Can I set an event to repeat on the Sunday before 9/11... or any weekday before/after a date?

Question

Title  really says it all. Is there a way to create such a repeating event?

Answer 1

I have come across an answer, a way to create the event using iCalendar code and then importing the event. I would much rather a way to do this inside the Calendar app, but this is better than nothing. Create a plain text file with this code:
BEGIN:VCALENDAR
Version:2.0
BEGIN:VEVENT
DTSTART:20150906
DTEND:20150906
RRULE:FREQ=YEARLY;INTERVAL=1;BYMONTH=9;BYDAY=SU;BYMONTHDAY=5,6,7,8,9,10,11
SUMMARY:World Trade Remembrance Service
END:VEVENT
END:VCALENDAR
Save as plain text. Rename to have a ".ics" extension and you should be able to double-click to load the event into your calendar. The code is pretty self-explanatory but I'll run through it quickly. Set the start and end to the first occurrence of the event. You can set this to any date, really, but the first entry will be on that date, so it won't necessarily match the rule you've created, so you'd want to delete the first one. The event happens every year, in the 9th month, and always on a certain weekday (SU), and it can only be the Sunday that falls on 5-11th (i.e. no more than a week before 9/11). The name of the event goes in the Summary field. Very powerful stuff! It'd be great to have a graphical interface to go along, but this works for now. BTW, I found this answer (and a thousand other amazing bits of iCal code) here: http://www.kanzaki.com/docs/ical/rrule.html.