def _get_grid_bbox(self, renderer):
boxes = [self._cells[pos].get_window_extent(renderer)<EOL>for pos in self._cells.keys()<EOL>if pos[<NUM_LIT:0>] >= <NUM_LIT:0> and pos[<NUM_LIT:1>] >= <NUM_LIT:0>]<EOL>bbox = Bbox.union(boxes)<EOL>return bbox.inverse_transformed(self.get_transform())<EOL>
Get a bbox, in axes co-ordinates for the cells.

        Only include those in the range (0,0) to (maxRow, maxCol)