Offset month repeat day.
Example: 4 days before the 1st Thursday of the month. Since the 1st Thursday in May was May 5, the event would be May 1. The 1st Thursday in June is June 2, so the next event is May 29. The 1st Thursday in July is July 7, so the following event is July 3. Etc....
This is useful for scheduling preparation for some monthly happening.
Another example is: our local elections come on Tuesday, 1 day after the 1st Monday in June. (Depending on the year, it might be the 1st or the 2nd Tuesday.)
Currently, I have to set such events manually every month; it would be wonderful to have it happen with a single click.
I know I can set a notification at such an offset, but since notifications don't hang around, I often miss doing a task if I try that workaround.
(There seems already to be an equivalent suggestion; it might even be mine. I give many more details here.)