[tz] Timezone in Brazil

[Guy Harris]

On Oct 9, 2015, at 12:43 PM, Matt Johnson <mj1856 at hotmail.com> wrote:

> "Metazone" is a CLDR term. See:
> http://www.unicode.org/reports/tr35/tr35-dates.html#Metazone_Names

And

	http://www.unicode.org/reports/tr35/tr35-dates.html#Using_Time_Zone_Names

as well.

To remove one layer of indirection, what's relevant in the section of the document pointed to by the first link is

	A metazone is an grouping of one or more internal TZIDs that share a common display name in current customary usage, or that have shared a common display name during some particular time period. For example, the zones Europe/Paris, Europe/Andorra, Europe/Tirane, Europe/Vienna, Europe/Sarajevo, Europe/Brussels, Europe/Zurich, Europe/Prague, Europe/Berlin, and so on are often simply designated Central European Time (or translated equivalent).

and what's relevant in the portion of the document pointed to by the second link is

	Metazone - a collection of time zones that share the same behavior and same name during some period. They may differ in daylight behavior (whether they have it and when).

	For example, the TZID America/Cambridge_Bay is in the following metazones during various periods:

	<timezone type="America/Cambridge_Bay">
	<usesMetazone to="1999-10-31 08:00" mzone="America_Mountain"/>
	<usesMetazone to="2000-10-29 07:00" from="1999-10-31 08:00" mzone="America_Central"/>
	<usesMetazone to="2000-11-05 05:00" from="2000-10-29 07:00" mzone="America_Eastern"/>
	<usesMetazone to="2001-04-01 09:00" from="2000-11-05 05:00" mzone="America_Central"/>
	<usesMetazone from="2001-04-01 09:00" mzone="America_Mountain"/>
	</timezone>

	Zones may join or leave a metazone over time. The data relating between zones and metazones is in the supplemental information; the locale data is restricted to translations of metazones and zones.

	Invariants:

		* At any given point in time, each zone belongs to no more than one metazone.
		* At a given point in time, a zone may not belong to any metazones.
		* Except for daylight savings, at any given time, all zones in a metazone have the same offset at that time.

Presumably "same name" is "same name modulo daylight savings time"; a zone or metazone can have "generic", "standard", and "daylight" versions of both "long" and "short" names ("short" name generally means "abbreviation").

The idea is, I guess, that you don't want to have to nationalize "Central European Time" N times for each tzdb zone to which it applies, so you put all the tzdb zones that use it in the same metazone.

This requires the CLDR to duplicate information from the tzdb, so that, for a given zone, there are rules in the CLDR to indicate which metazone applies during which periods if the zone name changes over time, as per the above example for America/Cambridge_Bay.

Would it be at all useful for the tzdb to itself maintain the notion of metazones, perhaps giving a metazone name as an additional component of a Zone line?