A string when not using an output range; void otherwise.
assert(DateTime(Date(2010, 7, 4), TimeOfDay(7, 6, 12)).toISOString() == "20100704T070612"); assert(DateTime(Date(1998, 12, 25), TimeOfDay(2, 15, 0)).toISOString() == "19981225T021500"); assert(DateTime(Date(0, 1, 5), TimeOfDay(23, 9, 59)).toISOString() == "00000105T230959"); assert(DateTime(Date(-4, 1, 5), TimeOfDay(0, 0, 2)).toISOString() == "-00040105T000002");
Converts this DateTime to a string with the format YYYYMMDDTHHMMSS. If writer is set, the resulting string will be written directly to it.