nbsp;&nbsp;&nbsp;<a href="#warn.113">113 Heuristic Expiration</a></li>
     663                     <li>7.6.5&nbsp;&nbsp;&nbsp;<a href="#warn.199">199 Miscellaneous Warning</a></li>
     664                     <li>7.6.6&nbsp;&nbsp;&nbsp;<a href="#warn.214">214 Transformation Applied</a></li>
     665                     <li>7.6.7&nbsp;&nbsp;&nbsp;<a href="#warn.299">299 Miscellaneous Persistent Warning</a></li>
     666                     <li>7.6.8&nbsp;&nbsp;&nbsp;<a href="#warn.code.extensions">Warn Code Extensions</a></li>
    662667                  </ul>
    663668               </li>
    664669            </ul>
    665670         </li>
    666          <li>4.&nbsp;&nbsp;&nbsp;<a href="#history.lists">History Lists</a></li>
    667          <li>5.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
    668                <li>5.1&nbsp;&nbsp;&nbsp;<a href="#cache.directive.registration">Cache Directive Registry</a></li>
    669                <li>5.2&nbsp;&nbsp;&nbsp;<a href="#warn.code.registration">Warn Code Registry</a></li>
    670                <li>5.3&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li>
     671         <li>8.&nbsp;&nbsp;&nbsp;<a href="#history.lists">History Lists</a></li>
     672         <li>9.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
     673               <li>9.1&nbsp;&nbsp;&nbsp;<a href="#cache.directive.registration">Cache Directive Registry</a></li>
     674               <li>9.2&nbsp;&nbsp;&nbsp;<a href="#warn.code.registration">Warn Code Registry</a></li>
     675               <li>9.3&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li>
    671676            </ul>
    672677         </li>
    673          <li>6.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a></li>
    674          <li>7.&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li>
    675          <li>8.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
    676                <li>8.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
    677                <li>8.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
     678         <li>10.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a></li>
     679         <li>11.&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li>
     680         <li>12.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
     681               <li>12.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
     682               <li>12.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
    678683            </ul>
    679684         </li>
     
    698703      </p>
    699704      <p id="rfc.section.1.1.p.2">The goal of caching in HTTP/1.1 is to significantly improve performance by reusing a prior response message to satisfy a current
    700          request. A stored response is considered "fresh", as defined in <a href="#expiration.model" title="Freshness Model">Section&nbsp;2.3</a>, if the response can be reused without "validation" (checking with the origin server to see if the cached response remains
     705         request. A stored response is considered "fresh", as defined in <a href="#expiration.model" title="Freshness Model">Section&nbsp;4.1</a>, if the response can be reused without "validation" (checking with the origin server to see if the cached response remains
    701706         valid for this request). A fresh cache response can therefore reduce both latency and network transfers each time it is reused.
    702          When a cached response is not fresh, it might still be reusable if it can be freshened by validation (<a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>) or if the origin is unavailable.
     707         When a cached response is not fresh, it might still be reusable if it can be freshened by validation (<a href="#validation.model" title="Validation Model">Section&nbsp;4.2</a>) or if the origin is unavailable.
    703708      </p>
    704709      <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a id="intro.terminology" href="#intro.terminology">Terminology</a></h2>
     
    825830      <div id="rfc.iref.c.4"></div>
    826831      <div id="rfc.iref.c.5"></div>
    827       <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="caching.overview" href="#caching.overview">Cache Operation</a></h1>
     832      <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="caching.overview" href="#caching.overview">Overview of Cache Operation</a></h1>
    828833      <p id="rfc.section.2.p.1">Proper cache operation preserves the semantics of HTTP transfers (<a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) while eliminating the transfer of information already held in the cache. Although caching is an entirely <em class="bcp14">OPTIONAL</em> feature of HTTP, we assume that reusing the cached response is desirable and that such reuse is the default behavior when
    829834         no requirement or locally-desired configuration prevents it. Therefore, HTTP cache requirements are focused on preventing
     
    832837      <p id="rfc.section.2.p.2">Each <dfn>cache entry</dfn> consists of a cache key and one or more HTTP responses corresponding to prior requests that used the same key. The most common
    833838         form of cache entry is a successful result of a retrieval request: i.e., a <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> response containing a representation of the resource identified by the request target. However, it is also possible to cache
    834          negative results (e.g., <a href="p2-semantics.html#status.404" class="smpl">404 (Not Found)</a>, incomplete results (e.g., <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a>), and responses to safe methods other than GET if the method's definition allows such caching and defines something suitable
     839         negative results (e.g., <a href="p2-semantics.html#status.404" class="smpl">404 (Not
     840            Found)</a>, incomplete results (e.g., <a href="p5-range.html#status.206" class="smpl">206 (Partial
     841            Content)</a>), and responses to safe methods other than GET if the method's definition allows such caching and defines something suitable
    835842         for use as a cache key.
    836843      </p>
     
    839846      </p>
    840847      <p id="rfc.section.2.p.4">If a request target is subject to content negotiation, its cache entry might consist of multiple stored responses, each differentiated
    841          by a secondary key for the values of the original request's selecting header fields (<a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>).
    842       </p>
    843       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="response.cacheability" href="#response.cacheability">Response Cacheability</a></h2>
    844       <p id="rfc.section.2.1.p.1">A cache <em class="bcp14">MUST NOT</em> store a response to any request, unless:
     848         by a secondary key for the values of the original request's selecting header fields (<a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>).
     849      </p>
     850      <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="response.cacheability" href="#response.cacheability">Storing Responses in Caches</a></h1>
     851      <p id="rfc.section.3.p.1">A cache <em class="bcp14">MUST NOT</em> store a response to any request, unless:
    845852      </p>
    846853      <ul>
    847854         <li>The request method is understood by the cache and defined as being cacheable, and</li>
    848855         <li>the response status code is understood by the cache, and</li>
    849          <li>the "no-store" cache directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section&nbsp;3.2</a>) does not appear in request or response header fields, and
    850          </li>
    851          <li>the "private" cache response directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>) does not appear in the response, if the cache is shared, and
    852          </li>
    853          <li>the <a href="p7-auth.html#header.authorization" class="smpl">Authorization</a> header field (see <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>) does not appear in the request, if the cache is shared, unless the response explicitly allows it (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section&nbsp;2.7</a>), and
     856         <li>the "no-store" cache directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section&nbsp;7.2</a>) does not appear in request or response header fields, and
     857         </li>
     858         <li>the "private" cache response directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>) does not appear in the response, if the cache is shared, and
     859         </li>
     860         <li>the <a href="p7-auth.html#header.authorization" class="smpl">Authorization</a> header field (see <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>) does not appear in the request, if the cache is shared, unless the response explicitly allows it (see <a href="#caching.authenticated.responses" title="Storing Responses to Authenticated Requests">Section&nbsp;3.2</a>), and
    854861         </li>
    855862         <li>the response either:
    856863            <ul>
    857                <li>contains an <a href="#header.expires" class="smpl">Expires</a> header field (see <a href="#header.expires" id="rfc.xref.header.expires.1" title="Expires">Section&nbsp;3.3</a>), or
     864               <li>contains an <a href="#header.expires" class="smpl">Expires</a> header field (see <a href="#header.expires" id="rfc.xref.header.expires.1" title="Expires">Section&nbsp;7.3</a>), or
    858865               </li>
    859                <li>contains a max-age response cache directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>), or
     866               <li>contains a max-age response cache directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>), or
    860867               </li>
    861868               <li>contains a s-maxage response cache directive and the cache is shared, or</li>
    862                <li>contains a Cache Control Extension (see <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;3.2.3</a>) that allows it to be cached, or
     869               <li>contains a Cache Control Extension (see <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;7.2.3</a>) that allows it to be cached, or
    863870               </li>
    864                <li>has a status code that can be served with heuristic freshness (see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section&nbsp;2.3.1.1</a>).
     871               <li>has a status code that can be served with heuristic freshness (see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section&nbsp;4.1.2</a>).
    865872               </li>
    866873            </ul>
    867874         </li>
    868875      </ul>
    869       <p id="rfc.section.2.1.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;3.2.3</a>.
    870       </p>
    871       <p id="rfc.section.2.1.p.3">In this context, a cache has "understood" a request method or a response status code if it recognizes it and implements any
     876      <p id="rfc.section.3.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;7.2.3</a>.
     877      </p>
     878      <p id="rfc.section.3.p.3">In this context, a cache has "understood" a request method or a response status code if it recognizes it and implements any
    872879         cache-specific behavior.
    873880      </p>
    874       <p id="rfc.section.2.1.p.4">Note that, in normal operation, most caches will not store a response that has neither a cache validator nor an explicit expiration
     881      <p id="rfc.section.3.p.4">Note that, in normal operation, most caches will not store a response that has neither a cache validator nor an explicit expiration
    875882         time, as such responses are not usually useful to store. However, caches are not prohibited from storing such responses.
    876883      </p>
    877       <p id="rfc.section.2.1.p.5">A response message is considered complete when all of the octets indicated by the message framing (<a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) are received prior to the connection being closed. If the request is GET, the response status is <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a>, and the entire response header block has been received, a cache <em class="bcp14">MAY</em> store an incomplete response message body if the cache entry is recorded as incomplete. Likewise, a <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> response <em class="bcp14">MAY</em> be stored as if it were an incomplete <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> cache entry. However, a cache <em class="bcp14">MUST NOT</em> store incomplete or partial content responses if it does not support the <a href="p5-range.html#range.retrieval.requests" class="smpl">Range</a> and <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> header fields or if it does not understand the range units used in those fields.
    878       </p>
    879       <p id="rfc.section.2.1.p.6">A cache <em class="bcp14">MAY</em> complete a stored incomplete response by making a subsequent range request (<a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) and combining the successful response with the stored entry, as defined in <a href="#combining.responses" title="Combining Partial Content">Section&nbsp;2.9</a>. A cache <em class="bcp14">MUST NOT</em> use an incomplete response to answer requests unless the response has been made complete or the request is partial and specifies
     884      <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="incomplete.responses" href="#incomplete.responses">Storing Incomplete Responses</a></h2>
     885      <p id="rfc.section.3.1.p.1">A response message is considered complete when all of the octets indicated by the message framing (<a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) are received prior to the connection being closed. If the request is GET, the response status is <a href="p2-semantics.html#status.200" class="smpl">200
     886            (OK)</a>, and the entire response header block has been received, a cache <em class="bcp14">MAY</em> store an incomplete response message body if the cache entry is recorded as incomplete. Likewise, a <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> response <em class="bcp14">MAY</em> be stored as if it were an incomplete <a href="p2-semantics.html#status.200" class="smpl">200
     887            (OK)</a> cache entry. However, a cache <em class="bcp14">MUST NOT</em> store incomplete or partial content responses if it does not support the <a href="p5-range.html#range.retrieval.requests" class="smpl">Range</a> and <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> header fields or if it does not understand the range units used in those fields.
     888      </p>
     889      <p id="rfc.section.3.1.p.2">A cache <em class="bcp14">MAY</em> complete a stored incomplete response by making a subsequent range request (<a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) and combining the successful response with the stored entry, as defined in <a href="#combining.responses" title="Combining Partial Content">Section&nbsp;4.4</a>. A cache <em class="bcp14">MUST NOT</em> use an incomplete response to answer requests unless the response has been made complete or the request is partial and specifies
    880890         a range that is wholly within the incomplete response. A cache <em class="bcp14">MUST NOT</em> send a partial response to a client without explicitly marking it as such using the <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a> status code.
    881891      </p>
    882       <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="constructing.responses.from.caches" href="#constructing.responses.from.caches">Constructing Responses from Caches</a></h2>
    883       <p id="rfc.section.2.2.p.1">For a presented request, a cache <em class="bcp14">MUST NOT</em> return a stored response, unless:
     892      <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="caching.authenticated.responses" href="#caching.authenticated.responses">Storing Responses to Authenticated Requests</a></h2>
     893      <p id="rfc.section.3.2.p.1">A shared cache <em class="bcp14">MUST NOT</em> use a cached response to a request with an <a href="p7-auth.html#header.authorization" class="smpl">Authorization</a> header field (<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>) to satisfy any subsequent request unless a cache directive that allows such responses to be stored is present in the response.
     894      </p>
     895      <p id="rfc.section.3.2.p.2">In this specification, the following <a href="#header.cache-control" class="smpl">Cache-Control</a> response directives (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>) have such an effect: must-revalidate, public, s-maxage.
     896      </p>
     897      <p id="rfc.section.3.2.p.3">Note that cached responses that contain the "must-revalidate" and/or "s-maxage" response directives are not allowed to be
     898         served stale (<a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;4.1.4</a>) by shared caches. In particular, a response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be used to satisfy
     899         a subsequent request without revalidating it on the origin server.
     900      </p>
     901      <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="constructing.responses.from.caches" href="#constructing.responses.from.caches">Constructing Responses from Caches</a></h1>
     902      <p id="rfc.section.4.p.1">For a presented request, a cache <em class="bcp14">MUST NOT</em> return a stored response, unless:
    884903      </p>
    885904      <ul>
     
    887906         </li>
    888907         <li>the request method associated with the stored response allows it to be used for the presented request, and</li>
    889          <li>selecting header fields nominated by the stored response (if any) match those presented (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>), and
    890          </li>
    891          <li>the presented request does not contain the no-cache pragma (<a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section&nbsp;3.4</a>), nor the no-cache cache directive (<a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;3.2.1</a>), unless the stored response is successfully validated (<a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>), and
    892          </li>
    893          <li>the stored response does not contain the no-cache cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>), unless it is successfully validated (<a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>), and
     908         <li>selecting header fields nominated by the stored response (if any) match those presented (see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>), and
     909         </li>
     910         <li>the presented request does not contain the no-cache pragma (<a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section&nbsp;7.4</a>), nor the no-cache cache directive (<a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;7.2.1</a>), unless the stored response is successfully validated (<a href="#validation.model" title="Validation Model">Section&nbsp;4.2</a>), and
     911         </li>
     912         <li>the stored response does not contain the no-cache cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>), unless it is successfully validated (<a href="#validation.model" title="Validation Model">Section&nbsp;4.2</a>), and
    894913         </li>
    895914         <li>the stored response is either:
    896915            <ul>
    897                <li>fresh (see <a href="#expiration.model" title="Freshness Model">Section&nbsp;2.3</a>), or
     916               <li>fresh (see <a href="#expiration.model" title="Freshness Model">Section&nbsp;4.1</a>), or
    898917               </li>
    899                <li>allowed to be served stale (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;2.3.3</a>), or
     918               <li>allowed to be served stale (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;4.1.4</a>), or
    900919               </li>
    901                <li>successfully validated (see <a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>).
     920               <li>successfully validated (see <a href="#validation.model" title="Validation Model">Section&nbsp;4.2</a>).
    902921               </li>
    903922            </ul>
    904923         </li>
    905924      </ul>
    906       <p id="rfc.section.2.2.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;3.2.3</a>.
    907       </p>
    908       <p id="rfc.section.2.2.p.3">When a stored response is used to satisfy a request without validation, a cache <em class="bcp14">MUST</em> include a single <a href="#header.age" class="smpl">Age</a> header field (<a href="#header.age" id="rfc.xref.header.age.1" title="Age">Section&nbsp;3.1</a>) in the response with a value equal to the stored response's current_age; see <a href="#age.calculations" title="Calculating Age">Section&nbsp;2.3.2</a>.
    909       </p>
    910       <p id="rfc.section.2.2.p.4">A cache <em class="bcp14">MUST</em> write through requests with methods that are unsafe (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 2.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) to the origin server; i.e., a cache is not allowed to generate a reply to such a request before having forwarded the request
     925      <p id="rfc.section.4.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;7.2.3</a>.
     926      </p>
     927      <p id="rfc.section.4.p.3">When a stored response is used to satisfy a request without validation, a cache <em class="bcp14">MUST</em> include a single <a href="#header.age" class="smpl">Age</a> header field (<a href="#header.age" id="rfc.xref.header.age.1" title="Age">Section&nbsp;7.1</a>) in the response with a value equal to the stored response's current_age; see <a href="#age.calculations" title="Calculating Age">Section&nbsp;4.1.3</a>.
     928      </p>
     929      <p id="rfc.section.4.p.4">A cache <em class="bcp14">MUST</em> write through requests with methods that are unsafe (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 2.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) to the origin server; i.e., a cache is not allowed to generate a reply to such a request before having forwarded the request
    911930         and having received a corresponding response.
    912931      </p>
    913       <p id="rfc.section.2.2.p.5">Also, note that unsafe requests might invalidate already stored responses; see <a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;2.6</a>.
    914       </p>
    915       <p id="rfc.section.2.2.p.6">When more than one suitable response is stored, a cache <em class="bcp14">MUST</em> use the most recent response (as determined by the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field). It can also forward a request with "Cache-Control: max-age=0" or "Cache-Control: no-cache" to disambiguate
     932      <p id="rfc.section.4.p.5">Also, note that unsafe requests might invalidate already stored responses; see <a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;6</a>.
     933      </p>
     934      <p id="rfc.section.4.p.6">When more than one suitable response is stored, a cache <em class="bcp14">MUST</em> use the most recent response (as determined by the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field). It can also forward a request with "Cache-Control: max-age=0" or "Cache-Control: no-cache" to disambiguate
    916935         which response to use.
    917936      </p>
    918       <p id="rfc.section.2.2.p.7">A cache that does not have a clock available <em class="bcp14">MUST NOT</em> use stored responses without revalidating them on every use. A cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard.
    919       </p>
    920       <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="expiration.model" href="#expiration.model">Freshness Model</a></h2>
    921       <p id="rfc.section.2.3.p.1">When a response is "fresh" in the cache, it can be used to satisfy subsequent requests without contacting the origin server,
     937      <p id="rfc.section.4.p.7">A cache that does not have a clock available <em class="bcp14">MUST NOT</em> use stored responses without revalidating them on every use. A cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard.
     938      </p>
     939      <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="expiration.model" href="#expiration.model">Freshness Model</a></h2>
     940      <p id="rfc.section.4.1.p.1">When a response is "fresh" in the cache, it can be used to satisfy subsequent requests without contacting the origin server,
    922941         thereby improving efficiency.
    923942      </p>
    924       <p id="rfc.section.2.3.p.2">The primary mechanism for determining freshness is for an origin server to provide an explicit expiration time in the future,
    925          using either the <a href="#header.expires" class="smpl">Expires</a> header field (<a href="#header.expires" id="rfc.xref.header.expires.2" title="Expires">Section&nbsp;3.3</a>) or the max-age response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>). Generally, origin servers will assign future explicit expiration times to responses in the belief that the representation
     943      <p id="rfc.section.4.1.p.2">The primary mechanism for determining freshness is for an origin server to provide an explicit expiration time in the future,
     944         using either the <a href="#header.expires" class="smpl">Expires</a> header field (<a href="#header.expires" id="rfc.xref.header.expires.2" title="Expires">Section&nbsp;7.3</a>) or the max-age response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>). Generally, origin servers will assign future explicit expiration times to responses in the belief that the representation
    926945         is not likely to change in a semantically significant way before the expiration time is reached.
    927946      </p>
    928       <p id="rfc.section.2.3.p.3">If an origin server wishes to force a cache to validate every request, it can assign an explicit expiration time in the past
     947      <p id="rfc.section.4.1.p.3">If an origin server wishes to force a cache to validate every request, it can assign an explicit expiration time in the past
    929948         to indicate that the response is already stale. Compliant caches will normally validate the cached response before reusing
    930          it for subsequent requests (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;2.3.3</a>).
    931       </p>
    932       <p id="rfc.section.2.3.p.4">Since origin servers do not always provide explicit expiration times, a cache <em class="bcp14">MAY</em> assign a heuristic expiration time when an explicit time is not specified, employing algorithms that use other header field
     949         it for subsequent requests (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;4.1.4</a>).
     950      </p>
     951      <p id="rfc.section.4.1.p.4">Since origin servers do not always provide explicit expiration times, a cache <em class="bcp14">MAY</em> assign a heuristic expiration time when an explicit time is not specified, employing algorithms that use other header field
    933952         values (such as the <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> time) to estimate a plausible expiration time. This specification does not provide specific algorithms, but does impose worst-case
    934953         constraints on their results.
     
