code: def xlabel(self, labels):
          
          if self.panel_scales_x[0].name is not None:
              return self.panel_scales_x[0].name
          else:
              return labels.get('x', '')
docs: Determine x-axis label
  
          Parameters
          ----------
          labels : dict
              Labels as specified by the user through the ``labs`` or
              ``xlab`` calls.
  
          Returns
          -------
          out : str
              x-axis label