code: def _child_extents(self):
          
          child_shape_elms = list(self.iter_shape_elms())
  
          if not child_shape_elms:
              return Emu(0), Emu(0), Emu(0), Emu(0)
  
          min_x = min([xSp.x for xSp in child_shape_elms])
          min_y = min([xSp.y for xSp in child_shape_elms])
          max_x = max([(xSp.x + xSp.cx) for xSp in child_shape_elms])
          max_y = max([(xSp.y + xSp.cy) for xSp in child_shape_elms])
  
          x = min_x
          y = min_y
          cx = max_x - min_x
          cy = max_y - min_y
  
          return x, y, cx, cy
docs: (x, y, cx, cy) tuple representing net position and size.
  
          The values are formed as a composite of the contained child shapes.