Further thoughts on BYSETPOS

["Thomas O'Dowd" <tom@xxxxxxxxxx>]

Hi all,

I'd like to comment further on my earlier posting and BYSETPOS. I'd
still like comments on my earlier posting as this posting is just
adding to earlier issues.

After thinking about BYSETPOS a little more with regards to weekly
freqencies, and after a little confusion initially, here are some
thoughts for you all.

First lets look at a simple weekly rule.

RRULE:FREQ=WEEKLY;BYDAY=WE,FR,SU

This means every week on Wed, Fri and Sun there is an event. Lets add
BYSETPOS to the rule.

RRULE:FREQ=WEEKLY;BYDAY=WE,FR,SU;BYSETPOS=1

Here it seems is another example of where the value of WKST comes into
play. The default is MO, so this rule will evaluate to every Wed in
the year. If I use WKST=SU, this changes however as below.

RRULE:FREQ=WEEKLY;BYDAY=WE,FR,SU;WKST=SU;BYSETPOS=1

The rule this time evaluates to every Sunday in the year.

I'm not sure if BYSETPOS is really useful when used with WEEKLY like
this as a week is more of a fixed time unless a constricting rule
applies. The only byRule that might constrict a WEEKLY frequency somehow
would be BYWEEKNO which won't effect the valuation of things as per
above.

If BYMONTHDAY was allowed in a WEEKLY rule though it might change the 
value of what BYSETPOS evaluated to, week by week. The proposals are
for BYMONTHDAY to not be allowed with a weekly rule frequency though
as per the following text.

   For WEEKLY recurrences (FREQ=WEEKLY) neither BYMONTHDAY nor
	BYYEARDAY may appear.

So how useful is BYSETPOS for a weekly rule? I'm not sure that it is
useful in my current understanding.

It is very useful though where the rule is MONTHLY and probably 
YEARLY although I've yet to really think about YEARLY rules and BYSETPOS.

Cheers,

Tom.
-- 
Thomas O'Dowd. - Nooping - http://nooper.com
tom@xxxxxxxxxx - Testing - http://nooper.co.jp/labs