public static function itemAjax(array $form, FormStateInterface $form_state) {
$button = $form_state
->getTriggeringElement();
// Go one level up in the form, to the widgets container.
$element = NestedArray::getValue($form, array_slice($button['#array_parents'], 0, -4));
$element['#prefix'] = '<div class="ajax-new-content">' . (isset($element['#prefix']) ? $element['#prefix'] : '');
$element['#suffix'] = (isset($element['#suffix']) ? $element['#suffix'] : '') . '</div>';
return $element;
}