title: Pygal: Displaying information for each data point
body: <p>I have been playing around with <code>Pygal</code>, creating some line graphs for a project I am working on. I currently have my <code>y axis</code> set to be the value recorded and the <code>x axis</code> being the <code>date / time</code> the test was conducted. However I would also like to link the serial number to each data point. At the moment when you hover on a data point you get the y value in bold and underneith that you get the date it was recorded. </p>
  
  <p>Does anyone know if it is possible to link information to data points without them being an axis label? </p>
  
  <p>For reference I currently have the serial numbers being added to the <code>list: 'sn_list'</code>. </p>
  
  <pre><code>        for row in line_graph_query:
              if str(row.date_time) &gt;= start_date and str(row.date_time) &lt;= end_date :
                  min_values.append(float(row.minimum_value))
                  max_values.append(float(row.maximum_value))
                  recorded_values.append(float(row.recorded_value))
                  sn_list.append(row.product_serial_number)
                  date_list.append(row.date_time)
                  number_of_records = number_of_records + 1
          print(min_values)
          print(max_values)
          print(recorded_values)
          distance_x_axis = math.floor(number_of_records/6)
          line_chart = pygal.Line(no_data_text='No result found', style=custom_style,x_labels_major_every=distance_x_axis, x_label_rotation=20, show_minor_x_labels=False )
          line_chart.title = 'Detailed Results of '+test_name+' tests of '+board_pn
          line_chart.x_labels = map(str,date_list)
          line_chart.add('Minimum', min_values)
          line_chart.add('Maximum', max_values)
          line_chart.add('Recorded', recorded_values)
          graph_render.append(line_chart.render_data_uri())
          graphs_to_render[test_name] = graph_render[-1]
  </code></pre>