Re: POSIX TS spec reverses the meaning of TZ offset compared to ISO (was: [FEATURE REQUEST] Timezone support in org-mode datestamps and org-agenda)

[Max Nikulin]

On 01/02/2023 20:26, Ihor Radchenko wrote:
> There is potential confusion coming from the different interpretations
> of the time zone offsets used in ISO8601 and POSIX TZ specs:

Ihor, I am sorry that I did not reply to your early question.

Is there a strong reason to support POSIX TZ? Time zones with fixed 
offsets are available as e.g. Etc/GMT-8 (unfortunately inverted sign as 
well).

In a link posted in this thread I noticed the following:
http://naggum.no/lugm-time.html
Erik Naggum. The Long, Painful History of Time. 1999
> 8.2 Timezone Representation
>
> David Olsen of Digital Equipment Corporation has laid down a tremendous
> amount of work in collecting the timezones of the world and their
> daylight saving time boundaries. Contrary to the Unix System V approach
> from New Jersey (insert appropriate booing for best effect), which
> codifies a daylight saving time regime only for the current year, and
> apply it to all years, David Olsen's approach is to maintain tables of
> all the timezone changes.

POSIX spec neglects history of changes. At certain moment Firefox used 
IANA TZ DB with accurate data while Chrome followed JavaScript spec that 
required POSIX-like approach for local time zone. The latter was pain. I 
consider POSIX TZ as legacy.