code: def add_significance_indicator(plot, col_a=0, col_b=1, significant=False):
      
      plot_bottom, plot_top = plot.get_ylim()
      # Give the plot a little room for the significance indicator
      line_height = vertical_percent(plot, 0.1)
      # Add some extra spacing below the indicator
      plot_top = plot_top + line_height
      # Add some extra spacing above the indicator
      plot.set_ylim(top=plot_top + line_height * 2)
      color = "black"
      line_top = plot_top + line_height
      plot.plot([col_a, col_a, col_b, col_b], [plot_top, line_top, line_top, plot_top], lw=1.5, color=color)
      indicator = "*" if significant else "ns"
      plot.text((col_a + col_b) * 0.5, line_top, indicator, ha="center", va="bottom", color=color)
docs: Add a p-value significance indicator.