[tz] [tz-announce] 2018f release of tz code and data available
Michael H Deckers
michael.h.deckers at googlemail.com
Sun Oct 21 21:24:47 UTC 2018
On 2018-10-21 03:00, Steve Allen wrote:
> Many examples of non-normalized dates and times exist in historical
For time stamps of UTC, or of a time scale derived from UTC
with a piecewise constant offset (as for civil time scales),
time-of-day values on or after 24 hours may be ambiguous due
to leap seconds.
The fictitious UTC time stamp "2016-12-31T25Z" could
indeed be taken to mean
2016-12-31T00Z + 25 h = 2017-01-01T00:59:59Z or else
2017-01-01T00Z + 01 h = 2017-01-01T00:00:00Z.
That is probably one reason why the draft new version
of ISO 8601 proposes to drop even the notation for the time
of day 24 h after midnight (does "2016-12-31T24Z" mean
2016-12-31T23:59:60Z or 2017-01-01T00:00:00Z?).
It is true that this ambiguity can arise at most for two
(or twelve) dates in a year, but a parser for zic input
has to deal with all cases, and cannot be written correctly
unless the notation is defined unambiguously.
There is no such ambiguity with day of the month numbers
less than 01 or > ultimo, so that it is always possible
to avoid any time-of-day values below 00 h or on or after 24 h
in time stamps of UTC or of civil times.
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