Method: Filter data for add to cart requests.

Method: Get hashes for items in the current cart. Useful for tracking changes.

Method: If variations are set, validate and format the values ready to add to the cart.

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.

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

Method: This method will take arrays of exceptions relating to stock, and will convert them to a WP_Error object.

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