Iterator over all level=0 records.

        :param str tag: If ``None`` is given (default) then return all level=0
            records, otherwise return level=0 records with the given tag.

def records0(self, tag=None):
        """Iterator over all level=0 records.

        :param str tag: If ``None`` is given (default) then return all level=0
            records, otherwise return level=0 records with the given tag.
        """
        _log.debug("in records0")
        for offset, xtag in self.index0:
            _log.debug("    records0: offset: %s; xtag: %s", offset, xtag)
            if tag is None or tag == xtag:
                yield self.read_record(offset)