Please run this demo from a WebServer, it will fail otherwise.

This demonstrations shows the use of Ajax form and field validations.
The form validation implements callback hooks, so please check the javascript console

Ajax validation
Desired username (ajax validation, only karnius is available) :

validate[required,custom[noSpecialCaracters],maxSize[20],ajax[ajaxUserCall]]

First name (ajax validation, only duncan is available):

validate[custom[onlyLetterSp],length[0,100],ajax[ajaxNameCall]]

Email address :

validate[required,custom[email]]