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Aug 3, 2011, 10:44:42 PM (8 years ago)
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  • draft-ietf-httpbis/latest/p6-cache.html

    r1373 r1375  
    556556         </li>
    557557         <li>2.&nbsp;&nbsp;&nbsp;<a href="#caching.overview">Cache Operation</a><ul>
    558                <li>2.1&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Response Cacheability</a><ul>
    559                      <li>2.1.1&nbsp;&nbsp;&nbsp;<a href="#errors.or.incomplete.response.cache.behavior">Storing Partial and Incomplete Responses</a></li>
    560                   </ul>
    561                </li>
     558               <li>2.1&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Response Cacheability</a></li>
    562559               <li>2.2&nbsp;&nbsp;&nbsp;<a href="#constructing.responses.from.caches">Constructing Responses from Caches</a></li>
    563560               <li>2.3&nbsp;&nbsp;&nbsp;<a href="#expiration.model">Freshness Model</a><ul>
    … …  
    574571               <li>2.6&nbsp;&nbsp;&nbsp;<a href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></li>
    575572               <li>2.7&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
    576                <li>2.8&nbsp;&nbsp;&nbsp;<a href="#combining.responses">Combining Responses</a></li>
     573               <li>2.8&nbsp;&nbsp;&nbsp;<a href="#combining.responses">Combining Partial Content</a></li>
     574               <li>2.9&nbsp;&nbsp;&nbsp;<a href="#freshening.responses">Freshening Responses</a></li>
    577575            </ul>
    578576         </li>
    … …  
    639637         Any client or server <em class="bcp14">MAY</em> employ a cache, though a cache cannot be used by a server that is acting as a tunnel.
    640638      </p>
    641       <p id="rfc.section.1.1.p.2">Caching would be useless if it did not significantly improve performance. The goal of caching in HTTP/1.1 is to reuse a prior
    642          response message to satisfy a current request. In some cases, a stored response can be reused without the need for a network
    643          request, reducing latency and network round-trips; a "freshness" mechanism is used for this purpose (see <a href="#expiration.model" title="Freshness Model">Section&nbsp;2.3</a>). Even when a new request is required, it is often possible to reuse all or parts of the payload of a prior response to satisfy
    644          the request, thereby reducing network bandwidth usage; a "validation" mechanism is used for this purpose (see <a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>).
     639      <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
     640         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
     641         valid for this request). A fresh cache response can therefore reduce both latency and network transfers each time it is reused.
     642         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.
    645643      </p>
    646644      <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>
    … …  
    657655         </p>
    658656         <ul class="empty">
    659             <li>A cache that is accessible to more than one user; usually (but not always) deployed as part of an intermediary.</li>
     657            <li>A cache that stores responses to be reused by more than one user; usually (but not always) deployed as part of an intermediary.</li>
    660658         </ul>
    661659      </div>
    … …  
    712710      <ul class="empty">
    713711         <li>A protocol element (e.g., an entity-tag or a Last-Modified time) that is used to find out whether a stored response is an
    714             equivalent copy of a representation.
     712            equivalent copy of a representation. See <a href="p4-conditional.html#weak.and.strong.validators" title="Weak versus Strong">Section 2.2.2</a> of <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
     713         </li>
     714      </ul>
     715      <p id="rfc.section.1.2.p.14"> <span id="rfc.iref.s.3"></span>  <span id="rfc.iref.v.2"></span>  <dfn>strong validator</dfn> 
     716      </p>
     717      <ul class="empty">
     718         <li>A validator that is defined by the origin server such that its current value will change if the representation body changes;
     719            i.e., an entity-tag that is not marked as weak (<a href="p4-conditional.html#header.etag" title="ETag">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>) or, if no entity-tag is provided, a Last-Modified value that is strong in the sense defined by <a href="p4-conditional.html#lastmod.comparison" title="Comparison">Section 2.1.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
    715720         </li>
    716721      </ul>
    … …  
    750755         its subsequent calculations overflows, it <em class="bcp14">MUST</em> consider the value to be 2147483648 (2<sup>31</sup>). Recipients parsing a delta-seconds value <em class="bcp14">SHOULD</em> use an arithmetic type of at least 31 bits of range, and senders <em class="bcp14">MUST NOT</em> send delta-seconds with a value greater than 2147483648.
    751756      </p>
     757      <div id="rfc.iref.c.4"></div>
     758      <div id="rfc.iref.c.5"></div>
    752759      <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="caching.overview" href="#caching.overview">Cache Operation</a></h1>
     760      <p id="rfc.section.2.p.1">Proper cache operation preserves the semantics of HTTP transfers (<a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[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
     761         no requirement or locally-desired configuration prevents it. Therefore, HTTP cache requirements are focused on preventing
     762         a cache from either storing a non-reusable response or reusing a stored response inappropriately.
     763      </p>
     764      <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
     765         form of cache entry is a successful result of a retrieval request: i.e., a 200 (OK) response containing a representation of
     766         the resource identified by the request target. However, it is also possible to cache negative results (e.g., 404 not found),
     767         incomplete results (e.g., 206 partial content), and responses to safe methods other than GET if the method's definition allows
     768         such caching and defines something suitable for use as a cache key.
