[tz] [tz-announce] 2018f release of tz code and data available

[Michael H Deckers]

    On 2018-10-21 03:00, Steve Allen wrote:

> Many examples of non-normalized dates and times exist in historical
> literature.

    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.

    Michael Deckers.