Paypal IPN - define empty

[Mikado]

Into Paypal I see the details of a transaction : see the attached file

In includes/languages/french/modules/payment/paypal.php I have this :
define('MODULE_PAYMENT_PAYPAL_PURCHASE_DECRIPTION_TITLE', STORE_NAME . ' Achat');
define('MODULE_PAYMENT_PAYPAL_PURCHASE_DESCRIPTION_ITEMNUM', 'Retour à la boutique');

Why "Titre de l'objet" contains MODULE_PAYMENT_PAYPAL_PURCHASE_DESCRIPTION_TITLE and no STORE_NAME . ' Achat' ?

[Mikado]

In paypal.php, for what is of use this define('MODULE_PAYMENT_PAYPAL_PURCHASE_DESCRIPTION_ITEMNUM', 'Store Receipt'); ?
What is it necessary to put in it indoors?