     769      </p>
     770      <p id="rfc.section.2.p.3">The default <dfn>cache key</dfn> consists of the request method and target URI. However, since HTTP caches in common use today are typically limited to caching
     771         responses to GET, most implementations simply decline other methods and use only the URI as the key.
     772      </p>
     773      <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
     774         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;2.7</a>).
     775      </p>
    753776      <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>
    754777      <p id="rfc.section.2.1.p.1">A cache <em class="bcp14">MUST NOT</em> store a response to any request, unless:
    … …  
    779802      <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>.
    780803      </p>
    781       <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 recognises it and implements any
    782          cache-specific behavior. In particular, 206 Partial Content responses cannot be cached by an implementation that does not
    783          handle partial content (see <a href="#errors.or.incomplete.response.cache.behavior" title="Storing Partial and Incomplete Responses">Section&nbsp;2.1.1</a>).
    784       </p>
    785       <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
     804      <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
     805         cache-specific behavior.
     806      </p>
     807      <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
    786808         time, as such responses are not usually useful to store. However, caches are not prohibited from storing such responses.
    787809      </p>
    788       <h3 id="rfc.section.2.1.1"><a href="#rfc.section.2.1.1">2.1.1</a>&nbsp;<a id="errors.or.incomplete.response.cache.behavior" href="#errors.or.incomplete.response.cache.behavior">Storing Partial and Incomplete Responses</a></h3>
    789       <p id="rfc.section.2.1.1.p.1">A cache that receives an incomplete response (for example, with fewer bytes of data than specified in a Content-Length header
    790          field) can store the response, but <em class="bcp14">MUST</em> treat it as a partial response <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. Partial responses can be combined as described in <a href="p5-range.html#combining.byte.ranges" title="Combining Ranges">Section 4</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>; the result might be a full response or might still be partial. A cache <em class="bcp14">MUST NOT</em> return a partial response to a client without explicitly marking it as such using the 206 (Partial Content) status code.
    791       </p>
    792       <p id="rfc.section.2.1.1.p.2">A cache that does not support the Range and Content-Range header fields <em class="bcp14">MUST NOT</em> store incomplete or partial responses.
     810      <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 200 (OK), and the entire
     811         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 206 (Partial Content)
     812         response <em class="bcp14">MAY</em> be stored as if it were an incomplete 200 (OK) cache entry. However, a cache <em class="bcp14">MUST NOT</em> store incomplete or partial content responses if it does not support the Range and Content-Range header fields or if it does
     813         not understand the range units used in those fields.
     814      </p>
     815      <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;2.8</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
     816         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 206 (Partial Content) status code.
    793817      </p>
    794818      <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>
    … …  
    796820      </p>
    797821      <ul>
    798          <li>The presented effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) and that of the stored response match, and
     822         <li>The presented effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) and that of the stored response match, and
    799823         </li>
    800824         <li>the request method associated with the stored response allows it to be used for the presented request, and</li>
    … …  
    818842      <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 Age 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>.
    819843      </p>
    820       <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 7.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) to the origin server; i.e., a cache must not generate a reply to such a request before having forwarded the request and
     844      <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 7.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) to the origin server; i.e., a cache must not generate a reply to such a request before having forwarded the request and
    821845         having received a corresponding response.
    822846      </p>
    … …  
    869893      <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>
    870894      <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
    871          to be used (including the following in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 8</a> of <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>: 200, 203, 206, 300, 301 and 410), 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.
     895         to be used (including the following in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 8</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>: 200, 203, 206, 300, 301 and 410), 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.
    872896      </p>
    873897      <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 Warning header field with a 113 warn-code to the response if its current_age is more than 24 hours and such a warning
    874898         is not already present.
    875899      </p>
    876       <p id="rfc.section.2.3.1.1.p.3">Also, if the response has a Last-Modified header field (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.1</a> of <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>), a cache <em class="bcp14">SHOULD NOT</em> use a heuristic expiration value that is more than some fraction of the interval since that time. A typical setting of this
     900      <p id="rfc.section.2.3.1.1.p.3">Also, if the response has a Last-Modified header field (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.1</a> of <a href="#Part4" id="rfc.xref.Part4.4"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>), a cache <em class="bcp14">SHOULD NOT</em> use a heuristic expiration value that is more than some fraction of the interval since that time. A typical setting of this
    877901         fraction might be 10%.
    878902      </p>
    … …  
    901925         <li>HTTP/1.1 requires origin servers to send a Date header field, if possible, with every response, giving the time at which the
    902926            response was generated. The term "date_value" denotes the value of the Date header field, in a form appropriate for arithmetic
    903             operations. See <a href="p1-messaging.html#header.date" title="Date">Section 9.3</a> of <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for the definition of the Date header field, and for requirements regarding responses without it.
     927            operations. See <a href="p1-messaging.html#header.date" title="Date">Section 9.3</a> of <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for the definition of the Date header field, and for requirements regarding responses without it.
    904928         </li>
    905929      </ul>
    … …  
    958982      <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>
    959983      <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
    960          fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.2"><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
     984         fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section&nbsp;2.7</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
    961985         update it. This process is known as "validating" or "revalidating" the stored response.
