This is more documentation supporting my assertion that recurrence rules are not as portable as many claim.
I would suggest using RDATE's and no RRULE or EXRULE. They are easy to unwind, only after clearly defined and consistently used.
On Thursday 02 June 2005 17:27, Sam Roberts wrote:
Quoting reinhold@xxxxxxxxxxxxx, on Tue, May 31, 2005 at 03:59:12PM +0200:
Hi Guys, 1) About the BYDAY rule part: Let's start with some examples RRULE:FREQ=YEARLY;BYDAY=3SU Okay, that's the third sunday of the year. But what exactly is RRULE:FREQ=YEARLY;BYDAY=5SU;BYMONTH=2 Is this the fith sunday in the year, if it is also in february?
Each BYDAY value can also be preceded by a positive (+n) or negative (-n) integer. If present, this indicates the nth occurrence of the specific day within the MONTHLY or YEARLY RRULE. For example, within a MONTHLY rule, +1MO (or simply 1MO) represents the first Monday within the month, whereas -1MO represents the last Monday of the month. If an integer modifier is not present, it means all days of this type within the specified frequency. For example, within a MONTHLY rule, MO represents all Mondays within the month.
Whether it is an offset within a month or year depends on the FREQ, not on
the presence of any other modifiers.
At first I thought so, too. But then, there are two reasons which seem to contradict this:
1) The RFC speaks of "within the MONTLY or YEARLY RRULE" (notice that they don't say "within the frequency", like they do four lines below). So I wondered if this might be the only place where it's relevant in which order the BY* parts are evaluated.
2) All VTIMEZONEs (at least those used by Exchange, Apple's iCal, and by libical and so by evolution, korganizer etc.) use RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
RFC2445bis should add an example for this since its an area of confusion.
from rfc 2445. What is RRULE:FREQ=YEARLY;BYDAY=5SU;BYMONTH=2,7 Is this the fifth sunday of the year, if it's in either February or July? Or is it the fifth sunday of febrary and july together (i.e. in feb if the feb in a leap year has 5 sundays, or the first sunday of july in all other years)?
Actually, if the RFC really meant "within the RRULE", when that would be the correct interpretation. That's why I ask.
Also notice that rfc 2445 says "For example, within a MONTHLY rule, +1MO (or simply 1MO) represents the first Monday within the month, whereas -1MO represents the last Monday of the month. ". So what does RRULE:FREQ=MONTHLY;BYYEARDAY=57,64;BYDAY=-1MO
Every month, the days that are the 57th&65th of the year (if in that month), and that are on the last monday of the month.
Depends. If you follow the RFC with the interpretation of "within the RRULE", you'll get:
In each month, that days that are days 57 or 64 of the year. Within this rrule (=within these days that match the rule so far), the last monday would be Feb 27, 2007, and March 5, 2007....
mean? The last monday of each month if it's also day #57 or #64 of the year (which the quote implies), or the last monday each month in the set of all days #57 and #64 of the year. In particular, in 2007, would the recurrence set be Feb 27 (=#57 of the year, and the last monday in february) without any occurence in march (march 5 is day #64, but it's not the last monday in the month, since rfc 2445 says -1MO means last monday of the month)? Or would it be Feb 27 (day #57 of the year, and last monday of all dates that match the BYYEARDAY in the february interval) and March 4 ( day #64 of the year and last monday of all dates in March that match the BYYEARDAY).
2) In Section 4.3.10 RFC 2445 says "The COUNT rule part defines the number of occurrences at which to range-bound the recurrence. The "DTSTART" property value, if specified, counts as the first occurrence.". So look at this rrule: DTSTART;TZID=whatever:20050530T120000 RRULE:FREQ=WEEKLY;COUNT=3;BYMONTH=6
I'm sorry, I can't find where it says it right now to quote, but I have the very distinct memory that RFC2445 says that the DTSTART property MUST specify a time that is valid according to the RRULE.
No, definitely not. E.g. even look at the examples given in RFC 2445. It explicitly gives an example where the DTSTART does NOT match the RRULE:
Every other week on Monday, Wednesday and Friday until December 24, 1997, but starting on Tuesday, September 2, 1997:
DTSTART;TZID=US-Eastern:19970902T090000 RRULE:FREQ=WEEKLY;INTERVAL=2;UNTIL=19971224T000000Z;WKST=SU; BYDAY=MO,WE,FR ==> (1997 9:00 AM EDT)September 2,3,5,15,17,19,29;October 1,3,13,15,17 (1997 9:00 AM EST)October 27,29,31;November 10,12,14,24,26,28; December 8,10,12,22
3) About the DTSTART and recurrence rules: Is the DTSTART always taken to match the rule (even if it doesn't fulfil the BY* parts)? In particular this is important for EXRULES: Is the DTSTART always the first occurence of the EXRULE? If that's the case, the DTSTART will always be excluded as soon as at least one EXRULE is present. And since exceptions overrule inclusions, there's no way to have an occurence on the DTSTART in that case... Is this really the intended behaviour?
I haven't implemented EXRULE (or ever seen one), but your argument that the DTSTART will always be excluded looks right to me.
That sounds like it would be a problem, but section 22.214.171.124 says this:
The "EXRULE" property can be used to exclude the value specified in ^^^ "DTSTART". However, in such cases the original "DTSTART" date MUST still be maintained by the calendaring and scheduling system because the original "DTSTART" value has inherent usage dependencies by other properties such as the "RECURRENCE-ID".
They say "can", maybe should say "would always" :-)
It appears to me that DTSTART is made an exception, then, and must be kept.
Yeah, the "can" is the issue. If I have a daily event that starts on a monday, and add an exrule, which excludes all events on thursdays and fridays (here the exrule uses the DTSTART, but it doesn't match the BY* parts). So, does the DTSTART always match the EXRULE by definition (i.e. is the first monday excluded, and all thursdays and fridays afterward), or does the first monday not match the EXRULE, and only all thursdays and fridays are excluded.
So, don't make events whose alleged "start" is excluded from the set of events. This actually seems reasonable, why not just start the event when it actually starts?
Good question. I haven't thought of this too much, but I haven't yet seen a case where it would really make a different (if I understand RECURRENCE-ID correctly, I don't see where this should matter, although RFC 2445 says it does).
Doug Royer | http://INET-Consulting.com -------------------------------|-----------------------------
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