docs: def signal_panel(self, ax, feature):
          """
          Plots each genomic signal as a line using the corresponding
          plotting_kwargs
          """
          for gs, kwargs in zip(self.genomic_signal_objs, self.plotting_kwargs):
              x, y = gs.local_coverage(feature, **self.local_coverage_kwargs)
              ax.plot(x, y, **kwargs)
          ax.axis('tight')
          return feature