We intend to allow versioned objects. All objects, including directories, have a VERSION-NUMBER field. In the current server implementation, the VERSION-NUMBER field is always zero, which means ``unversioned''. It need not be in future server implementations.
In commands and responses, providing a zero value for the object-version token means to retrieve the current version of the object. Specifying explicit values means that a particular version of the object is required. Explicit object version numbers (when they are established) will always be positive integers.