Possible enumeration values:

NameValueDescription
NoPurchaseAllowed

1

If the product is out of stock, the customer cannot buy this product

AllowPurchaseWithWarning

2

If the product is out of stock, the customer will be allowed to buy the product, but will also receive a warning - perhaps about the delivery delay

AllowPurchase

3

Treat this product like it is in stock. Allow the customer to purchase it and do not give any indication about it's unavailability