Generate a (tag, offset, length) 3-tuple for each of the tables in
        this font file.

def _iter_table_records(self):
        """
        Generate a (tag, offset, length) 3-tuple for each of the tables in
        this font file.
        """
        count = self._table_count
        bufr = self._stream.read(offset=12, length=count*16)
        tmpl = '>4sLLL'
        for i in range(count):
            offset = i * 16
            tag, checksum, off, len_ = unpack_from(tmpl, bufr, offset)
            yield tag.decode('utf-8'), off, len_