Comment 6 for bug 307680

RFC2445 allows for repeating tasks.

However, it does not explain how completion information might be kept separately
for different instances. (There at most one set of completion properties per
VTODO, so it appears to me that a single VTODO cannot represent multiple
instances in different states of completion.)

One partial workaround is to disable completion fields on a repeating task.
This is ok for users who just want a reminder in their calendar, but not for
users who want to be able to check the task off each time it comes up.

Are there examples of calendars which support repeating tasks that save/export
to iCal (RFC2445) format? How do they store a repeating VTODO where different
instances are in different states of completion?