[LEAPSECS] Leap second relationship to ISO 8601

[Clive D.W. Feather]

Brooks Harris said:
>> ISO 8601 does not represent daylight saving nor time zones.
> It can represent both, but incompletely, or ambiguously. The "time 
> element" called "zone designator" conflates "offset from UTC" and 
> "Daylight Savings offset" in the "time element" called "zone designator".

No. Its "zone designator" is actually offset from UTC. This is because it
is using a different meaning for the term "zone" than the TZ list does.

Compare the "military time zones". Without physically moving, for part of
the year I am in "zone" Zulu and for part of the year I am in "zone" Alpha.
That's their definition of "time zone". The TZ list would say that, at all
times, I am in "zone" Europe/London.

> Incorrect where? 2014-07-04T00:00:00-05:00 would have been correct in 
> Chicago. We only know this because we know a-priori Daylight Savings was 
> in effect in that jurisdiction.

No. Because we know that Chicago was using offset UTC-5 at the time.

> It was 2014-07-04T00:00:00-06:00 
> "Mountain Daylight Time" while it was 2014-07-04T00:00:00-07:00 in 
> Arizona, which does not observe Daylight Savings.

But note that these are *DIFFERENT* times. That one happened an hour after
the other one.

> Strictly from the 8601 representation we don't know if Daylight was in 
> effect or even if it is observed in the jurisdiction, so we can't 
> distinguish the "fixed offset from UTC to the local jurisdiction".

I've just looked at ISO 8601:2004 and can't find this phrase at all. What I
*do* find is:

2.1.14
standard time
time scale derived from coordinated universal time, UTC, by a time shift
established in a given location by the competent authority
[IEC 60050-111]
NOTE This time shift may be varied in the course of a year.

It is made clear in 4.2.5.1 and 4.2.5.2 that the offset notation shows
"the difference between the time scale of local time and UTC", and nothing
else. It is also noted in 4.2.2.1 that "no provisions have been made to
prevent ambiguities in expressions that result from discontinuities in the
time scale of local time (e.g. daylight saving time).".

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Clive D.W. Feather          | If you lie to the compiler,
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