<!doctype html public "-//W3C//DTD W3 HTML//EN">
<html><head><style type="text/css"><!--
blockquote, dl, ul, ol, li { padding-top: 0 ; padding-bottom: 0 }
--></style><title>Re: [whatwg] <time></title></head><body>
<div>At 19:01 -0500 14/03/09, Robert J Burns wrote:</div>
<blockquote type="cite" cite>The problem isn't that negative integers
are not well-defined and understood well. The problem is understanding
how an ISO 8601 representation - such as these examples include -
maps to an author's or user's understanding of the year 2 BC (or is it
1 BC?). ISO 8601 provides no clear way out of that
ambiguity.</blockquote>
<div><br></div>
<div>I disagree. It lays out a clear way of labelling dates,
that happens to correspond to the Gregorian calendar after its
introduction.</div>
<div><br></div>
<div>It has a year 0 (because both it uses normal integers to count
years, and because this keeps the leap year calculation correct).
In everyday usage, 1BC (1BCE) precedes 1AD (1CE). So, yes, there
is a adjustment of 1 moving between the two.</div>
<div><br></div>
<blockquote type="cite" cite>It isn't a matter of denial or belief.
This is an issue of precisely defining a Gregorian calendar to apply
to the past: a calendar which was defined in 1582 with only the future
in mind. ISO 8601 could have stepped in an further defined the
Gregorian calendar but it punted.</blockquote>
<div><br></div>
<div>Since it defines both zero and negative years, how did it
punt?</div>
<div><br></div>
<blockquote type="cite" cite>If I understand current proleptic
Gregorian calendar use correctly (such as that used by astronomers)
the implication is that HTML will not match the other uses of that
calendar. ISO 8601 has unambiguous leap year rules which are to be
applied to 000 and negative years as well. If we accept year 0, then
-0001 would mean 2 BC. That's fine, but we need to make it clear to
authors and there's some concern authors would make the mistake of
thinking -0001 was instead 1 BC.</blockquote>
<div><br></div>
<div>A note pointing this out might be prudent.</div>
<div><br></div>
<blockquote type="cite" cite>However, if the UA displays the
information in a non-machine readable form, how does it make that
conversion for presentation purposes. Does 0000-01-01 get displayed as
1 January 1 BC? Or as 1 January 00?</blockquote>
<div><br></div>
<div>UA choice; it might display it in a different (mappable)
calendar system entirely. That's one of the major points of
having a well-defined day-labelling system - it can be mapped to any
other well-defined system.</div>
<div><br></div>
<blockquote type="cite" cite><br>
<blockquote type="cite" cite>Here his the only debate I see over
this:<br>
ISO 8601:2000 and above suggest that year 0000 be used and be
considered year 1 BC, and then -0001 is 2 BC, etc.</blockquote>
</blockquote>
<blockquote type="cite" cite><br>
Could you cite specifically where you get that from ISO 8601:2000? I'm
looking at ISO 8601:2004 and don't see a clear indication of that
anywhere.</blockquote>
<div><br></div>
<div>"<font color="#000000">Consecutive calendar years are
identified by sequentially assigned year numbers</font>"</div>
<div><br></div>
<div>In sequential numbers, zero precedes 1. In case of doubt,
it even says, emphasizing that there is a year labelled as 0:</div>
<div><br></div>
<div>"<font size="-1" color="#000000">In the proleptic Gregorian
calendar, the calendar year [0000] is a leap year.</font> "</div>
<div><br></div>
<div>It doesn't comment on mapping to other uses; it merely
labels days and years. If you want to map to a calendar that
omits the label "0" but uses 1BC (BCE) instead, then you'll
need to adjust by 1. It could (but should not) have sections on
mapping to any number of other calendar formats.</div>
<div><br></div>
<blockquote type="cite" cite>We aren't really asking much of UAs in
terms of implementation here. The HTML5 draft includes algorithms to
parse the dates, but whatever happens with them after they are parsed
are left up to other processors and other standards. This means that
allowing keyword differentiation of alternate calendars (with clear
norms for an omitted keyword and a "Gregorian" keyword)
requires very little of UAs.</blockquote>
<div><br></div>
<div>It requires a huge amount; instead of mapping ISO 8601 to
whatever they want to present, they have to be ready for arbitrary
numbers of source formats, and they'll fail if the source format is
unrecognized.</div>
<div><br></div>
<div>If the author can't convert it, why assume the UA can?</div>
<div><br></div>
<div>At 13:14 +0100 16/03/09, Leif Halvard Silli wrote:</div>
<blockquote type="cite" cite>I can live with @datetime limited to
ISO-8601, as long as @datetime also lives up to ISO-8601's own
limitations: It isn't valid beyond 1582-10-15</blockquote>
<div><br></div>
<div>I assume you mean 'before'. On the contrary, it says
explicitly:</div>
<div><font size="-1" color="#000000">"The Gregorian calendar was
introduced on 15 October 1582. In the calendar set by this standard
the</font><font face="Helvetica" size="+1"
color="#000000"></font></div>
<div><font size="-1" color="#000000">calendar day preceding that
calendar day is referred to as 14 October 1582.</font>"</div>
<div><br></div>
<div>At 8:00 -0500 16/03/09, Robert J Burns wrote:</div>
<blockquote type="cite" cite>The other problem I think you're missing
is that dates referenced in historical documents are often
non-Gregorian dates. It isn't "standard" to use the
proleptic Gregorian calendar to reference the date of historical
events. It is "standard" to use whatever calendar is used
locally (or elsewhere in the world) at the time of the event
(especially for Julian calendar usage).</blockquote>
<div><br></div>
<div>Right; you write the source document's date in the body
text, and you provide, if you can, the ISO 8601 label of that day, in
the attribute.</div>
<div><br></div>
<div><time datetime="<ISO 8601 day-label>">The
ides of march, 14 BC</time></div>
<div><br></div>
<div>This allows the UA to present the day in any calendar mappable
from an ISO 8601 day-label, to the user, in whatever accessibility
modality the user wants.</div>
<div><br></div>
<div>At 15:59 +0200 16/03/09, Mikko Rantalainen wrote:</div>
<blockquote type="cite" cite>How about specifying that the content of
<time> element will be parsed<br>
for the date only if 'datetime' attribute is empty. In addition,
the<br>
spec should explicitly say that if the content is time in any
other<br>
calendar system but Proleptic Gregorian calendar then the datetime
MUST<br>
contain equivalent time in standard format (whatever the spec
for</blockquote>
<blockquote type="cite" cite>'datetime' will be).</blockquote>
<div><br></div>
<div>Don't forget that there are plenty of cases where, alas, the
exact day referred to is uncertain and cannot be mapped to any other
calendar.</div>
<x-sigsep><pre>--
</pre></x-sigsep>
<div>David Singer<br>
Multimedia Standards, Apple Inc.</div>
</body>
</html>