On 2010-10-13 18:29, Arthur David Olson wrote on superfluous time zone rules:
(Note that the time zone compiler notices that nothing changes on the first Friday of September, 2010 and does not produce any "extra" output.)
Yes, obviously a switch to winter time directly after another switch to winter time should not hurt. But such "overlapping" switches may confuse a human reader, and in some (imaginary) cases, even the compiler. Consider a rule like # Rule NAME FROM TO TYPE IN ON AT SAVE Rule Palestine 2009 max - Mar lastFri 0:00 1 It says that summer time is used from its value [a] 2009-03-27 + 01 h onwards if winter time has applied before that instant. If summer time had already applied before that instant, then the rule would say that summer time is used from its value [b] 2009-03-27 + 00 h onwards which is, in fact, one hour earlier. Together with the (fictitious) "overlapping" rule # Rule NAME FROM TO TYPE IN ON AT SAVE Rule Palestine 2009 only - Mar 26 23:30 1 which specifies summer time from [c] 2009-03-27 + 00:30 h onwards, the interpretation becomes doubtful: if the second rule [c] is honored, then [a] cannot really apply because local time never took the value 2009-03-27 + 00 h; but [b] implies that [c] cannot apply because local time could never have taken the value 2009-03-26 + 23:30 h. I am not saying that this is a real problem -- I am just proposing to avoid any "overlapping" (useless and potentially confusing) rules. Michael Deckers.