Method: Selects a shipping rate.

Method: Based on the core cart class but returns errors rather than rendering notices directly.

Method: Validates an existing cart coupon and returns any errors.

Method: Validate all coupons in the cart and check for errors.

Method: Validate all items in the cart and get a list of errors.

Method: Validate all items in the cart and get a list of errors.

Method: Generates the error message for out of stock products and adds product names to it.

Method: Takes a string describing the type of stock extension, whether there is a single product or multiple products causing this exception and returns an appropriate error message.