decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
+ The expiration_time is only stored *locally*,
+ within the :class:`.CacheRegion` instance, and not
+ in the cache itself. Only the *creation time* of a
+ particular value is stored along with it in the cache.
+ This means an individual :class:`.CacheRegion` can
+ be modified to have a different expiration time, which
+ will have an immediate effect on data in the cache without
+ the need to set new values.
:param arguments: Optional. The structure here is passed
directly to the constructor of the :class:`.CacheBackend`