Percentage multiplier used to calculate the expiration date of
a binary object if the expiration date is not explicitly specified.
This percentage is multiplied by the age of the object to calculate
the freshness time of the object. The expiration date is
the sum of the freshness time and the date the object was last
retrieved from the server or verified was up-to-date. The object
will be considered stale after its expiration date and a subsequent
If-Modified-Since (IMS) request will be revalidated with the
server by the cache engine.
If zero, the calculated expiration time will indicate that the
the object expires immediately.