    936955      <div id="rfc.figure.u.4"></div>
    937956      <p>The calculation to determine if a response is fresh is:</p>  <pre class="text">   response_is_fresh = (freshness_lifetime &gt; current_age)
    938 </pre> <p id="rfc.section.2.3.p.6">The freshness_lifetime is defined in <a href="#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section&nbsp;2.3.1</a>; the current_age is defined in <a href="#age.calculations" title="Calculating Age">Section&nbsp;2.3.2</a>.
    939       </p>
    940       <p id="rfc.section.2.3.p.7">Additionally, clients can influence freshness calculation — either constraining it relaxing it — by using the max-age and
    941          min-fresh request cache directives. See <a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;3.2.1</a> for details.
    942       </p>
    943       <p id="rfc.section.2.3.p.8">Note that freshness applies only to cache operation; it cannot be used to force a user agent to refresh its display or reload
    944          a resource. See <a href="#history.lists" title="History Lists">Section&nbsp;4</a> for an explanation of the difference between caches and history mechanisms.
    945       </p>
    946       <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a>&nbsp;<a id="calculating.freshness.lifetime" href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></h3>
    947       <p id="rfc.section.2.3.1.p.1">A cache can calculate the freshness lifetime (denoted as freshness_lifetime) of a response by using the first match of: </p>
     957</pre> <p id="rfc.section.4.1.p.6">The freshness_lifetime is defined in <a href="#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section&nbsp;4.1.1</a>; the current_age is defined in <a href="#age.calculations" title="Calculating Age">Section&nbsp;4.1.3</a>.
     958      </p>
     959      <p id="rfc.section.4.1.p.7">Additionally, clients can influence freshness calculation — either constraining it relaxing it — by using the max-age and
     960         min-fresh request cache directives. See <a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;7.2.1</a> for details.
     961      </p>
     962      <p id="rfc.section.4.1.p.8">Note that freshness applies only to cache operation; it cannot be used to force a user agent to refresh its display or reload
     963         a resource. See <a href="#history.lists" title="History Lists">Section&nbsp;8</a> for an explanation of the difference between caches and history mechanisms.
     964      </p>
     965      <h3 id="rfc.section.4.1.1"><a href="#rfc.section.4.1.1">4.1.1</a>&nbsp;<a id="calculating.freshness.lifetime" href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></h3>
     966      <p id="rfc.section.4.1.1.p.1">A cache can calculate the freshness lifetime (denoted as freshness_lifetime) of a response by using the first match of: </p>
    948967      <ul>
    949          <li>If the cache is shared and the s-maxage response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>) is present, use its value, or
    950          </li>
    951          <li>If the max-age response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>) is present, use its value, or
    952          </li>
    953          <li>If the <a href="#header.expires" class="smpl">Expires</a> response header field (<a href="#header.expires" id="rfc.xref.header.expires.3" title="Expires">Section&nbsp;3.3</a>) is present, use its value minus the value of the <a href="p2-semantics.html#header.date" class="smpl">Date</a> response header field, or
    954          </li>
    955          <li>Otherwise, no explicit expiration time is present in the response. A heuristic freshness lifetime might be applicable; see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section&nbsp;2.3.1.1</a>.
    956          </li>
    957       </ul>
    958       <p id="rfc.section.2.3.1.p.2">Note that this calculation is not vulnerable to clock skew, since all of the information comes from the origin server.</p>
    959       <p id="rfc.section.2.3.1.p.3">When there is more than one value present for a given directive (e.g., two <a href="#header.expires" class="smpl">Expires</a> header fields, multiple Cache-Control: max-age directives), it is considered invalid. Caches are encouraged to consider responses
     968         <li>If the cache is shared and the s-maxage response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>) is present, use its value, or
     969         </li>
     970         <li>If the max-age response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>) is present, use its value, or
     971         </li>
     972         <li>If the <a href="#header.expires" class="smpl">Expires</a> response header field (<a href="#header.expires" id="rfc.xref.header.expires.3" title="Expires">Section&nbsp;7.3</a>) is present, use its value minus the value of the <a href="p2-semantics.html#header.date" class="smpl">Date</a> response header field, or
     973         </li>
     974         <li>Otherwise, no explicit expiration time is present in the response. A heuristic freshness lifetime might be applicable; see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section&nbsp;4.1.2</a>.
     975         </li>
     976      </ul>
     977      <p id="rfc.section.4.1.1.p.2">Note that this calculation is not vulnerable to clock skew, since all of the information comes from the origin server.</p>
     978      <p id="rfc.section.4.1.1.p.3">When there is more than one value present for a given directive (e.g., two <a href="#header.expires" class="smpl">Expires</a> header fields, multiple Cache-Control: max-age directives), it is considered invalid. Caches are encouraged to consider responses
    960979         that have invalid freshness information to be stale.
    961980      </p>
    962       <h4 id="rfc.section.2.3.1.1"><a href="#rfc.section.2.3.1.1">2.3.1.1</a>&nbsp;<a id="heuristic.freshness" href="#heuristic.freshness">Calculating Heuristic Freshness</a></h4>
    963       <p id="rfc.section.2.3.1.1.p.1">If no explicit expiration time is present in a stored response that has a status code whose definition allows heuristic freshness
    964          to be used (including the following in <a href="p2-semantics.html#status.codes" title="Status Codes">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>: <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a>, <a href="p2-semantics.html#status.203" class="smpl">203
    965             (Non-Authoritative Information)</a>, <a href="p5-range.html#status.206" class="smpl">206 (Partial Content)</a>, <a href="p2-semantics.html#status.300" class="smpl">300 (Multiple Choices)</a>, <a href="p2-semantics.html#status.301" class="smpl">301 (Moved Permanently)</a> and <a href="p2-semantics.html#status.410" class="smpl">410 (Gone)</a>), a cache <em class="bcp14">MAY</em> calculate a heuristic expiration time. A cache <em class="bcp14">MUST NOT</em> use heuristics to determine freshness for responses with status codes that do not explicitly allow it.
    966       </p>
    967       <p id="rfc.section.2.3.1.1.p.2">When a heuristic is used to calculate freshness lifetime, a cache <em class="bcp14">SHOULD</em> attach a <a href="#header.warning" class="smpl">Warning</a> header field with a 113 warn-code to the response if its current_age is more than 24 hours and such a warning is not already
     981      <h3 id="rfc.section.4.1.2"><a href="#rfc.section.4.1.2">4.1.2</a>&nbsp;<a id="heuristic.freshness" href="#heuristic.freshness">Calculating Heuristic Freshness</a></h3>
     982      <p id="rfc.section.4.1.2.p.1">If no explicit expiration time is present in a stored response that has a status code whose definition allows heuristic freshness
     983         to be used (including the following in <a href="p2-semantics.html#status.codes" title="Status Codes">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>: <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a>, <a href="p2-semantics.html#status.203" class="smpl">203 (Non-Authoritative Information)</a>, <a href="p5-range.html#status.206" class="smpl">206 (Partial
     984            Content)</a>, <a href="p2-semantics.html#status.300" class="smpl">300 (Multiple Choices)</a>, <a href="p2-semantics.html#status.301" class="smpl">301 (Moved
     985            Permanently)</a> and <a href="p2-semantics.html#status.410" class="smpl">410 (Gone)</a>), a cache <em class="bcp14">MAY</em> calculate a heuristic expiration time. A cache <em class="bcp14">MUST NOT</em> use heuristics to determine freshness for responses with status codes that do not explicitly allow it.
     986      </p>
     987      <p id="rfc.section.4.1.2.p.2">When a heuristic is used to calculate freshness lifetime, a cache <em class="bcp14">SHOULD</em> attach a <a href="#header.warning" class="smpl">Warning</a> header field with a 113 warn-code to the response if its current_age is more than 24 hours and such a warning is not already
    968988         present.
    969989      </p>
    970       <p id="rfc.section.2.3.1.1.p.3">Also, if the response has a <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> header field (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.4"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>), caches are encouraged to use a heuristic expiration value that is no more than some fraction of the interval since that
     990      <p id="rfc.section.4.1.2.p.3">Also, if the response has a <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> header field (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.4"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>), caches are encouraged to use a heuristic expiration value that is no more than some fraction of the interval since that
    971991         time. A typical setting of this fraction might be 10%.
    972992      </p>
    973       <div class="note" id="rfc.section.2.3.1.1.p.4">
     993      <div class="note" id="rfc.section.4.1.2.p.4">
    974994         <p> <b>Note:</b> RFC 2616 (<a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>, <a href="http://tools.ietf.org/html/rfc2616#section-13.9">Section 13.9</a>) required that caches do not calculate heuristic freshness for URIs with query components (i.e., those containing '?'). In
    975995            practice, this has not been widely implemented. Therefore, servers are encouraged to send explicit directives (e.g., Cache-Control:
     
    977997         </p>
    978998      </div>
    979       <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a>&nbsp;<a id="age.calculations" href="#age.calculations">Calculating Age</a></h3>
    980       <p id="rfc.section.2.3.2.p.1">HTTP/1.1 uses the <a href="#header.age" class="smpl">Age</a> header field to convey the estimated age of the response message when obtained from a cache. The Age field value is the cache's
     999      <h3 id="rfc.section.4.1.3"><a href="#rfc.section.4.1.3">4.1.3</a>&nbsp;<a id="age.calculations" href="#age.calculations">Calculating Age</a></h3>
     1000      <p id="rfc.section.4.1.3.p.1">HTTP/1.1 uses the <a href="#header.age" class="smpl">Age</a> header field to convey the estimated age of the response message when obtained from a cache. The Age field value is the cache's
    9811001         estimate of the amount of time since the response was generated or validated by the origin server. In essence, the Age value
    9821002         is the sum of the time that the response has been resident in each of the caches along the path from the origin server, plus
    9831003         the amount of time it has been in transit along network paths.
    9841004      </p>
    985       <p id="rfc.section.2.3.2.p.2">The following data is used for the age calculation:</p>
    986       <p id="rfc.section.2.3.2.p.3"> <dfn>age_value</dfn> 
     1005      <p id="rfc.section.4.1.3.p.2">The following data is used for the age calculation:</p>
     1006      <p id="rfc.section.4.1.3.p.3"> <dfn>age_value</dfn> 
    9871007      </p>
    9881008      <ul class="empty">
    989          <li>The term "age_value" denotes the value of the <a href="#header.age" class="smpl">Age</a> header field (<a href="#header.age" id="rfc.xref.header.age.2" title="Age">Section&nbsp;3.1</a>), in a form appropriate for arithmetic operation; or 0, if not available.
    990          </li>
    991       </ul>
    992       <p id="rfc.section.2.3.2.p.4"> <dfn>date_value</dfn> 
     1009         <li>The term "age_value" denotes the value of the <a href="#header.age" class="smpl">Age</a> header field (<a href="#header.age" id="rfc.xref.header.age.2" title="Age">Section&nbsp;7.1</a>), in a form appropriate for arithmetic operation; or 0, if not available.
     1010         </li>
     1011      </ul>
     1012      <p id="rfc.section.4.1.3.p.4"> <dfn>date_value</dfn> 
    9931013      </p>
    9941014      <ul class="empty">
     
    9971017         </li>
    9981018      </ul>
    999       <p id="rfc.section.2.3.2.p.5"> <dfn>now</dfn> 
     1019      <p id="rfc.section.4.1.3.p.5"> <dfn>now</dfn> 
    10001020      </p>
    10011021      <ul class="empty">
     
    10031023         </li>
    10041024      </ul>
    1005       <p id="rfc.section.2.3.2.p.6"> <dfn>request_time</dfn> 
     1025      <p id="rfc.section.4.1.3.p.6"> <dfn>request_time</dfn> 
    10061026      </p>
    10071027      <ul class="empty">
    10081028         <li>The current value of the clock at the host at the time the request resulting in the stored response was made.</li>
    10091029      </ul>
    1010       <p id="rfc.section.2.3.2.p.7"> <dfn>response_time</dfn> 
     1030      <p id="rfc.section.4.1.3.p.7"> <dfn>response_time</dfn> 
    10111031      </p>
    10121032      <ul class="empty">
    10131033         <li>The current value of the clock at the host at the time the response was received.</li>
    10141034      </ul>
    1015       <p id="rfc.section.2.3.2.p.8">A response's age can be calculated in two entirely independent ways: </p>
     1035      <p id="rfc.section.4.1.3.p.8">A response's age can be calculated in two entirely independent ways: </p>
    10161036      <ol>
    10171037         <li>the "apparent_age": response_time minus date_value, if the local clock is reasonably well synchronized to the origin server's
     
    10281048      <p>These <em class="bcp14">SHOULD</em> be combined as
    10291049      </p>  <pre class="text">  corrected_initial_age = max(apparent_age, corrected_age_value);
    1030 </pre><p id="rfc.section.2.3.2.p.11">unless the cache is confident in the value of the <a href="#header.age" class="smpl">Age</a> header field (e.g., because there are no HTTP/1.0 hops in the <a href="p1-messaging.html#header.via" class="smpl">Via</a> header field), in which case the corrected_age_value <em class="bcp14">MAY</em> be used as the corrected_initial_age.
    1031       </p>
    1032       <p id="rfc.section.2.3.2.p.12">The current_age of a stored response can then be calculated by adding the amount of time (in seconds) since the stored response
     1050</pre><p id="rfc.section.4.1.3.p.11">unless the cache is confident in the value of the <a href="#header.age" class="smpl">Age</a> header field (e.g., because there are no HTTP/1.0 hops in the <a href="p1-messaging.html#header.via" class="smpl">Via</a> header field), in which case the corrected_age_value <em class="bcp14">MAY</em> be used as the corrected_initial_age.
     1051      </p>
     1052      <p id="rfc.section.4.1.3.p.12">The current_age of a stored response can then be calculated by adding the amount of time (in seconds) since the stored response
    10331053         was last validated by the origin server to the corrected_initial_age.
    10341054      </p>
    10351055      <div id="rfc.figure.u.7"></div><pre class="text">  resident_time = now - response_time;
    10361056  current_age = corrected_initial_age + resident_time;
    1037 </pre><p id="rfc.section.2.3.2.p.14">Additionally, to avoid common problems in date parsing:</p>
    1038       <p id="rfc.section.2.3.2.p.15"> </p>
     1057</pre><p id="rfc.section.4.1.3.p.14">Additionally, to avoid common problems in date parsing:</p>
     1058      <p id="rfc.section.4.1.3.p.15"> </p>
    10391059      <ul>
    10401060         <li>HTTP/1.1 clients and caches <em class="bcp14">SHOULD</em> assume that an RFC-850 date which appears to be more than 50 years in the future is in fact in the past (this helps solve
     
    10501070         </li>
    10511071      </ul>
    1052       <h3 id="rfc.section.2.3.3"><a href="#rfc.section.2.3.3">2.3.3</a>&nbsp;<a id="serving.stale.responses" href="#serving.stale.responses">Serving Stale Responses</a></h3>
    1053       <p id="rfc.section.2.3.3.p.1">A "stale" response is one that either has explicit expiry information or is allowed to have heuristic expiry calculated, but
    1054          is not fresh according to the calculations in <a href="#expiration.model" title="Freshness Model">Section&nbsp;2.3</a>.
    1055       </p>
    1056       <p id="rfc.section.2.3.3.p.2">A cache <em class="bcp14">MUST NOT</em> return a stale response if it is prohibited by an explicit in-protocol directive (e.g., by a "no-store" or "no-cache" cache
     1072      <h3 id="rfc.section.4.1.4"><a href="#rfc.section.4.1.4">4.1.4</a>&nbsp;<a id="serving.stale.responses" href="#serving.stale.responses">Serving Stale Responses</a></h3>
     1073      <p id="rfc.section.4.1.4.p.1">A "stale" response is one that either has explicit expiry information or is allowed to have heuristic expiry calculated, but
     1074         is not fresh according to the calculations in <a href="#expiration.model" title="Freshness Model">Section&nbsp;4.1</a>.
     1075      </p>
     1076      <p id="rfc.section.4.1.4.p.2">A cache <em class="bcp14">MUST NOT</em> return a stale response if it is prohibited by an explicit in-protocol directive (e.g., by a "no-store" or "no-cache" cache
    10571077         directive, a "must-revalidate" cache-response-directive, or an applicable "s-maxage" or "proxy-revalidate" cache-response-directive;
    1058          see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>).
    1059       </p>
    1060       <p id="rfc.section.2.3.3.p.3">A cache <em class="bcp14">MUST NOT</em> return stale responses unless it is disconnected (i.e., it cannot contact the origin server or otherwise find a forward path)
    1061          or doing so is explicitly allowed (e.g., by the max-stale request directive; see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;3.2.1</a>).
    1062       </p>
    1063       <p id="rfc.section.2.3.3.p.4">A cache <em class="bcp14">SHOULD</em> append a <a href="#header.warning" class="smpl">Warning</a> header field with the 110 warn-code (see <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">Section&nbsp;3.6</a>) to stale responses. Likewise, a cache <em class="bcp14">SHOULD</em> add the 112 warn-code to stale responses if the cache is disconnected.
    1064       </p>
    1065       <p id="rfc.section.2.3.3.p.5">If a cache receives a first-hand response (either an entire response, or a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response) that it would normally forward to the requesting client, and the received response is no longer fresh, the cache
     1078         see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>).
     1079      </p>
     1080      <p id="rfc.section.4.1.4.p.3">A cache <em class="bcp14">MUST NOT</em> return stale responses unless it is disconnected (i.e., it cannot contact the origin server or otherwise find a forward path)
     1081         or doing so is explicitly allowed (e.g., by the max-stale request directive; see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;7.2.1</a>).
     1082      </p>
     1083      <p id="rfc.section.4.1.4.p.4">A cache <em class="bcp14">SHOULD</em> append a <a href="#header.warning" class="smpl">Warning</a> header field with the 110 warn-code (see <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">Section&nbsp;7.6</a>) to stale responses. Likewise, a cache <em class="bcp14">SHOULD</em> add the 112 warn-code to stale responses if the cache is disconnected.
     1084      </p>
     1085      <p id="rfc.section.4.1.4.p.5">If a cache receives a first-hand response (either an entire response, or a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response) that it would normally forward to the requesting client, and the received response is no longer fresh, the cache
    10661086         can forward it to the requesting client without adding a new <a href="#header.warning" class="smpl">Warning</a> (but without removing any existing Warning header fields). A cache shouldn't attempt to validate a response simply because
    10671087         that response became stale in transit.
    10681088      </p>
    1069       <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a id="validation.model" href="#validation.model">Validation Model</a></h2>
    1070       <p id="rfc.section.2.4.p.1">When a cache has one or more stored responses for a requested URI, but cannot serve any of them (e.g., because they are not
    1071          fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a> in the forwarded request to give the origin server an opportunity to both select a valid stored response to be used, and to
     1089      <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="validation.model" href="#validation.model">Validation Model</a></h2>
     1090      <p id="rfc.section.4.2.p.1">When a cache has one or more stored responses for a requested URI, but cannot serve any of them (e.g., because they are not
     1091         fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a> in the forwarded request to give the origin server an opportunity to both select a valid stored response to be used, and to
    10721092         update it. This process is known as "validating" or "revalidating" the stored response.
    10731093      </p>
    1074       <p id="rfc.section.2.4.p.2">When sending such a conditional request, a cache adds an <a href="p4-conditional.html#header.if-modified-since" class="smpl">If-Modified-Since</a> header field whose value is that of the <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> header field from the selected (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>) stored response, if available.
    1075       </p>
    1076       <p id="rfc.section.2.4.p.3">Additionally, a cache can add an <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> header field whose value is that of the <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> header field(s) from all responses stored for the requested URI, if present. However, if any of the stored responses contains
     1094      <p id="rfc.section.4.2.p.2">When sending such a conditional request, a cache adds an <a href="p4-conditional.html#header.if-modified-since" class="smpl">If-Modified-Since</a> header field whose value is that of the <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> header field from the selected (see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>) stored response, if available.
     1095      </p>
     1096      <p id="rfc.section.4.2.p.3">Additionally, a cache can add an <a href="p4-conditional.html#header.if-none-match" class="smpl">If-None-Match</a> header field whose value is that of the <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> header field(s) from all responses stored for the requested URI, if present. However, if any of the stored responses contains
    10771097         only partial content, the cache shouldn't include its entity-tag in the If-None-Match header field unless the request is for
    10781098         a range that would be fully satisfied by that stored response.
    10791099      </p>
    1080       <p id="rfc.section.2.4.p.4">Cache handling of a response to a conditional request is dependent upon its status code:</p>
    1081       <p id="rfc.section.2.4.p.5"> </p>
     1100      <p id="rfc.section.4.2.p.4">Cache handling of a response to a conditional request is dependent upon its status code:</p>
     1101      <p id="rfc.section.4.2.p.5"> </p>
    10821102      <ul>
    1083          <li>A <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response status code indicates that the stored response can be updated and reused; see <a href="#freshening.responses" title="Freshening Responses with 304 Not Modified">Section&nbsp;2.4.1</a>.
     1103         <li>A <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response status code indicates that the stored response can be updated and reused; see <a href="#freshening.responses" title="Freshening Responses with 304 Not Modified">Section&nbsp;4.2.1</a>.
    10841104         </li>
    10851105         <li>A full response (i.e., one with a response body) indicates that none of the stored responses nominated in the conditional
     
    10871107         </li>
    10881108         <li>However, if a cache receives a <a href="p2-semantics.html#status.5xx" class="smpl">5xx (Server Error)</a> response while attempting to validate a response, it can either forward this response to the requesting client, or act as
    1089             if the server failed to respond. In the latter case, it can return a previously stored response (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;2.3.3</a>).
    1090          </li>
    1091       </ul>
    1092       <h3 id="rfc.section.2.4.1"><a href="#rfc.section.2.4.1">2.4.1</a>&nbsp;<a id="freshening.responses" href="#freshening.responses">Freshening Responses with 304 Not Modified</a></h3>
    1093       <p id="rfc.section.2.4.1.p.1">When a cache receives a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response and already has one or more stored <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> responses for the same cache key, the cache needs to identify which of the stored responses are updated by this new response
     1109            if the server failed to respond. In the latter case, it can return a previously stored response (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;4.1.4</a>).
     1110         </li>
     1111      </ul>
     1112      <h3 id="rfc.section.4.2.1"><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;<a id="freshening.responses" href="#freshening.responses">Freshening Responses with 304 Not Modified</a></h3>
     1113      <p id="rfc.section.4.2.1.p.1">When a cache receives a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response and already has one or more stored <a href="p2-semantics.html#status.200" class="smpl">200 (OK)</a> responses for the same cache key, the cache needs to identify which of the stored responses are updated by this new response
    10941114         and then update the stored response(s) with the new information provided in the <a href="p4-conditional.html#status.304" class="smpl">304</a> response.
    10951115      </p>
     
    11061126         </li>
    11071127      </ul>
    1108       <p id="rfc.section.2.4.1.p.2">If a stored response is selected for update, the cache <em class="bcp14">MUST</em>:
     1128      <p id="rfc.section.4.2.1.p.2">If a stored response is selected for update, the cache <em class="bcp14">MUST</em>:
    11091129      </p>
    11101130      <ul>
    1111          <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.2" title="Warning">Section&nbsp;3.6</a>);
     1131         <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.2" title="Warning">Section&nbsp;7.6</a>);
    11121132         </li>
    11131133         <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and,
     
