code: def _update_trsys(self, event):
          
          for ch in self.children:
              ch._update_trsys(event)
          self.events.transform_change()
          self.update()
docs: Called when  has changed.
          
          This allows the node and its children to react (notably, VisualNode
          uses this to update its TransformSystem).
          
          Note that this method is only called when one transform is replaced by
          another; it is not called if an existing transform internally changes
          its state.