discovering the root of a deep lock

(see also issue LOCKS_SHOULD_THEY_USE_AN_IF_HEADER_TO_VERIFY)

Proposed syntax:

12.1  activelock XML Element

Name:
activelock
Namespace:
DAV:
Purpose:
Describes a lock on a resource.

   <!ELEMENT activelock (lockscope, locktype, depth, owner?, timeout?,
locktoken?, lockroot?) >


12.1.x  lockroot XML Element

Name:
lockroot
Namespace:
DAV:
Purpose:
For locks with depth infinity, servers SHOULD report the root of the lock
using the DAV:lockroot element. This enables clients to know the scope of
resources affected by a subsequent UNLOCK with the given lock token. For
lock with depth 0, the DAV:lockroot element MUST NOT be present.

   <!ELEMENT lockroot (href) >


--

Note: I made it a "SHOULD" in order not to break existing implementations.