Connected: An Internet Encyclopedia
13.13 History Lists
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13 Caching in HTTP
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13.13 History Lists
13.13 History Lists
User agents often have history mechanisms, such as "Back" buttons and
history lists, which can be used to redisplay an entity retrieved
earlier in a session.
History mechanisms and caches are different. In particular history
mechanisms SHOULD NOT try to show a semantically transparent view of
the current state of a resource. Rather, a history mechanism is meant
to show exactly what the user saw at the time when the resource was
retrieved.
By default, an expiration time does not apply to history mechanisms.
If the entity is still in storage, a history mechanism should display
it even if the entity has expired, unless the user has specifically
configured the agent to refresh expired history documents.
This should not be construed to prohibit the history mechanism from
telling the user that a view may be stale.
Note: if history list mechanisms unnecessarily prevent users from
viewing stale resources, this will tend to force service authors to
avoid using HTTP expiration controls and cache controls when they
would otherwise like to. Service authors may consider it important
that users not be presented with error messages or warning messages
when they use navigation controls (such as BACK) to view previously
fetched resources. Even though sometimes such resources ought not
to cached, or ought to expire quickly, user interface
considerations may force service authors to resort to other means
of preventing caching (e.g. "once-only" URLs) in order not to
suffer the effects of improperly functioning history mechanisms.
Next: 14 Header Field Definitions
Connected: An Internet Encyclopedia
13.13 History Lists