    11161136         </li>
    11171137      </ul>
    1118       <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="head.effects" href="#head.effects">Updating Caches with HEAD Responses</a></h2>
    1119       <p id="rfc.section.2.5.p.1">A response to the HEAD method is identical to what an equivalent request made with a GET would have been, except it lacks
     1138      <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a id="caching.negotiated.responses" href="#caching.negotiated.responses">Using Negotiated Responses</a></h2>
     1139      <p id="rfc.section.4.3.p.1">When a cache receives a request that can be satisfied by a stored response that has a <a href="#header.vary" class="smpl">Vary</a> header field (<a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section&nbsp;7.5</a>), it <em class="bcp14">MUST NOT</em> use that response unless all of the selecting header fields nominated by the Vary header field match in both the original
     1140         request (i.e., that associated with the stored response), and the presented request.
     1141      </p>
     1142      <p id="rfc.section.4.3.p.2">The selecting header fields from two requests are defined to match if and only if those in the first request can be transformed
     1143         to those in the second request by applying any of the following:
     1144      </p>
     1145      <ul>
     1146         <li>adding or removing whitespace, where allowed in the header field's syntax</li>
     1147         <li>combining multiple header fields with the same field name (see <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</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>)
     1148         </li>
     1149         <li>normalizing both header field values in a way that is known to have identical semantics, according to the header field's specification
     1150            (e.g., re-ordering field values when order is not significant; case-normalization, where values are defined to be case-insensitive)
     1151         </li>
     1152      </ul>
     1153      <p id="rfc.section.4.3.p.3">If (after any normalization that might take place) a header field is absent from a request, it can only match another request
     1154         if it is also absent there.
     1155      </p>
     1156      <p id="rfc.section.4.3.p.4">A <a href="#header.vary" class="smpl">Vary</a> header field-value of "*" always fails to match, and subsequent requests to that resource can only be properly interpreted
     1157         by the origin server.
     1158      </p>
     1159      <p id="rfc.section.4.3.p.5">The stored response with matching selecting header fields is known as the selected response.</p>
     1160      <p id="rfc.section.4.3.p.6">If multiple selected responses are available, the most recent response (as determined by the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field) is used; see <a href="#constructing.responses.from.caches" title="Constructing Responses from Caches">Section&nbsp;4</a>.
     1161      </p>
     1162      <p id="rfc.section.4.3.p.7">If no selected response is available, the cache can forward the presented request to the origin server in a conditional request;
     1163         see <a href="#validation.model" title="Validation Model">Section&nbsp;4.2</a>.
     1164      </p>
     1165      <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a>&nbsp;<a id="combining.responses" href="#combining.responses">Combining Partial Content</a></h2>
     1166      <p id="rfc.section.4.4.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or
     1167         more Range specifiers (<a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>). After several such transfers, a cache might have received several ranges of the same representation. A cache <em class="bcp14">MAY</em> combine these ranges into a single stored response, and reuse that response to satisfy later requests, if they all share the
     1168         same strong validator and the cache complies with the client requirements in <a href="p5-range.html#combining.byte.ranges" title="Combining Ranges">Section 4.2</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>.
     1169      </p>
     1170      <p id="rfc.section.4.4.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>:
     1171      </p>
     1172      <ul>
     1173         <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section&nbsp;7.6</a>);
     1174         </li>
     1175         <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and,
     1176         </li>
     1177         <li>use other header fields provided in the new response, aside from <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a>, to replace all instances of the corresponding header fields in the stored response.
     1178         </li>
     1179      </ul>
     1180      <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="head.effects" href="#head.effects">Updating Caches with HEAD Responses</a></h1>
     1181      <p id="rfc.section.5.p.1">A response to the HEAD method is identical to what an equivalent request made with a GET would have been, except it lacks
    11201182         a body. This property of HEAD responses is used to both invalidate and update cached GET responses.
    11211183      </p>
    1122       <p id="rfc.section.2.5.p.2">If one or more stored GET responses can be selected (as per <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>) for a HEAD request, and the <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a>, <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> or <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> value of a HEAD response differs from that in a selected GET response, the cache <em class="bcp14">MUST</em> consider that selected response to be stale.
    1123       </p>
    1124       <p id="rfc.section.2.5.p.3">If the <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a>, <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> and <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> values of a HEAD response (when present) are the same as that in a selected GET response (as per <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>), the cache <em class="bcp14">SHOULD</em> update the remaining headers in the stored response using the following rules:
     1184      <p id="rfc.section.5.p.2">If one or more stored GET responses can be selected (as per <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>) for a HEAD request, and the <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a>, <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> or <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> value of a HEAD response differs from that in a selected GET response, the cache <em class="bcp14">MUST</em> consider that selected response to be stale.
     1185      </p>
     1186      <p id="rfc.section.5.p.3">If the <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a>, <a href="p4-conditional.html#header.etag" class="smpl">ETag</a> and <a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> values of a HEAD response (when present) are the same as that in a selected GET response (as per <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>), the cache <em class="bcp14">SHOULD</em> update the remaining headers in the stored response using the following rules:
    11251187      </p>
    11261188      <ul>
    1127          <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section&nbsp;3.6</a>);
     1189         <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;7.6</a>);
    11281190         </li>
    11291191         <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and,
     
    11331195         </li>
    11341196      </ul>
    1135       <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a>&nbsp;<a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></h2>
    1136       <p id="rfc.section.2.6.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 2.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them
     1197      <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></h1>
     1198      <p id="rfc.section.6.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 2.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them
    11371199         to keep their contents up-to-date.
    11381200      </p>
    1139       <p id="rfc.section.2.6.p.2">A cache <em class="bcp14">MUST</em> invalidate the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</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>) as well as the URI(s) in the <a href="p2-semantics.html#header.location" class="smpl">Location</a> and <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> response header fields (if present) when a non-error response to a request with an unsafe method is received.
    1140       </p>
    1141       <p id="rfc.section.2.6.p.3">However, a cache <em class="bcp14">MUST NOT</em> invalidate a URI from a <a href="p2-semantics.html#header.location" class="smpl">Location</a> or <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> response header field if the host part of that URI differs from the host part in the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</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>). This helps prevent denial of service attacks.
    1142       </p>
    1143       <p id="rfc.section.2.6.p.4">A cache <em class="bcp14">MUST</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</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>) when it receives a non-error response to a request with a method whose safety is unknown.
    1144       </p>
    1145       <p id="rfc.section.2.6.p.5">Here, a "non-error response" is one with a <a href="p2-semantics.html#status.2xx" class="smpl">2xx (Successful)</a> or <a href="p2-semantics.html#status.3xx" class="smpl">3xx (Redirection)</a> status code. "Invalidate" means that the cache will either remove all stored responses related to the effective request URI,
     1201      <p id="rfc.section.6.p.2">A cache <em class="bcp14">MUST</em> invalidate the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</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>) as well as the URI(s) in the <a href="p2-semantics.html#header.location" class="smpl">Location</a> and <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> response header fields (if present) when a non-error response to a request with an unsafe method is received.
     1202      </p>
     1203      <p id="rfc.section.6.p.3">However, a cache <em class="bcp14">MUST NOT</em> invalidate a URI from a <a href="p2-semantics.html#header.location" class="smpl">Location</a> or <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> response header field if the host part of that URI differs from the host part in the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</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>). This helps prevent denial of service attacks.
     1204      </p>
     1205      <p id="rfc.section.6.p.4">A cache <em class="bcp14">MUST</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</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>) when it receives a non-error response to a request with a method whose safety is unknown.
     1206      </p>
     1207      <p id="rfc.section.6.p.5">Here, a "non-error response" is one with a <a href="p2-semantics.html#status.2xx" class="smpl">2xx (Successful)</a> or <a href="p2-semantics.html#status.3xx" class="smpl">3xx (Redirection)</a> status code. "Invalidate" means that the cache will either remove all stored responses related to the effective request URI,
    11461208         or will mark these as "invalid" and in need of a mandatory validation before they can be returned in response to a subsequent
    11471209         request.
    11481210      </p>
    1149       <p id="rfc.section.2.6.p.6">Note that this does not guarantee that all appropriate responses are invalidated. For example, the request that caused the
     1211      <p id="rfc.section.6.p.6">Note that this does not guarantee that all appropriate responses are invalidated. For example, the request that caused the
    11501212         change at the origin server might not have gone through the cache where a response is stored.
    11511213      </p>
    1152       <h2 id="rfc.section.2.7"><a href="#rfc.section.2.7">2.7</a>&nbsp;<a id="caching.authenticated.responses" href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></h2>
    1153       <p id="rfc.section.2.7.p.1">A shared cache <em class="bcp14">MUST NOT</em> use a cached response to a request with an <a href="p7-auth.html#header.authorization" class="smpl">Authorization</a> header field (<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>) to satisfy any subsequent request unless a cache directive that allows such responses to be stored is present in the response.
    1154       </p>
    1155       <p id="rfc.section.2.7.p.2">In this specification, the following <a href="#header.cache-control" class="smpl">Cache-Control</a> response directives (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>) have such an effect: must-revalidate, public, s-maxage.
    1156       </p>
    1157       <p id="rfc.section.2.7.p.3">Note that cached responses that contain the "must-revalidate" and/or "s-maxage" response directives are not allowed to be
    1158          served stale (<a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;2.3.3</a>) by shared caches. In particular, a response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be used to satisfy
    1159          a subsequent request without revalidating it on the origin server.
    1160       </p>
    1161       <h2 id="rfc.section.2.8"><a href="#rfc.section.2.8">2.8</a>&nbsp;<a id="caching.negotiated.responses" href="#caching.negotiated.responses">Caching Negotiated Responses</a></h2>
    1162       <p id="rfc.section.2.8.p.1">When a cache receives a request that can be satisfied by a stored response that has a <a href="#header.vary" class="smpl">Vary</a> header field (<a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section&nbsp;3.5</a>), it <em class="bcp14">MUST NOT</em> use that response unless all of the selecting header fields nominated by the Vary header field match in both the original
    1163          request (i.e., that associated with the stored response), and the presented request.
    1164       </p>
    1165       <p id="rfc.section.2.8.p.2">The selecting header fields from two requests are defined to match if and only if those in the first request can be transformed
    1166          to those in the second request by applying any of the following:
    1167       </p>
    1168       <ul>
    1169          <li>adding or removing whitespace, where allowed in the header field's syntax</li>
    1170          <li>combining multiple header fields with the same field name (see <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</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>)
    1171          </li>
    1172          <li>normalizing both header field values in a way that is known to have identical semantics, according to the header field's specification
    1173             (e.g., re-ordering field values when order is not significant; case-normalization, where values are defined to be case-insensitive)
    1174          </li>
    1175       </ul>
    1176       <p id="rfc.section.2.8.p.3">If (after any normalization that might take place) a header field is absent from a request, it can only match another request
    1177          if it is also absent there.
    1178       </p>
    1179       <p id="rfc.section.2.8.p.4">A <a href="#header.vary" class="smpl">Vary</a> header field-value of "*" always fails to match, and subsequent requests to that resource can only be properly interpreted
    1180          by the origin server.
    1181       </p>
    1182       <p id="rfc.section.2.8.p.5">The stored response with matching selecting header fields is known as the selected response.</p>
    1183       <p id="rfc.section.2.8.p.6">If multiple selected responses are available, the most recent response (as determined by the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field) is used; see <a href="#constructing.responses.from.caches" title="Constructing Responses from Caches">Section&nbsp;2.2</a>.
    1184       </p>
    1185       <p id="rfc.section.2.8.p.7">If no selected response is available, the cache can forward the presented request to the origin server in a conditional request;
    1186          see <a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>.
    1187       </p>
    1188       <h2 id="rfc.section.2.9"><a href="#rfc.section.2.9">2.9</a>&nbsp;<a id="combining.responses" href="#combining.responses">Combining Partial Content</a></h2>
    1189       <p id="rfc.section.2.9.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or
    1190          more Range specifiers (<a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>). After several such transfers, a cache might have received several ranges of the same representation. A cache <em class="bcp14">MAY</em> combine these ranges into a single stored response, and reuse that response to satisfy later requests, if they all share the
    1191          same strong validator and the cache complies with the client requirements in <a href="p5-range.html#combining.byte.ranges" title="Combining Ranges">Section 4.2</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>.
    1192       </p>
    1193       <p id="rfc.section.2.9.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>:
    1194       </p>
    1195       <ul>
    1196          <li>delete any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;3.6</a>);
    1197          </li>
    1198          <li>retain any <a href="#header.warning" class="smpl">Warning</a> header fields in the stored response with warn-code 2xx; and,
    1199          </li>
    1200          <li>use other header fields provided in the new response, aside from <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a>, to replace all instances of the corresponding header fields in the stored response.
    1201          </li>
    1202       </ul>
    1203       <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1>
    1204       <p id="rfc.section.3.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p>
     1214      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1>
     1215      <p id="rfc.section.7.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p>
    12051216      <div id="rfc.iref.a.2"></div>
    12061217      <div id="rfc.iref.h.2"></div>
    1207       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="header.age" href="#header.age">Age</a></h2>
    1208       <p id="rfc.section.3.1.p.1">The "Age" header field conveys the sender's estimate of the amount of time since the response was generated or successfully
    1209          validated at the origin server. Age values are calculated as specified in <a href="#age.calculations" title="Calculating Age">Section&nbsp;2.3.2</a>.
     1218      <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="header.age" href="#header.age">Age</a></h2>
     1219      <p id="rfc.section.7.1.p.1">The "Age" header field conveys the sender's estimate of the amount of time since the response was generated or successfully
     1220         validated at the origin server. Age values are calculated as specified in <a href="#age.calculations" title="Calculating Age">Section&nbsp;4.1.3</a>.
    12101221      </p>
    12111222      <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.2"></span>  <a href="#header.age" class="smpl">Age</a> = <a href="#delta-seconds" class="smpl">delta-seconds</a>
    1212 </pre><p id="rfc.section.3.1.p.3">Age field-values are non-negative integers, representing time in seconds (see <a href="#delta-seconds" title="Delta Seconds">Section&nbsp;1.4.3</a>).
    1213       </p>
    1214       <p id="rfc.section.3.1.p.4">The presence of an Age header field in a response implies that a response is not first-hand. However, the converse is not
     1223</pre><p id="rfc.section.7.1.p.3">Age field-values are non-negative integers, representing time in seconds (see <a href="#delta-seconds" title="Delta Seconds">Section&nbsp;1.4.3</a>).
     1224      </p>
     1225      <p id="rfc.section.7.1.p.4">The presence of an Age header field in a response implies that a response is not first-hand. However, the converse is not
    12151226         true, since HTTP/1.0 caches might not implement the Age header field.
    12161227      </p>
    12171228      <div id="rfc.iref.c.6"></div>
    12181229      <div id="rfc.iref.h.3"></div>
    1219       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="header.cache-control" href="#header.cache-control">Cache-Control</a></h2>
    1220       <p id="rfc.section.3.2.p.1">The "Cache-Control" header field is used to specify directives for caches along the request/response chain. Such cache directives
     1230      <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="header.cache-control" href="#header.cache-control">Cache-Control</a></h2>
     1231      <p id="rfc.section.7.2.p.1">The "Cache-Control" header field is used to specify directives for caches along the request/response chain. Such cache directives
    12211232         are unidirectional in that the presence of a directive in a request does not imply that the same directive is to be given
    12221233         in the response.
    12231234      </p>
    1224       <p id="rfc.section.3.2.p.2">A cache <em class="bcp14">MUST</em> obey the requirements of the Cache-Control directives defined in this section. See <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;3.2.3</a> for information about how Cache-Control directives defined elsewhere are handled.
    1225       </p>
    1226       <div class="note" id="rfc.section.3.2.p.3">
    1227          <p> <b>Note:</b> 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.2" title="Pragma">Section&nbsp;3.4</a>).
     1235      <p id="rfc.section.7.2.p.2">A cache <em class="bcp14">MUST</em> obey the requirements of the Cache-Control directives defined in this section. See <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;7.2.3</a> for information about how Cache-Control directives defined elsewhere are handled.
     1236      </p>
     1237      <div class="note" id="rfc.section.7.2.p.3">
     1238         <p> <b>Note:</b> 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.2" title="Pragma">Section&nbsp;7.4</a>).
    12281239         </p>
    12291240      </div>
    1230       <p id="rfc.section.3.2.p.4">A proxy, whether or not it implements a cache, <em class="bcp14">MUST</em> pass cache directives through in forwarded messages, regardless of their significance to that application, since the directives
     1241      <p id="rfc.section.7.2.p.4">A proxy, whether or not it implements a cache, <em class="bcp14">MUST</em> pass cache directives through in forwarded messages, regardless of their significance to that application, since the directives
    12311242         might be applicable to all recipients along the request/response chain. It is not possible to target a directive to a specific
    12321243         cache.
    12331244      </p>
    1234       <p id="rfc.section.3.2.p.5">Cache directives are identified by a token, to be compared case-insensitively, and have an optional argument, that can use
     1245      <p id="rfc.section.7.2.p.5">Cache directives are identified by a token, to be compared case-insensitively, and have an optional argument, that can use
    12351246         both token and quoted-string syntax. For the directives defined below that define arguments, recipients ought to accept both
    12361247         forms, even if one is documented to be preferred. For any directive not defined by this specification, recipients <em class="bcp14">MUST</em> accept both forms.
     
