Tooltip is not shown when configured for 'const' value.

[alshan]

See cell 15 : https://nbviewer.org/github/JetBrains/lets-plot-docs/blob/master/source/examples/cookbook/tooltip_config.ipynb

# By default tooltip never shows values defined via layer parameters (constants).
# Still, these values can be added to a layer tooltip using the 'layer_tooltips()' function.
data= {}
data['x'] = np.append(np.random.normal(0,1,100), np.random.normal(3,1,100))
data['y'] = np.append(np.random.normal(0,1,100), np.random.normal(3,1,100))

(ggplot(data, aes('x', 'y')) 
  + geom_point()
  + geom_vline(xintercept=np.mean(data['x']), color="red", linetype="dashed", size=1,
               tooltips=layer_tooltips()
                   .format('^xintercept', '.4f')
                   .line('mean = ^xintercept'))
) 

The vline still doesn't have a tooltip.