docs: def backup_config(self, filename):
          """Backup the current config file.
          """
          backup_name = filename + '-' + self.version
          warn('Moving current configuration to ' + backup_name)
          try:
              shutil.copy2(filename, backup_name)
              return True
          except (IOError, OSError) as e:
              print('Error copying %s: %s' % (filename, e.strerror or e), file=sys.stderr)
              return False