Subject: [Ietf-calsify] Section 4.2.19 Time Zone Identifier: TZID parameter specified on DATE property

From: bernard.desruisseaux at oracle.com (Bernard Desruisseaux)
Date: Wed Jun 27 10:18:53 2007

Section 4.2.19 Time Zone Identifier of RFC 2445 says nothing about the
use of the TZID parameter on DATE properties. This section specifies
when this parameter MUST or MUST NOT be specified on DATE-TIME or TIME
values, but says nothing about DATE.

Furthermore, unlike section 4.3.5 Date-Time, section 4.3.4 Date doesn't
discuss the TZID parameter at all.

I'm bringing this up since Mozilla Sunbird specifies the TZID parameter
on DTSTART and DTEND of "All Day" events. For instance, here's an All
Day VEVENT created by Mozilla Sunbird with my time zone set to
Asia/Shanghai (UTC+08:00):

BEGIN:VEVENT
CREATED:20070627T160534Z
LAST-MODIFIED:20070627T160607Z
DTSTAMP:20070627T160650Z
UID:d9a9e2e4-4123-4b06-8dca-c10f791f8700
SUMMARY:All Day Event June 28th 2007 (Asia/Shanghai UTC+08:00)
DTSTART;VALUE=DATE;TZID=/mozilla.org/20070129_1/Asia/Shanghai:20070628
DTEND;VALUE=DATE;TZID=/mozilla.org/20070129_1/Asia/Shanghai:20070629
END:VEVENT

To find out whether Mozilla Sunbird actually cares about the TZID
itself I changed my time zone to America/Montreal (UTC-4:00). Given
that June 28th, 2007 00:00 (midnight) Asia/Shanghai corresponds to
June 27th, 12:00 (noon) America/Montreal I was wondering if this
All Day event would be displayed on June 27th, 2007. It turns out
that Mozilla Sunbird still displayed the event on June 28th.

    Note: If you want to try this yourself with Mozilla Sunbird,
    you'll actually need to change the time zone of your OS to
    match the time zone you configured in Mozilla Sunbird.  Else
    Mozilla Sunbird will end up creating the All Day event on the
    wrong day altogether. For instance, if you configure Sunbird
    with Asia/Shanghai but have your OS configured with
    America/Montreal and create an All Day event on June 28th, 2007,
    Mozilla Sunbird will create an All Day event that start on
    June 29th!

While iCalendar currently doesn't forbid the use of the TZID parameter
on DATE value properties, it certainly doesn't look like it was ever
meant to be used. If one wants to ground a given DATE to midnight of
a specific time zone I believe one should simply use a DATE-TIME value.

I propose to change the following statement in section 4.2.19 Time Zone
Identifier, from:

 > The TZID property parameter MUST NOT be applied to DATE-TIME or TIME
 > properties whose time values are specified in UTC.

to:

 > The TZID property parameter MUST NOT be applied to DATE properties,
 > and DATE-TIME or TIME properties whose time values are specified in
 > UTC.

Cheers,
Bernard

---

From: cmtalbert at gmail.com (Clint Talbert)
Date: Wed Jun 27 10:46:19 2007

> discuss the TZID parameter at all.
I'm glad that you're addressing this because I believe the behavior you 
note resulted from a misunderstanding of section 4.3.4.
> .. snip..

> that Mozilla Sunbird still displayed the event on June 28th.
I believe this is the proper behavior, to tie the all-day event to a 
specific numerical date.  It sounds like you also think so, given the 
change you suggest below.
>    Mozilla Sunbird will create an All Day event that start on
This is an unfortunate, known issue in Sunbird/Lightning that we are 
addressing in our next (0.7) release (work is actually underway on it, 
though the bug report below does not reflect it). I apologize for the 
inconvenience. 

For more information, please see: 
https://bugzilla.mozilla.org/show_bug.cgi?id=337191.  And if you'd like 
to be notified of changes to the bug, feel free to CC yourself on it.
> > and DATE-TIME or TIME properties whose time values are specified in
Hooray!  I second the change.

I'll file another bug to no longer add TZID to DATE properties in 
Sunbird as well.  Thanks for bringing this to our attention. :-)

Thanks,

Clint Talbert
Mozilla Calendar Project QA Coordinator

---

From: Nigel.Swinson at rockliffe.com (Nigel Swinson)
Date: Wed Jun 27 13:29:14 2007

> Hooray!  I second the change.

We'd encountered this issue and come to similar conclusions, so I'd also be happy for the clarity offered by this change.

Nigel

---

From: reinhold at kainhofer.com (Reinhold Kainhofer)
Date: Wed Jun 27 14:04:55 2007

Am Mittwoch, 27. Juni 2007 schrieb Nigel Swinson:
> We'd encountered this issue and come to similar conclusions, so I'd also be
> happy for the clarity offered by this change.

Just another "Me too" from my side.
Reinhold

- -- 
- ------------------------------------------------------------------
Reinhold Kainhofer, Vienna University of Technology, Austria
email: [email-masked], http://reinhold.kainhofer.com/
 * Financial and Actuarial Mathematics, TU Wien, http://www.fam.tuwien.ac.at/
 * K Desktop Environment, http://www.kde.org, KOrganizer maintainer
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