You can configure availability rule based on quantity, amount, weight, etc. that determines if a shipping method should become available for selection during customer checkout.
The availability rule can also use XSL transform to determine whether this shipping method is available for selection during checkout. The expected output should return "true" to indicate this shipping method is available for selection, otherwise "false" if disallowed. 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.