Whether daylight saving time is being observed:
standardZoneRule: A hyphen, a kind of
nullvalue, means that we have not set our clocks ahead of standard time.
PeriodZoneRule: An amount of time (usually but not necessarily
1:00meaning one hour) means that we have set our clocks ahead by that amount.
BasedZoneRule: Some alphabetic string means that we might have set our clocks ahead; and we need to check the rule the name of which is the given alphabetic string.