code: def _tooltip_data(self, node, value, x, y, classes=None, xlabel=None):
          
          self.svg.node(node, 'desc', class_="value").text = value
          if classes is None:
              classes = []
              if x > self.view.width / 2:
                  classes.append('left')
              if y > self.view.height / 2:
                  classes.append('top')
              classes = ' '.join(classes)
  
          self.svg.node(node, 'desc', class_="x " + classes).text = to_str(x)
          self.svg.node(node, 'desc', class_="y " + classes).text = to_str(y)
          if xlabel:
              self.svg.node(node, 'desc', class_="x_label").text = to_str(xlabel)
docs: Insert in desc tags informations for the javascript tooltip