Calendar provides an API for building Calendar data structures. Using
the simple iterator and it's "query" API, a user interface can easily be
built on top of the calendar data structure, at the same time easily
connecting it
to some kind of underlying data store, where "event" information is
being held.

It provides different calculation "engines" the default being based on
Unix timestamps (offering fastest performance) with an alternative using
PEAR::Date
which extends the calendar past the limitations of Unix timestamps. Other
engines
should be implementable for other types of calendar (e.g. a Chinese
Calendar based
on lunar cycles).