Форуми / Craftwork / Server-side / Error handling with Ajax and PHP

I'm wondering what in Cotonti the best way is to handle errors with an Ajax submitted form to a PHP file.

Normally with a simple form the errors can be handled with Cotonti's cot_error(); function like this:

cot_error('someErrorMessage', '');
cot_redirect(cot_url('myPlug', 'm=form', '', true));

How would you guys handle something like this if the form is submitted with Ajax?