Re: UTC or not UTC for timestamps in the past ([FEATURE REQUEST] Timezone support in org-mode)

[Thomas S. Dye]

Aloha Jean Louis,
Jean Louis <bugs@gnu.support> writes:

> * Thomas S. Dye <tsd@tsdye.online> [2023-01-22 20:36]:
> > > After all, for a person in Berlin [2023-01-22 Sun 
> > > 08:29@+1100] may
> > > tell more than [2023-01-22 Sun 08:29@Australia/Sydney].
> >
> > I'm not sure to follow this.  IIUC, the timestamp with offset 
> > refers to
> > absolute time, whereas the timestamp with the Australia/Sydney 
> > timezone
> > refers to a region of space/time whose relation to absolute 
> > time is fixed
> > for any moment, but potentially variable over time.
>
> I understand above that it is easier understandable when reading
> [2023-01-22 Sun 08:29@+1100] as it is assumed by poster (I guess 
> Max)
> that user will understand that there is +11 hours ahead.
Yes, the offset here is ambiguous--is it offset from some timezone 
or from UTC?

> That is assumption by poster. I do not find it easier.
>
> As when user sees 08:29 that user will think of time in Berlin, 
> of
> time which is not in UTC, and not time in UTC plus 11 hours.
>
> What is easier is what is generally accepted in any type of 
> software
> worldwide, just represent it in local time zone.
>
> Difference between offset time and time with time zone is that 
> time
> zone includes rules of daylight savings and other anomalies.

Right.  The difficulty with scheduling is that it has to take into 
account two time zones in some cases.

Here is a proposal for a terminology of events that honors 
Ramsey's distinction between events and occurrences and hopes to 
cover all of Org's use cases.

* Kinds of event
- No-host event :: An event that takes place at an absolute time. 
Participants must know their local timezone offset from UTC. 
Example [2023-01-23 06:00@UTC].
- Situated event :: An event that takes place at a time local to 
the event site.  Participants must know their local timezone 
offset from UTC and the event site timezone offset from UTC at 
the time of the event.  Example [2023-01-22 Sun 
08:29@Australia/Sydney].
- [Itinerant | Traveling | Mobile] event :: An event that takes 
place at a time local to the event site, which might change after 
the event has been scheduled.  Participants must know their local 
timezone offset from UTC and the event site timezone offset from 
UTC at the time of the event.  Examples might be a regular staff 
meeting that takes place at 9:00 AM wherever the boss happens to 
be, or a proposal to meet with a traveler when it is noon on 
Sunday for the traveler. Example [2023-01-23 06:00].  In this 
case timezone is set according to user timezone preference in 
scope.

The Org user should be able to toggle timestamp representation. 
In the case of a no-host event, user might toggle between UTC and 
local time.  In the case of situated or itinerant event, user 
might toggle among UTC, local time, and local time at the event 
site.

WDYT?

All the best,
Tom

--
Thomas S. Dye
https://tsdye.online/tsdye