protected function stackGetLastKey()
    {
        $depth = false;
        for ($i = count($this->stackTT) - 1; $i >= 0; $i--) {
            if ($this->stackTT[$i] === self::TTYPE_NAME) {
                $depth = $i;
                break;
            }
        }
        if ($depth !== false) {
            return $this->stackTV[$depth];
        }
        return null;
    }