Parses the production rule::
                value : TERM (',' TERM)*

            Returns list of string terms.

def _rule_value(self):
        """ Parses the production rule::
                value : TERM (',' TERM)*

            Returns list of string terms.
            """

        terms = [self._get_token()]

        # consume additional terms if available
        while self._lookahead_token() == ',':
            self._get_token()  # chomp the comma
            terms.append(self._get_token())

        return terms