docs: def _is_nmrstar(string):
          """Test if input string is in NMR-STAR format.
  
          :param string: Input string.
          :type string: :py:class:`str` or :py:class:`bytes`
          :return: Input string if in NMR-STAR format or False otherwise.
          :rtype: :py:class:`str` or :py:obj:`False`
          """
          if (string[0:5] == u"data_" and u"save_" in string) or (string[0:5] == b"data_" and b"save_" in string):
              return string
          return False