code: private boolean validInstanceOfExpression(Node expr) {
      // The expression must have two children:
      // - The instanceOf keyword
      // - A string
      if (!checkParameterCount(expr, Keywords.INSTANCEOF)) {
        return false;
      }
      if (!validTypeTransformationExpression(getCallArgument(expr, 0))) {
        warnInvalidInside(Keywords.INSTANCEOF.name, expr);
        return false;
      }
      return true;
    }
docs: A typeOfVar expression must be of the form instanceOf('name')