def ref_string_matches_ref_sequence(self, ref_sequence):
        '''Returns true iff the REF string in the record agrees with
        the given ref_sequence'''
        # you never know what you're gonna get...
        if self.POS < 0:
            return False

        end_pos = self.ref_end_pos()
        if end_pos >= len(ref_sequence):
            return False

        return self.REF == ref_sequence[self.POS:end_pos + 1]
Returns true iff the REF string in the record agrees with
        the given ref_sequence