    962986      </p>
    … …  
    967991         that stored response.
    968992      </p>
    969       <p id="rfc.section.2.4.p.4">A 304 (Not Modified) response status code indicates that the stored response can be updated and reused; see <a href="#combining.responses" title="Combining Responses">Section&nbsp;2.8</a>.
     993      <p id="rfc.section.2.4.p.4">A 304 (Not Modified) response status code indicates that the stored response can be updated and reused; see <a href="#freshening.responses" title="Freshening Responses">Section&nbsp;2.9</a>.
    970994      </p>
    971995      <p id="rfc.section.2.4.p.5">A full response (i.e., one with a response body) indicates that none of the stored responses nominated in the conditional
    972          request is suitable. Instead, a cache <em class="bcp14">SHOULD</em> use the full response to satisfy the request and <em class="bcp14">MAY</em> replace the stored response.
     996         request is suitable. Instead, a cache <em class="bcp14">SHOULD</em> use the full response to satisfy the request and <em class="bcp14">MAY</em> replace the stored response(s).
    973997      </p>
    974998      <p id="rfc.section.2.4.p.6">If a cache receives a 5xx response while attempting to validate a response, it <em class="bcp14">MAY</em> either forward this response to the requesting client, or act as if the server failed to respond. In the latter case, it <em class="bcp14">MAY</em> return a previously stored response (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section&nbsp;2.3.3</a>).
    975999      </p>
    9761000      <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></h2>
    977       <p id="rfc.section.2.5.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 7.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them
     1001      <p id="rfc.section.2.5.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 7.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them
    9781002         to keep their contents up-to-date.
    9791003      </p>
    980       <p id="rfc.section.2.5.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 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) as well as the URI(s) in the Location and Content-Location header fields (if present) when a non-error response to a request
     1004      <p id="rfc.section.2.5.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 4.3</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 Location and Content-Location header fields (if present) when a non-error response to a request
    9811005         with an unsafe method is received.
    9821006      </p>
    9831007      <p id="rfc.section.2.5.p.3">However, a cache <em class="bcp14">MUST NOT</em> invalidate a URI from a Location or Content-Location header field if the host part of that URI differs from the host part
    984          in the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</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.
    985       </p>
    986       <p id="rfc.section.2.5.p.4">A cache <em class="bcp14">SHOULD</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</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.
     1008         in the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</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.
     1009      </p>
     1010      <p id="rfc.section.2.5.p.4">A cache <em class="bcp14">SHOULD</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</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.
    9871011      </p>
    9881012      <p id="rfc.section.2.5.p.5">Here, a "non-error response" is one with a 2xx or 3xx status code. "Invalidate" means that the cache will either remove all
    … …  
    10111035      <ul>
    10121036         <li>adding or removing whitespace, where allowed in the header field's syntax</li>
    1013          <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>)
     1037         <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.Part1.17"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>)
    10141038         </li>
    10151039         <li>normalizing both header field values in a way that is known to have identical semantics, according to the header field's specification
    … …  
    10281052      <p id="rfc.section.2.7.p.7">If no selected response is available, the cache <em class="bcp14">MAY</em> forward the presented request to the origin server in a conditional request; see <a href="#validation.model" title="Validation Model">Section&nbsp;2.4</a>.
    10291053      </p>
    1030       <h2 id="rfc.section.2.8"><a href="#rfc.section.2.8">2.8</a>&nbsp;<a id="combining.responses" href="#combining.responses">Combining Responses</a></h2>
    1031       <p id="rfc.section.2.8.p.1">When a cache receives a 304 (Not Modified) response or a 206 (Partial Content) response (in this section, the "new" response"),
    1032          it needs to create an updated response by combining the stored response with the new one, so that the updated response can
    1033          be used to satisfy the request, and potentially update the cached response.
    1034       </p>
    1035       <p id="rfc.section.2.8.p.2">If the new response contains an ETag, it identifies the stored response to use. <span class="comment" id="TODO-mention-CL">[<a href="#TODO-mention-CL" class="smpl">TODO-mention-CL</a>: might need language about Content-Location here]</span><span class="comment" id="TODO-select-for-combine">[<a href="#TODO-select-for-combine" class="smpl">TODO-select-for-combine</a>: Shouldn't this be the selected response?]</span>
    1036       </p>
    1037       <p id="rfc.section.2.8.p.3">When the new response's status code is 206 (partial content), a cache <em class="bcp14">MUST NOT</em> combine it with the old response if either response does not have a validator, and <em class="bcp14">MUST NOT</em> combine it with the old response when those validators do not match with the strong comparison function (see <a href="p4-conditional.html#weak.and.strong.validators" title="Weak versus Strong">Section 2.2.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
    1038       </p>
    1039       <p id="rfc.section.2.8.p.4">The stored response header fields are used as those of the updated response, except that </p>
    1040       <ul>
    1041          <li>a cache <em class="bcp14">MUST</em> delete any stored Warning header fields with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.2" title="Warning">Section&nbsp;3.6</a>).
    1042          </li>
    1043          <li>a cache <em class="bcp14">MUST</em> retain any stored Warning header fields with warn-code 2xx.
