Version 2023.1

Upstream version 2023a released 2023-03-22T19:39:33+00:00

Briefly:

Egypt now uses DST again, from April through October. This year Morocco springs
forward April 23, not April 30. Palestine delays the start of DST this year.
Much of Greenland still uses DST from 2024 on. America/Yellowknife now links to
America/Edmonton. tzselect can now use current time to help infer timezone. The
code now defaults to C99 or later. Fix use of C23 attributes.

Changes to future timestamps

Starting in 2023, Egypt will observe DST from April's last Friday through
October's last Thursday. (Thanks to Ahmad ElDardiry.) Assume the transition
times are 00:00 and 24:00, respectively.

In 2023 Morocco's spring-forward transition after Ramadan will occur April 23,
not April 30. (Thanks to Milamber.) Adjust predictions for future years
accordingly. This affects predictions for 2023, 2031, 2038, and later years.

This year Palestine will delay its spring forward from March 25 to April 29 due
to Ramadan. (Thanks to Heba Hamad.) Make guesses for future Ramadans too.

Much of Greenland, represented by America/Nuuk, will continue to observe DST
using European Union rules. When combined with Greenland's decision not to
change the clocks in fall 2023, America/Nuuk therefore changes from -03/-02 to
-02/-01 effective 2023-10-29 at 01:00 UTC. (Thanks to Thomas M. Steenholdt.)
This change from 2022g doesn't affect timestamps until 2024-03-30, and doesn't
affect tm_isdst until 2023-03-25.

Changes to past timestamps

America/Yellowknife has changed from a Zone to a backward compatibility Link, as
it no longer differs from America/Edmonton since 1970. (Thanks to Almaz
Mingaleev.) This affects some pre-1948 timestamps. The old data are now in
'backzone'.

Changes to past time zone abbreviations

When observing Moscow time, Europe/Kirov and Europe/Volgograd now use the
abbreviations MSK/MSD instead of numeric abbreviations, for consistency with
other timezones observing Moscow time.

Changes to commentary

tz-link.html has a new section "Coordinating with governments and distributors".
(Thanks to Neil Fuller for some of the text.)

To improve tzselect diagnostics, zone1970.tab's comments column is now limited
to countries that have multiple timezones.

Note that leap seconds are planned to be discontinued by 2035.