code: def _Completion(self, match):
      # pylint: disable=C6114
      r
      # Strip the outer '[[' & ']]' and replace with ()? regexp pattern.
      word = str(match.group())[2:-2]
      return '(' + ('(').join(word) + ')?' * len(word)
docs: r"""Replaces double square brackets with variable length completion.
  
      Completion cannot be mixed with regexp matching or '\' characters
      i.e. '[[(\n)]] would become (\(n)?)?.'
  
      Args:
        match: A regex Match() object.
  
      Returns:
        String of the format '(a(b(c(d)?)?)?)?'.