    1044          </li>
    1045          <li>a cache <em class="bcp14">MUST</em> use other header fields provided in the new response to replace all instances of the corresponding header fields from the
    1046             stored response.
    1047          </li>
    1048       </ul>
    1049       <p id="rfc.section.2.8.p.5">A cache <em class="bcp14">MUST</em> use the updated response header fields to replace those of the stored response (unless the stored response is removed). In
    1050          the case of a 206 response, a cache <em class="bcp14">MAY</em> store the combined representation.
    1051       </p>
     1054      <h2 id="rfc.section.2.8"><a href="#rfc.section.2.8">2.8</a>&nbsp;<a id="combining.responses" href="#combining.responses">Combining Partial Content</a></h2>
     1055      <p id="rfc.section.2.8.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or
     1056         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
     1057         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</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>.
     1058      </p>
     1059      <p id="rfc.section.2.8.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>:
     1060      </p>
     1061      <ul>
     1062         <li>delete any Warning 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>);
     1063         </li>
     1064         <li>retain any Warning header fields in the stored response with warn-code 2xx; and,</li>
     1065         <li>use other header fields provided in the new response, aside from Content-Range, to replace all instances of the corresponding
     1066            header fields in the stored response.
     1067         </li>
     1068      </ul>
     1069      <h2 id="rfc.section.2.9"><a href="#rfc.section.2.9">2.9</a>&nbsp;<a id="freshening.responses" href="#freshening.responses">Freshening Responses</a></h2>
     1070      <p id="rfc.section.2.9.p.1">When a cache receives a 304 (Not Modified) response and already has one or more stored 200 (OK) responses for the same cache
     1071         key, the cache needs to identify which of the stored responses are updated by this new response and then update the stored
     1072         response(s) with the new information provided in the 304 response.
     1073      </p>
     1074      <ul>
     1075         <li>If the new response contains a strong validator, then that strong validator identifies the selected representation. All of
     1076            the stored responses with the same strong validator are selected. If none of the stored responses contain the same strong
     1077            validator, then this new response corresponds to a new selected representation and <em class="bcp14">MUST NOT</em> update the existing stored responses.
     1078         </li>
     1079         <li>If the new response contains a weak validator and that validator corresponds to one of the cache's stored responses, then
     1080            the most recent of those matching stored responses is selected.
     1081         </li>
     1082         <li>If the new response does not include any form of validator, there is only one stored response, and that stored response also
     1083            lacks a validator, then that stored response is selected.
     1084         </li>
     1085      </ul>
     1086      <p id="rfc.section.2.9.p.2">If a stored response is selected for update, the cache <em class="bcp14">MUST</em>:
     1087      </p>
     1088      <ul>
     1089         <li>delete any Warning 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>);
     1090         </li>
     1091         <li>retain any Warning header fields in the stored response with warn-code 2xx; and,</li>
     1092         <li>use other header fields provided in the 304 response to replace all instances of the corresponding header fields in the stored
     1093            response.
     1094         </li>
     1095      </ul>
    10521096      <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
    10531097      <p id="rfc.section.3.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p>
    … …  
    10641108         true, since HTTP/1.0 caches might not implement the Age header field.
    10651109      </p>
    1066       <div id="rfc.iref.c.4"></div>
     1110      <div id="rfc.iref.c.6"></div>
    10671111      <div id="rfc.iref.h.3"></div>
    10681112      <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>
    … …  
    10971141     / "only-if-cached"
    10981142     / <a href="#header.cache-control" class="smpl">cache-extension</a>
    1099 </pre><p id="rfc.section.3.2.1.p.2"> <dfn>no-cache</dfn>  <span id="rfc.iref.c.5"></span>  <span id="rfc.iref.n.1"></span> 
     1143</pre><p id="rfc.section.3.2.1.p.2"> <dfn>no-cache</dfn>  <span id="rfc.iref.c.7"></span>  <span id="rfc.iref.n.1"></span> 
    11001144      </p>
    11011145      <ul class="empty">
    … …  
    11031147         </li>
    11041148      </ul>
    1105       <p id="rfc.section.3.2.1.p.3"> <dfn>no-store</dfn>  <span id="rfc.iref.c.6"></span>  <span id="rfc.iref.n.2"></span> 
     1149      <p id="rfc.section.3.2.1.p.3"> <dfn>no-store</dfn>  <span id="rfc.iref.c.8"></span>  <span id="rfc.iref.n.2"></span> 
    11061150      </p>
    11071151      <ul class="empty">
    … …  
    11151159         </li>
    11161160      </ul>
    1117       <p id="rfc.section.3.2.1.p.4"> <dfn>max-age</dfn>  <span id="rfc.iref.c.7"></span>  <span id="rfc.iref.m.1"></span> 
     1161      <p id="rfc.section.3.2.1.p.4"> <dfn>max-age</dfn>  <span id="rfc.iref.c.9"></span>  <span id="rfc.iref.m.1"></span> 
    11181162      </p>
    11191163      <ul class="empty">
    … …  
    11221166         </li>
    11231167      </ul>
    1124       <p id="rfc.section.3.2.1.p.5"> <dfn>max-stale</dfn>  <span id="rfc.iref.c.8"></span>  <span id="rfc.iref.m.2"></span> 
     1168      <p id="rfc.section.3.2.1.p.5"> <dfn>max-stale</dfn>  <span id="rfc.iref.c.10"></span>  <span id="rfc.iref.m.2"></span> 
    11251169      </p>
    11261170      <ul class="empty">
    … …  
    11311175         </li>
    11321176      </ul>
    1133       <p id="rfc.section.3.2.1.p.6"> <dfn>min-fresh</dfn>  <span id="rfc.iref.c.9"></span>  <span id="rfc.iref.m.3"></span> 
     1177      <p id="rfc.section.3.2.1.p.6"> <dfn>min-fresh</dfn>  <span id="rfc.iref.c.11"></span>  <span id="rfc.iref.m.3"></span> 
    11341178      </p>
    11351179      <ul class="empty">
    … …  
    11391183         </li>
    11401184      </ul>
    1141       <p id="rfc.section.3.2.1.p.7"> <dfn>no-transform</dfn>  <span id="rfc.iref.c.10"></span>  <span id="rfc.iref.n.3"></span> 
     1185      <p id="rfc.section.3.2.1.p.7"> <dfn>no-transform</dfn>  <span id="rfc.iref.c.12"></span>  <span id="rfc.iref.n.3"></span> 
    11421186      </p>
    11431187      <ul class="empty">
    … …  
    11451189         </li>
    11461190      </ul>
    1147       <p id="rfc.section.3.2.1.p.8"> <dfn>only-if-cached</dfn>  <span id="rfc.iref.c.11"></span>  <span id="rfc.iref.o.1"></span> 
     1191      <p id="rfc.section.3.2.1.p.8"> <dfn>only-if-cached</dfn>  <span id="rfc.iref.c.13"></span>  <span id="rfc.iref.o.1"></span> 
    11481192      </p>
    11491193      <ul class="empty">
    … …  
    11661210     / "s-maxage" "=" <a href="#delta-seconds" class="smpl">delta-seconds</a>
    11671211     / <a href="#header.cache-control" class="smpl">cache-extension</a>
    1168 </pre><p id="rfc.section.3.2.2.p.2"> <dfn>public</dfn>  <span id="rfc.iref.c.12"></span>  <span id="rfc.iref.p.2"></span> 
     1212</pre><p id="rfc.section.3.2.2.p.2"> <dfn>public</dfn>  <span id="rfc.iref.c.14"></span>  <span id="rfc.iref.p.2"></span> 
    11691213      </p>
    11701214      <ul class="empty">
    … …  
    11721216         </li>
    11731217      </ul>
    1174       <p id="rfc.section.3.2.2.p.3"> <dfn>private</dfn>  <span id="rfc.iref.c.13"></span>  <span id="rfc.iref.p.3"></span> 
     1218      <p id="rfc.section.3.2.2.p.3"> <dfn>private</dfn>  <span id="rfc.iref.c.15"></span>  <span id="rfc.iref.p.3"></span> 
    11751219      </p>
    11761220      <ul class="empty">
    … …  
    11851229         </li>
    11861230      </ul>
    1187       <p id="rfc.section.3.2.2.p.4"> <dfn>no-cache</dfn>  <span id="rfc.iref.c.14"></span>  <span id="rfc.iref.n.4"></span> 
     1231      <p id="rfc.section.3.2.2.p.4"> <dfn>no-cache</dfn>  <span id="rfc.iref.c.16"></span>  <span id="rfc.iref.n.4"></span> 
    11881232      </p>
    11891233      <ul class="empty">
    … …  
    12021246         </li>
    12031247      </ul>
    1204       <p id="rfc.section.3.2.2.p.5"> <dfn>no-store</dfn>  <span id="rfc.iref.c.15"></span>  <span id="rfc.iref.n.5"></span> 
     1248      <p id="rfc.section.3.2.2.p.5"> <dfn>no-store</dfn>  <span id="rfc.iref.c.17"></span>  <span id="rfc.iref.n.5"></span> 
    12051249      </p>
    12061250      <ul class="empty">
    … …  
    12111255         </li>
    12121256      </ul>
    1213       <p id="rfc.section.3.2.2.p.6"> <dfn>must-revalidate</dfn>  <span id="rfc.iref.c.16"></span>  <span id="rfc.iref.m.4"></span> 
     1257      <p id="rfc.section.3.2.2.p.6"> <dfn>must-revalidate</dfn>  <span id="rfc.iref.c.18"></span>  <span id="rfc.iref.m.4"></span> 
    12141258      </p>
    12151259      <ul class="empty">
    … …  
    12231267         </li>
    12241268      </ul>
    1225       <p id="rfc.section.3.2.2.p.7"> <dfn>proxy-revalidate</dfn>  <span id="rfc.iref.c.17"></span>  <span id="rfc.iref.p.4"></span> 
     1269      <p id="rfc.section.3.2.2.p.7"> <dfn>proxy-revalidate</dfn>  <span id="rfc.iref.c.19"></span>  <span id="rfc.iref.p.4"></span> 
    12261270      </p>
    12271271      <ul class="empty">
    … …  
    12301274         </li>
    12311275      </ul>
    1232       <p id="rfc.section.3.2.2.p.8"> <dfn>max-age</dfn>  <span id="rfc.iref.c.18"></span>  <span id="rfc.iref.m.5"></span> 
     1276      <p id="rfc.section.3.2.2.p.8"> <dfn>max-age</dfn>  <span id="rfc.iref.c.20"></span>  <span id="rfc.iref.m.5"></span> 
    12331277      </p>
    12341278      <ul class="empty">
    … …  
    12371281         </li>
    12381282      </ul>
    1239       <p id="rfc.section.3.2.2.p.9"> <dfn>s-maxage</dfn>  <span id="rfc.iref.c.19"></span>  <span id="rfc.iref.s.3"></span> 
     1283      <p id="rfc.section.3.2.2.p.9"> <dfn>s-maxage</dfn>  <span id="rfc.iref.c.21"></span>  <span id="rfc.iref.s.4"></span> 
    12401284      </p>
    12411285      <ul class="empty">
    … …  
    12451289         </li>
    12461290      </ul>
    1247       <p id="rfc.section.3.2.2.p.10"> <dfn>no-transform</dfn>  <span id="rfc.iref.c.20"></span>  <span id="rfc.iref.n.6"></span> 
     1291      <p id="rfc.section.3.2.2.p.10"> <dfn>no-transform</dfn>  <span id="rfc.iref.c.22"></span>  <span id="rfc.iref.n.6"></span> 
    12481292      </p>
    12491293      <ul class="empty">
    … …  
    12951339         that time.
