There are different ways to validate fields data in version 6
The Easy way
Use the validation settings inside the field settings area, then make sure you have a "Validate fields" action at the top of the form "submit" event with an "Event loader" in the fail event in order to reload the form when a validation rule fails.
The other way
Use a "Validate data" action and set the data provider to whatever data set you want to check, for example you can use the default request data set {data:}, then list the fields you want to validate in the data set along with the rule to be tested and the error message to be shown.
field1/required:this field is required field1/email:it should have an email address
Custom validation function
1 - Custom JavaScript validation function
In the "Validation rules" box, write your custom validation function name followed by the error message to use: customfn:please enter a valid username.
Drag a JavaScript element into your section, and add the follwoing code:
jQuery.fn.form.settings.rules.customfn = function(value, param) {
return false;
};
2 - Custom PHP validation function
Add a PHP action and write the code needed to do the validation you desire, then return some value, say "true" or "false" based on the codition success.
assuming the PHP action name is "php4", you will then need to have an "Event switcher" action with the data provider set to {var:php4}, set the "Event list" to true,false (which are the anticipated results of the data provider) and click "Update events", now you can add the actions you need to the new events which will be triggered based on the result of the PHP function.