def value(self, index, extra):
        """Returns ('Simple', #codewords) or ('Complex', HSKIP)
        """
        if index==1:
            if extra>3:
                raise ValueError('value: extra out of range')
            return 'Simple', extra+1
        if extra:
            raise ValueError('value: extra out of range')
        return 'Complex', index
Returns ('Simple', #codewords) or ('Complex', HSKIP)