The set of days in a month on which a scheduled action
should take place. There are two sets of bits one can
use to define the day within a month:
Enumerations starting with the letter 'd' indicate a
day in a month relative to the first day of a month.
The first day of the month can therefore be specified
by setting the bit d1(0) and d31(30) means the last
day of a month with 31 days.
Enumerations starting with the letter 'r' indicate a
day in a month in reverse order, relative to the last
day of a month. The last day in the month can therefore
be specified by setting the bit r1(31) and r31(61) means
the first day of a month with 31 days.
Setting multiple bits will include several days in the set
of possible days for this schedule. Setting all bits will
cause the scheduler to ignore the day within a month.
Setting all bits starting with the letter 'd' or the
letter 'r' will also cause the scheduler to ignore the
day within a month.
Note that implementations which maintain a list of pending
activations must re-calculate them when this object is
changed.