Re: DTSTART for recurrence instances

Olivier presented an excellent case showing that a RECCURRENCE-ID's
primary role is that of an 'identifier'; and not a 'date/time' value
that can
be relied on as the 'effective start' for a recurrence instance.  This
is made
even more clear in the following from 2445:
 
Section 4.8.4.4 Recurrence ID
. . .
   The date/time value (RECURRENCE-ID) is set to the time when the
original recurrence
   instance would occur; meaning that if the intent is to change a
   Friday meeting to Thursday, the date/time (RECURRENCE-ID) is still
set to the
   original Friday meeting.
 
With RECURRENCE-ID consigned to the role of an identifier
it clearly falls to DTSTART to represent a recurrence instance's
effective start time.
 
Doug wrote:
> For a recurring instance the effective start of an instance
> is defined in 2445 to be the RECURRENCE-ID.
 
That is not quite correct.  The effective start of an instance
is its DTSTART.  RECURRENCE-ID gets DTSTART as its 
initial value:
 
4.8.4.4 Recurrence ID
. . .                                               The property
   value is the effective value of the "DTSTART" property of the
   recurrence instance.
 
This statement makes it clear that a recurrence instance has a 
DTSTART property containing the "effective" value  ... and this is
where RECURRENCE-ID gets its initial value.  Initially, DTSTART
and RECURRENCE-ID have the same value.  If the instance is 
changed to a different time, DTSTART changes and 
RECURRENCE-ID does not.
 
Craig J