time zone object

[Paul Eggert]

   Date: Mon, 29 Sep 1997 16:59:50 -0700 (PDT)
   From: ncm at cantrip.org (Nathan Myers)

   we also need to ... specify caching of retrieved information with
   preference for the cached data up to an expiry date.  This requires
   representing the expiry date in the cached file.

I don't think it's realistic to insist on an expiry date for time zone rules.
In practice, these rules can change with very little notice.  For example,
last year the Sri Lankan government gave less than 24 hours' notice
of an emergency rule change that moved the clocks ahead by an hour.
See ``Sri Lanka advances clock by an hour to avoid blackout'',
http://www.virtual-pc.com/lankaweb/news/items/240596-2.html
(1996-05-24).

In general, time zone rules are ``until further notice'',
and any automated system for propagating time zone rules
will just have to take this into account.