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[whatwg] <time>

From: Tom Duhamel <tom420.duhamel@gmail.com>
Date: Mon, 9 Mar 2009 16:17:01 -0400
Message-ID: <22c1222d0903091317i4dccafd0peb182de2ba008e4b@mail.gmail.com>
There have been a lot of discussion around the <time> element lately, and I
followed most of it since I'm pretty interested in this element, and frankly
I believe it will be very useful in the future. However, I too have opinions
around this. I do agree with some argument presented before, and disagree
with others. This post is not meant to be very long, I just wanted to state
a bit about my opinion, although I don't consider myself knowledgeable
enough to discuss the entire set of issues.

Precise Date/Time

My understanding is that the current protocol will only accept this format
for a valid precise date:
2009-03-09
And this format for a valid precise time:
15:10 or 15:10:19

My opinion is that all the following dates are precise:
2009
2009-03
2009-03-09

There are numerous reason to use dates which are not very precise, but are
still precise nevertheless. I'm going to release the new version of my
current project in <time datetime="2009-04">April</time> but I cannot tell
as of now the exact day of the release.

The later is more precise, but the three are all precise in my opinion. On
the other hand, those are NOT precise dates:
Last year
About a month ago
Last summer
Somewhere during the summer of 2010

The same would apply to times. "This morning", "I'll be there in an hour"
are not precise.


Gregorian Calendar

There have been requests that the <time> element accepts dates expressed in
other calendars than Gregorian. This is not doable, although I do understand
those who mentioned this, mostly about the Julian calendar.

Julian for instance cannot give a precise date (we are not considering the
fact that it was not precise enough) because it was based on some events in
history, often the arrival of a new leader. For example, when Bush was
elected in Nov 2000, we would have considered that year to be the new year
1. Thus Bush was elected in November 1, re-elected in November 5. Then Obama
was elected in November 9 of the Bush era, which was also Novemember 1 of
Obama era.

Wikipedia is often mentioned as a use-case, but based on my own experience
(I am not an historian or anything, so my use of Wikipedia for historical
events is sporadic) they most usually convert Julian dates to the Gregorian
calendar. Julius Caesar died in 14 BC, not 52 of the Julius era on the
Julian calendar (or whatever date it would convert to).


Historic Dates

>From my understanding of the current draft, the earlier date that can be
used is 1970-01-01. The Unix epoch. Why that limit?

Gregorian calendar entered common use somewhere during the 15th century, I
believe. Dates in 16th, 17th, 18th, 19th and 20th centuries are very common.
Dates before the 15th centurie are less common, they are usually not precise
(just 14th century, for example, as the exact year cannot be determined),
but there are cases where the exact date is known. Julius Caesar is one
instance where a precise date is known (for both his birth and death) and
this is around 50 BC. I don't think there are many known precise date before
that. I would accept that dates before year 1 be not represented. I would
even accept that dates before 15th century be not representable since those
cannot be accurately represented (I'm not historian, I hope people more
knowleadgeable than me will point out the correct date for the event).
However I think 1970 is not that good, as for sure even recent historic
events cannot be pinpointed correctly.

If the protocol is to be kept as is, it should be made clear that the <time>
element is for current dates, not historic dates, as I would assume that
would be the reason for the choice of 1970 (which is actually a good choice
for simplicity of implementation). If this was not the intended use (that
is, it was also meant for historic dates) than the limit would really need
to be changed. In my opinion, 1 or 1400 are not a good limit if we are to
allow use for historic dates. I would allow all dates, including BC dates.

The upper limit does not seem to be mentioned. It should be, and it should
be at least 9999, although no limit would be better (although I understand
it becomes more difficult to implement past 9999 -- actually I think it's
already diffucult to implement up to 9999).
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