Implements hook_node_submit().
function menu_node_submit($node, $form, $form_state) {
// Decompose the selected menu parent option into 'menu_name' and 'plid', if
// the form used the default parent selection widget.
if (!empty($form_state['values']['menu']['parent'])) {
list($node->menu['menu_name'], $node->menu['plid']) = explode(':', $form_state['values']['menu']['parent']);
}
}