PUT, COPY, and MOVE
Use with: 403 Forbidden
(precondition) -- Servers MAY reject requests to create a scheduling object resource with an iCalendar "UID" property value already in use by another scheduling object resource owned by the same user in other calendar collections. Servers SHOULD report the URL of the scheduling object resource that is already making use of the same "UID" property value in the DAV:href element.
<!ELEMENT unique-scheduling-object-resource (DAV:href?)>