DateTime::Set is a module for datetime sets. It can be used to handle two
different types of sets. The first is a fixed set of predefined datetime
objects. For example, if we wanted to create a set of datetimes containing
the birthdays of people in our family. The second type of set that it can
handle is one based on the idea of a recurrence, such as "every Wednesday",
or "noon on the 15th day of every month". This type of set can have fixed
starting and ending datetimes, but neither is required. So our "every
Wednesday set" could be "every Wednesday from the beginning of time until
the end of time", or "every Wednesday after 2003-03-05 until the end of
time", or "every Wednesday between 2003-03-05 and 2004-01-07".
