``<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.

def defRPr(self):
        """
        ``<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.
        """
        p = self.p_lst[0]
        pPr = p.get_or_add_pPr()
        defRPr = pPr.get_or_add_defRPr()
        return defRPr