    12391250
    12401251  <a href="#header.cache-control" class="smpl">cache-directive</a> = <a href="#core.rules" class="smpl">token</a> [ "=" ( <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a> ) ]
    1241 </pre><p id="rfc.section.3.2.p.7">For the cache directives defined below, no argument is defined (nor allowed) otherwise stated otherwise.</p>
    1242       <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a id="cache-request-directive" href="#cache-request-directive">Request Cache-Control Directives</a></h3>
     1252</pre><p id="rfc.section.7.2.p.7">For the cache directives defined below, no argument is defined (nor allowed) otherwise stated otherwise.</p>
     1253      <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a id="cache-request-directive" href="#cache-request-directive">Request Cache-Control Directives</a></h3>
    12431254      <div id="rfc.iref.c.7"></div>
    12441255      <div id="rfc.iref.n.1"></div>
    1245       <h4 id="rfc.section.3.2.1.1"><a href="#rfc.section.3.2.1.1">3.2.1.1</a>&nbsp;<a id="cache-request-directive.no-cache" href="#cache-request-directive.no-cache">no-cache</a></h4>
    1246       <p id="rfc.section.3.2.1.1.p.1">The no-cache request directive indicates that a cache <em class="bcp14">MUST NOT</em> use a stored response to satisfy the request without successful validation on the origin server.
     1256      <h4 id="rfc.section.7.2.1.1"><a href="#rfc.section.7.2.1.1">7.2.1.1</a>&nbsp;<a id="cache-request-directive.no-cache" href="#cache-request-directive.no-cache">no-cache</a></h4>
     1257      <p id="rfc.section.7.2.1.1.p.1">The no-cache request directive indicates that a cache <em class="bcp14">MUST NOT</em> use a stored response to satisfy the request without successful validation on the origin server.
    12471258      </p>
    12481259      <div id="rfc.iref.c.8"></div>
    12491260      <div id="rfc.iref.n.2"></div>
    1250       <h4 id="rfc.section.3.2.1.2"><a href="#rfc.section.3.2.1.2">3.2.1.2</a>&nbsp;<a id="cache-request-directive.no-store" href="#cache-request-directive.no-store">no-store</a></h4>
    1251       <p id="rfc.section.3.2.1.2.p.1">The no-store request directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either this request or any response to it. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it.
    1252       </p>
    1253       <p id="rfc.section.3.2.1.2.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches
     1261      <h4 id="rfc.section.7.2.1.2"><a href="#rfc.section.7.2.1.2">7.2.1.2</a>&nbsp;<a id="cache-request-directive.no-store" href="#cache-request-directive.no-store">no-store</a></h4>
     1262      <p id="rfc.section.7.2.1.2.p.1">The no-store request directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either this request or any response to it. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it.
     1263      </p>
     1264      <p id="rfc.section.7.2.1.2.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches
    12541265         might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping.
    12551266      </p>
    1256       <p id="rfc.section.3.2.1.2.p.3">Note that if a request containing this directive is satisfied from a cache, the no-store request directive does not apply
     1267      <p id="rfc.section.7.2.1.2.p.3">Note that if a request containing this directive is satisfied from a cache, the no-store request directive does not apply
    12571268         to the already stored response.
    12581269      </p>
    12591270      <div id="rfc.iref.c.9"></div>
    12601271      <div id="rfc.iref.m.1"></div>
    1261       <h4 id="rfc.section.3.2.1.3"><a href="#rfc.section.3.2.1.3">3.2.1.3</a>&nbsp;<a id="cache-request-directive.max-age" href="#cache-request-directive.max-age">max-age</a></h4>
    1262       <p id="rfc.section.3.2.1.3.p.1">Argument syntax: </p>
     1272      <h4 id="rfc.section.7.2.1.3"><a href="#rfc.section.7.2.1.3">7.2.1.3</a>&nbsp;<a id="cache-request-directive.max-age" href="#cache-request-directive.max-age">max-age</a></h4>
     1273      <p id="rfc.section.7.2.1.3.p.1">Argument syntax: </p>
    12631274      <ul class="empty">
    12641275         <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section&nbsp;1.4.3</a>)
    12651276         </li>
    12661277      </ul>
    1267       <p id="rfc.section.3.2.1.3.p.2">The max-age request directive indicates that the client is unwilling to accept a response whose age is greater than the specified
     1278      <p id="rfc.section.7.2.1.3.p.2">The max-age request directive indicates that the client is unwilling to accept a response whose age is greater than the specified
    12681279         number of seconds. Unless the max-stale request directive is also present, the client is not willing to accept a stale response.
    12691280      </p>
    1270       <p id="rfc.section.3.2.1.3.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
     1281      <p id="rfc.section.7.2.1.3.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
    12711282      </p>
    12721283      <div id="rfc.iref.c.10"></div>
    12731284      <div id="rfc.iref.m.2"></div>
    1274       <h4 id="rfc.section.3.2.1.4"><a href="#rfc.section.3.2.1.4">3.2.1.4</a>&nbsp;<a id="cache-request-directive.max-stale" href="#cache-request-directive.max-stale">max-stale</a></h4>
    1275       <p id="rfc.section.3.2.1.4.p.1">Argument syntax: </p>
     1285      <h4 id="rfc.section.7.2.1.4"><a href="#rfc.section.7.2.1.4">7.2.1.4</a>&nbsp;<a id="cache-request-directive.max-stale" href="#cache-request-directive.max-stale">max-stale</a></h4>
     1286      <p id="rfc.section.7.2.1.4.p.1">Argument syntax: </p>
    12761287      <ul class="empty">
    12771288         <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section&nbsp;1.4.3</a>)
    12781289         </li>
    12791290      </ul>
    1280       <p id="rfc.section.3.2.1.4.p.2">The max-stale request directive indicates that the client is willing to accept a response that has exceeded its expiration
     1291      <p id="rfc.section.7.2.1.4.p.2">The max-stale request directive indicates that the client is willing to accept a response that has exceeded its expiration
    12811292         time. If max-stale is assigned a value, then the client is willing to accept a response that has exceeded its expiration time
    12821293         by no more than the specified number of seconds. If no value is assigned to max-stale, then the client is willing to accept
    12831294         a stale response of any age.
    12841295      </p>
    1285       <p id="rfc.section.3.2.1.4.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-stale=10', not 'max-stale="10"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
     1296      <p id="rfc.section.7.2.1.4.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-stale=10', not 'max-stale="10"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
    12861297      </p>
    12871298      <div id="rfc.iref.c.11"></div>
    12881299      <div id="rfc.iref.m.3"></div>
    1289       <h4 id="rfc.section.3.2.1.5"><a href="#rfc.section.3.2.1.5">3.2.1.5</a>&nbsp;<a id="cache-request-directive.min-fresh" href="#cache-request-directive.min-fresh">min-fresh</a></h4>
    1290       <p id="rfc.section.3.2.1.5.p.1">Argument syntax: </p>
     1300      <h4 id="rfc.section.7.2.1.5"><a href="#rfc.section.7.2.1.5">7.2.1.5</a>&nbsp;<a id="cache-request-directive.min-fresh" href="#cache-request-directive.min-fresh">min-fresh</a></h4>
     1301      <p id="rfc.section.7.2.1.5.p.1">Argument syntax: </p>
    12911302      <ul class="empty">
    12921303         <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section&nbsp;1.4.3</a>)
    12931304         </li>
    12941305      </ul>
    1295       <p id="rfc.section.3.2.1.5.p.2">The min-fresh request directive indicates that the client is willing to accept a response whose freshness lifetime is no less
     1306      <p id="rfc.section.7.2.1.5.p.2">The min-fresh request directive indicates that the client is willing to accept a response whose freshness lifetime is no less
    12961307         than its current age plus the specified time in seconds. That is, the client wants a response that will still be fresh for
    12971308         at least the specified number of seconds.
    12981309      </p>
    1299       <p id="rfc.section.3.2.1.5.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'min-fresh=20', not 'min-fresh="20"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
     1310      <p id="rfc.section.7.2.1.5.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'min-fresh=20', not 'min-fresh="20"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
    13001311      </p>
    13011312      <div id="rfc.iref.c.12"></div>
    13021313      <div id="rfc.iref.n.3"></div>
    1303       <h4 id="rfc.section.3.2.1.6"><a href="#rfc.section.3.2.1.6">3.2.1.6</a>&nbsp;<a id="cache-request-directive.no-transform" href="#cache-request-directive.no-transform">no-transform</a></h4>
    1304       <p id="rfc.section.3.2.1.6.p.1">The no-transform request directive indicates that an intermediary (whether or not it implements a cache) <em class="bcp14">MUST NOT</em> change the <a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a>, <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> or <a href="p2-semantics.html#header.content-type" class="smpl">Content-Type</a> request header fields, nor the request representation.
     1314      <h4 id="rfc.section.7.2.1.6"><a href="#rfc.section.7.2.1.6">7.2.1.6</a>&nbsp;<a id="cache-request-directive.no-transform" href="#cache-request-directive.no-transform">no-transform</a></h4>
     1315      <p id="rfc.section.7.2.1.6.p.1">The no-transform request directive indicates that an intermediary (whether or not it implements a cache) <em class="bcp14">MUST NOT</em> change the <a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a>, <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> or <a href="p2-semantics.html#header.content-type" class="smpl">Content-Type</a> request header fields, nor the request representation.
    13051316      </p>
    13061317      <div id="rfc.iref.c.13"></div>
    13071318      <div id="rfc.iref.o.1"></div>
    1308       <h4 id="rfc.section.3.2.1.7"><a href="#rfc.section.3.2.1.7">3.2.1.7</a>&nbsp;<a id="cache-request-directive.only-if-cached" href="#cache-request-directive.only-if-cached">only-if-cached</a></h4>
    1309       <p id="rfc.section.3.2.1.7.p.1">The only-if-cached request directive indicates that the client only wishes to obtain a stored response. If it receives 3ive,
    1310          a cache <em class="bcp14">SHOULD</em> either respond using a stored response that is consistent with the other constraints of the request, or respond with a <a href="p2-semantics.html#status.504" class="smpl">504
    1311             (Gateway Timeout)</a> status code. If a group of caches is being operated as a unified system with good internal connectivity, a member cache <em class="bcp14">MAY</em> forward such a request within that group of caches.
    1312       </p>
    1313       <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a id="cache-response-directive" href="#cache-response-directive">Response Cache-Control Directives</a></h3>
     1319      <h4 id="rfc.section.7.2.1.7"><a href="#rfc.section.7.2.1.7">7.2.1.7</a>&nbsp;<a id="cache-request-directive.only-if-cached" href="#cache-request-directive.only-if-cached">only-if-cached</a></h4>
     1320      <p id="rfc.section.7.2.1.7.p.1">The only-if-cached request directive indicates that the client only wishes to obtain a stored response. If it receives 3ive,
     1321         a cache <em class="bcp14">SHOULD</em> either respond using a stored response that is consistent with the other constraints of the request, or respond with a <a href="p2-semantics.html#status.504" class="smpl">504 (Gateway
     1322            Timeout)</a> status code. If a group of caches is being operated as a unified system with good internal connectivity, a member cache <em class="bcp14">MAY</em> forward such a request within that group of caches.
     1323      </p>
     1324      <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a id="cache-response-directive" href="#cache-response-directive">Response Cache-Control Directives</a></h3>
    13141325      <div id="rfc.iref.c.14"></div>
    13151326      <div id="rfc.iref.p.2"></div>
    1316       <h4 id="rfc.section.3.2.2.1"><a href="#rfc.section.3.2.2.1">3.2.2.1</a>&nbsp;<a id="cache-response-directive.only-if-cached" href="#cache-response-directive.only-if-cached">public</a></h4>
    1317       <p id="rfc.section.3.2.2.1.p.1">The public response directive indicates that a response whose associated request contains an 'Authentication' header <em class="bcp14">MAY</em> be stored (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section&nbsp;2.7</a>).
     1327      <h4 id="rfc.section.7.2.2.1"><a href="#rfc.section.7.2.2.1">7.2.2.1</a>&nbsp;<a id="cache-response-directive.only-if-cached" href="#cache-response-directive.only-if-cached">public</a></h4>
     1328      <p id="rfc.section.7.2.2.1.p.1">The public response directive indicates that a response whose associated request contains an 'Authentication' header <em class="bcp14">MAY</em> be stored (see <a href="#caching.authenticated.responses" title="Storing Responses to Authenticated Requests">Section&nbsp;3.2</a>).
    13181329      </p>
    13191330      <div id="rfc.iref.c.15"></div>
    13201331      <div id="rfc.iref.p.3"></div>
    1321       <h4 id="rfc.section.3.2.2.2"><a href="#rfc.section.3.2.2.2">3.2.2.2</a>&nbsp;<a id="cache-response-directive.private" href="#cache-response-directive.private">private</a></h4>
    1322       <p id="rfc.section.3.2.2.2.p.1">Argument syntax: </p>
     1332      <h4 id="rfc.section.7.2.2.2"><a href="#rfc.section.7.2.2.2">7.2.2.2</a>&nbsp;<a id="cache-response-directive.private" href="#cache-response-directive.private">private</a></h4>
     1333      <p id="rfc.section.7.2.2.2.p.1">Argument syntax: </p>
    13231334      <ul class="empty">
    13241335         <li>#<a href="#abnf.dependencies" class="smpl">field-name</a>
    13251336         </li>
    13261337      </ul>
    1327       <p id="rfc.section.3.2.2.2.p.2">The private response directive indicates that the response message is intended for a single user and <em class="bcp14">MUST NOT</em> be stored by a shared cache. A private cache <em class="bcp14">MAY</em> store the response.
    1328       </p>
    1329       <p id="rfc.section.3.2.2.2.p.3">If the private response directive specifies one or more field-names, this requirement is limited to the field-values associated
     1338      <p id="rfc.section.7.2.2.2.p.2">The private response directive indicates that the response message is intended for a single user and <em class="bcp14">MUST NOT</em> be stored by a shared cache. A private cache <em class="bcp14">MAY</em> store the response.
     1339      </p>
     1340      <p id="rfc.section.7.2.2.2.p.3">If the private response directive specifies one or more field-names, this requirement is limited to the field-values associated
    13301341         with the listed response header fields. That is, a shared cache <em class="bcp14">MUST NOT</em> store the specified field-names(s), whereas it <em class="bcp14">MAY</em> store the remainder of the response message.
    13311342      </p>
    1332       <p id="rfc.section.3.2.2.2.p.4">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are
     1343      <p id="rfc.section.7.2.2.2.p.4">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are
    13331344         case-insensitive.
    13341345      </p>
    1335       <p id="rfc.section.3.2.2.2.p.5"> <b>Note:</b> This usage of the word "private" only controls where the response can be stored; it cannot ensure the privacy of the message
     1346      <p id="rfc.section.7.2.2.2.p.5"> <b>Note:</b> This usage of the word "private" only controls where the response can be stored; it cannot ensure the privacy of the message
    13361347         content. Also, private response directives with field-names are often handled by implementations as if an unqualified private
    13371348         directive was received; i.e., the special handling for the qualified form is not widely implemented.
    13381349      </p>
    1339       <p id="rfc.section.3.2.2.2.p.6"> <b>Note:</b> This directive uses the quoted-string form of the argument syntax. Senders <em class="bcp14">SHOULD NOT</em> use the token form (even if quoting appears not to be needed for single-entry lists).
     1350      <p id="rfc.section.7.2.2.2.p.6"> <b>Note:</b> This directive uses the quoted-string form of the argument syntax. Senders <em class="bcp14">SHOULD NOT</em> use the token form (even if quoting appears not to be needed for single-entry lists).
    13401351      </p>
    13411352      <div id="rfc.iref.c.16"></div>
    13421353      <div id="rfc.iref.n.4"></div>
    1343       <h4 id="rfc.section.3.2.2.3"><a href="#rfc.section.3.2.2.3">3.2.2.3</a>&nbsp;<a id="cache-response-directive.no-cache" href="#cache-response-directive.no-cache">no-cache</a></h4>
    1344       <p id="rfc.section.3.2.2.3.p.1">Argument syntax: </p>
     1354      <h4 id="rfc.section.7.2.2.3"><a href="#rfc.section.7.2.2.3">7.2.2.3</a>&nbsp;<a id="cache-response-directive.no-cache" href="#cache-response-directive.no-cache">no-cache</a></h4>
     1355      <p id="rfc.section.7.2.2.3.p.1">Argument syntax: </p>
    13451356      <ul class="empty">
    13461357         <li>#<a href="#abnf.dependencies" class="smpl">field-name</a>
    13471358         </li>
    13481359      </ul>
    1349       <p id="rfc.section.3.2.2.3.p.2">The no-cache response directive indicates that the response <em class="bcp14">MUST NOT</em> be used to satisfy a subsequent request without successful validation on the origin server. This allows an origin server to
     1360      <p id="rfc.section.7.2.2.3.p.2">The no-cache response directive indicates that the response <em class="bcp14">MUST NOT</em> be used to satisfy a subsequent request without successful validation on the origin server. This allows an origin server to
    13501361         prevent a cache from using it to satisfy a request without contacting it, even by caches that have been configured to return
    13511362         stale responses.
    13521363      </p>
    1353       <p id="rfc.section.3.2.2.3.p.3">If the no-cache response directive specifies one or more field-names, then a cache <em class="bcp14">MAY</em> use the response to satisfy a subsequent request, subject to any other restrictions on caching. However, any header fields
     1364      <p id="rfc.section.7.2.2.3.p.3">If the no-cache response directive specifies one or more field-names, then a cache <em class="bcp14">MAY</em> use the response to satisfy a subsequent request, subject to any other restrictions on caching. However, any header fields
    13541365         in the response that have the field-name(s) listed <em class="bcp14">MUST NOT</em> be sent in the response to a subsequent request without successful revalidation with the origin server. This allows an origin
    13551366         server to prevent the re-use of certain header fields in a response, while still allowing caching of the rest of the response.
    13561367      </p>
    1357       <p id="rfc.section.3.2.2.3.p.4">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are
     1368      <p id="rfc.section.7.2.2.3.p.4">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are
    13581369         case-insensitive.
    13591370      </p>
    1360       <p id="rfc.section.3.2.2.3.p.5"> <b>Note:</b> Most HTTP/1.0 caches will not recognize or obey this directive. Also, no-cache response directives with field-names are often
     1371      <p id="rfc.section.7.2.2.3.p.5"> <b>Note:</b> Most HTTP/1.0 caches will not recognize or obey this directive. Also, no-cache response directives with field-names are often
    13611372         handled by implementations as if an unqualified no-cache directive was received; i.e., the special handling for the qualified
    13621373         form is not widely implemented.
    13631374      </p>
    1364       <p id="rfc.section.3.2.2.3.p.6"> <b>Note:</b> This directive uses the quoted-string form of the argument syntax. Senders <em class="bcp14">SHOULD NOT</em> use the token form (even if quoting appears not to be needed for single-entry lists).
     1375      <p id="rfc.section.7.2.2.3.p.6"> <b>Note:</b> This directive uses the quoted-string form of the argument syntax. Senders <em class="bcp14">SHOULD NOT</em> use the token form (even if quoting appears not to be needed for single-entry lists).
    13651376      </p>
    13661377      <div id="rfc.iref.c.17"></div>
    13671378      <div id="rfc.iref.n.5"></div>
    1368       <h4 id="rfc.section.3.2.2.4"><a href="#rfc.section.3.2.2.4">3.2.2.4</a>&nbsp;<a id="cache-response-directive.no-store" href="#cache-response-directive.no-store">no-store</a></h4>
    1369       <p id="rfc.section.3.2.2.4.p.1">The no-store response directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either the immediate request or response. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it.
    1370       </p>
    1371       <p id="rfc.section.3.2.2.4.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches
     1379      <h4 id="rfc.section.7.2.2.4"><a href="#rfc.section.7.2.2.4">7.2.2.4</a>&nbsp;<a id="cache-response-directive.no-store" href="#cache-response-directive.no-store">no-store</a></h4>
     1380      <p id="rfc.section.7.2.2.4.p.1">The no-store response directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either the immediate request or response. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it.
     1381      </p>
     1382      <p id="rfc.section.7.2.2.4.p.2">This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches
    13721383         might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping.
    13731384      </p>
    13741385      <div id="rfc.iref.c.18"></div>
    13751386      <div id="rfc.iref.m.4"></div>
    1376       <h4 id="rfc.section.3.2.2.5"><a href="#rfc.section.3.2.2.5">3.2.2.5</a>&nbsp;<a id="cache-response-directive.must-revalidate" href="#cache-response-directive.must-revalidate">must-revalidate</a></h4>
    1377       <p id="rfc.section.3.2.2.5.p.1">The must-revalidate response directive indicates that once it has become stale, a cache <em class="bcp14">MUST NOT</em> use the response to satisfy subsequent requests without successful validation on the origin server.
    1378       </p>
    1379       <p id="rfc.section.3.2.2.5.p.2">The must-revalidate directive is necessary to support reliable operation for certain protocol features. In all circumstances
     1387      <h4 id="rfc.section.7.2.2.5"><a href="#rfc.section.7.2.2.5">7.2.2.5</a>&nbsp;<a id="cache-response-directive.must-revalidate" href="#cache-response-directive.must-revalidate">must-revalidate</a></h4>
     1388      <p id="rfc.section.7.2.2.5.p.1">The must-revalidate response directive indicates that once it has become stale, a cache <em class="bcp14">MUST NOT</em> use the response to satisfy subsequent requests without successful validation on the origin server.
     1389      </p>
     1390      <p id="rfc.section.7.2.2.5.p.2">The must-revalidate directive is necessary to support reliable operation for certain protocol features. In all circumstances
    13801391         a cache <em class="bcp14">MUST</em> obey the must-revalidate directive; in particular, if a cache cannot reach the origin server for any reason, it <em class="bcp14">MUST</em> generate a <a href="p2-semantics.html#status.504" class="smpl">504 (Gateway Timeout)</a> response.
    13811392      </p>
    1382       <p id="rfc.section.3.2.2.5.p.3">The must-revalidate directive ought to be used by servers if and only if failure to validate a request on the representation
     1393      <p id="rfc.section.7.2.2.5.p.3">The must-revalidate directive ought to be used by servers if and only if failure to validate a request on the representation
    13831394         could result in incorrect operation, such as a silently unexecuted financial transaction.
    13841395      </p>
    13851396      <div id="rfc.iref.c.19"></div>
    13861397      <div id="rfc.iref.p.4"></div>
    1387       <h4 id="rfc.section.3.2.2.6"><a href="#rfc.section.3.2.2.6">3.2.2.6</a>&nbsp;<a id="cache-response-directive.proxy-revalidate" href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></h4>
    1388       <p id="rfc.section.3.2.2.6.p.1">The proxy-revalidate response directive has the same meaning as the must-revalidate response directive, except that it does
     1398      <h4 id="rfc.section.7.2.2.6"><a href="#rfc.section.7.2.2.6">7.2.2.6</a>&nbsp;<a id="cache-response-directive.proxy-revalidate" href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></h4>
     1399      <p id="rfc.section.7.2.2.6.p.1">The proxy-revalidate response directive has the same meaning as the must-revalidate response directive, except that it does
    13891400         not apply to private caches.
    13901401      </p>
    13911402      <div id="rfc.iref.c.20"></div>
    13921403      <div id="rfc.iref.m.5"></div>
    1393       <h4 id="rfc.section.3.2.2.7"><a href="#rfc.section.3.2.2.7">3.2.2.7</a>&nbsp;<a id="cache-response-directive.max-age" href="#cache-response-directive.max-age">max-age</a></h4>
    1394       <p id="rfc.section.3.2.2.7.p.1">Argument syntax: </p>
     1404      <h4 id="rfc.section.7.2.2.7"><a href="#rfc.section.7.2.2.7">7.2.2.7</a>&nbsp;<a id="cache-response-directive.max-age" href="#cache-response-directive.max-age">max-age</a></h4>
     1405      <p id="rfc.section.7.2.2.7.p.1">Argument syntax: </p>
    13951406      <ul class="empty">
    13961407         <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section&nbsp;1.4.3</a>)
    13971408         </li>
    13981409      </ul>
    1399       <p id="rfc.section.3.2.2.7.p.2">The max-age response directive indicates that the response is to be considered stale after its age is greater than the specified
     1410      <p id="rfc.section.7.2.2.7.p.2">The max-age response directive indicates that the response is to be considered stale after its age is greater than the specified
    14001411         number of seconds.
    14011412      </p>
    1402       <p id="rfc.section.3.2.2.7.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
     1413      <p id="rfc.section.7.2.2.7.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 'max-age=5', not 'max-age="5"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
    14031414      </p>
    14041415      <div id="rfc.iref.c.21"></div>
    14051416      <div id="rfc.iref.s.4"></div>
    1406       <h4 id="rfc.section.3.2.2.8"><a href="#rfc.section.3.2.2.8">3.2.2.8</a>&nbsp;<a id="cache-response-directive.s-maxage" href="#cache-response-directive.s-maxage">s-maxage</a></h4>
    1407       <p id="rfc.section.3.2.2.8.p.1">Argument syntax: </p>
     1417      <h4 id="rfc.section.7.2.2.8"><a href="#rfc.section.7.2.2.8">7.2.2.8</a>&nbsp;<a id="cache-response-directive.s-maxage" href="#cache-response-directive.s-maxage">s-maxage</a></h4>
     1418      <p id="rfc.section.7.2.2.8.p.1">Argument syntax: </p>
    14081419      <ul class="empty">
    14091420         <li> <a href="#delta-seconds" class="smpl">delta-seconds</a> (see <a href="#delta-seconds" title="Delta Seconds">Section&nbsp;1.4.3</a>)
    14101421         </li>
    14111422      </ul>
    1412       <p id="rfc.section.3.2.2.8.p.2">The s-maxage response directive indicates that, in shared caches, the maximum age specified by this directive overrides the
     1423      <p id="rfc.section.7.2.2.8.p.2">The s-maxage response directive indicates that, in shared caches, the maximum age specified by this directive overrides the
    14131424         maximum age specified by either the max-age directive or the <a href="#header.expires" class="smpl">Expires</a> header field. The s-maxage directive also implies the semantics of the proxy-revalidate response directive.
    14141425      </p>
    1415       <p id="rfc.section.3.2.2.8.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 's-maxage=10', not 's-maxage="10"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
     1426      <p id="rfc.section.7.2.2.8.p.3"> <b>Note:</b> This directive uses the token form of the argument syntax; e.g., 's-maxage=10', not 's-maxage="10"'. Senders <em class="bcp14">SHOULD NOT</em> use the quoted-string form.
    14161427      </p>
    14171428      <div id="rfc.iref.c.22"></div>
    14181429      <div id="rfc.iref.n.6"></div>
    1419       <h4 id="rfc.section.3.2.2.9"><a href="#rfc.section.3.2.2.9">3.2.2.9</a>&nbsp;<a id="cache-response-directive.no-transform" href="#cache-response-directive.no-transform">no-transform</a></h4>
    1420       <p id="rfc.section.3.2.2.9.p.1">The no-transform response directive indicates that an intermediary (regardless of whether it implements a cache) <em class="bcp14">MUST NOT</em> change the <a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a>, <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> or <a href="p2-semantics.html#header.content-type" class="smpl">Content-Type</a> response header fields, nor the response representation.
    1421       </p>
    1422       <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;<a id="cache.control.extensions" href="#cache.control.extensions">Cache Control Extensions</a></h3>
    1423       <p id="rfc.section.3.2.3.p.1">The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional
     1430      <h4 id="rfc.section.7.2.2.9"><a href="#rfc.section.7.2.2.9">7.2.2.9</a>&nbsp;<a id="cache-response-directive.no-transform" href="#cache-response-directive.no-transform">no-transform</a></h4>
     1431      <p id="rfc.section.7.2.2.9.p.1">The no-transform response directive indicates that an intermediary (regardless of whether it implements a cache) <em class="bcp14">MUST NOT</em> change the <a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a>, <a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> or <a href="p2-semantics.html#header.content-type" class="smpl">Content-Type</a> response header fields, nor the response representation.
     1432      </p>
     1433      <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;<a id="cache.control.extensions" href="#cache.control.extensions">Cache Control Extensions</a></h3>
     1434      <p id="rfc.section.7.2.3.p.1">The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional
    14241435         value. Informational extensions (those that do not require a change in cache behavior) can be added without changing the semantics
    14251436         of other directives. Behavioral extensions are designed to work by acting as modifiers to the existing base of cache directives.
     
