[tz] Some rules in tz specification files seem to be applied (by zic) outside of their declared period of applicability

[Michael H Deckers]

On 2019-01-15 20:48, Parsifal Herzog wrote:


I am trying to read the zic manual page as a specification, and I do not 
understand why
> zic inserts that transition. It seems to me that either the last Zone 
> line (SAST) would
>
> remain in effect until 1994, as there is no other transition defined, 
> or that period is in
> an undefined state, as the SAST transition is not in effect after1990 
> March 21.
>
> Can someone correct my understanding?
>
    Let me try.

    Your observation is correct: a "transition" in a tzdb
    zone time like Africa/Windhoek does not always imply
    a change in the time; it can also mean a change in the
    abbreviation, or in the value of the dst bit (or any
    combination of the three).

    In the case at hand, the abbreviation changes from SAST
    (for South African Standard Time) to CAT (Central African Time).
    This change is appropriate at the date when Namibia became
    independent from South Africa.

    Michael Deckers.