If the cache entry was revalidated after the cache synchronization date and there are no server revalidation requirements that make the cached entry invalid, the entry from the cache is used.
如果缓存项的重新验证日期比缓存同步日期晚，而且没有使缓存项无效的服务器重新验证要求，则使用缓存中的项。
Revalidation can fail, for example, if the user credentials have changed on the server.
例如，如果服务器上的用户凭据已更改，则重新验证将会失败。
If the cache entry was last revalidated prior to the cache synchronization date, revalidation with the server occurs.
如果缓存项的上次重新验证日期比缓存同步日期早，则发生服务器重新验证。
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