    14291440         can be made without requiring changes to the base protocol.
    14301441      </p>
    1431       <p id="rfc.section.3.2.3.p.2">This extension mechanism depends on an HTTP cache obeying all of the cache-control directives defined for its native HTTP-version,
     1442      <p id="rfc.section.7.2.3.p.2">This extension mechanism depends on an HTTP cache obeying all of the cache-control directives defined for its native HTTP-version,
    14321443         obeying certain extensions, and ignoring all directives that it does not understand.
    14331444      </p>
    1434       <p id="rfc.section.3.2.3.p.3">For example, consider a hypothetical new response directive called "community" that acts as a modifier to the private directive.
     1445      <p id="rfc.section.7.2.3.p.3">For example, consider a hypothetical new response directive called "community" that acts as a modifier to the private directive.
    14351446         We define this new directive to mean that, in addition to any private cache, any cache that is shared only by members of the
    14361447         community named within its value is allowed to cache the response. An origin server wishing to allow the UCI community to
     
    14381449      </p>
    14391450      <div id="rfc.figure.u.10"></div><pre class="text">  Cache-Control: private, community="UCI"
    1440 </pre><p id="rfc.section.3.2.3.p.5">A cache seeing this header field will act correctly even if the cache does not understand the community cache-extension, since
     1451</pre><p id="rfc.section.7.2.3.p.5">A cache seeing this header field will act correctly even if the cache does not understand the community cache-extension, since
    14411452         it will also see and understand the private directive and thus default to the safe behavior.
    14421453      </p>
    1443       <p id="rfc.section.3.2.3.p.6">A cache <em class="bcp14">MUST</em> ignore unrecognized cache directives; it is assumed that any cache directive likely to be unrecognized by an HTTP/1.1 cache
     1454      <p id="rfc.section.7.2.3.p.6">A cache <em class="bcp14">MUST</em> ignore unrecognized cache directives; it is assumed that any cache directive likely to be unrecognized by an HTTP/1.1 cache
    14441455         will be combined with standard directives (or the response's default cacheability) such that the cache behavior will remain
    14451456         minimally correct even if the cache does not understand the extension(s).
    14461457      </p>
    1447       <p id="rfc.section.3.2.3.p.7">New extension directives ought to consider defining:</p>
    1448       <p id="rfc.section.3.2.3.p.8"> </p>
     1458      <p id="rfc.section.7.2.3.p.7">New extension directives ought to consider defining:</p>
     1459      <p id="rfc.section.7.2.3.p.8"> </p>
    14491460      <ul>
    14501461         <li>What it means for a directive to be specified multiple times,</li>
     
    14521463         <li>When the directive requires an argument, what it means when it is missing.</li>
    14531464      </ul>
    1454       <p id="rfc.section.3.2.3.p.9">The HTTP Cache Directive Registry defines the name space for the cache directives.</p>
    1455       <p id="rfc.section.3.2.3.p.10">A registration <em class="bcp14">MUST</em> include the following fields:
     1465      <p id="rfc.section.7.2.3.p.9">The HTTP Cache Directive Registry defines the name space for the cache directives.</p>
     1466      <p id="rfc.section.7.2.3.p.10">A registration <em class="bcp14">MUST</em> include the following fields:
    14561467      </p>
    14571468      <ul>
     
    14591470         <li>Pointer to specification text</li>
    14601471      </ul>
    1461       <p id="rfc.section.3.2.3.p.11">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).
    1462       </p>
    1463       <p id="rfc.section.3.2.3.p.12">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>&gt;.
     1472      <p id="rfc.section.7.2.3.p.11">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).
     1473      </p>
     1474      <p id="rfc.section.7.2.3.p.12">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>&gt;.
    14641475      </p>
    14651476      <div id="rfc.iref.e.2"></div>
    14661477      <div id="rfc.iref.h.4"></div>
    1467       <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a id="header.expires" href="#header.expires">Expires</a></h2>
    1468       <p id="rfc.section.3.3.p.1">The "Expires" header field gives the date/time after which the response is considered stale. See <a href="#expiration.model" title="Freshness Model">Section&nbsp;2.3</a> for further discussion of the freshness model.
    1469       </p>
    1470       <p id="rfc.section.3.3.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
     1478      <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a>&nbsp;<a id="header.expires" href="#header.expires">Expires</a></h2>
     1479      <p id="rfc.section.7.3.p.1">The "Expires" header field gives the date/time after which the response is considered stale. See <a href="#expiration.model" title="Freshness Model">Section&nbsp;4.1</a> for further discussion of the freshness model.
     1480      </p>
     1481      <p id="rfc.section.7.3.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
    14711482         that time.
    14721483      </p>
    1473       <p id="rfc.section.3.3.p.3">The field-value is an absolute date and time as defined by HTTP-date in <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 5.1</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>; a sender <em class="bcp14">MUST</em> use the rfc1123-date format.
     1484      <p id="rfc.section.7.3.p.3">The field-value is an absolute date and time as defined by HTTP-date in <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 5.1</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>; a sender <em class="bcp14">MUST</em> use the rfc1123-date format.
    14741485      </p>
    14751486      <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.5"></span>  <a href="#header.expires" class="smpl">Expires</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a>
    14761487</pre><div id="rfc.figure.u.12"></div>
    14771488      <p>For example</p>  <pre class="text">  Expires: Thu, 01 Dec 1994 16:00:00 GMT
    1478 </pre><p id="rfc.section.3.3.p.6">A cache <em class="bcp14">MUST</em> treat other invalid date formats, especially including the value "0", as in the past (i.e., "already expired").
    1479       </p>
    1480       <div class="note" id="rfc.section.3.3.p.7">
    1481          <p> <b>Note:</b> If a response includes a <a href="#header.cache-control" class="smpl">Cache-Control</a> field with the max-age directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;3.2.2</a>), that directive overrides the Expires field. Likewise, the s-maxage directive overrides Expires in shared caches.
     1489</pre><p id="rfc.section.7.3.p.6">A cache <em class="bcp14">MUST</em> treat other invalid date formats, especially including the value "0", as in the past (i.e., "already expired").
     1490      </p>
     1491      <div class="note" id="rfc.section.7.3.p.7">
     1492         <p> <b>Note:</b> If a response includes a <a href="#header.cache-control" class="smpl">Cache-Control</a> field with the max-age directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section&nbsp;7.2.2</a>), that directive overrides the Expires field. Likewise, the s-maxage directive overrides Expires in shared caches.
    14821493         </p>
    14831494      </div>
    1484       <p id="rfc.section.3.3.p.8">Historically, HTTP required the Expires field-value to be no more than a year in the future. While longer freshness lifetimes
     1495      <p id="rfc.section.7.3.p.8">Historically, HTTP required the Expires field-value to be no more than a year in the future. While longer freshness lifetimes
    14851496         are no longer prohibited, extremely large values have been demonstrated to cause problems (e.g., clock overflows due to use
    14861497         of 32-bit integers for time values), and most caches will evict a response far sooner than that. Therefore, senders ought
    14871498         not produce them.
    14881499      </p>
    1489       <p id="rfc.section.3.3.p.9">An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires values to a response unless these values were associated with the resource by a system or user with a reliable
     1500      <p id="rfc.section.7.3.p.9">An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires values to a response unless these values were associated with the resource by a system or user with a reliable
    14901501         clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration"
    14911502         of responses without storing separate Expires values for each resource).
     
    14931504      <div id="rfc.iref.p.5"></div>
    14941505      <div id="rfc.iref.h.5"></div>
    1495       <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a id="header.pragma" href="#header.pragma">Pragma</a></h2>
    1496       <p id="rfc.section.3.4.p.1">The "Pragma" header field allows backwards compatibility with HTTP/1.0 caches, so that clients can specify a "no-cache" request
     1506      <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a>&nbsp;<a id="header.pragma" href="#header.pragma">Pragma</a></h2>
     1507      <p id="rfc.section.7.4.p.1">The "Pragma" header field allows backwards compatibility with HTTP/1.0 caches, so that clients can specify a "no-cache" request
    14971508         that they will understand (as <a href="#header.cache-control" class="smpl">Cache-Control</a> was not defined until HTTP/1.1). When the Cache-Control header field is also present and understood in a request, Pragma is
    14981509         ignored.
    14991510      </p>
    1500       <p id="rfc.section.3.4.p.2">In HTTP/1.0, Pragma was defined as an extensible field for implementation-specified directives for recipients. This specification
     1511      <p id="rfc.section.7.4.p.2">In HTTP/1.0, Pragma was defined as an extensible field for implementation-specified directives for recipients. This specification
    15011512         deprecates such extensions to improve interoperability.
    15021513      </p>
     
    15041515  <a href="#header.pragma" class="smpl">pragma-directive</a> = "no-cache" / <a href="#header.pragma" class="smpl">extension-pragma</a>
    15051516  <a href="#header.pragma" class="smpl">extension-pragma</a> = <a href="#core.rules" class="smpl">token</a> [ "=" ( <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a> ) ]
    1506 </pre><p id="rfc.section.3.4.p.4">When the <a href="#header.cache-control" class="smpl">Cache-Control</a> header field is not present in a request, the no-cache request pragma-directive <em class="bcp14">MUST</em> have the same effect on caches as if "Cache-Control: no-cache" were present (see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;3.2.1</a>).
    1507       </p>
    1508       <p id="rfc.section.3.4.p.5">When sending a no-cache request, a client ought to include both the pragma and cache-control directives, unless Cache-Control:
     1517</pre><p id="rfc.section.7.4.p.4">When the <a href="#header.cache-control" class="smpl">Cache-Control</a> header field is not present in a request, the no-cache request pragma-directive <em class="bcp14">MUST</em> have the same effect on caches as if "Cache-Control: no-cache" were present (see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section&nbsp;7.2.1</a>).
     1518      </p>
     1519      <p id="rfc.section.7.4.p.5">When sending a no-cache request, a client ought to include both the pragma and cache-control directives, unless Cache-Control:
    15091520         no-cache is purposefully omitted to target other <a href="#header.cache-control" class="smpl">Cache-Control</a> response directives at HTTP/1.1 caches. For example:
    15101521      </p>
     
    15141525Pragma: no-cache
    15151526
    1516 </pre> <p id="rfc.section.3.4.p.7">will constrain HTTP/1.1 caches to serve a response no older than 30 seconds, while precluding implementations that do not
     1527</pre> <p id="rfc.section.7.4.p.7">will constrain HTTP/1.1 caches to serve a response no older than 30 seconds, while precluding implementations that do not
    15171528         understand <a href="#header.cache-control" class="smpl">Cache-Control</a> from serving a cached response.
    15181529      </p>
    1519       <div class="note" id="rfc.section.3.4.p.8">
     1530      <div class="note" id="rfc.section.7.4.p.8">
    15201531         <p> <b>Note:</b> Because the meaning of "Pragma: no-cache" in responses is not specified, it does not provide a reliable replacement for "Cache-Control:
    15211532            no-cache" in them.
     
    15241535      <div id="rfc.iref.v.3"></div>
    15251536      <div id="rfc.iref.h.6"></div>
    1526       <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="header.vary" href="#header.vary">Vary</a></h2>
    1527       <p id="rfc.section.3.5.p.1">The "Vary" header field conveys the set of header fields that were used to select the representation.</p>
    1528       <p id="rfc.section.3.5.p.2">Caches use this information, in part, to determine whether a stored response can be used to satisfy a given request; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>. determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request
    1529          without validation; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.8</a>.
    1530       </p>
    1531       <p id="rfc.section.3.5.p.3">In uncacheable or stale responses, the Vary field value advises the user agent about the criteria that were used to select
     1537      <h2 id="rfc.section.7.5"><a href="#rfc.section.7.5">7.5</a>&nbsp;<a id="header.vary" href="#header.vary">Vary</a></h2>
     1538      <p id="rfc.section.7.5.p.1">The "Vary" header field conveys the set of header fields that were used to select the representation.</p>
     1539      <p id="rfc.section.7.5.p.2">Caches use this information, in part, to determine whether a stored response can be used to satisfy a given request; see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>. determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request
     1540         without validation; see <a href="#caching.negotiated.responses" title="Using Negotiated Responses">Section&nbsp;4.3</a>.
     1541      </p>
     1542      <p id="rfc.section.7.5.p.3">In uncacheable or stale responses, the Vary field value advises the user agent about the criteria that were used to select
    15321543         the representation.
    15331544      </p>
    15341545      <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  <a href="#header.vary" class="smpl">Vary</a> = "*" / 1#<a href="#abnf.dependencies" class="smpl">field-name</a>
    1535 </pre><p id="rfc.section.3.5.p.5">The set of header fields named by the Vary field value is known as the selecting header fields.</p>
    1536       <p id="rfc.section.3.5.p.6">A 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
     1546</pre><p id="rfc.section.7.5.p.5">The set of header fields named by the Vary field value is known as the selecting header fields.</p>
     1547      <p id="rfc.section.7.5.p.6">A 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
    15371548         to properly interpret future requests on that resource and informs the user agent about the presence of negotiation on that
    15381549         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
    15391550         the user agent with useful information about the dimensions over which the response varies at the time of the response.
    15401551      </p>
    1541       <p id="rfc.section.3.5.p.7">A Vary field value of "*" signals that unspecified parameters not limited to the header fields (e.g., the network address
     1552      <p id="rfc.section.7.5.p.7">A Vary field value of "*" signals that unspecified parameters not limited to the header fields (e.g., the network address
    15421553         of the client), play a role in the selection of the response representation; therefore, a cache cannot determine whether this
    15431554         response is appropriate. A proxy <em class="bcp14">MUST NOT</em> generate the "*" value.
    15441555      </p>
    1545       <p id="rfc.section.3.5.p.8">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are
     1556      <p id="rfc.section.7.5.p.8">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are
    15461557         case-insensitive.
    15471558      </p>
    15481559      <div id="rfc.iref.w.1"></div>
    15491560      <div id="rfc.iref.h.7"></div>
    1550       <h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6</a>&nbsp;<a id="header.warning" href="#header.warning">Warning</a></h2>
    1551       <p id="rfc.section.3.6.p.1">The "Warning" header field is used to carry additional information about the status or transformation of a message that might
     1561      <h2 id="rfc.section.7.6"><a href="#rfc.section.7.6">7.6</a>&nbsp;<a id="header.warning" href="#header.warning">Warning</a></h2>
     1562      <p id="rfc.section.7.6.p.1">The "Warning" header field is used to carry additional information about the status or transformation of a message that might
    15521563         not be reflected in the message. This information is typically used to warn about possible incorrectness introduced by caching
    15531564         operations or transformations applied to the payload of the message.
    15541565      </p>
    1555       <p id="rfc.section.3.6.p.2">Warnings can be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status
     1566      <p id="rfc.section.7.6.p.2">Warnings can be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status
    15561567         code, distinguishes these responses from true failures.
    15571568      </p>
    1558       <p id="rfc.section.3.6.p.3">Warning header fields can in general be applied to any message, however some warn-codes are specific to caches and can only
     1569      <p id="rfc.section.7.6.p.3">Warning header fields can in general be applied to any message, however some warn-codes are specific to caches and can only
    15591570         be applied to response messages.
    15601571      </p>
     
    15701581  <a href="#header.warning" class="smpl">warn-text</a>  = <a href="#core.rules" class="smpl">quoted-string</a>
    15711582  <a href="#header.warning" class="smpl">warn-date</a>  = <a href="#notation" class="smpl">DQUOTE</a> <a href="#abnf.dependencies" class="smpl">HTTP-date</a> <a href="#notation" class="smpl">DQUOTE</a>
    1572 </pre><p id="rfc.section.3.6.p.5">Multiple warnings can be attached to a response (either by the origin server or by a cache), including multiple warnings with
     1583</pre><p id="rfc.section.7.6.p.5">Multiple warnings can be attached to a response (either by the origin server or by a cache), including multiple warnings with
    15731584         the same code number, only differing in warn-text.
    15741585      </p>
    1575       <p id="rfc.section.3.6.p.6">When this occurs, the user agent <em class="bcp14">SHOULD</em> inform the user of as many of them as possible, in the order that they appear in the response.
    1576       </p>
    1577       <p id="rfc.section.3.6.p.7">Systems that generate multiple Warning header fields are encouraged to order them with this user agent behavior in mind. New
     1586      <p id="rfc.section.7.6.p.6">When this occurs, the user agent <em class="bcp14">SHOULD</em> inform the user of as many of them as possible, in the order that they appear in the response.
     1587      </p>
     1588      <p id="rfc.section.7.6.p.7">Systems that generate multiple Warning header fields are encouraged to order them with this user agent behavior in mind. New
    15781589         Warning header fields are added after any existing Warning headers fields.
    15791590      </p>
    1580       <p id="rfc.section.3.6.p.8">Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning is required to be deleted from
     1591      <p id="rfc.section.7.6.p.8">Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning is required to be deleted from
    15811592         a stored response after validation:
    15821593      </p>
     
    15881599         </li>
    15891600      </ul>
    1590       <p id="rfc.section.3.6.p.9">If an implementation sends a message with one or more Warning header fields to a receiver whose version is HTTP/1.0 or lower,
     1601      <p id="rfc.section.7.6.p.9">If an implementation sends a message with one or more Warning header fields to a receiver whose version is HTTP/1.0 or lower,
    15911602         then the sender <em class="bcp14">MUST</em> include in each warning-value a warn-date that matches the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field in the message.
    15921603      </p>
    1593       <p id="rfc.section.3.6.p.10">If a system receives a message with a warning-value that includes a warn-date, and that warn-date is different from the <a href="p2-semantics.html#header.date" class="smpl">Date</a> value in the response, then that warning-value <em class="bcp14">MUST</em> be deleted from the message before storing, forwarding, or using it. (preventing the consequences of naive caching of Warning
     1604      <p id="rfc.section.7.6.p.10">If a system receives a message with a warning-value that includes a warn-date, and that warn-date is different from the <a href="p2-semantics.html#header.date" class="smpl">Date</a> value in the response, then that warning-value <em class="bcp14">MUST</em> be deleted from the message before storing, forwarding, or using it. (preventing the consequences of naive caching of Warning
    15941605         header fields.) If all of the warning-values are deleted for this reason, the Warning header field <em class="bcp14">MUST</em> be deleted as well.
    15951606      </p>
    1596       <p id="rfc.section.3.6.p.11">The following warn-codes are defined by this specification, each with a recommended warn-text in English, and a description
     1607      <p id="rfc.section.7.6.p.11">The following warn-codes are defined by this specification, each with a recommended warn-text in English, and a description
    15971608         of its meaning.
    15981609      </p>
    15991610      <div id="rfc.iref.76"></div>
    16001611      <div id="rfc.iref.w.2"></div>
    1601       <h3 id="rfc.section.3.6.1"><a href="#rfc.section.3.6.1">3.6.1</a>&nbsp;<a id="warn.110" href="#warn.110">110 Response is Stale</a></h3>
    1602       <p id="rfc.section.3.6.1.p.1">A cache <em class="bcp14">SHOULD</em> include this whenever the returned response is stale.
     1612      <h3 id="rfc.section.7.6.1"><a href="#rfc.section.7.6.1">7.6.1</a>&nbsp;<a id="warn.110" href="#warn.110">110 Response is Stale</a></h3>
     1613      <p id="rfc.section.7.6.1.p.1">A cache <em class="bcp14">SHOULD</em> include this whenever the returned response is stale.
    16031614      </p>
    16041615      <div id="rfc.iref.77"></div>
    16051616      <div id="rfc.iref.w.3"></div>
    1606       <h3 id="rfc.section.3.6.2"><a href="#rfc.section.3.6.2">3.6.2</a>&nbsp;<a id="warn.111" href="#warn.111">111 Revalidation Failed</a></h3>
    1607       <p id="rfc.section.3.6.2.p.1">A cache <em class="bcp14">SHOULD</em> include this when returning a stale response because an attempt to validate the response failed, due to an inability to reach
     1617      <h3 id="rfc.section.7.6.2"><a href="#rfc.section.7.6.2">7.6.2</a>&nbsp;<a id="warn.111" href="#warn.111">111 Revalidation Failed</a></h3>
     1618      <p id="rfc.section.7.6.2.p.1">A cache <em class="bcp14">SHOULD</em> include this when returning a stale response because an attempt to validate the response failed, due to an inability to reach
    16081619         the server.
    16091620      </p>
    16101621      <div id="rfc.iref.78"></div>
    16111622      <div id="rfc.iref.w.4"></div>
    1612       <h3 id="rfc.section.3.6.3"><a href="#rfc.section.3.6.3">3.6.3</a>&nbsp;<a id="warn.112" href="#warn.112">112 Disconnected Operation</a></h3>
    1613       <p id="rfc.section.3.6.3.p.1">A cache <em class="bcp14">SHOULD</em> include this if it is intentionally disconnected from the rest of the network for a period of time.
     1623      <h3 id="rfc.section.7.6.3"><a href="#rfc.section.7.6.3">7.6.3</a>&nbsp;<a id="warn.112" href="#warn.112">112 Disconnected Operation</a></h3>
     1624      <p id="rfc.section.7.6.3.p.1">A cache <em class="bcp14">SHOULD</em> include this if it is intentionally disconnected from the rest of the network for a period of time.
    16141625      </p>
    16151626      <div id="rfc.iref.79"></div>
    16161627      <div id="rfc.iref.w.5"></div>
    1617       <h3 id="rfc.section.3.6.4"><a href="#rfc.section.3.6.4">3.6.4</a>&nbsp;<a id="warn.113" href="#warn.113">113 Heuristic Expiration</a></h3>
    1618       <p id="rfc.section.3.6.4.p.1">A cache <em class="bcp14">SHOULD</em> include this if it heuristically chose a freshness lifetime greater than 24 hours and the response's age is greater than 24
     1628      <h3 id="rfc.section.7.6.4"><a href="#rfc.section.7.6.4">7.6.4</a>&nbsp;<a id="warn.113" href="#warn.113">113 Heuristic Expiration</a></h3>
     1629      <p id="rfc.section.7.6.4.p.1">A cache <em class="bcp14">SHOULD</em> include this if it heuristically chose a freshness lifetime greater than 24 hours and the response's age is greater than 24
    16191630         hours.
    16201631      </p>
    16211632      <div id="rfc.iref.80"></div>
    16221633      <div id="rfc.iref.w.6"></div>
    1623       <h3 id="rfc.section.3.6.5"><a href="#rfc.section.3.6.5">3.6.5</a>&nbsp;<a id="warn.199" href="#warn.199">199 Miscellaneous Warning</a></h3>
    1624       <p id="rfc.section.3.6.5.p.1">The warning text can 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.
     1634      <h3 id="rfc.section.7.6.5"><a href="#rfc.section.7.6.5">7.6.5</a>&nbsp;<a id="warn.199" href="#warn.199">199 Miscellaneous Warning</a></h3>
     1635      <p id="rfc.section.7.6.5.p.1">The warning text can 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.
    16251636      </p>
    16261637      <div id="rfc.iref.81"></div>
    16271638      <div id="rfc.iref.w.7"></div>
    1628       <h3 id="rfc.section.3.6.6"><a href="#rfc.section.3.6.6">3.6.6</a>&nbsp;<a id="warn.214" href="#warn.214">214 Transformation Applied</a></h3>
    1629       <p id="rfc.section.3.6.6.p.1"> <em class="bcp14">MUST</em> be added by a proxy if it applies any transformation to the representation, such as changing the content-coding, media-type,
     1639      <h3 id="rfc.section.7.6.6"><a href="#rfc.section.7.6.6">7.6.6</a>&nbsp;<a id="warn.214" href="#warn.214">214 Transformation Applied</a></h3>
     1640      <p id="rfc.section.7.6.6.p.1"> <em class="bcp14">MUST</em> be added by a proxy if it applies any transformation to the representation, such as changing the content-coding, media-type,
    16301641         or modifying the representation data, unless this Warning code already appears in the response.
    16311642      </p>
    16321643      <div id="rfc.iref.82"></div>
    16331644      <div id="rfc.iref.w.8"></div>
    1634       <h3 id="rfc.section.3.6.7"><a href="#rfc.section.3.6.7">3.6.7</a>&nbsp;<a id="warn.299" href="#warn.299">299 Miscellaneous Persistent Warning</a></h3>
    1635       <p id="rfc.section.3.6.7.p.1">The warning text can 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.
    1636       </p>
    1637       <h3 id="rfc.section.3.6.8"><a href="#rfc.section.3.6.8">3.6.8</a>&nbsp;<a id="warn.code.extensions" href="#warn.code.extensions">Warn Code Extensions</a></h3>
    1638       <p id="rfc.section.3.6.8.p.1">The HTTP Warn Code Registry defines the name space for warn codes.</p>
    1639       <p id="rfc.section.3.6.8.p.2">A registration <em class="bcp14">MUST</em> include the following fields:
     1645      <h3 id="rfc.section.7.6.7"><a href="#rfc.section.7.6.7">7.6.7</a>&nbsp;<a id="warn.299" href="#warn.299">299 Miscellaneous Persistent Warning</a></h3>
     1646      <p id="rfc.section.7.6.7.p.1">The warning text can 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.
     1647      </p>
     1648      <h3 id="rfc.section.7.6.8"><a href="#rfc.section.7.6.8">7.6.8</a>&nbsp;<a id="warn.code.extensions" href="#warn.code.extensions">Warn Code Extensions</a></h3>
     1649      <p id="rfc.section.7.6.8.p.1">The HTTP Warn Code Registry defines the name space for warn codes.</p>
     1650      <p id="rfc.section.7.6.8.p.2">A registration <em class="bcp14">MUST</em> include the following fields:
    16401651      </p>
    16411652      <ul>
     
