Case
Calendar.RecurrenceRule.Weekday.nth(_:_:)
iOS 18.0+
iPadOS 18.0+
Mac Catalyst 18.0+
macOS 15.0+
tvOS 18.0+
watchOS 11.0+
Repeat on the n-th instance of the specified weekday in a month, if the recurrence has a monthly frequency. If the recurrence has a yearly frequency, repeat on the n-th week of the year.
Discussion
If n is negative, repeat on the n-to-last of the given weekday.