[tz] Why is "AEST" the abbreviation for Australia/Sydney in 1900?

[brian.inglis at systematicsw.ab.ca]

On 2024-05-02 12:35, Paul Eggert via tz wrote:
> On 2024-04-30 16:21, Arthur David Olson via tz wrote:
>> For a given zone, each line describing the zone except for the last ends
>> with an until time. The creation of the transition time entry for the until
>> time is deferred until the following zone line has been completely
>> processed. (It happens at the bottom of the giant for loop in outzone.)
>> That deferral means that the time zone abbreviations in use have been
>> computed, so the appropriate abbreviation can be applied to the until time.
> 
> OK, but this wouldn't address the issue of what happens with the last zone line, 
> as that lacks an until time. For example:
> 
>   Rule Aus 1917 only - Jan 1 2:00 1:00 D
>   Rule Aus 1917 only - Mar 1 2:00 0    S
>   Zone Australia/Sydney 10:00 Aus AE%sT
> 
> zic generates a TZif file where time type 0 (the time type before 1917) uses the 
> abbreviation "AEST" - but where did that "S" come from? The documentation 
> doesn't say. I think this is Jonathan's main point.
> 
> When computing %s for timestamps that come before the earliest rule, zic uses 
> the LETTER/S field of the earliest rule that specifies standard time. I 
> installed the attached to try to document this.

I would expect it to default to "S" to allow "%s" in zones without rules.

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry