code: def bubbleSize_xml(self):
          
          return self._bubbleSize_tmpl.format(**{
              'nsdecls':    '',
              'numRef_xml': self.numRef_xml(
                  self._series.bubble_sizes_ref, self._series.number_format,
                  self._series.bubble_sizes
              ),
          })
docs: Return the ``<c:bubbleSize>`` element for this series as unicode
          text. This element contains the bubble size values for all the
          data points in the chart.