Calendar::build() -- Abstract method for building the children of a calendar object.
Calendar::fetch() -- Iterator method for fetching child Calendar subclass objects (e.g. a
minute from an hour object). On reaching the end of the collection,
returns false and resets the collection for further iteratations.
Calendar::fetchAll() -- Fetches all child from the current collection of children
Calendar_Month_Weekdays::build() -- Builds Day objects in tabular form, to allow display of calendar month
with empty cells if the first day of the week does not fall on the first
day of the month.