[Alpine-info] ical display confuses me about timezones.

[D. Hugh Redelmeier]

I rarely deal with ical but I'm glad Alpine knows how to display ical 
entries.

I've noticed times reported as "Eastern Standard Time" even if they are 
actually in "Easter Daylight Savings Time".  In this message I explore 
why.

Here's an example:
   Start Date: Wed 2022-10-12 09:30 AM (Eastern Standard Time)
   End Date: Wed 2022-10-12 10:20 AM (Eastern Standard Time)
Those are really Eastern Daylight Times.  The time is right for EDT.

Here's what I've been reading about the ical standard with respect to 
timezones:
<https://icalendar.org/iCalendar-RFC-5545/3-6-5-time-zone-component.html>

Here's an example of the timezone part of an ical entry that displays
incorrectly in Alpine.  It was generated by some Microsoft thing.  I
have added indention to make the structure clear.

BEGIN:VTIMEZONE
	TZID:Eastern Standard Time
	BEGIN:STANDARD
		DTSTART:16010101T020000
		TZOFFSETFROM:-0400
		TZOFFSETTO:-0500
		RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=1SU;BYMONTH=11
	END:STANDARD
	BEGIN:DAYLIGHT
		DTSTART:16010101T020000
		TZOFFSETFROM:-0500
		TZOFFSETTO:-0400
		RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=2SU;BYMONTH=3
	END:DAYLIGHT
END:VTIMEZONE

It would make more sense if the STANDARD and DAYLIGHT sections
contained TZID.  The ical standard allows this but does not require
this.  Microsoft doesn't seem to generate these optional TZIDs.

What can/should Alpine do?

- lobby ical to make tzid mandatory standardc and daylightc sections.
  Not likely to happen and even if it did, it would take a long time
  to filter down to implementations.

- does Alpine even know if daylight time is in effect for a particular 
  date?

- does Alpine know the daylight name of the timezone (clearly not the 
  TZID)?  Is it easy to derive one?

I do think something should be done since the current displayed timezone 
is actually incorrect for times falling in daylight dates.