Internationalization: Support for IANA time zones

Shawn Steele Shawn.Steele at
Thu Feb 28 16:13:41 PST 2013

For #5 I might prefer falling back to English or something.  I don't think UTC offset is a good idea because that doesn't really represent a Timezone very well.  (If a meeting gets moved to a following week, that offset might change or be wrong)


-----Original Message-----
From: es-discuss-bounces at [mailto:es-discuss-bounces at] On Behalf Of Norbert Lindenberg
Sent: Thursday, February 28, 2013 3:36 PM
To: es-discuss
Subject: Internationalization: Support for IANA time zones

I'm updating the ECMAScript Internationalization API spec to support the names of the IANA Time Zone Database [1] in DateTimeFormat. I'd like to highlight a few key points of my draft to see whether there are comments:

1) The supported names are the Link and Zone names of the IANA Time Zone Database. Names are matched ASCII-case-insensitively.

2) These names are canonicalized to the corresponding Zone name in the casing used in the IANA Time Zone Database. Etc/GMT and Etc/UTC are canonicalized to UTC. (The subtle differences between GMT and UTC probably don't matter to users of this API.)

3) Implementations must recognize all registered Zone and Link names, reject strings that are not registered, and use best available current and historical information about their offsets from UTC and their daylight saving time rules in calculations. (This is different from language tags and currency codes, where we accept strings that fit a general pattern without requiring reference to the actual registry. The IANA Time Zone Database doesn't specify a general pattern for time zone names, and accepting a string for which UTC offset and DST rules aren't known can only lead to errors.)

4) If no time zone name is provided to the DateTimeFormat constructor, DateTimeFormat.prototype.resolvedOptions returns the canonicalized Zone name of the host environment's current time zone. (This potentially incompatible change was pre-announced in a note in section 12.3.3.)

5) The set of combinations of time zone name and language tag for which localized time zone names are available is implementation dependent. Where no localized time zone name is available, the canonicalized name is used in formatted output.

The last one I'm not entirely comfortable with: IANA time zone names can be long and unfamiliar (e.g., America/Indiana/Tell_City), and sometimes people think the wrong representative city was selected (e.g., Shanghai rather than Beijing for China). An alternative might be to prescribe formatting as an offset from UTC.



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