def _regroup(self, new_group):
<EOL>if self.__group is None or self.__group != new_group:<EOL><INDENT>self.__group = new_group<EOL>self.do_regroup()<EOL>self._draw()<EOL>if self.__num_children > <NUM_LIT:0>:<EOL><INDENT>self.do_regroup_children()<EOL><DEDENT><DEDENT>
Change the `pyglet.graphics.Group` associated with this widget.

Three callbacks are invoked to allow the widget to react to this 
change: `do_regroup()`, `do_draw()`, and `do_regroup_children()`.  The 
last initiates a recursive descent down the widget hierarchy updating 
the groups of the widget's children and all of their children.