Enables form submission and validation via AJAX.
Only install if required by another module.
Also check out the ajax module, which offers a similar API as well as a UI for designating forms to have Ajax submit handling.
$form['#ajaxsubmit'] = TRUE;
Developers can designate one or more custom callbacks to be called when
data are returned from an Ajax submit.
$form['#ajaxsubmit_callbacks'] = array(