On 12/31/20 11:22 AM, Brian Park wrote:
The thing that I was wondering was whether the semantics of the zone info text files actually mandated a transition from 2:00 to 1:00 for Grand_Turk, if the Zone entry was set to 2:00, instead of its current 3:00 value. Or whether the special case in the zic compiler was an additional rule on top of the normal semantics of the zone info text files, in order to parse the Grand_Turk case properly.
The latter. That is, original semantics would have required two transitions there, but when this sort of problem was discovered in the mid-1990s the zic behavior was changed by adding the special case. Unfortunately, this special case wasn't documented in the zic man page until recently. The recent doc change is here: https://github.com/eggert/tz/commit/b804a741d5cdb5d1b761de9ad053ba916fa08636 and you can see a recent message about this here: https://mm.icann.org/pipermail/tz/2020-December/029616.html