docs: def plot_residual(self, x, y1, y2, label1='Raw data', label2='Fit/theory', 
               xlabel=None, ylabel=None, show_legend=True,
               **kws):
          """plot after clearing current plot """
  
          panel = self.get_panel('top')
          panel.plot(x, y1, label=label1, **kws)
          panel = self.get_panel('top')
          panel.oplot(x, y2, label=label2, ylabel=ylabel, show_legend=show_legend, **kws)
          panel = self.get_panel('bottom')
          panel.plot(x, (y2-y1), ylabel='residual', show_legend=False, **kws)
          
          if xlabel is not None:
              self.xlabel = xlabel
          if self.xlabel is not None:
              self.panel_bot.set_xlabel(self.xlabel)