[tz] Discussion in ECMA about tz identifiers in JavaScript

Mark Davis ☕ mark at macchiato.com
Tue Mar 5 08:22:06 UTC 2013

The main issue for CLDR and other clients like it is to be able to have
completely stable canonical identifiers. The zone.tab doesn't quite work
for that, because of changes like Asia/Kolkata. As far as CLDR is
concerned, the TZIDs are purely internal identifiers, and it makes no
difference whether one is spelled Calcutta or Kolkata; end users should
never ever see those anyway. What is a great concern is maintaining
stability of the identifiers, so that they are stable keys for translations
and other related usage. That's why CLDR needs to keep its own list (not
really wanting to). These use the zone.tab IDs, but are stabilized (eg, no
changes in spelling). CLDR also adds one identifier "Etc/Unknown", which is
used in circumstances where a field is required, but there is no valid,
known TZID.

Note: I was wrong about the removal of IDs: I was thinking of the removal
of Timbuktu in 2006, but that was moved to the backward file.


Not germane to the above, but FYI:

CLDR also adds BCP47-compatible stable short identifiers. BCP47 has the
historical restriction of no more than 8 characters, and only ASCII letters
and digits. The short identifiers use UN [LOCODE] 5-letter codes wherever
possible. There are a few identifiers of length not equal to 5, used where
there is no corresponding LOCODE, such as "usnavajo" for "America/Shiprock
Navajo", or "utcw01" for "Etc/GMT+1". Example:

<type name="inccu" alias="Asia/Calcutta Asia/Kolkata" description="Kolkata,

There is one other (minor) issue with the identifiers. The TZDB separates
zones by country in zone.tab, but it is missing the following BCP47 regions:

Ascension Island [AC]
Bouvet Island [BV]
Clipperton Island [CP]
Diego Garcia [DG]
Ceuta and Melilla [EA]
Heard Island and McDonald Islands [HM]
Canary Islands [IC]
Tristan da Cunha [TA]

Some of these are simply rocks with no permanent inhabitants, but for
testing completeness it is useful to have them.

Mark <https://plus.google.com/114199149796022210033>
*— Il meglio è l’inimico del bene —*

On Mon, Mar 4, 2013 at 11:37 PM, Paul Eggert <eggert at cs.ucla.edu> wrote:

> That discussion seems to be predicated on the assumption that
> tz zone names can and do "disappear", but they don't.  For example,
> we renamed Asia/Calcutta to Asia/Kolkata, but kept the old name
> as an alias for the new one.
> I'm not sure it's worth my time to join that discussion (I am
> already on too many mailing lists) but you might want to forward
> this information.
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