Relying on HTML 'required' for simple form validation

Question

My question is simple, I\'m writing a simple login/registration form for my website using HTML, PHP and jQuery.

Is it neccesary to write the form validation in PHP also

Answer 1

It might help to think of client side validation being a usability issue and the server side validation being a security issue.

Where usability might be described as being a "nice to have", security is definitely a "must have".