docs: def _repr_html_(self):
          """Build the HTML representation for IPython."""
          self.chart_id = '_'.join(['bearcart', uuid4().hex])
          self.template_vars.update({'chart_id': self.chart_id,
                                     'y_axis_id': self.y_axis_id,
                                     'legend_id': self.legend_id,
                                     'slider_id': self.slider_id,
                                     'export_json': json.dumps(self.json_data)})
  
          self._build_graph()
          html = self.env.get_template('ipynb_repr.html')
          return html.render(self.template_vars)