    16441655         <li>Pointer to specification text</li>
    16451656      </ul>
    1646       <p id="rfc.section.3.6.8.p.3">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).
    1647       </p>
    1648       <p id="rfc.section.3.6.8.p.4">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-warn-codes">http://www.iana.org/assignments/http-warn-codes</a>&gt;.
    1649       </p>
    1650       <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="history.lists" href="#history.lists">History Lists</a></h1>
    1651       <p id="rfc.section.4.p.1">User agents often have history mechanisms, such as "Back" buttons and history lists, that can be used to redisplay a representation
     1657      <p id="rfc.section.7.6.8.p.3">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).
     1658      </p>
     1659      <p id="rfc.section.7.6.8.p.4">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-warn-codes">http://www.iana.org/assignments/http-warn-codes</a>&gt;.
     1660      </p>
     1661      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="history.lists" href="#history.lists">History Lists</a></h1>
     1662      <p id="rfc.section.8.p.1">User agents often have history mechanisms, such as "Back" buttons and history lists, that can be used to redisplay a representation
    16521663         retrieved earlier in a session.
    16531664      </p>
    1654       <p id="rfc.section.4.p.2">The freshness model (<a href="#expiration.model" title="Freshness Model">Section&nbsp;2.3</a>) does not necessarily apply to history mechanisms. I.e., a history mechanism can display a previous representation even if
     1665      <p id="rfc.section.8.p.2">The freshness model (<a href="#expiration.model" title="Freshness Model">Section&nbsp;4.1</a>) does not necessarily apply to history mechanisms. I.e., a history mechanism can display a previous representation even if
    16551666         it has expired.
    16561667      </p>
    1657       <p id="rfc.section.4.p.3">This does not prohibit the history mechanism from telling the user that a view might be stale, or from honoring cache directives
     1668      <p id="rfc.section.8.p.3">This does not prohibit the history mechanism from telling the user that a view might be stale, or from honoring cache directives
    16581669         (e.g., Cache-Control: no-store).
    16591670      </p>
    1660       <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
    1661       <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="cache.directive.registration" href="#cache.directive.registration">Cache Directive Registry</a></h2>
    1662       <p id="rfc.section.5.1.p.1">The registration procedure for HTTP Cache Directives is defined by <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;3.2.3</a> of this document.
    1663       </p>
    1664       <p id="rfc.section.5.1.p.2">The HTTP Cache Directive Registry shall be created at &lt;<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>&gt; and be populated with the registrations below:
     1671      <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
     1672      <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a id="cache.directive.registration" href="#cache.directive.registration">Cache Directive Registry</a></h2>
     1673      <p id="rfc.section.9.1.p.1">The registration procedure for HTTP Cache Directives is defined by <a href="#cache.control.extensions" title="Cache Control Extensions">Section&nbsp;7.2.3</a> of this document.
     1674      </p>
     1675      <p id="rfc.section.9.1.p.2">The HTTP Cache Directive Registry shall be created at &lt;<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>&gt; and be populated with the registrations below:
    16651676      </p>
    16661677      <div id="rfc.table.1">
     
    16761687               <tr>
    16771688                  <td class="left">max-age</td>
    1678                   <td class="left"> <a href="#cache-request-directive.max-age" title="max-age">Section&nbsp;3.2.1.3</a>, <a href="#cache-response-directive.max-age" title="max-age">Section&nbsp;3.2.2.7</a>
     1689                  <td class="left"> <a href="#cache-request-directive.max-age" title="max-age">Section&nbsp;7.2.1.3</a>, <a href="#cache-response-directive.max-age" title="max-age">Section&nbsp;7.2.2.7</a>
    16791690                  </td>
    16801691               </tr>
    16811692               <tr>
    16821693                  <td class="left">max-stale</td>
    1683                   <td class="left"> <a href="#cache-request-directive.max-stale" title="max-stale">Section&nbsp;3.2.1.4</a>
     1694                  <td class="left"> <a href="#cache-request-directive.max-stale" title="max-stale">Section&nbsp;7.2.1.4</a>
    16841695                  </td>
    16851696               </tr>
    16861697               <tr>
    16871698                  <td class="left">min-fresh</td>
    1688                   <td class="left"> <a href="#cache-request-directive.min-fresh" title="min-fresh">Section&nbsp;3.2.1.5</a>
     1699                  <td class="left"> <a href="#cache-request-directive.min-fresh" title="min-fresh">Section&nbsp;7.2.1.5</a>
    16891700                  </td>
    16901701               </tr>
    16911702               <tr>
    16921703                  <td class="left">must-revalidate</td>
    1693                   <td class="left"> <a href="#cache-response-directive.must-revalidate" title="must-revalidate">Section&nbsp;3.2.2.5</a>
     1704                  <td class="left"> <a href="#cache-response-directive.must-revalidate" title="must-revalidate">Section&nbsp;7.2.2.5</a>
    16941705                  </td>
    16951706               </tr>
    16961707               <tr>
    16971708                  <td class="left">no-cache</td>
    1698                   <td class="left"> <a href="#cache-request-directive.no-cache" title="no-cache">Section&nbsp;3.2.1.1</a>, <a href="#cache-response-directive.no-cache" title="no-cache">Section&nbsp;3.2.2.3</a>
     1709                  <td class="left"> <a href="#cache-request-directive.no-cache" title="no-cache">Section&nbsp;7.2.1.1</a>, <a href="#cache-response-directive.no-cache" title="no-cache">Section&nbsp;7.2.2.3</a>
    16991710                  </td>
    17001711               </tr>
    17011712               <tr>
    17021713                  <td class="left">no-store</td>
    1703                   <td class="left"> <a href="#cache-request-directive.no-store" title="no-store">Section&nbsp;3.2.1.2</a>, <a href="#cache-response-directive.no-store" title="no-store">Section&nbsp;3.2.2.4</a>
     1714                  <td class="left"> <a href="#cache-request-directive.no-store" title="no-store">Section&nbsp;7.2.1.2</a>, <a href="#cache-response-directive.no-store" title="no-store">Section&nbsp;7.2.2.4</a>
    17041715                  </td>
    17051716               </tr>
    17061717               <tr>
    17071718                  <td class="left">no-transform</td>
    1708                   <td class="left"> <a href="#cache-request-directive.no-transform" title="no-transform">Section&nbsp;3.2.1.6</a>, <a href="#cache-response-directive.no-transform" title="no-transform">Section&nbsp;3.2.2.9</a>
     1719                  <td class="left"> <a href="#cache-request-directive.no-transform" title="no-transform">Section&nbsp;7.2.1.6</a>, <a href="#cache-response-directive.no-transform" title="no-transform">Section&nbsp;7.2.2.9</a>
    17091720                  </td>
    17101721               </tr>
    17111722               <tr>
    17121723                  <td class="left">only-if-cached</td>
    1713                   <td class="left"> <a href="#cache-request-directive.only-if-cached" title="only-if-cached">Section&nbsp;3.2.1.7</a>
     1724                  <td class="left"> <a href="#cache-request-directive.only-if-cached" title="only-if-cached">Section&nbsp;7.2.1.7</a>
    17141725                  </td>
    17151726               </tr>
    17161727               <tr>
    17171728                  <td class="left">private</td>
    1718                   <td class="left"> <a href="#cache-response-directive.private" title="private">Section&nbsp;3.2.2.2</a>
     1729                  <td class="left"> <a href="#cache-response-directive.private" title="private">Section&nbsp;7.2.2.2</a>
    17191730                  </td>
    17201731               </tr>
    17211732               <tr>
    17221733                  <td class="left">proxy-revalidate</td>
    1723                   <td class="left"> <a href="#cache-response-directive.proxy-revalidate" title="proxy-revalidate">Section&nbsp;3.2.2.6</a>
     1734                  <td class="left"> <a href="#cache-response-directive.proxy-revalidate" title="proxy-revalidate">Section&nbsp;7.2.2.6</a>
    17241735                  </td>
    17251736               </tr>
    17261737               <tr>
    17271738                  <td class="left">public</td>
    1728                   <td class="left"> <a href="#cache-response-directive.only-if-cached" title="public">Section&nbsp;3.2.2.1</a>
     1739                  <td class="left"> <a href="#cache-response-directive.only-if-cached" title="public">Section&nbsp;7.2.2.1</a>
    17291740                  </td>
    17301741               </tr>
    17311742               <tr>
    17321743                  <td class="left">s-maxage</td>
    1733                   <td class="left"> <a href="#cache-response-directive.s-maxage" title="s-maxage">Section&nbsp;3.2.2.8</a>
     1744                  <td class="left"> <a href="#cache-response-directive.s-maxage" title="s-maxage">Section&nbsp;7.2.2.8</a>
    17341745                  </td>
    17351746               </tr>
     
    17471758         </table>
    17481759      </div>
    1749       <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a id="warn.code.registration" href="#warn.code.registration">Warn Code Registry</a></h2>
    1750       <p id="rfc.section.5.2.p.1">The registration procedure for HTTP Warn Codes is defined by <a href="#warn.code.extensions" title="Warn Code Extensions">Section&nbsp;3.6.8</a> of this document.
    1751       </p>
    1752       <p id="rfc.section.5.2.p.2">The HTTP Warn Code Registry shall be created at &lt;<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>&gt; and be populated with the registrations below:
     1760      <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a id="warn.code.registration" href="#warn.code.registration">Warn Code Registry</a></h2>
     1761      <p id="rfc.section.9.2.p.1">The registration procedure for HTTP Warn Codes is defined by <a href="#warn.code.extensions" title="Warn Code Extensions">Section&nbsp;7.6.8</a> of this document.
     1762      </p>
     1763      <p id="rfc.section.9.2.p.2">The HTTP Warn Code Registry shall be created at &lt;<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>&gt; and be populated with the registrations below:
    17531764      </p>
    17541765      <div id="rfc.table.2">
     
    17661777                  <td class="left">110</td>
    17671778                  <td class="left">Response is Stale</td>
    1768                   <td class="left"> <a href="#warn.110" id="rfc.xref.warn.110.1" title="110 Response is Stale">Section&nbsp;3.6.1</a>
     1779                  <td class="left"> <a href="#warn.110" id="rfc.xref.warn.110.1" title="110 Response is Stale">Section&nbsp;7.6.1</a>
    17691780                  </td>
    17701781               </tr>
     
    17721783                  <td class="left">111</td>
    17731784                  <td class="left">Revalidation Failed</td>
    1774                   <td class="left"> <a href="#warn.111" id="rfc.xref.warn.111.1" title="111 Revalidation Failed">Section&nbsp;3.6.2</a>
     1785                  <td class="left"> <a href="#warn.111" id="rfc.xref.warn.111.1" title="111 Revalidation Failed">Section&nbsp;7.6.2</a>
    17751786                  </td>
    17761787               </tr>
     
    17781789                  <td class="left">112</td>
    17791790                  <td class="left">Disconnected Operation</td>
    1780                   <td class="left"> <a href="#warn.112" id="rfc.xref.warn.112.1" title="112 Disconnected Operation">Section&nbsp;3.6.3</a>
     1791                  <td class="left"> <a href="#warn.112" id="rfc.xref.warn.112.1" title="112 Disconnected Operation">Section&nbsp;7.6.3</a>
    17811792                  </td>
    17821793               </tr>
     
    17841795                  <td class="left">113</td>
    17851796                  <td class="left">Heuristic Expiration</td>
    1786                   <td class="left"> <a href="#warn.113" id="rfc.xref.warn.113.1" title="113 Heuristic Expiration">Section&nbsp;3.6.4</a>
     1797                  <td class="left"> <a href="#warn.113" id="rfc.xref.warn.113.1" title="113 Heuristic Expiration">Section&nbsp;7.6.4</a>
    17871798                  </td>
    17881799               </tr>
     
    17901801                  <td class="left">199</td>
    17911802                  <td class="left">Miscellaneous Warning</td>
    1792                   <td class="left"> <a href="#warn.199" id="rfc.xref.warn.199.1" title="199 Miscellaneous Warning">Section&nbsp;3.6.5</a>
     1803                  <td class="left"> <a href="#warn.199" id="rfc.xref.warn.199.1" title="199 Miscellaneous Warning">Section&nbsp;7.6.5</a>
    17931804                  </td>
    17941805               </tr>
     
    17961807                  <td class="left">214</td>
    17971808                  <td class="left">Transformation Applied</td>
    1798                   <td class="left"> <a href="#warn.214" id="rfc.xref.warn.214.1" title="214 Transformation Applied">Section&nbsp;3.6.6</a>
     1809                  <td class="left"> <a href="#warn.214" id="rfc.xref.warn.214.1" title="214 Transformation Applied">Section&nbsp;7.6.6</a>
    17991810                  </td>
    18001811               </tr>
     
    18021813                  <td class="left">299</td>
    18031814                  <td class="left">Miscellaneous Persistent Warning</td>
    1804                   <td class="left"> <a href="#warn.299" id="rfc.xref.warn.299.1" title="299 Miscellaneous Persistent Warning">Section&nbsp;3.6.7</a>
     1815                  <td class="left"> <a href="#warn.299" id="rfc.xref.warn.299.1" title="299 Miscellaneous Persistent Warning">Section&nbsp;7.6.7</a>
    18051816                  </td>
    18061817               </tr>
     
    18081819         </table>
    18091820      </div>
    1810       <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;<a id="header.field.registration" href="#header.field.registration">Header Field Registration</a></h2>
    1811       <p id="rfc.section.5.3.p.1">The Message Header Field Registry located at &lt;<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>&gt; shall be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>):
     1821      <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a id="header.field.registration" href="#header.field.registration">Header Field Registration</a></h2>
     1822      <p id="rfc.section.9.3.p.1">The Message Header Field Registry located at &lt;<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>&gt; shall be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>):
    18121823      </p>
    18131824      <div id="rfc.table.3">
     
    18271838                  <td class="left">http</td>
    18281839                  <td class="left">standard</td>
    1829                   <td class="left"> <a href="#header.age" id="rfc.xref.header.age.3" title="Age">Section&nbsp;3.1</a>
     1840                  <td class="left"> <a href="#header.age" id="rfc.xref.header.age.3" title="Age">Section&nbsp;7.1</a>
    18301841                  </td>
    18311842               </tr>
     
    18341845                  <td class="left">http</td>
    18351846                  <td class="left">standard</td>
    1836                   <td class="left"> <a href="#header.cache-control" id="rfc.xref.header.cache-control.2" title="Cache-Control">Section&nbsp;3.2</a>
     1847                  <td class="left"> <a href="#header.cache-control" id="rfc.xref.header.cache-control.2" title="Cache-Control">Section&nbsp;7.2</a>
    18371848                  </td>
    18381849               </tr>
     
    18411852                  <td class="left">http</td>
    18421853                  <td class="left">standard</td>
    1843                   <td class="left"> <a href="#header.expires" id="rfc.xref.header.expires.4" title="Expires">Section&nbsp;3.3</a>
     1854                  <td class="left"> <a href="#header.expires" id="rfc.xref.header.expires.4" title="Expires">Section&nbsp;7.3</a>
    18441855                  </td>
    18451856               </tr>
     
    18481859                  <td class="left">http</td>
    18491860                  <td class="left">standard</td>
    1850                   <td class="left"> <a href="#header.pragma" id="rfc.xref.header.pragma.3" title="Pragma">Section&nbsp;3.4</a>
     1861                  <td class="left"> <a href="#header.pragma" id="rfc.xref.header.pragma.3" title="Pragma">Section&nbsp;7.4</a>
    18511862                  </td>
    18521863               </tr>
     
    18551866                  <td class="left">http</td>
    18561867                  <td class="left">standard</td>
    1857                   <td class="left"> <a href="#header.vary" id="rfc.xref.header.vary.2" title="Vary">Section&nbsp;3.5</a>
     1868                  <td class="left"> <a href="#header.vary" id="rfc.xref.header.vary.2" title="Vary">Section&nbsp;7.5</a>
    18581869                  </td>
    18591870               </tr>
     
    18621873                  <td class="left">http</td>
    18631874                  <td class="left">standard</td>
    1864                   <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section&nbsp;3.6</a>
     1875                  <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section&nbsp;7.6</a>
    18651876                  </td>
    18661877               </tr>
     
    18681879         </table>
    18691880      </div>
    1870       <p id="rfc.section.5.3.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
    1871       <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
    1872       <p id="rfc.section.6.p.1">Caches expose additional potential vulnerabilities, since the contents of the cache represent an attractive target for malicious
     1881      <p id="rfc.section.9.3.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
     1882      <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
     1883      <p id="rfc.section.10.p.1">Caches expose additional potential vulnerabilities, since the contents of the cache represent an attractive target for malicious
    18731884         exploitation. Because cache contents persist after an HTTP request is complete, an attack on the cache can reveal information
    18741885         long after a user believes that the information has been removed from the network. Therefore, cache contents need to be protected
    18751886         as sensitive information.
    18761887      </p>
    1877       <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="acks" href="#acks">Acknowledgments</a></h1>
    1878       <p id="rfc.section.7.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 9</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>.
    1879       </p>
    1880       <h1 id="rfc.references"><a id="rfc.section.8" href="#rfc.section.8">8.</a> References
     1888      <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a>&nbsp;<a id="acks" href="#acks">Acknowledgments</a></h1>
     1889      <p id="rfc.section.11.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 9</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>.
     1890      </p>
     1891      <h1 id="rfc.references"><a id="rfc.section.12" href="#rfc.section.12">12.</a> References
    18811892      </h1>
    1882       <h2 id="rfc.references.1"><a href="#rfc.section.8.1" id="rfc.section.8.1">8.1</a> Normative References
     1893      <h2 id="rfc.references.1"><a href="#rfc.section.12.1" id="rfc.section.12.1">12.1</a> Normative References
    18831894      </h2>
    18841895      <table>             
     
    19191930         </tr>
    19201931      </table>
    1921       <h2 id="rfc.references.2"><a href="#rfc.section.8.2" id="rfc.section.8.2">8.2</a> Informative References
     1932      <h2 id="rfc.references.2"><a href="#rfc.section.12.2" id="rfc.section.12.2">12.2</a> Informative References
    19221933      </h2>
    19231934      <table>         
     
    19641975      </div>
    19651976      <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1>
    1966       <p id="rfc.section.A.p.1">Make the specified age calculation algorithm less conservative. (<a href="#age.calculations" title="Calculating Age">Section&nbsp;2.3.2</a>)
    1967       </p>
    1968       <p id="rfc.section.A.p.2">Remove requirement to consider <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> in successful responses in order to determine the appropriate response to use. (<a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>)
    1969       </p>
    1970       <p id="rfc.section.A.p.3">Clarify denial of service attack avoidance requirement. (<a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;2.6</a>)
    1971       </p>
    1972       <p id="rfc.section.A.p.4">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section&nbsp;3</a>)
    1973       </p>
    1974       <p id="rfc.section.A.p.5">Do not mention RFC 2047 encoding and multiple languages in <a href="#header.warning" class="smpl">Warning</a> header fields anymore, as these aspects never were implemented. (<a href="#header.warning" id="rfc.xref.header.warning.6" title="Warning">Section&nbsp;3.6</a>)
     1977      <p id="rfc.section.A.p.1">Make the specified age calculation algorithm less conservative. (<a href="#age.calculations" title="Calculating Age">Section&nbsp;4.1.3</a>)
     1978      </p>
     1979      <p id="rfc.section.A.p.2">Remove requirement to consider <a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> in successful responses in order to determine the appropriate response to use. (<a href="#validation.model" title="Validation Model">Section&nbsp;4.2</a>)
     1980      </p>
     1981      <p id="rfc.section.A.p.3">Clarify denial of service attack avoidance requirement. (<a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section&nbsp;6</a>)
     1982      </p>
     1983      <p id="rfc.section.A.p.4">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section&nbsp;7</a>)
     1984      </p>
     1985      <p id="rfc.section.A.p.5">Do not mention RFC 2047 encoding and multiple languages in <a href="#header.warning" class="smpl">Warning</a> header fields anymore, as these aspects never were implemented. (<a href="#header.warning" id="rfc.xref.header.warning.6" title="Warning">Section&nbsp;7.6</a>)
    19751986      </p>
    19761987      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1>
     
