public function isChildOf($head, $target)
    {
        if (!is_array($head)) {
            $head = $this->getNode($head);
        }
        if (!is_array($target)) {
            $target = $this->getNode($target);
        }
        $config = $this->config;
        $headLft = $head[$config['lft']];
        $headRgt = $head[$config['rgt']];
        $targetLft = $target[$config['lft']];
        $targetRgt = $target[$config['rgt']];
        if ($headLft > $targetLft && $headRgt < $targetRgt) {
            return TRUE;
        } else {
            return FALSE;
        }
    }