> Yeah, this stuff is weird, but only finitely so, because ultimately a computer’s gotta implement them Historic data can be recorded. Rules like "last Sunday

> Yeah, this stuff is weird, but only finitely so, because ultimately a computer’s gotta implement them Historic data can be recorded. Rules like "last Sunday in October" or "first day of Ramadan" can be implemented and handled automatically (even if the current Unix implementations don’t do non-Gregorian calendars out-of-the-box). But there can be time zones whose DST rules are "if the groundhog sees its shadow, we start DST two weeks later, otherwise, there is no DST this year". Some countries actually implement this, except the groundhog is replaced by your friendly local regime.