code: def _add_textbox_sp(self, x, y, cx, cy):
          
          id_ = self._next_shape_id
          name = 'TextBox %d' % (id_-1)
          sp = self._spTree.add_textbox(id_, name, x, y, cx, cy)
          return sp
docs: Return newly-appended textbox `p:sp` element.
  
          Element has position (*x*, *y*) and size (*cx*, *cy*).