code: def bubbleSize(self):
          
          xml = self._bubbleSize_tmpl.format(**{
              'nsdecls':    ' %s' % nsdecls('c'),
              'numRef_xml': self.numRef_xml(
                  self._series.bubble_sizes_ref, self._series.number_format,
                  self._series.bubble_sizes
              ),
          })
          return parse_xml(xml)
docs: Return the ``<c:bubbleSize>`` element for this series as an oxml
          element. This element contains the bubble size values for this
          series.