Creates a zoned date-time value, with a date and time of day on that date, and a time zone.
The date part of the format is quite flexible, the main issue is avoid ambiguous dates. Dates like 4/8/2000 could be interpreted as 4th August or 8th April. This issue can be avoided in several ways: you can use the ISO format (e.g. datetime{2010-04-05 12:34} is 5th April), or you can use a month name, e.g. date{5 April 2010 4:56}
For the time part, you can use the 24-hour clock or AM/PM. Fractional seconds are allowed.
Time zones can be specified in two ways. The simplest is as an offset from UTC, e.g. +10:00 is ten hours ahead of UTC, -01:30 is one and a half hours behind. The alternative is to use a continent/city format, e.g. Europe/London. The city format will use the UTC offset that the official local time used on the given date, so datetimezoned{2019-01-14 03:40 Europe/London} is 03:40 UTC as London operates on UTC in the winter, but datetimezoned{2019-05-14 03:40 Europe/London} is 04:40 UTC because London is one hour ahead during the summer.