    20512062         <ul class="ind">
    20522063            <li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul>
    2053                   <li>110 Response is Stale (warn code)&nbsp;&nbsp;<a href="#rfc.iref.76"><b>3.6.1</b></a>, <a href="#rfc.xref.warn.110.1">5.2</a></li>
    2054                   <li>111 Revalidation Failed (warn code)&nbsp;&nbsp;<a href="#rfc.iref.77"><b>3.6.2</b></a>, <a href="#rfc.xref.warn.111.1">5.2</a></li>
    2055                   <li>112 Disconnected Operation (warn code)&nbsp;&nbsp;<a href="#rfc.iref.78"><b>3.6.3</b></a>, <a href="#rfc.xref.warn.112.1">5.2</a></li>
    2056                   <li>113 Heuristic Expiration (warn code)&nbsp;&nbsp;<a href="#rfc.iref.79"><b>3.6.4</b></a>, <a href="#rfc.xref.warn.113.1">5.2</a></li>
    2057                   <li>199 Miscellaneous Warning (warn code)&nbsp;&nbsp;<a href="#rfc.iref.80"><b>3.6.5</b></a>, <a href="#rfc.xref.warn.199.1">5.2</a></li>
     2064                  <li>110 Response is Stale (warn code)&nbsp;&nbsp;<a href="#rfc.iref.76"><b>7.6.1</b></a>, <a href="#rfc.xref.warn.110.1">9.2</a></li>
     2065                  <li>111 Revalidation Failed (warn code)&nbsp;&nbsp;<a href="#rfc.iref.77"><b>7.6.2</b></a>, <a href="#rfc.xref.warn.111.1">9.2</a></li>
     2066                  <li>112 Disconnected Operation (warn code)&nbsp;&nbsp;<a href="#rfc.iref.78"><b>7.6.3</b></a>, <a href="#rfc.xref.warn.112.1">9.2</a></li>
     2067                  <li>113 Heuristic Expiration (warn code)&nbsp;&nbsp;<a href="#rfc.iref.79"><b>7.6.4</b></a>, <a href="#rfc.xref.warn.113.1">9.2</a></li>
     2068                  <li>199 Miscellaneous Warning (warn code)&nbsp;&nbsp;<a href="#rfc.iref.80"><b>7.6.5</b></a>, <a href="#rfc.xref.warn.199.1">9.2</a></li>
    20582069               </ul>
    20592070            </li>
    20602071            <li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul>
    2061                   <li>214 Transformation Applied (warn code)&nbsp;&nbsp;<a href="#rfc.iref.81"><b>3.6.6</b></a>, <a href="#rfc.xref.warn.214.1">5.2</a></li>
    2062                   <li>299 Miscellaneous Persistent Warning (warn code)&nbsp;&nbsp;<a href="#rfc.iref.82"><b>3.6.7</b></a>, <a href="#rfc.xref.warn.299.1">5.2</a></li>
     2072                  <li>214 Transformation Applied (warn code)&nbsp;&nbsp;<a href="#rfc.iref.81"><b>7.6.6</b></a>, <a href="#rfc.xref.warn.214.1">9.2</a></li>
     2073                  <li>299 Miscellaneous Persistent Warning (warn code)&nbsp;&nbsp;<a href="#rfc.iref.82"><b>7.6.7</b></a>, <a href="#rfc.xref.warn.299.1">9.2</a></li>
    20632074               </ul>
    20642075            </li>
    20652076            <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul>
    20662077                  <li>age&nbsp;&nbsp;<a href="#rfc.iref.a.1">1.2</a></li>
    2067                   <li>Age header field&nbsp;&nbsp;<a href="#rfc.xref.header.age.1">2.2</a>, <a href="#rfc.xref.header.age.2">2.3.2</a>, <a href="#rfc.iref.a.2"><b>3.1</b></a>, <a href="#rfc.xref.header.age.3">5.3</a></li>
     2078                  <li>Age header field&nbsp;&nbsp;<a href="#rfc.xref.header.age.1">4</a>, <a href="#rfc.xref.header.age.2">4.1.3</a>, <a href="#rfc.iref.a.2"><b>7.1</b></a>, <a href="#rfc.xref.header.age.3">9.3</a></li>
    20682079               </ul>
    20692080            </li>
     
    20722083                  <li>Cache Directives&nbsp;&nbsp;
    20732084                     <ul>
    2074                         <li>max-age&nbsp;&nbsp;<a href="#rfc.iref.c.9"><b>3.2.1.3</b></a>, <a href="#rfc.iref.c.20"><b>3.2.2.7</b></a></li>
    2075                         <li>max-stale&nbsp;&nbsp;<a href="#rfc.iref.c.10"><b>3.2.1.4</b></a></li>
    2076                         <li>min-fresh&nbsp;&nbsp;<a href="#rfc.iref.c.11"><b>3.2.1.5</b></a></li>
    2077                         <li>must-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.18"><b>3.2.2.5</b></a></li>
    2078                         <li>no-cache&nbsp;&nbsp;<a href="#rfc.iref.c.7"><b>3.2.1.1</b></a>, <a href="#rfc.iref.c.16"><b>3.2.2.3</b></a></li>
    2079                         <li>no-store&nbsp;&nbsp;<a href="#rfc.iref.c.8"><b>3.2.1.2</b></a>, <a href="#rfc.iref.c.17"><b>3.2.2.4</b></a></li>
    2080                         <li>no-transform&nbsp;&nbsp;<a href="#rfc.iref.c.12"><b>3.2.1.6</b></a>, <a href="#rfc.iref.c.22"><b>3.2.2.9</b></a></li>
    2081                         <li>only-if-cached&nbsp;&nbsp;<a href="#rfc.iref.c.13"><b>3.2.1.7</b></a></li>
    2082                         <li>private&nbsp;&nbsp;<a href="#rfc.iref.c.15"><b>3.2.2.2</b></a></li>
    2083                         <li>proxy-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.19"><b>3.2.2.6</b></a></li>
    2084                         <li>public&nbsp;&nbsp;<a href="#rfc.iref.c.14"><b>3.2.2.1</b></a></li>
    2085                         <li>s-maxage&nbsp;&nbsp;<a href="#rfc.iref.c.21"><b>3.2.2.8</b></a></li>
     2085                        <li>max-age&nbsp;&nbsp;<a href="#rfc.iref.c.9"><b>7.2.1.3</b></a>, <a href="#rfc.iref.c.20"><b>7.2.2.7</b></a></li>
     2086                        <li>max-stale&nbsp;&nbsp;<a href="#rfc.iref.c.10"><b>7.2.1.4</b></a></li>
     2087                        <li>min-fresh&nbsp;&nbsp;<a href="#rfc.iref.c.11"><b>7.2.1.5</b></a></li>
     2088                        <li>must-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.18"><b>7.2.2.5</b></a></li>
     2089                        <li>no-cache&nbsp;&nbsp;<a href="#rfc.iref.c.7"><b>7.2.1.1</b></a>, <a href="#rfc.iref.c.16"><b>7.2.2.3</b></a></li>
     2090                        <li>no-store&nbsp;&nbsp;<a href="#rfc.iref.c.8"><b>7.2.1.2</b></a>, <a href="#rfc.iref.c.17"><b>7.2.2.4</b></a></li>
     2091                        <li>no-transform&nbsp;&nbsp;<a href="#rfc.iref.c.12"><b>7.2.1.6</b></a>, <a href="#rfc.iref.c.22"><b>7.2.2.9</b></a></li>
     2092                        <li>only-if-cached&nbsp;&nbsp;<a href="#rfc.iref.c.13"><b>7.2.1.7</b></a></li>
     2093                        <li>private&nbsp;&nbsp;<a href="#rfc.iref.c.15"><b>7.2.2.2</b></a></li>
     2094                        <li>proxy-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.19"><b>7.2.2.6</b></a></li>
     2095                        <li>public&nbsp;&nbsp;<a href="#rfc.iref.c.14"><b>7.2.2.1</b></a></li>
     2096                        <li>s-maxage&nbsp;&nbsp;<a href="#rfc.iref.c.21"><b>7.2.2.8</b></a></li>
    20862097                     </ul>
    20872098                  </li>
    20882099                  <li>cache entry&nbsp;&nbsp;<a href="#rfc.iref.c.4">2</a></li>
    20892100                  <li>cache key&nbsp;&nbsp;<a href="#rfc.iref.c.5">2</a></li>
    2090                   <li>Cache-Control header field&nbsp;&nbsp;<a href="#rfc.xref.header.cache-control.1">2.1</a>, <a href="#rfc.iref.c.6"><b>3.2</b></a>, <a href="#rfc.xref.header.cache-control.2">5.3</a></li>
     2101                  <li>Cache-Control header field&nbsp;&nbsp;<a href="#rfc.xref.header.cache-control.1">3</a>, <a href="#rfc.iref.c.6"><b>7.2</b></a>, <a href="#rfc.xref.header.cache-control.2">9.3</a></li>
    20912102                  <li>cacheable&nbsp;&nbsp;<a href="#rfc.iref.c.3">1.2</a></li>
    20922103               </ul>
    20932104            </li>
    20942105            <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul>
    2095                   <li>Expires header field&nbsp;&nbsp;<a href="#rfc.xref.header.expires.1">2.1</a>, <a href="#rfc.xref.header.expires.2">2.3</a>, <a href="#rfc.xref.header.expires.3">2.3.1</a>, <a href="#rfc.iref.e.2"><b>3.3</b></a>, <a href="#rfc.xref.header.expires.4">5.3</a></li>
     2106                  <li>Expires header field&nbsp;&nbsp;<a href="#rfc.xref.header.expires.1">3</a>, <a href="#rfc.xref.header.expires.2">4.1</a>, <a href="#rfc.xref.header.expires.3">4.1.1</a>, <a href="#rfc.iref.e.2"><b>7.3</b></a>, <a href="#rfc.xref.header.expires.4">9.3</a></li>
    20962107                  <li>explicit expiration time&nbsp;&nbsp;<a href="#rfc.iref.e.1">1.2</a></li>
    20972108               </ul>
     
    21062117                  <li><tt>Grammar</tt>&nbsp;&nbsp;
    21072118                     <ul>
    2108                         <li><tt>Age</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>3.1</b></a></li>
    2109                         <li><tt>Cache-Control</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>3.2</b></a></li>
    2110                         <li><tt>cache-directive</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>3.2</b></a></li>
     2119                        <li><tt>Age</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>7.1</b></a></li>
     2120                        <li><tt>Cache-Control</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>7.2</b></a></li>
     2121                        <li><tt>cache-directive</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>7.2</b></a></li>
    21112122                        <li><tt>delta-seconds</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>1.4.3</b></a></li>
    2112                         <li><tt>Expires</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>3.3</b></a></li>
    2113                         <li><tt>extension-pragma</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>3.4</b></a></li>
    2114                         <li><tt>Pragma</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>3.4</b></a></li>
    2115                         <li><tt>pragma-directive</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>3.4</b></a></li>
    2116                         <li><tt>Vary</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>3.5</b></a></li>
    2117                         <li><tt>warn-agent</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.13"><b>3.6</b></a></li>
    2118                         <li><tt>warn-code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>3.6</b></a></li>
    2119                         <li><tt>warn-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>3.6</b></a></li>
    2120                         <li><tt>warn-text</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>3.6</b></a></li>
    2121                         <li><tt>Warning</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>3.6</b></a></li>
    2122                         <li><tt>warning-value</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>3.6</b></a></li>
     2123                        <li><tt>Expires</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>7.3</b></a></li>
     2124                        <li><tt>extension-pragma</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>7.4</b></a></li>
     2125                        <li><tt>Pragma</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>7.4</b></a></li>
     2126                        <li><tt>pragma-directive</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>7.4</b></a></li>
     2127                        <li><tt>Vary</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>7.5</b></a></li>
     2128                        <li><tt>warn-agent</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.13"><b>7.6</b></a></li>
     2129                        <li><tt>warn-code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>7.6</b></a></li>
     2130                        <li><tt>warn-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>7.6</b></a></li>
     2131                        <li><tt>warn-text</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>7.6</b></a></li>
     2132                        <li><tt>Warning</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>7.6</b></a></li>
     2133                        <li><tt>warning-value</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>7.6</b></a></li>
    21232134                     </ul>
    21242135                  </li>
     
    21282139                  <li>Header Fields&nbsp;&nbsp;
    21292140                     <ul>
    2130                         <li>Age&nbsp;&nbsp;<a href="#rfc.xref.header.age.1">2.2</a>, <a href="#rfc.xref.header.age.2">2.3.2</a>, <a href="#rfc.iref.h.2"><b>3.1</b></a>, <a href="#rfc.xref.header.age.3">5.3</a></li>
    2131                         <li>Cache-Control&nbsp;&nbsp;<a href="#rfc.xref.header.cache-control.1">2.1</a>, <a href="#rfc.iref.h.3"><b>3.2</b></a>, <a href="#rfc.xref.header.cache-control.2">5.3</a></li>
    2132                         <li>Expires&nbsp;&nbsp;<a href="#rfc.xref.header.expires.1">2.1</a>, <a href="#rfc.xref.header.expires.2">2.3</a>, <a href="#rfc.xref.header.expires.3">2.3.1</a>, <a href="#rfc.iref.h.4"><b>3.3</b></a>, <a href="#rfc.xref.header.expires.4">5.3</a></li>
    2133                         <li>Pragma&nbsp;&nbsp;<a href="#rfc.xref.header.pragma.1">2.2</a>, <a href="#rfc.xref.header.pragma.2">3.2</a>, <a href="#rfc.iref.h.5"><b>3.4</b></a>, <a href="#rfc.xref.header.pragma.3">5.3</a></li>
    2134                         <li>Vary&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.8</a>, <a href="#rfc.iref.h.6"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.3</a></li>
    2135                         <li>Warning&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.5</a>, <a href="#rfc.xref.header.warning.4">2.9</a>, <a href="#rfc.iref.h.7"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.5">5.3</a>, <a href="#rfc.xref.header.warning.6">A</a></li>
     2141                        <li>Age&nbsp;&nbsp;<a href="#rfc.xref.header.age.1">4</a>, <a href="#rfc.xref.header.age.2">4.1.3</a>, <a href="#rfc.iref.h.2"><b>7.1</b></a>, <a href="#rfc.xref.header.age.3">9.3</a></li>
     2142                        <li>Cache-Control&nbsp;&nbsp;<a href="#rfc.xref.header.cache-control.1">3</a>, <a href="#rfc.iref.h.3"><b>7.2</b></a>, <a href="#rfc.xref.header.cache-control.2">9.3</a></li>
     2143                        <li>Expires&nbsp;&nbsp;<a href="#rfc.xref.header.expires.1">3</a>, <a href="#rfc.xref.header.expires.2">4.1</a>, <a href="#rfc.xref.header.expires.3">4.1.1</a>, <a href="#rfc.iref.h.4"><b>7.3</b></a>, <a href="#rfc.xref.header.expires.4">9.3</a></li>
     2144                        <li>Pragma&nbsp;&nbsp;<a href="#rfc.xref.header.pragma.1">4</a>, <a href="#rfc.xref.header.pragma.2">7.2</a>, <a href="#rfc.iref.h.5"><b>7.4</b></a>, <a href="#rfc.xref.header.pragma.3">9.3</a></li>
     2145                        <li>Vary&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">4.3</a>, <a href="#rfc.iref.h.6"><b>7.5</b></a>, <a href="#rfc.xref.header.vary.2">9.3</a></li>
     2146                        <li>Warning&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">4.1.4</a>, <a href="#rfc.xref.header.warning.2">4.2.1</a>, <a href="#rfc.xref.header.warning.3">4.4</a>, <a href="#rfc.xref.header.warning.4">5</a>, <a href="#rfc.iref.h.7"><b>7.6</b></a>, <a href="#rfc.xref.header.warning.5">9.3</a>, <a href="#rfc.xref.header.warning.6">A</a></li>
    21362147                     </ul>
    21372148                  </li>
     
    21422153                  <li>max-age&nbsp;&nbsp;
    21432154                     <ul>
    2144                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.1"><b>3.2.1.3</b></a>, <a href="#rfc.iref.m.5"><b>3.2.2.7</b></a></li>
     2155                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.1"><b>7.2.1.3</b></a>, <a href="#rfc.iref.m.5"><b>7.2.2.7</b></a></li>
    21452156                     </ul>
    21462157                  </li>
    21472158                  <li>max-stale&nbsp;&nbsp;
    21482159                     <ul>
    2149                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.2"><b>3.2.1.4</b></a></li>
     2160                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.2"><b>7.2.1.4</b></a></li>
    21502161                     </ul>
    21512162                  </li>
    21522163                  <li>min-fresh&nbsp;&nbsp;
    21532164                     <ul>
    2154                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.3"><b>3.2.1.5</b></a></li>
     2165                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.3"><b>7.2.1.5</b></a></li>
    21552166                     </ul>
    21562167                  </li>
    21572168                  <li>must-revalidate&nbsp;&nbsp;
    21582169                     <ul>
    2159                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.4"><b>3.2.2.5</b></a></li>
     2170                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.m.4"><b>7.2.2.5</b></a></li>
    21602171                     </ul>
    21612172                  </li>
     
    21652176                  <li>no-cache&nbsp;&nbsp;
    21662177                     <ul>
    2167                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.n.1"><b>3.2.1.1</b></a>, <a href="#rfc.iref.n.4"><b>3.2.2.3</b></a></li>
     2178                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.n.1"><b>7.2.1.1</b></a>, <a href="#rfc.iref.n.4"><b>7.2.2.3</b></a></li>
    21682179                     </ul>
    21692180                  </li>
    21702181                  <li>no-store&nbsp;&nbsp;
    21712182                     <ul>
    2172                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.n.2"><b>3.2.1.2</b></a>, <a href="#rfc.iref.n.5"><b>3.2.2.4</b></a></li>
     2183                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.n.2"><b>7.2.1.2</b></a>, <a href="#rfc.iref.n.5"><b>7.2.2.4</b></a></li>
    21732184                     </ul>
    21742185                  </li>
    21752186                  <li>no-transform&nbsp;&nbsp;
    21762187                     <ul>
    2177                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.n.3"><b>3.2.1.6</b></a>, <a href="#rfc.iref.n.6"><b>3.2.2.9</b></a></li>
     2188                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.n.3"><b>7.2.1.6</b></a>, <a href="#rfc.iref.n.6"><b>7.2.2.9</b></a></li>
    21782189                     </ul>
    21792190                  </li>
     
    21832194                  <li>only-if-cached&nbsp;&nbsp;
    21842195                     <ul>
    2185                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.o.1"><b>3.2.1.7</b></a></li>
     2196                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.o.1"><b>7.2.1.7</b></a></li>
    21862197                     </ul>
    21872198                  </li>
     
    21892200            </li>
    21902201            <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
    2191                   <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.3</a>, <a href="#rfc.xref.Part1.2">1.4</a>, <a href="#rfc.xref.Part1.3">1.4.1</a>, <a href="#rfc.xref.Part1.4">1.4.1</a>, <a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a>, <a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.9">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a>, <a href="#rfc.xref.Part1.11">2.1</a>, <a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.6</a>, <a href="#rfc.xref.Part1.14">2.6</a>, <a href="#rfc.xref.Part1.15">2.6</a>, <a href="#rfc.xref.Part1.16">2.8</a>, <a href="#rfc.xref.Part1.17">7</a>, <a href="#Part1"><b>8.1</b></a><ul>
     2202                  <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.3</a>, <a href="#rfc.xref.Part1.2">1.4</a>, <a href="#rfc.xref.Part1.3">1.4.1</a>, <a href="#rfc.xref.Part1.4">1.4.1</a>, <a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a>, <a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.9">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a>, <a href="#rfc.xref.Part1.11">3.1</a>, <a href="#rfc.xref.Part1.12">4</a>, <a href="#rfc.xref.Part1.13">4.3</a>, <a href="#rfc.xref.Part1.14">6</a>, <a href="#rfc.xref.Part1.15">6</a>, <a href="#rfc.xref.Part1.16">6</a>, <a href="#rfc.xref.Part1.17">11</a>, <a href="#Part1"><b>12.1</b></a><ul>
    21922203                        <li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">1.4</a></li>
    21932204                        <li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.3</a></li>
    21942205                        <li><em>Section 2.7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a></li>
    21952206                        <li><em>Section 3.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.4">1.4.1</a></li>
    2196                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.16">2.8</a></li>
     2207                        <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.13">4.3</a></li>
    21972208                        <li><em>Section 3.2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a></li>
    2198                         <li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.6</a>, <a href="#rfc.xref.Part1.14">2.6</a>, <a href="#rfc.xref.Part1.15">2.6</a></li>
     2209                        <li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.12">4</a>, <a href="#rfc.xref.Part1.14">6</a>, <a href="#rfc.xref.Part1.15">6</a>, <a href="#rfc.xref.Part1.16">6</a></li>
    21992210                        <li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.9">1.4.2</a></li>
    2200                         <li><em>Section 9</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.17">7</a></li>
    2201                      </ul>
    2202                   </li>
    2203                   <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.2">2</a>, <a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.4">2.3.1.1</a>, <a href="#rfc.xref.Part2.5">2.3.2</a>, <a href="#rfc.xref.Part2.6">2.6</a>, <a href="#rfc.xref.Part2.7">3.3</a>, <a href="#Part2"><b>8.1</b></a><ul>
    2204                         <li><em>Section 2.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.6">2.6</a></li>
    2205                         <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.4">2.3.1.1</a></li>
    2206                         <li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.7">3.3</a></li>
    2207                         <li><em>Section 9.10</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.5">2.3.2</a></li>
    2208                      </ul>
    2209                   </li>
    2210                   <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">1.2</a>, <a href="#rfc.xref.Part4.2">1.2</a>, <a href="#rfc.xref.Part4.3">1.2</a>, <a href="#rfc.xref.Part4.4">2.3.1.1</a>, <a href="#rfc.xref.Part4.5">2.4</a>, <a href="#Part4"><b>8.1</b></a><ul>
     2211                        <li><em>Section 9</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.17">11</a></li>
     2212                     </ul>
     2213                  </li>
     2214                  <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.2">2</a>, <a href="#rfc.xref.Part2.3">4</a>, <a href="#rfc.xref.Part2.4">4.1.2</a>, <a href="#rfc.xref.Part2.5">4.1.3</a>, <a href="#rfc.xref.Part2.6">6</a>, <a href="#rfc.xref.Part2.7">7.3</a>, <a href="#Part2"><b>12.1</b></a><ul>
     2215                        <li><em>Section 2.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.3">4</a>, <a href="#rfc.xref.Part2.6">6</a></li>
     2216                        <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.4">4.1.2</a></li>
     2217                        <li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.7">7.3</a></li>
     2218                        <li><em>Section 9.10</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.5">4.1.3</a></li>
     2219                     </ul>
     2220                  </li>
     2221                  <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">1.2</a>, <a href="#rfc.xref.Part4.2">1.2</a>, <a href="#rfc.xref.Part4.3">1.2</a>, <a href="#rfc.xref.Part4.4">4.1.2</a>, <a href="#rfc.xref.Part4.5">4.2</a>, <a href="#Part4"><b>12.1</b></a><ul>
    22112222                        <li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">1.2</a></li>
    2212                         <li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.4">2.3.1.1</a></li>
     2223                        <li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.4">4.1.2</a></li>
    22132224                        <li><em>Section 2.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">1.2</a></li>
    22142225                        <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.2">1.2</a></li>
    22152226                     </ul>
    22162227                  </li>
    2217                   <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.1</a>, <a href="#rfc.xref.Part5.2">2.9</a>, <a href="#rfc.xref.Part5.3">2.9</a>, <a href="#Part5"><b>8.1</b></a><ul>
    2218                         <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.3">2.9</a></li>
    2219                      </ul>
    2220                   </li>
    2221                   <li><em>Part7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.7</a>, <a href="#Part7"><b>8.1</b></a><ul>
    2222                         <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.7</a></li>
    2223                      </ul>
    2224                   </li>
    2225                   <li>Pragma header field&nbsp;&nbsp;<a href="#rfc.xref.header.pragma.1">2.2</a>, <a href="#rfc.xref.header.pragma.2">3.2</a>, <a href="#rfc.iref.p.5"><b>3.4</b></a>, <a href="#rfc.xref.header.pragma.3">5.3</a></li>
     2228                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">3.1</a>, <a href="#rfc.xref.Part5.2">4.4</a>, <a href="#rfc.xref.Part5.3">4.4</a>, <a href="#Part5"><b>12.1</b></a><ul>
     2229                        <li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.3">4.4</a></li>
     2230                     </ul>
     2231                  </li>
     2232                  <li><em>Part7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">3</a>, <a href="#rfc.xref.Part7.2">3.2</a>, <a href="#Part7"><b>12.1</b></a><ul>
     2233                        <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">3</a>, <a href="#rfc.xref.Part7.2">3.2</a></li>
     2234                     </ul>
     2235                  </li>
     2236                  <li>Pragma header field&nbsp;&nbsp;<a href="#rfc.xref.header.pragma.1">4</a>, <a href="#rfc.xref.header.pragma.2">7.2</a>, <a href="#rfc.iref.p.5"><b>7.4</b></a>, <a href="#rfc.xref.header.pragma.3">9.3</a></li>
    22262237                  <li>private&nbsp;&nbsp;
    22272238                     <ul>
    2228                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.p.3"><b>3.2.2.2</b></a></li>
     2239                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.p.3"><b>7.2.2.2</b></a></li>
    22292240                     </ul>
    22302241                  </li>
     
