[tz] [PROPOSED] Document POSIX versions more carefully

[Paul Eggert]

On 2024-01-28 07:23, Paul Gilmartin wrote:
> Is a draft of that next POSIX publicly available?

You can get a copy by signing up as per the News section of:

https://www.opengroup.org/austin/


> One significant(?)
> UNIX-branded implementation supports only “POSIX.1-2017-like TZ strings”:
>     <https://www.ibm.com/docs/en/zos/3.1.0?topic=variable-command-format>

Thanks, I wasn't aware that z/OS supports only POSIX.1-2017 syntax for 
TZ strings. This behavior was common in older platforms, and I assume 
can happen even today in stripped-down platforms other than z/OS.

As a transition aid for these systems, it's helpful to have a mapping 
from TZDB settings like TZ='Europe/London' to POSIX.1-2017 
approximations like TZ='GMT0BST,M3.5.0/1,M10.5.0'. Perhaps TZDB itself 
should support such a mapping, though now's not the best time to add 
that as we're so close to a release. In the meantime I installed the 
attached documentation patch, which references the posix_tz_db package 
that generates mapping tables.
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