docs: def plot(self, x, y, panel='top', xlabel=None, **kws):
          """plot after clearing current plot """
          panel = self.get_panel(panel)
          panel.plot(x, y, **kws)
          if xlabel is not None:
              self.xlabel = xlabel
          if self.xlabel is not None:
              self.panel_bot.set_xlabel(self.xlabel)