CSS form builder / Form toolkit hook up own validation functions

I'm evry happy with both extensions they allow me to build a decent form within minutes. I like the server validation but there is still one thing I'm missing.

There are scenarios where you still have to write your own validations. It would be nice if both form toolkit and css form builder had the possibility of hooking up your own validation functions by means of a callback script.

It would greatly benefit the functionallity of both extensions.

For instance, now I'm building a site wich uses the phpbb membership for the whole site. I've constructed it that way that users can register on my site and automatically are members of the forum. To exclude spambots people can only register on my site on a form build by css form builder. This is very efficient, I haven't had any spambot until today.

But I had to add two more validations, one that checked if the username allreay existed and one that checked if the email existed. It's not very hard to do but building it into the css formbuilder form was very contra productive. In that case it would have been nice if I could hookup these functions in the css form builder (or form toolkit) validation.

I think there are many more of these scenarios and having the ability to hook up your own validation functions in both web assist extensions would speed up designing and building these forms and would benefit the functionality and quality of these extensions so maybe it's a good idea for the next upgrade?