Identifies the URL of any WebDAV collections that contain calendar collections owned by the associated principal resource.
This property SHOULD be defined on a principal resource. If defined, it MAY be protected and SHOULD NOT be returned by a PROPFIND DAV:allprop request (as defined in Section 12.14.1 of [RFC2518]).
The CALDAV users to easily find the calendar collections owned by the principal. Typically, users will group all the calendar collections that they own under a common collection. This property specifies the URL of collections that are either calendar collections or ordinary collections that have child or descendant calendar collections owned by the principal.