There's nothing to 'register'. The validation logic is baked into the
However, you can customize the behavior of many methods for Xperience's built-in types, like
Here's an example of customizing the OrderInfoProvider. The process is identical for
ShoppingCartInfoProvider. You will want to make sure that customized code is referenced by both the Administration application and Live site application.
You'll want to override
protected virtual IEnumerable<IValidationError> ValidateShoppingCartInternal(ShoppingCartInfo cart) which uses the
ShoppingCartValidator on the cart and
ShoppingCartItemValidator on each item in the cart.