5.1.1.3.

BYSETPOS — This RRULE property is useful in that it has the “payday” use case, ie. last workday of the month, but can be complicated to implement. The sender could use RDATEs as well but could be a lengthy list if this goes on yearly, etc. It is better to send a list of RDATEs with exceptions already taken into account, and refresh this at appropriate intervals to extend the set. If that is recommended in the RFC, then this property could be removed. Recommend going to the CALSIFY list to see if this is deemed a workable solution.