This class handles the cases where you have a time
period with holes. These can be created by the
^ or | operators on time ranges.
Constant
nulltimerange
constant nulltimerange = TimeRange
Description
This represents the null time range,
which, to differ from the zero time range
(the zero-length time range), isn't placed
in time. This is the result of for instance
`& between two strict non-overlapping
timeranges - no time at all.
It has a constant, is_nulltimerange, which
is non-zero. `! on this timerange is true.
Calendar.Ruleset()->set_abbr2zone()