[tz] Idea for internationalized time point unique time zone abbreviations

[Ian Abbott]

On 2012-06-08 18:10, Mark Davis ☕ wrote:
> Just FYI.
>
> In Unicode CLDR we needed to define a set of abbreviations for timezone
> IDs. They have a different purpose than what's been discussed here; they
> are purely internal ids, and only required because of restrictions in
> BCP47 (so they all needed to be sequences of 3 to 8 ASCII alphanumerics
> - case not significant).
>
> What we did was use the United Nations LOCODE values whenever available,
> which are all 5 characters long and start with the country code. When
> there wasn't one available, we used values that were not of length 5 so
> that they wouldn't collide with future values. So America/Los_Angeles
> gets "uslax", while Etc/GMT-1 gets "utce01".
>
> http://unicode.org/repos/cldr/tags/release-21-0-2/common/bcp47/timezone.xml

Those are abbreviations for the zone names, but a particular zone may 
need different abbreviations at different times, depending on daylight 
savings.  We probably don't want more than 6 characters for the 
abbreviations, which is the SUSv3 value of {_POSIX_TZNAME_MAX}.

Incidentally, Microsoft use the older value 3 for _POSIX_TZNAME_MAX and 
the value 10 for TZNAME_MAX, but their tzname[] values are typically 
longer than that, e.g. "GMT Standard Time" and "GMT Daylight Time". They 
don't make for easy parsing either!

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