    12961340      </p>
    1297       <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="p1-messaging.html#date.time.formats.full.date" title="Date/Time Formats: Full Date">Section 6.1</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>; a sender <em class="bcp14">MUST</em> use the rfc1123-date format.
     1341      <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="p1-messaging.html#date.time.formats.full.date" title="Date/Time Formats: Full Date">Section 6.1</a> of <a href="#Part1" id="rfc.xref.Part1.18"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>; a sender <em class="bcp14">MUST</em> use the rfc1123-date format.
    12981342      </p>
    12991343      <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.7"></span>  <a href="#header.expires" class="smpl">Expires</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a>
    … …  
    13391383         </p>
    13401384      </div>
    1341       <div id="rfc.iref.v.2"></div>
     1385      <div id="rfc.iref.v.3"></div>
    13421386      <div id="rfc.iref.h.6"></div>
    13431387      <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>
    … …  
    16051649                  <td class="left">http</td>
    16061650                  <td class="left">standard</td>
    1607                   <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section&nbsp;3.6</a>
     1651                  <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;3.6</a>
    16081652                  </td>
    16091653               </tr>
    … …  
    16191663      </p>
    16201664      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="acks" href="#acks">Acknowledgments</a></h1>
    1621       <p id="rfc.section.7.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 12</a> of <a href="#Part1" id="rfc.xref.Part1.18"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
     1665      <p id="rfc.section.7.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 12</a> of <a href="#Part1" id="rfc.xref.Part1.19"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
    16221666      </p>
    16231667      <h1 id="rfc.references"><a id="rfc.section.8" href="#rfc.section.8">8.</a> References
    … …  
    17231767      </p>
    17241768      <p id="rfc.section.A.p.5">Do not mention RFC 2047 encoding and multiple languages in Warning header fields anymore, as these aspects never were implemented.
    1725          (<a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section&nbsp;3.6</a>)
     1769         (<a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section&nbsp;3.6</a>)
    17261770      </p>
    17271771      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1>
    … …  
    19972041                  <li>Cache Directives&nbsp;&nbsp;
    19982042                     <ul>
    1999                         <li>max-age&nbsp;&nbsp;<a href="#rfc.iref.c.7"><b>3.2.1</b></a>, <a href="#rfc.iref.c.18"><b>3.2.2</b></a></li>
    2000                         <li>max-stale&nbsp;&nbsp;<a href="#rfc.iref.c.8"><b>3.2.1</b></a></li>
    2001                         <li>min-fresh&nbsp;&nbsp;<a href="#rfc.iref.c.9"><b>3.2.1</b></a></li>
    2002                         <li>must-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.16"><b>3.2.2</b></a></li>
    2003                         <li>no-cache&nbsp;&nbsp;<a href="#rfc.iref.c.5"><b>3.2.1</b></a>, <a href="#rfc.iref.c.14"><b>3.2.2</b></a></li>
    2004                         <li>no-store&nbsp;&nbsp;<a href="#rfc.iref.c.6"><b>3.2.1</b></a>, <a href="#rfc.iref.c.15"><b>3.2.2</b></a></li>
    2005                         <li>no-transform&nbsp;&nbsp;<a href="#rfc.iref.c.10"><b>3.2.1</b></a>, <a href="#rfc.iref.c.20"><b>3.2.2</b></a></li>
    2006                         <li>only-if-cached&nbsp;&nbsp;<a href="#rfc.iref.c.11"><b>3.2.1</b></a></li>
    2007                         <li>private&nbsp;&nbsp;<a href="#rfc.iref.c.13"><b>3.2.2</b></a></li>
    2008                         <li>proxy-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.17"><b>3.2.2</b></a></li>
    2009                         <li>public&nbsp;&nbsp;<a href="#rfc.iref.c.12"><b>3.2.2</b></a></li>
    2010                         <li>s-maxage&nbsp;&nbsp;<a href="#rfc.iref.c.19"><b>3.2.2</b></a></li>
    2011                      </ul>
    2012                   </li>
    2013                   <li>Cache-Control header field&nbsp;&nbsp;<a href="#rfc.xref.header.cache-control.1">2.1</a>, <a href="#rfc.xref.header.cache-control.2">2.2</a>, <a href="#rfc.iref.c.4"><b>3.2</b></a>, <a href="#rfc.xref.header.cache-control.3">5.2</a></li>
     2043                        <li>max-age&nbsp;&nbsp;<a href="#rfc.iref.c.9"><b>3.2.1</b></a>, <a href="#rfc.iref.c.20"><b>3.2.2</b></a></li>
     2044                        <li>max-stale&nbsp;&nbsp;<a href="#rfc.iref.c.10"><b>3.2.1</b></a></li>
     2045                        <li>min-fresh&nbsp;&nbsp;<a href="#rfc.iref.c.11"><b>3.2.1</b></a></li>
     2046                        <li>must-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.18"><b>3.2.2</b></a></li>
     2047                        <li>no-cache&nbsp;&nbsp;<a href="#rfc.iref.c.7"><b>3.2.1</b></a>, <a href="#rfc.iref.c.16"><b>3.2.2</b></a></li>
