[whatwg] 'datetime-local' and 'datetime' comments

[TAMURA, Kent]

On Thu, Nov 22, 2012 at 2:15 PM, Ian Hickson <ian at hixie.ch> wrote:

> > What do you think would be a good UI? Does something that would allow
> > selecting a date/time in the current user's TZ and then have the
> > information sent to the server in UTC would be a good UI?

> That would probably be a reasonable first UI. A more mature UI would also
> let you pick the time for a specific other time zone (e.g. because you
> know you'll be there), or compare multiple time zones at the same time to
> pick a time convenient for multiple people, etc.


I have made some UI ideas, but I still have no reasonable one.  It's very
hard because there are various levels of user knowledge and local computer
knowledge.

User-A: He doesn't know there are multiple timezones in the world.
User-B: He knows there are multiple timezones, and doesn't know his
timezone offset.
User-C: He knows there are two timezone offsets in his region; the standard
time and the daylight saving time.
User-D: He knows the start date and the end date of the daylight saving
time.
User-E: He knows there is an invalid time and ambiguous time when we switch
between the standard time and the daylight saving time.
   Note: 2012-03-11 2:30 a.m. didn't exist in USA, and there were
two 2012-11-04 1:30 a.m.
User-F: He knows timezone offsets of the standard time and the daylight
saving time.

Computer-A: It doesn't know its local timezone offset.
Computer-B: It knows its local timezone offset.
Computer-C: It knows the start date and the end date of the daylight saving
time according to the latest law about the daylight saving time.
Computer-D: It knows them for the past years too even if the law was
changed.
Computer-E: It knows them for the future years too!

If UI depended on a local timezone, we would need Computer-E and extra
handling for invalid/ambiguous time. If UI was independent from a local
timezone, only User-D/E/F could use it.

-- 
TAMURA Kent
Software Engineer, Google