anchor.diff:  
           if (next(TokenType.COLON)) {
             var COLON = current;
  -          var val = parseValueOrVariable();
  +          var val = parseInputValue();
             if (val != null)
               return new DirectiveContext(
                   ARROBA, NAME, COLON, null, null, null, val);
  
positive.code:   DefaultValueContext parseDefaultValue() {
      if (next(TokenType.EQUALS)) {
        var EQUALS = current;
        var value = parseValue();
        if (value != null) {
          return new DefaultValueContext(EQUALS, value);
        } else {
  
negative.code:                   ARROBA, NAME, null, LPAREN, current, arg, null);
              } else {
                errors.add(
                    new SyntaxError('Missing \')\'', arg.value.span));
                return null;
              }
            } else {
  