Custom page in plugin visible in menu

Question

I'm trying to understand creating custom plugin pages and menus in admin panel, but I get what I don't need. I've got:

function my_plugin_add_pages() {
   add_menu_page(__('Custom quiz', 'custom-quiz'), __('Custom quiz', 'custom-quiz'), 5, 'custom-quiz-listing-page', 'custom_quiz_list_page');
   add_submenu_page('custom-quiz-listing-page', __('Add quiz'), __('Add quiz'), 6, 'custom_quiz_add_quiz', 'custom_quiz_add_quiz');
   add_submenu_page('custom-quiz-listing-page', __('Edit quiz'), __('Edit quiz'), 6, 'custom_quiz_edit_quiz', 'custom_quiz_edit_quiz');
}

function custom_quiz_list_page() {
    require_once('includes/quiz-listing.php');
}

function custom_quiz_add_quiz() {
   if (!empty($_POST)) {
      CreateQuiz($_POST);
      echo '<meta http-equiv="refresh" content="0;url=?page=custom-quiz-listing-page" />';
   }
   require_once('includes/add-quiz.php');
}

function custom_quiz_edit_quiz() {
   if (!empty($_GET['quiz_id']) && !empty($_POST))
      UpdateQuiz($_POST);
   require_once('includes/edit-quiz.php');
}

And the problem is that all these pages (even subpages) are created in menu sidebar in admin panel. How to create page correctly without sticking it into admin menu?

Answer 1

I found the answer on Wordpress Forum: http://wordpress.org/support/topic/add-backend-page-without-menu-item#post-2135050

It requires add_submenu_page() with slug = null (first argument). In Wordpress documentation it's marked as 'required' so it looks like it's required but can be null.