[Evolution] Differing ical interpretations

[Nigel Metheringham <Nigel Metheringham dev intechnology co uk>]

I'm generating a bunch of ical events from a db application which I want
to make available to various applications including evolution,
phpicalendar, ical and the mozilla calendar stuff.

However each of these appears to implement a slightly different
interpretation of the standard - especially where recurrences are involved.

At present I am playing with different ways of expressing the same thing
(the ical standard is frankly too big and too flexible, so everyone
handles the bits differently).

For example evolution expresses recurrance rules (RRULE) until a date,
with the date set as just a date.  If that is fed to ical then the last
recurrance is dropped since the until date appears to be interpreted as
00:00 (ie midnight) at the start of that day.  Instead ical does untils
with a time of 23:59:59Z on the date.  I haven't even started testing
how exceptions are handled....

Does anyone (like the calendar hackers) know of any interoperability
standards for ical?
Or hints how to express things so they work for pretty much everyone?

Cheers
    Nigel.