[Ietf-calsify] Section 4.8.5.4 Recurrence Rule: Allowed value type of DTSTART and DTEND

[Bernard Desruisseaux]

Section 4.3.5 Date-Time of RFC 2445 defines 3 forms for DATE-TIME
values, that is:

   FORM #1: DATE WITH LOCAL TIME

   FORM #2: DATE WITH UTC TIME

   FORM #3: DATE WITH LOCAL TIME AND TIME ZONE REFERENCE

In section 4.8.5.4 Recurrence Rule of RFC 2445 it says:

 > The "DTSTART" and "DTEND" property pair or "DTSTART" and "DURATION"
 > property pair, specified within the iCalendar object defines the
 > first instance of the recurrence. When used with a recurrence rule,
 > the "DTSTART" and "DTEND" properties MUST be specified in local time
 > and the appropriate set of "VTIMEZONE" calendar components MUST be
 > included. For detail on the usage of the "VTIMEZONE" calendar
 > component, see the "VTIMEZONE" calendar component definition.

My understanding is:

- The DTSTART property in a STANDARD or DAYLIGHT sub-component of
   a VTIMEZONE component MUST be of FORM #1 (DATE WITH LOCAL TIME)
   [See section 4.6.5 Time Zone Component];

- The DTSTART property in a VEVENT, VTODO or VJOURNAL component
   MUST be either a DATE value or a DATE-TIME value of FORM #1
   (DATE WITH LOCAL TIME) or FORM #3 (DATE WITH LOCAL TIME AND
   TIME ZONE REFERENCE).

As such, the text should be clarified to specify that DTSTART and
DTEND MUST be specified as a DATE or as a DATE-TIME of FORM #1
(DATE WITH LOCAL TIME) or FORM #3 (DATE WITH LOCAL TIME AND TIME
ZONE REFERENCE).

All that being said, I would like to point out that in section 4.4.2
Modify A Recurring Instance of RFC 2446 (iTIP) there is an example
of a DTSTART value specified in FORM #2 (DATE WITH UTC TIME) used
with a recurrence rule. My understanding is that this is not valid.

Cheers,
Bernard