Changeset 478 for draft-ietf-httpbis
- Timestamp:
- 04/03/09 03:34:49 (13 years ago)
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- 1 edited
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draft-ietf-httpbis/latest-roy/p6-cache.xml
r477 r478 473 473 <t>HTTP caching works best when caches can entirely avoid making requests to the origin 474 474 server. When a response is "fresh" in the cache, it can be used to satisfy subsequent 475 requests without contacting the origin server. This is also referred to as "expiration."<cref source="JRE">What exactly is called 'expiration'?</cref>.</t>476 <t> Expirationapplies only to responses taken from a cache and not to first-hand responses.475 requests without contacting the origin server.</t> 476 <t>This mechanism applies only to responses taken from a cache and not to first-hand responses. 477 477 It cannot be used to force a user agent to refresh its display or reload a resource; its 478 478 semantics apply only to caches. See <xref target="history.lists" /> for an explanation of … … 483 483 target="cache-response-directive" />). Generally, origin servers will assign future 484 484 explicit expiration times to responses in the belief that the entity is not likely to 485 change in a semantically significant way before the expiration time is reached. This 486 normally preserves cache correctness, as long as the server's expiration times are 487 carefully chosen.</t> 485 change in a semantically significant way before the expiration time is reached.</t> 488 486 <t>If an origin server wishes to force a cache to validate every request, it &MAY; 489 487 assign an explicit expiration time in the past. This means that the response is always 490 stale, so that caches should validate it before using it for subsequent requests. </t>488 stale, so that caches should validate it before using it for subsequent requests. <cref>This wording may cause confusion, because the response may still be served stale.</cref></t> 491 489 <t>Since origin servers do not always provide explicit expiration times, HTTP caches may 492 490 assign heuristic expiration times when they are not specified, employing algorithms that
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