WebDAV RFC 4918 allows a full url or a path as <D:href>:
http://www.webdav.org/specs/rfc4918.html#ELEMENT_href
Some clients can NOT deal with one or the other:
- KAddressbook (at least in 3.5) can NOT subscribe to addressbooks (it
does not find them) if just a path is used
- iCal in OS X 10.6 generates wrong requests, if a full url is used