code: def defRPr(self):
          
          p = self.p_lst[0]
          pPr = p.get_or_add_pPr()
          defRPr = pPr.get_or_add_defRPr()
          return defRPr
docs: ``<a:defRPr>`` element of required first ``p`` child, added with its
          ancestors if not present. Used when element is a ``<c:txPr>`` in
          a chart and the ``p`` element is used only to specify formatting, not
          content.