Notifies all listeners that have registered interest for notification on ZGroupEvents that a child has been added to the group, then percolates the event up scenegraph, notifying any listeners on any higher ZGroup nodes.
Notifies all listeners that have registered interest for notification on ZGroupEvents that a child has been removed from the group, then percolates the event up scenegraph, notifying any listeners on any higher ZGroup nodes.
Compute the bounds of this handle using the handles locator to determine the center point of the bounds and the DEFAULT_HANDLE_SIZE to determine the extent.