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

[Robert Horn]

Ihor Radchenko <yantar92@posteo.net> writes:

> Robert Horn <rjhorn@panix.com> writes:
>
>>> 1. Time (YYYY-MM-DD HH:MM) not continuous and may change arbitrarily at
>>>    certain times a year or in future or in the past:
>>>    - DST transitions are not stable and change from year to year
>>>      according to strange rules that may involve Julian dates or
>>>      counting weekdays
>>>    - DST transition rules may change over time
>>>    - The new year day itself is not necessarily fixed (England
>>>    - Julian/Gregorian transitions happened at different times in
>>>      different countries
>>
>> Note that as a result "time when it happened" has different rules than
>> "future time when it is scheduled".  There are lots of other times that are
>> scheduled as "future local time, subject to changing DST rules".  This
>> is particularly tricky for repeating times for regularly scheduled events.
>
> Not really. Countries may change DST at any moment in future. Or decide
> to switch calendars (consider countries near the day transition line).
>
> And "past local time, according to the DST rules in effect at the time"
> is also an option that might be useful in certain scenarios.
>

The issue is clarity of the expected rules for the format.  If I
schedule a meeting for 10:05 DST, but the rules change so that it is not
DST at that location at that time in the future, what is the expected
interpretation?  It could be:

 a) the meeting should be at 10:05 ST, because the intent was to meet at
 10AM in the then local time.
 
 b) the meeting should be at 11:05 ST, because the time was chosen to
 correspond to a particular sun angle.

Getting the rules and explanation clear is the issue.  It's a mistake
that a great many people make with scheduling meetings.  Those two
behaviors need different encodings because they behave differently.

-- 
Robert Horn
rjhorn@alum.mit.edu