public void addUndo()
{
if (!_undone)
{
_undone = true;
Undo undo_object = createUndo();
undo_object.undoable(this);
//Debug.on();Debug.print("add " + undo_object);Debug.off();
// constrainer().addUndo(undo_object);
constrainer().addUndo(undo_object,this);
}
}