     2048                        <li>no-store&nbsp;&nbsp;<a href="#rfc.iref.c.8"><b>3.2.1</b></a>, <a href="#rfc.iref.c.17"><b>3.2.2</b></a></li>
     2049                        <li>no-transform&nbsp;&nbsp;<a href="#rfc.iref.c.12"><b>3.2.1</b></a>, <a href="#rfc.iref.c.22"><b>3.2.2</b></a></li>
     2050                        <li>only-if-cached&nbsp;&nbsp;<a href="#rfc.iref.c.13"><b>3.2.1</b></a></li>
     2051                        <li>private&nbsp;&nbsp;<a href="#rfc.iref.c.15"><b>3.2.2</b></a></li>
     2052                        <li>proxy-revalidate&nbsp;&nbsp;<a href="#rfc.iref.c.19"><b>3.2.2</b></a></li>
     2053                        <li>public&nbsp;&nbsp;<a href="#rfc.iref.c.14"><b>3.2.2</b></a></li>
     2054                        <li>s-maxage&nbsp;&nbsp;<a href="#rfc.iref.c.21"><b>3.2.2</b></a></li>
     2055                     </ul>
     2056                  </li>
     2057                  <li>cache entry&nbsp;&nbsp;<a href="#rfc.iref.c.4">2</a></li>
     2058                  <li>cache key&nbsp;&nbsp;<a href="#rfc.iref.c.5">2</a></li>
     2059                  <li>Cache-Control header field&nbsp;&nbsp;<a href="#rfc.xref.header.cache-control.1">2.1</a>, <a href="#rfc.xref.header.cache-control.2">2.2</a>, <a href="#rfc.iref.c.6"><b>3.2</b></a>, <a href="#rfc.xref.header.cache-control.3">5.2</a></li>
    20142060                  <li>cacheable&nbsp;&nbsp;<a href="#rfc.iref.c.3">1.2</a></li>
    20152061               </ul>
    … …  
    20582104                        <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">5.2</a></li>
    20592105                        <li>Vary&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.7</a>, <a href="#rfc.iref.h.6"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.2</a></li>
    2060                         <li>Warning&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.8</a>, <a href="#rfc.iref.h.7"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.3">5.2</a>, <a href="#rfc.xref.header.warning.4">A</a></li>
     2106                        <li>Warning&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.8</a>, <a href="#rfc.xref.header.warning.3">2.9</a>, <a href="#rfc.iref.h.7"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.4">5.2</a>, <a href="#rfc.xref.header.warning.5">A</a></li>
    20612107                     </ul>
    20622108                  </li>
    … …  
    21142160            </li>
    21152161            <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
    2116                   <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.4</a>, <a href="#rfc.xref.Part1.2">1.4.1</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">1.4.2</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">2.2</a>, <a href="#rfc.xref.Part1.12">2.3.2</a>, <a href="#rfc.xref.Part1.13">2.5</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a>, <a href="#rfc.xref.Part1.16">2.7</a>, <a href="#rfc.xref.Part1.17">3.3</a>, <a href="#rfc.xref.Part1.18">7</a>, <a href="#Part1"><b>8.1</b></a><ul>
     2162                  <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.4</a>, <a href="#rfc.xref.Part1.2">1.4.1</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">1.4.2</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">2.3.2</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a>, <a href="#rfc.xref.Part1.16">2.5</a>, <a href="#rfc.xref.Part1.17">2.7</a>, <a href="#rfc.xref.Part1.18">3.3</a>, <a href="#rfc.xref.Part1.19">7</a>, <a href="#Part1"><b>8.1</b></a><ul>
    21172163                        <li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.4</a></li>
    21182164                        <li><em>Section 1.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">1.4.1</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></li>
    21192165                        <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>
    2120                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.6">1.4.2</a>, <a href="#rfc.xref.Part1.16">2.7</a></li>
    2121                         <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.11">2.2</a>, <a href="#rfc.xref.Part1.13">2.5</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a></li>
    2122                         <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.17">3.3</a></li>
    2123                         <li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.12">2.3.2</a></li>
     2166                        <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.6">1.4.2</a>, <a href="#rfc.xref.Part1.17">2.7</a></li>
     2167                        <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a>, <a href="#rfc.xref.Part1.16">2.5</a></li>
     2168                        <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.18">3.3</a></li>
     2169                        <li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.13">2.3.2</a></li>
    21242170                        <li><em>Section 9.9</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.9">1.4.2</a></li>
    2125                         <li><em>Section 12</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.18">7</a></li>
    2126                      </ul>
    2127                   </li>
