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Re: [whatwg] <time>

From: Robert J Burns <rob@robburns.com>
Date: Mon, 16 Mar 2009 08:00:03 -0500
Message-Id: <4A7F8FB8-3820-45A6-9F0F-1662ED5F60F2@robburns.com>
To: Mikko Rantalainen <mikko.rantalainen@peda.net>
Cc: "public-html@w3.org WG" <public-html@w3.org>
Hi Mikko,

On Mar 16, 2009, at 6:55 AM, Mikko Rantalainen wrote:

> The author has clearly the means to convert the 'value' attribute to
> Proleptic Gregorian, but instead he opts to use different calendar
> system and an offset. Why on earth? Is it because Julian calendar
> happens to use somewhat similar counting system (days, months, years)?
>
> How this would help the author or the user? Why is this any better  
> than
> always using Proleptic Gregorian calendar for datetime attribute, no
> exceptions allowed?

The issue is more about _when_ to convert a date and also about  
allowing authors the ability to more precisely encode dates. In other  
words I'm arguing that we should let the UAs do the conversion or let  
even the user do the conversion leaving it to a runtime rather than  
compile time conversion (to use a familiar metaphor). In that way we  
allow authors to encode precise dates: not converting dates based on  
some loose conversion that is presumed to be the proper conversion at  
the time of authorship (since conversions between these calendars are  
subject to dispute and the accepted wisdom changes from time-to-time).

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historical documents are often non-Gregorian dates.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).

Finally, allowing a keyword to distinguish various uniform calendar  
mechanisms does not really place a burden upon UAs. If they are merely  
required to support the Gregorian keyword and the absence of a  
keyword, the implementation requirements are hardly different from  
supporting only Gregorian calendar dates. However, the support in  
document conformance for alternative calendar dates does provide  
benefits for both authors and users. So I haven't really seen any  
convincing reasons not to support these keyword differentiations for  
alternative calendars. It would be trivial to enhance ISO 8601 to say  
that it also includes an optional keyword indicating a standardized  
calendar and whose components are still ordered from big to small  
(years to days) and separated by hyphens. In a sense its like a  
uniform date identifier (a UDI as opposed to a uniform resource  
identifier).

Take care,
Rob
Received on Monday, 16 March 2009 13:01:07 UTC

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