[tz] Version in zoneinfo files?

[Paul_Koning at dell.com]

> On Oct 27, 2015, at 12:20 PM, lester at lsces.co.uk wrote:
> 
> The major problem all the time is identifying just what rules were applied when processing historic data, which may actually only be a current meeting diary. One can not assume that the current rule set actually correctly translates the current data if one set predates a later change. 

I'm not sure I understood correctly what you intended.  Are you talking about this case:  I make a calendar entry for 9 am local time next year.  The calendar system translates that to UTC and stores that time in its database.  A few months later, the TZ rules change, and that same UTC time is now 10 am local.

The difficulty with cases like this is that it is not obvious what the desired outcome is.  It might be that I want this event to occur at 9 am local time, and I don't care what that is in UTC.  But it is also possible that I want it to occur at whatever UTC corresponds to 9 am local -- for example, because this is a teleconference with people in several countries.

It might even be true that the desired answer varies depending on which calendar entry you're looking at.  A dentist appointment is probably strictly in local time; a call with a colleague in another continent is probably primarily in UTC.

This doesn't feel like a zoneinfo issue; it's a user interface design question for calendar applications.

	paul