    2128                   <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">2.2</a>, <a href="#rfc.xref.Part2.2">2.3.1.1</a>, <a href="#rfc.xref.Part2.3">2.5</a>, <a href="#Part2"><b>8.1</b></a><ul>
    2129                         <li><em>Section 7.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">2.2</a>, <a href="#rfc.xref.Part2.3">2.5</a></li>
    2130                         <li><em>Section 8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.2">2.3.1.1</a></li>
    2131                      </ul>
    2132                   </li>
    2133                   <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">2.3.1.1</a>, <a href="#rfc.xref.Part4.2">2.4</a>, <a href="#rfc.xref.Part4.3">2.8</a>, <a href="#Part4"><b>8.1</b></a><ul>
    2134                         <li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">2.3.1.1</a></li>
    2135                         <li><em>Section 2.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">2.8</a></li>
    2136                      </ul>
    2137                   </li>
    2138                   <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.1.1</a>, <a href="#rfc.xref.Part5.2">2.1.1</a>, <a href="#Part5"><b>8.1</b></a><ul>
    2139                         <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.2">2.1.1</a></li>
     2171                        <li><em>Section 12</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.19">7</a></li>
     2172                     </ul>
     2173                  </li>
     2174                  <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">2</a>, <a href="#rfc.xref.Part2.2">2.2</a>, <a href="#rfc.xref.Part2.3">2.3.1.1</a>, <a href="#rfc.xref.Part2.4">2.5</a>, <a href="#Part2"><b>8.1</b></a><ul>
     2175                        <li><em>Section 7.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.2">2.2</a>, <a href="#rfc.xref.Part2.4">2.5</a></li>
     2176                        <li><em>Section 8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.3">2.3.1.1</a></li>
     2177                     </ul>
     2178                  </li>
     2179                  <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>
     2180                        <li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.4">2.3.1.1</a></li>
     2181                        <li><em>Section 2.1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">1.2</a></li>
     2182                        <li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.2">1.2</a></li>
     2183                        <li><em>Section 2.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">1.2</a></li>
     2184                     </ul>
     2185                  </li>
     2186                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.1</a>, <a href="#rfc.xref.Part5.2">2.8</a>, <a href="#rfc.xref.Part5.3">2.8</a>, <a href="#Part5"><b>8.1</b></a><ul>
     2187                        <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.3">2.8</a></li>
    21402188                     </ul>
    21412189                  </li>
    … …  
    21892237                  <li>s-maxage&nbsp;&nbsp;
    21902238                     <ul>
    2191                         <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.s.3"><b>3.2.2</b></a></li>
     2239                        <li>Cache Directive&nbsp;&nbsp;<a href="#rfc.iref.s.4"><b>3.2.2</b></a></li>
    21922240                     </ul>
    21932241                  </li>
    21942242                  <li>shared cache&nbsp;&nbsp;<a href="#rfc.iref.s.1">1.2</a></li>
    21952243                  <li>stale&nbsp;&nbsp;<a href="#rfc.iref.s.2">1.2</a></li>
     2244                  <li>strong validator&nbsp;&nbsp;<a href="#rfc.iref.s.3">1.2</a></li>
    21962245               </ul>
    21972246            </li>
    21982247            <li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul>
    21992248                  <li>validator&nbsp;&nbsp;<a href="#rfc.iref.v.1">1.2</a></li>
    2200                   <li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.7</a>, <a href="#rfc.iref.v.2"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.2</a></li>
     2249                  <li>validator, strong&nbsp;&nbsp;<a href="#rfc.iref.v.2">1.2</a></li>
     2250                  <li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">2.7</a>, <a href="#rfc.iref.v.3"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.2</a></li>
    22012251               </ul>
    22022252            </li>
    22032253            <li><a id="rfc.index.W" href="#rfc.index.W"><b>W</b></a><ul>
    2204                   <li>Warning header field&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.8</a>, <a href="#rfc.iref.w.1"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.3">5.2</a>, <a href="#rfc.xref.header.warning.4">A</a></li>
     2254                  <li>Warning header field&nbsp;&nbsp;<a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.8</a>, <a href="#rfc.xref.header.warning.3">2.9</a>, <a href="#rfc.iref.w.1"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.4">5.2</a>, <a href="#rfc.xref.header.warning.5">A</a></li>
    22052255               </ul>
    22062256            </li>
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