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Re: <time> values in HTML5

From: John Cowan <cowan@mercury.ccil.org>
Date: Sun, 4 Dec 2011 14:00:21 -0500
To: Toby Inkster <tai@g5n.co.uk>
Cc: tantek@cs.stanford.edu, John Cowan <cowan@ccil.org>, Jeni Tennison <jeni@jenitennison.com>, www-xml-schema-comments@w3.org, HTML Data Task Force WG <public-html-data-tf@w3.org>, RDFa WG <public-rdfa-wg@w3.org>, public-html-xml@w3.org
Message-ID: <20111204190021.GC27311@mercury.ccil.org>
Toby Inkster scripsit:

> In areas that observe daylight savings, some days are 3600 seconds
> longer or shorter than usual. [...] There are also leap seconds
> to contend with. [...] And then there's oddities like the 30th of
> December 2011 which, according to the government of Samoa, simply will
> not exist.  [...]

All of these cases except leap seconds have to do with time zones,
but the ISO 8601 / XML Schema model of time does not understand time
zones, only time zone *offsets*.  New York always has the same time zone
(U.S. Eastern, or in Olson-speak America/New_York), but its offset just
changed from -04:00 to -05:00.  Similarly, Samoa's offset will change
from -11:00 to +13:00.  That means that *given a fixed offset* 1 day is
always exactly 24 hours.

As for leap seconds, they simply aren't in the 8601 model at all.
A duration that goes through a leap second is reported as one second
shorter than a true clock will observe it to be.

-- 
John Cowan  cowan@ccil.org    http://ccil.org/~cowan
No man is an island, entire of itself; every man is a piece of the
continent, a part of the main.  If a clod be washed away by the sea,
Europe is the less, as well as if a promontory were, as well as if a
manor of thy friends or of thine own were: any man's death diminishes me,
because I am involved in mankind, and therefore never send to know for
whom the bell tolls; it tolls for thee.  --John Donne
Received on Sunday, 4 December 2011 19:00:59 GMT

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