@abc.abstractmethod<EOL><INDENT>def register_for_changed_book_hierarchy_for_descendants(self, book_id):<DEDENT>
pass<EOL>
Registers for notification of an updated book hierarchy structure.

        ``BookReceiver.changedChildOfBooks()`` is invoked when the
        specified node or any of its descendants experiences a change in
        its children.

        :param book_id: the ``Id`` of the ``Book`` node to monitor
        :type book_id: ``osid.id.Id``
        :raise: ``NullArgument`` -- ``book_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*