docs: def setDataset(self, dataset):
          """
          Sets the dataset instance associated with this item.
          
          :param      dataset | <XChartDataset>
          """
          self._dataset = dataset
          
          # setup the tooltip
          tip = []
          tip.append('<b>%s</b>' % dataset.name())
          for value in dataset.values():
              value_text = []
              for key, val in sorted(value.items()):
                  if val == dataset.name():
                      continue
                  
                  axis = self.axis(key)
                  if axis and axis.labelFormat():
                      val = axis.labelFormat().format(val)
                  value_text.append('%s: %s' % (key, val))
              
              tip.append('<p>%s</p>' % ', '.join(value_text))
          self.setToolTip(''.join(tip))