public function addOrders(array $orders)
    {
        foreach ($orders as $key => $order) {
            $this->addOrder($order);

            /** Name the expression if $key is a non-numeric string. */
            if (is_string($key) && !is_numeric($key)) {
                $order = end($this->orders);
                $order->setName($key);
            }
        }

        return $this;
    }