protected function _checkFlags( $value )
	{
		$value = (int) $value;

		if( $value < MShop_Order_Item_Base_Product_Abstract::FLAG_NONE ||
			$value > MShop_Order_Item_Base_Product_Abstract::FLAG_IMMUTABLE ) {
				throw new MShop_Order_Exception( sprintf( 'Flags "%1$s" not within allowed range', $value ) );
		}
	}