I have seen som different webpage that has a user-friendly validation approach in front end.

For instance when you want to register a new account in gmail or yahoo and if you have a input box and then you forgot to add last name, a message when display below the input box.

This approach happens only in client mode and you don't need to affect the backend.

I'm fully aware that you need to have validation, both front and backend due to security.

My question is: Do you know where I can retrieve the source code based on jQuery?

Thanks!