Re: [Tzdist] How should tzdist support rscale?

[Cyrus Daboo <[e-mail]>]

Hi Jonathan,

--On January 5, 2015 at 5:01:02 PM -0500 Jonathan Lennox 
<[e-mail]> wrote:

> A question recently occured to me about the interaction of rscale and
> tzdist.
>
> Should it be possible for a VTIMEZONE -- either inline in an iCalendar
> document, or distributed by tzdist -- to use an RSCALE?

If a time zone were indeed defined in terms of a non-Gregorian recurrence 
then it would seem reasonable to support that.

> There are some natural use cases for this -- Iran uses the Persian
> calendar to set its DST observances, and Israel used the Hebrew calendar
> from 2005-2012.  Right now the IANA tzdata just expands non-Gregorian
> rules to a list of dates, but in principle, RSCALE would be a much more
> natural (and compact) way of representing rules like these.
>
> However, tzdist has no way to negotiate the use of iCalendar extensions.
> Should one be defined?

If tz data publishers actually start wantint to produce data using 
non-Gregorian rules, then we can easily define an extension to the 
capabilities response to indicate that is an option.

> For that matter, the rscale draft doesn't talk about its use in VTIMEZONE
> at all (indeed, it asserts that VTIMEZONEs are always specified in
> Gregorian time).  Should it?

Actually the rscale document only mentions time zones once in Section 1 - 
and there it states that time zone rules (i.e., what comes from a 
publisher) is specified in terms of the Gregorian calendar - that does not 
imply VTIMEZONE itself is limited to Gregorian rules - just that no time 
zone data uses non-Gregorian. If you think that text needs re-wording to 
clarify that, I can certainly change it.

At this point, I think the use of non-Gregorian rules in VTIMEZONE should 
not be ruled out, but tzdist does not need to support it until we have 
publishers actually wanting to use it. Of course at that point things will 
get tricky for the publisher as they will want to keep the Gregorian rules 
around for backwards compatibility.

-- 
Cyrus Daboo