AJAX form callback: Selects for the ajax_forms_test_lazy_load_form() form.
This function returns nothing, because all we're interested in testing is ajax_render() adding commands for JavaScript and CSS added during the page request, such as the ones added in ajax_forms_test_lazy_load_form_submit().
function ajax_forms_test_lazy_load_form_ajax($form, &$form_state) {
return NULL;
}