public function isChild($id)
    {
        $base = (substr($this->id, -2) == '.0')
            ? substr($this->id, 0, -1)
            : rtrim($this->id, '.') . '.';

        return ((($base == 0) && ($id != 0)) ||
                (strpos(strval($id), strval($base)) === 0));
    }