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

[Max Nikulin]

On 05/02/2023 04:38, Ypo wrote:
> If I wanted to assist to a "Mastering Emacs book club" meeting in 
> America/Vancouver, while living in Spain: Doubt: Should I use local time 
> of America/Vancouver to schedule the meeting?. Like: [2024-02-04 12:00 
> @America/Vancouver] (I don't like space before the @, for the Poll).

Below is my vision. Others may have their own opinions concerning 
particular details.

Depending of choice of persons in charge of this event you should add to 
your .org file either
- <2024-02-04 12:00 @America/Vancouver> if convenience of local 
participants is the most important point
- <2024-02-04 Sun 20:00:00 @Z> == <2024-02-04 Sun 12:00:00 @-0800> if 
enough online participants are expected, so the time is fixed for 
everybody independently of possible changes of the America/Vancouver 
time zone.

You may add <2024-02-04 do. 21:00>, but it will increase maintenance 
burden, see below.

> 1. Doubt: I suppose my agenda timestamp would be: [2024-02-04 do. 
> 21:00]. (Spain local time). Correct?

Agenda may display timestamps in your current time zone using overlays 
or just by formatting during generation of agenda.

> 2. If I went on vacation to Brasília, my agenda timestamp should change 
> to: [2024-02-04 do. 17:00]. (Brasília local time).
>     Doubt: How must the local time zone be updated to get that timestamp 
> changed?

If you have in your file either <2024-02-04 12:00 @America/Vancouver> or 
<2024-02-04 Sun 20:00:00 @Z> then you do not need to update anything. 
You just set your current time zone to proper location in Brazil (and 
perhaps regenerate agenda)

> 3. Back to Spain, I see that, for political reasons, Vancouver's winter 
> time-zone changed from UTC-8 to UTC-9.
>     Doubt: How would my tz database be updated?

On Linux tzdata package is updated several times every year, this case 
you just need to keep your system up to date.

>     Doubt: After updating the tz database, my agenda timestamp would 
> change automatically to  [2024-02-04 do. 22:00]. Correct?

If you saved the event as <2024-02-04 do. 21:00> certainly it is up to 
you to find an update entries (and unsure that no timestamps is updated 
twice) to <2024-02-04 do. 22:00>. In the case of <2024-02-04 12:00 
@America/Vancouver> or <2024-02-04 Sun 20:00:00 @Z> just regenerate 
agenda after update of time zone database (perhaps emacs restart will be 
required).

> 4. For the Poll: What would be the expected behavior if we used the UTC 
> offset?  [2024-02-04 12:00 @-08,America/Vancouver]
>      - We should know beforehand the DST of Vancouver,

Obtaining offset from UTC is not a problem:

LANG=en_US.UTF-8 TZ=America/Vancouver date  -d '2024-02-04 12:00' '+<%F 
%a %T @%z>'
<2024-02-04 Sun 12:00:00 @-0800>

> or there would be 
> warnings. It seems more difficult for the user: maybe the "-08," should 
> be optional?

I expect that both time zone identifier and offset are added either to 
resolve ambiguity of local time around change of time offset or to catch 
updates of timezone database. In the latter case it is optional, but it 
helps to notify you that event time is updated.

>      - Case 3: After updating the tz database we would get warnings too. 
> To correct those warnings, should the UTC offset be changed manually in 
> the timestamp?. If there were 35 meetings in Vancouver throughout the 
> year, to change all the UTC offsets could be non trivial for a normal 
> user: UTC of the summer and winter would differ.

org-lint may present list of inconsistent timestamps. I am afraid, in 
some cases you will have to contact organizers to ensure that event was 
scheduled correctly (either in respect to local time or bound to UTC). 
Communications may require significantly more efforts than fixing 3 
dozens of timestamps.