Name: caldav_historical_age
Type: DURATION
Default-Value: 7d
Last-Modified: 3.1.8

How long after an occurrence of event or task has concluded that it is
considered 'historical'.  Changes to historical occurrences of events or
tasks WILL NOT have invite or reply messages sent for them.  A negative
value means that events and tasks are NEVER considered historical.

For backward compatibility, if no unit is specified, days is assumed.
