Description: This property MAY be defined on a scheduling Inbox collection. If present, it contains zero or one DAV:href XM elements. When a DAV:href element is present, its value indicates a URL to a calendar collection that is used as the default calendar. When no DAV:href element is present, it indicates that there is no default calendar. In the absence of this property, there is no default calendar. When there is no default calendar, the server is free to choose the calendar in which a new scheduling object resource is created.
stub added in r4430 (30df948c1127)
probably still not really the correct behavior