docs: def subscript(self):
          """
          |True| if `w:vertAlign/@w:val` is 'subscript'. |False| if
          `w:vertAlign/@w:val` contains any other value. |None| if
          `w:vertAlign` is not present.
          """
          vertAlign = self.vertAlign
          if vertAlign is None:
              return None
          if vertAlign.val == ST_VerticalAlignRun.SUBSCRIPT:
              return True
          return False