Convert between dates, times and days of the respective types. For
instance time-tai->time-utc accepts a time object of type
time-tai and returns an object of type time-utc.
The ! variants may modify their time argument to form
their return. The plain functions create a new object.
For conversions to dates, tz-offset is seconds east of
Greenwich. The default is the local timezone, at the given time, as
provided by the system, using localtime (see Time).
On 32-bit systems, localtime is limited to a 32-bit
time_t, so a default tz-offset is only available for
times between Dec 1901 and Jan 2038. For prior dates an application
might like to use the value in 1902, though some locations have zone
changes prior to that. For future dates an application might like to
assume today’s rules extend indefinitely. But for correct daylight
savings transitions it will be necessary to take an offset for the
same day and time but a year in range and which has the same starting
weekday and same leap/non-leap (to support rules like last Sunday in
October).