Re: [FEATURE REQUEST] Timezone support in org-mode datestamps and org-agenda

[Tim Cross]

Jean Louis <bugs@gnu.support> writes:

> * Tim Cross <theophilusx@gmail.com> [2023-01-28 00:15]:
>> >
>> >> What kinds of representations would a calendar system capable of
>> >> handling timezones require?
>> >> 
>> >> • Instant (fixed)
>> >>   • This is referring to an unambiguous moment in time
>> >>   • e.g., 2007-02-03T05:00:00.000Z
>> >> • Offset (fixed)
>> >>   • This captures the idea of "when did it happen for the person who
>> >>     made the observation"
>> >>   • e.g., 2007-02-03T04:00:00.000+01:00
>> >
>> > Offset is not that fixed, maybe from viewpoint of storage as maybe it
>> > is considered fixed in it's representation, but you have to keep in
>> > mind that time offset by it's definition is changing itself, suddenly,
>> > depending of daylight saving and time zone.
>> >
>> 
>> I think your misinterpreting the intent here. If you specify a timestamp
>> with offset, it is fixed.
>
> That is what you say. And I am pointing out to international standard
> references.
>
> If you use offset as "fixed" it means such use would not be by
> standard, and you would confusing users and programmers who are using
> standard for calculations in programs.
>
>> It does not change with daylight savings or any other change in
>> rules for a time zone. It does not even specify a time zone.
>
> And while and before making that decision, did you review the standard
> that time zone offset is influenced and changed by daylight savings?
>
> It does not specify time zone. But it is derived from time zone, and
> is not same from time zone.
>
> Are you aware that time zone offset could have "skipped time" or
> "added time" due to daylight savings?
>
> That implies that by using time offset, you would forget daylight
> savings which are international standard, and make calculations wrong,
> because you started applying own standard in Org.
>

I think your still misunderstanding what is meant by offset.

Yes, a timezone is defined by the offset it has from UTC
Yes, a location time zone may change due to various reasons, such as
daylight savings time, which also means the offset for that timezone
changes. However, it is the time zone definition which has
changed. THink of it as a time zone with a new offset rather than a time
zone with a chagned offset. 

When you specify a date+time wiht an explicit offset, that offset is
fixed. That date+time is fixed. It will not change when daylight davings
comes in or goes out because it isn't a time zone. It is only an offset
and has no location reference and therefore no time zone.

Saying that an offset is a fixed value is very different from saying
that a time zone has a fixed offset. I think this is where your
confusion is coming from.