Moodle: Get courses recursively

Hello,

How to get all courses of a category recursively?

<?php

global $CFG;
require_once($CFG->dirroot . '/lib/coursecatlib.php');
$categoryid = 1;
$allcourses = coursecat::get($categoryid)->get_courses(array('recursive' => true));

How to get all courses of a hidden category?

<?php

global $CFG;
require_once($CFG->dirroot . '/lib/coursecatlib.php');
$categoryid = 1;
$allcourses = coursecat::get($categoryid, MUST_EXIST, true)->get_courses(array('recursive' => true));

Best regards!