[tz] Austin Group POSIX TZ changes and Time Zone Taxonomy

Paul Eggert eggert at cs.ucla.edu
Wed Feb 22 22:48:17 UTC 2023

On 2/22/23 11:19, Brian Inglis via tz wrote:

>      https://www.austingroupbugs.net/view.php?id=1619    TZ=Area/Location
> Some of the zones could be categorized as they have proposed, but that 
> uses terminology that I don't think we would approve of, leaves a lot of 
> zones in the tzdb unsupported and unaddressed, and omits a whole reality 
> which I have attempted to categorize in the attached.

Not sure what wording improvements you have in mind. Of the timezones 
you mentioned, the only thing the Austin Group proposal would seem to 
rule out is the rarely used TZDB option of installing leap seconds as 
standard so that TZ="Etc/UTC", TZ="GMT0", etc. have leap seconds. 
Current POSIX already prohibits leap seconds for TZ="GMT0", TZ="GMT-0" 
and TZ="GMT+0"; if POSIX adds a similar prohibition against leap seconds 
in TZ="Etc/UTC" that isn't much of a stretch.

Nothing in the proposed wording would prohibit other legacy names like 
TZ="CET" or TZ="Japan" as extensions, any more than the current POSIX 
wording does.

The biggest glitch I can see with the wording as applied is that it says 
that TZ="America/New_York" will set "The timezone names for standard 
time (std) and, if observed, for DST (dst) to be used by tzset()." This 
suggests that there are at most two abbreviations (one for standard time 
and maybe another for DST). This is not how it works - for example, 
TZ="America/Los_Angeles" supports five abbreviations (LMT, PDT, PPT, 
PST, PWT) to cover past historical practice.

Presumably this glitch is related to POSIX also considering adding 
support for tm_gmtoff and tm_zone - do you know what's going on there?

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