docs: def set_xtick_suffix(self, suffix):
          """Set the suffix for the ticks of the x-axis.
  
          :param suffix: string added after each tick. If the value is
                         `degree` or `precent` the corresponding symbols
                         will be added.
  
          """
          if suffix == 'degree':
              suffix = r'^\circ'
          elif suffix == 'percent':
              suffix = r'\%'
  
          self.ticks['xsuffix'] = suffix