Re: [POLL] Proposed syntax for timestamps with time zone info (was: [FEATURE REQUEST] Timezone support in org-mode datestamps and org-agenda)

[Tim Cross]

<tomas@tuxteam.de> writes:

> [[PGP Signed Part:Undecided]]
> On Tue, Jan 31, 2023 at 11:12:00PM +0300, Jean Louis wrote:
>> * Ihor Radchenko <yantar92@posteo.net> [2023-01-31 16:46]:
>> > Specifying just @Europe/Berlin is ambiguous around the daylight savings
>> > transition.
>> 
>> Sorry, I cannot see practical example why is it ambiguous. Unless
>> programmer does not take all information in account, it is not
>> ambigous. People on this planet agree on time zones in advance, so
>> there are few changes that people cannot plan in advance.
>
> (snipped the huge CC list)
>
> Either I understand you wrong, or you don't know what you are
> talking about. 2023-03-23 02:30 @Europe/Berlin refers to /two/
> points in time, thus it /is/ ambiguous. If you use disambiguating
> "time zones" (MEZ vs MESZ in this case) you can resolve that.
>

I think the confusion relates to context interpretation. If you see
@Europe/Berlin in isolation, then it is ambiguous as it can refer to two
different time zone definitions (standard v daylight savings).  However,
if you consider it in conjunction with a date and time, as in 2023-03-23
02:30 @Europe/Berlin, then it isn't ambiguous - in that case, it really
just says 'Lookup the time zone offset in the databse for Berlin as of
that date and time. Now that could change - for example, the German
government might make a temporary or permanent change that would change
the offset from UTC for that date+time the day after I look at it (or
export it). 

Personally, I cannot see the use case of including both a fully
qualitifed time zone (as in @Europe/Berlin) and an offset, but I also
don't know all possible use cases - there could well be use cases where
you want/need to record both the location time zone as well as the
offset at the point when you recorded the timestamp. This is why I'm in
favor of a flexible and extensible syntax and strongly disagree with any
argument which says we don't need UTC or we don't need abbreviated TZ
names or .....