docs: def save_assets(self, dest_path):
          """Save plot assets alongside dest_path.
  
          Some plots may have assets, like bitmap files, which need to be
          saved alongside the rendered plot file.
  
          :param dest_path: path of the main output file.
  
          """
          for idx, subplot in enumerate(self.subplots):
              subplot.save_assets(dest_path, suffix='_%d' % idx)