A product type promotion allows you to offer a storewide price promotion on products (e.g. 10% discount on all the products in your store, or 10% discount on all products belonging to a category or perhaps even an additional 5% to members only on top of the first discount). Customers will see the discounted price before adding item to the shopping cart.
The promotion rule can also use XSL transform and will apply on products described in the rule. The expected output should return the discounted promotion price, otherwise the regular price. The Storefront comes with several pre-defined rules that you can simply modify the values without needing to know XSL. To learn more about XSL, please see the XSL Transform section.