    22322243                  <li>proxy-revalidate&nbsp;&nbsp;
    22332244                     <ul>
    2234                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.p.4"><b>3.2.2.6</b></a></li>
     2245                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.p.4"><b>7.2.2.6</b></a></li>
    22352246                     </ul>
    22362247                  </li>
    22372248                  <li>public&nbsp;&nbsp;
    22382249                     <ul>
    2239                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.p.2"><b>3.2.2.1</b></a></li>
     2250                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.p.2"><b>7.2.2.1</b></a></li>
    22402251                     </ul>
    22412252                  </li>
     
    22432254            </li>
    22442255            <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul>
    2245                   <li><em>RFC1305</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1305.1">2.2</a>, <a href="#rfc.xref.RFC1305.2">2.3.2</a>, <a href="#RFC1305"><b>8.2</b></a></li>
    2246                   <li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.3</a>, <a href="#RFC2119"><b>8.1</b></a></li>
    2247                   <li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">2.3.1.1</a>, <a href="#RFC2616"><b>8.2</b></a><ul>
    2248                         <li><em>Section 13.9</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">2.3.1.1</a></li>
    2249                      </ul>
    2250                   </li>
    2251                   <li><em>RFC3864</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3864.1">5.3</a>, <a href="#RFC3864"><b>8.2</b></a></li>
    2252                   <li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">3.2.3</a>, <a href="#rfc.xref.RFC5226.2">3.6.8</a>, <a href="#RFC5226"><b>8.2</b></a><ul>
    2253                         <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">3.2.3</a>, <a href="#rfc.xref.RFC5226.2">3.6.8</a></li>
    2254                      </ul>
    2255                   </li>
    2256                   <li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.4</a>, <a href="#rfc.xref.RFC5234.2">1.4</a>, <a href="#RFC5234"><b>8.1</b></a><ul>
     2256                  <li><em>RFC1305</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1305.1">4</a>, <a href="#rfc.xref.RFC1305.2">4.1.3</a>, <a href="#RFC1305"><b>12.2</b></a></li>
     2257                  <li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.3</a>, <a href="#RFC2119"><b>12.1</b></a></li>
     2258                  <li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">4.1.2</a>, <a href="#RFC2616"><b>12.2</b></a><ul>
     2259                        <li><em>Section 13.9</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">4.1.2</a></li>
     2260                     </ul>
     2261                  </li>
     2262                  <li><em>RFC3864</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3864.1">9.3</a>, <a href="#RFC3864"><b>12.2</b></a></li>
     2263                  <li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">7.2.3</a>, <a href="#rfc.xref.RFC5226.2">7.6.8</a>, <a href="#RFC5226"><b>12.2</b></a><ul>
     2264                        <li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">7.2.3</a>, <a href="#rfc.xref.RFC5226.2">7.6.8</a></li>
     2265                     </ul>
     2266                  </li>
     2267                  <li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.4</a>, <a href="#rfc.xref.RFC5234.2">1.4</a>, <a href="#RFC5234"><b>12.1</b></a><ul>
    22572268                        <li><em>Appendix B.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.2">1.4</a></li>
    22582269                     </ul>
    22592270                  </li>
    2260                   <li><em>RFC5861</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5861.1">5.1</a>, <a href="#rfc.xref.RFC5861.2">5.1</a>, <a href="#RFC5861"><b>8.2</b></a><ul>
    2261                         <li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5861.2">5.1</a></li>
    2262                         <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5861.1">5.1</a></li>
     2271                  <li><em>RFC5861</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5861.1">9.1</a>, <a href="#rfc.xref.RFC5861.2">9.1</a>, <a href="#RFC5861"><b>12.2</b></a><ul>
     2272                        <li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5861.2">9.1</a></li>
     2273                        <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5861.1">9.1</a></li>
    22632274                     </ul>
    22642275                  </li>
     
    22682279                  <li>s-maxage&nbsp;&nbsp;
    22692280                     <ul>
    2270                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.s.4"><b>3.2.2.8</b></a></li>
     2281                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.s.4"><b>7.2.2.8</b></a></li>
    22712282                     </ul>
    22722283                  </li>
     
    22812292                     </ul>
    22822293                  </li>
    2283                   <li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.8</a>, <a href="#rfc.iref.v.3"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.3</a></li>
     2294                  <li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">4.3</a>, <a href="#rfc.iref.v.3"><b>7.5</b></a>, <a href="#rfc.xref.header.vary.2">9.3</a></li>
    22842295               </ul>
    22852296            </li>
     
    22872298                  <li>Warn Codes&nbsp;&nbsp;
    22882299                     <ul>
    2289                         <li>110 Response is Stale&nbsp;&nbsp;<a href="#rfc.iref.w.2"><b>3.6.1</b></a>, <a href="#rfc.xref.warn.110.1">5.2</a></li>
    2290                         <li>111 Revalidation Failed&nbsp;&nbsp;<a href="#rfc.iref.w.3"><b>3.6.2</b></a>, <a href="#rfc.xref.warn.111.1">5.2</a></li>
    2291                         <li>112 Disconnected Operation&nbsp;&nbsp;<a href="#rfc.iref.w.4"><b>3.6.3</b></a>, <a href="#rfc.xref.warn.112.1">5.2</a></li>
    2292                         <li>113 Heuristic Expiration&nbsp;&nbsp;<a href="#rfc.iref.w.5"><b>3.6.4</b></a>, <a href="#rfc.xref.warn.113.1">5.2</a></li>
    2293                         <li>199 Miscellaneous Warning&nbsp;&nbsp;<a href="#rfc.iref.w.6"><b>3.6.5</b></a>, <a href="#rfc.xref.warn.199.1">5.2</a></li>
    2294                         <li>214 Transformation Applied&nbsp;&nbsp;<a href="#rfc.iref.w.7"><b>3.6.6</b></a>, <a href="#rfc.xref.warn.214.1">5.2</a></li>
    2295                         <li>299 Miscellaneous Persistent Warning&nbsp;&nbsp;<a href="#rfc.iref.w.8"><b>3.6.7</b></a>, <a href="#rfc.xref.warn.299.1">5.2</a></li>
    2296                      </ul>
    2297                   </li>
    2298                   <li>Warning header field&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.5</a>, <a href="#rfc.xref.header.warning.4">2.9</a>, <a href="#rfc.iref.w.1"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.5">5.3</a>, <a href="#rfc.xref.header.warning.6">A</a></li>
     2300                        <li>110 Response is Stale&nbsp;&nbsp;<a href="#rfc.iref.w.2"><b>7.6.1</b></a>, <a href="#rfc.xref.warn.110.1">9.2</a></li>
     2301                        <li>111 Revalidation Failed&nbsp;&nbsp;<a href="#rfc.iref.w.3"><b>7.6.2</b></a>, <a href="#rfc.xref.warn.111.1">9.2</a></li>
     2302                        <li>112 Disconnected Operation&nbsp;&nbsp;<a href="#rfc.iref.w.4"><b>7.6.3</b></a>, <a href="#rfc.xref.warn.112.1">9.2</a></li>
     2303                        <li>113 Heuristic Expiration&nbsp;&nbsp;<a href="#rfc.iref.w.5"><b>7.6.4</b></a>, <a href="#rfc.xref.warn.113.1">9.2</a></li>
     2304                        <li>199 Miscellaneous Warning&nbsp;&nbsp;<a href="#rfc.iref.w.6"><b>7.6.5</b></a>, <a href="#rfc.xref.warn.199.1">9.2</a></li>
     2305                        <li>214 Transformation Applied&nbsp;&nbsp;<a href="#rfc.iref.w.7"><b>7.6.6</b></a>, <a href="#rfc.xref.warn.214.1">9.2</a></li>
     2306                        <li>299 Miscellaneous Persistent Warning&nbsp;&nbsp;<a href="#rfc.iref.w.8"><b>7.6.7</b></a>, <a href="#rfc.xref.warn.299.1">9.2</a></li>
     2307                     </ul>
     2308                  </li>
     2309                  <li>Warning header field&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">4.1.4</a>, <a href="#rfc.xref.header.warning.2">4.2.1</a>, <a href="#rfc.xref.header.warning.3">4.4</a>, <a href="#rfc.xref.header.warning.4">5</a>, <a href="#rfc.iref.w.1"><b>7.6</b></a>, <a href="#rfc.xref.header.warning.5">9.3</a>, <a href="#rfc.xref.header.warning.6">A</a></li>
    22992310               </ul>
    23002311            </li>
  • draft-ietf-httpbis/latest/p6-cache.xml

    r1746 r1751  
    416416</section>
    417417
    418 <section anchor="caching.overview" title="Cache Operation">
     418<section anchor="caching.overview" title="Overview of Cache Operation">
    419419<iref item="cache entry" />
    420420<iref item="cache key" />
     
    453453   fields (<xref target="caching.negotiated.responses"/>).
    454454</t>
    455 
    456 <section anchor="response.cacheability" title="Response Cacheability">
     455</section>
     456
     457<section anchor="response.cacheability" title="Storing Responses in Caches">
    457458<t>
    458459   A cache &MUST-NOT; store a response to any request, unless:
     
    503504   prohibited from storing such responses.
    504505</t>
     506
     507<section anchor="incomplete.responses" title="Storing Incomplete Responses">
    505508<t>
    506509   A response message is considered complete when all of the octets indicated
     
    526529   using the <x:ref>206 (Partial Content)</x:ref> status code.
    527530</t>
     531</section>
     532
     533
     534<section anchor="caching.authenticated.responses"
     535   title="Storing Responses to Authenticated Requests">
     536<t>
     537   A shared cache &MUST-NOT; use a cached response to a request with an
     538   <x:ref>Authorization</x:ref> header field (&header-authorization;) to
     539   satisfy any subsequent request unless a cache directive that allows such
     540   responses to be stored is present in the response.
     541</t>
     542
     543<t>
     544   In this specification, the following <x:ref>Cache-Control</x:ref> response
     545   directives (<xref target="cache-response-directive"/>) have such an effect:
     546   must-revalidate, public, s-maxage.
     547</t>
     548
     549<t>
     550   Note that cached responses that contain the "must-revalidate" and/or
     551   "s-maxage" response directives are not allowed to be served stale (<xref
     552   target="serving.stale.responses"/>) by shared caches. In particular, a
     553   response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be
     554   used to satisfy a subsequent request without revalidating it on the origin
     555   server.
     556</t>
     557</section>
    528558</section>
    529559
     
    594624</t>
    595625
    596 </section>
    597626
    598627<section anchor="expiration.model" title="Freshness Model">
     
    682711   responses that have invalid freshness information to be stale.
    683712</t>
     713</section>
    684714
    685715<section anchor="heuristic.freshness" title="Calculating Heuristic Freshness">
     
    717747   </t>
    718748</x:note>
    719 </section>
    720749</section>
    721750
     
    9871016</section>
    9881017
    989 <section anchor="head.effects" title="Updating Caches with HEAD Responses">
    990 <t>
    991    A response to the HEAD method is identical to what an equivalent request
    992    made with a GET would have been, except it lacks a body. This property
    993    of HEAD responses is used to both invalidate and update cached GET
    994    responses.
    995 </t>
    996 <t>
    997    If one or more stored GET responses can be selected (as per <xref
    998    target="caching.negotiated.responses"/>) for a HEAD request, and the
    999    <x:ref>Content-Length</x:ref>, <x:ref>ETag</x:ref> or
    1000    <x:ref>Last-Modified</x:ref> value of a HEAD response differs from that in a
    1001    selected GET response, the cache &MUST; consider that selected response to
    1002    be stale.
    1003 </t>
    1004 <t>
    1005    If the <x:ref>Content-Length</x:ref>, <x:ref>ETag</x:ref> and
    1006    <x:ref>Last-Modified</x:ref> values of a HEAD response (when present) are
    1007    the same as that in a selected GET response (as per
    1008    <xref target="caching.negotiated.responses"/>), the cache &SHOULD; update
    1009    the remaining headers in the stored response using the following rules:
    1010    <list style="symbols">
    1011       <t>delete any <x:ref>Warning</x:ref> header fields in the stored response
    1012          with warn-code 1xx (see <xref target="header.warning" />);</t>
    1013       <t>retain any <x:ref>Warning</x:ref> header fields in the stored response
    1014          with warn-code 2xx; and,</t>
    1015       <t>use other header fields provided in the response to replace
    1016          all instances of the corresponding header fields in the stored
    1017          response.</t>
    1018    </list>
    1019 </t>
    1020 
    1021 </section>
    1022 
    1023 <section anchor="invalidation.after.updates.or.deletions"
    1024    title="Request Methods that Invalidate">
    1025 <t>
    1026    Because unsafe request methods (&safe-methods;) such as PUT, POST or DELETE
    1027    have the potential for changing state on the origin server, intervening
    1028    caches can use them to keep their contents up-to-date.
    1029 </t>
    1030 <t>
    1031    A cache &MUST; invalidate the effective Request URI
    1032    (&effective-request-uri;) as well as the URI(s) in the
    1033    <x:ref>Location</x:ref> and <x:ref>Content-Location</x:ref> response header
    1034    fields (if present) when a non-error response to a request with an unsafe
    1035    method is received.
    1036 </t>
    1037 <t>
    1038    However, a cache &MUST-NOT; invalidate a URI from a <x:ref>Location</x:ref>
    1039    or <x:ref>Content-Location</x:ref> response header field if the host part of
    1040    that URI differs from the host part in the effective request URI
    1041    (&effective-request-uri;). This helps prevent denial of service attacks.
    1042 </t>
    1043 <t>
    1044    A cache &MUST; invalidate the effective request URI
    1045    (&effective-request-uri;) when it receives a non-error response
    1046    to a request with a method whose safety is unknown.
    1047 </t>
    1048 <t>
    1049    Here, a "non-error response" is one with a <x:ref>2xx (Successful)</x:ref>
    1050    or <x:ref>3xx (Redirection)</x:ref> status code. "Invalidate" means that
    1051    the cache will either remove all stored responses related to the effective
    1052    request URI, or will mark these as "invalid" and in need of a mandatory
    1053    validation before they can be returned in response to a subsequent request.
    1054 </t>
    1055 <t>
    1056    Note that this does not guarantee that all appropriate responses are
    1057    invalidated. For example, the request that caused the change at the origin
    1058    server might not have gone through the cache where a response is stored.
    1059 </t>
    1060 </section>
    1061 
    1062 <section anchor="caching.authenticated.responses"
    1063    title="Shared Caching of Authenticated Responses">
    1064 <t>
    1065    A shared cache &MUST-NOT; use a cached response to a request with an
    1066    <x:ref>Authorization</x:ref> header field (&header-authorization;) to
    1067    satisfy any subsequent request unless a cache directive that allows such
    1068    responses to be stored is present in the response.
    1069 </t>
    1070 
    1071 <t>
    1072    In this specification, the following <x:ref>Cache-Control</x:ref> response
    1073    directives (<xref target="cache-response-directive"/>) have such an effect:
    1074    must-revalidate, public, s-maxage.
    1075 </t>
    1076 
    1077 <t>
    1078    Note that cached responses that contain the "must-revalidate" and/or
    1079    "s-maxage" response directives are not allowed to be served stale (<xref
    1080    target="serving.stale.responses"/>) by shared caches. In particular, a
    1081    response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be
    1082    used to satisfy a subsequent request without revalidating it on the origin
    1083    server.
    1084 </t>
    1085 </section>
    1086 
    10871018<section anchor="caching.negotiated.responses"
    1088    title="Caching Negotiated Responses">
     1019   title="Using Negotiated Responses">
    10891020<t>
    10901021   When a cache receives a request that can be satisfied by a stored response
     
    11421073</section>
    11431074
     1075
    11441076<section anchor="combining.responses" title="Combining Partial Content">
    11451077<t>
     
    11661098</t>
    11671099</section>
    1168 
    1169 
    1170 </section>
     1100</section>
     1101
     1102
     1103<section anchor="head.effects" title="Updating Caches with HEAD Responses">
     1104<t>
     1105   A response to the HEAD method is identical to what an equivalent request
     1106   made with a GET would have been, except it lacks a body. This property
     1107   of HEAD responses is used to both invalidate and update cached GET
     1108   responses.
     1109</t>
     1110<t>
     1111   If one or more stored GET responses can be selected (as per <xref
     1112   target="caching.negotiated.responses"/>) for a HEAD request, and the
     1113   <x:ref>Content-Length</x:ref>, <x:ref>ETag</x:ref> or
     1114   <x:ref>Last-Modified</x:ref> value of a HEAD response differs from that in a
     1115   selected GET response, the cache &MUST; consider that selected response to
     1116   be stale.
     1117</t>
     1118<t>
     1119   If the <x:ref>Content-Length</x:ref>, <x:ref>ETag</x:ref> and
     1120   <x:ref>Last-Modified</x:ref> values of a HEAD response (when present) are
     1121   the same as that in a selected GET response (as per
     1122   <xref target="caching.negotiated.responses"/>), the cache &SHOULD; update
     1123   the remaining headers in the stored response using the following rules:
     1124   <list style="symbols">
     1125      <t>delete any <x:ref>Warning</x:ref> header fields in the stored response
     1126         with warn-code 1xx (see <xref target="header.warning" />);</t>
     1127      <t>retain any <x:ref>Warning</x:ref> header fields in the stored response
     1128         with warn-code 2xx; and,</t>
     1129      <t>use other header fields provided in the response to replace
     1130         all instances of the corresponding header fields in the stored
     1131         response.</t>
     1132   </list>
     1133</t>
     1134
     1135</section>
     1136
     1137
     1138<section anchor="invalidation.after.updates.or.deletions"
     1139   title="Request Methods that Invalidate">
     1140<t>
     1141   Because unsafe request methods (&safe-methods;) such as PUT, POST or DELETE
     1142   have the potential for changing state on the origin server, intervening
     1143   caches can use them to keep their contents up-to-date.
     1144</t>
     1145<t>
     1146   A cache &MUST; invalidate the effective Request URI
     1147   (&effective-request-uri;) as well as the URI(s) in the
     1148   <x:ref>Location</x:ref> and <x:ref>Content-Location</x:ref> response header
     1149   fields (if present) when a non-error response to a request with an unsafe
     1150   method is received.
     1151</t>
     1152<t>
     1153   However, a cache &MUST-NOT; invalidate a URI from a <x:ref>Location</x:ref>
     1154   or <x:ref>Content-Location</x:ref> response header field if the host part of
     1155   that URI differs from the host part in the effective request URI
     1156   (&effective-request-uri;). This helps prevent denial of service attacks.
     1157</t>
     1158<t>
     1159   A cache &MUST; invalidate the effective request URI
     1160   (&effective-request-uri;) when it receives a non-error response
     1161   to a request with a method whose safety is unknown.
     1162</t>
     1163<t>
     1164   Here, a "non-error response" is one with a <x:ref>2xx (Successful)</x:ref>
     1165   or <x:ref>3xx (Redirection)</x:ref> status code. "Invalidate" means that
     1166   the cache will either remove all stored responses related to the effective
     1167   request URI, or will mark these as "invalid" and in need of a mandatory
     1168   validation before they can be returned in response to a subsequent request.
     1169</t>
     1170<t>
     1171   Note that this does not guarantee that all appropriate responses are
     1172   invalidated. For example, the request that caused the change at the origin
     1173   server might not have gone through the cache where a response is stored.
     1174</t>
     1175</section>
     1176
     1177
     1178
    11711179
    11721180<section anchor="header.field.definitions" title="Header Field Definitions">
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