RRULEFREQYEARLYBYMONTH11BYDAY1SU

RRULEFREQYEARLY is a component of the iCalendar RRULE recurrence rule used to express events that occur annually. In iCalendar, RRULE is a property that defines how an event repeats; FREQ indicates the frequency, and YEARLY specifies repetition once per year. The rule can be refined by several parameters, the most common being INTERVAL, BYMONTH, BYMONTHDAY and BYDAY.

An event that takes place on December 25 each year can be represented as FREQ=YEARLY; BYMONTH=12; BYMONTHDAY=25. An event that occurs every two years on January 1 can be FREQ=YEARLY; INTERVAL=2; BYMONTH=1; BYMONTHDAY=1.

If you need to specify occurrences within a year that depend on a weekday, you can combine BYDAY and BYSETPOS with BYMONTH. For instance, the first Monday in September could be represented as FREQ=YEARLY; BYMONTH=9; BYDAY=MO; BYSETPOS=1.

RRULEs are widely supported by calendar software and are stored in .ics files. They enable precise control of yearly events and calendars across time zones, with occasional variations due to daylight saving and locale settings.