The Shipping Guide makes an effort to always be backwards compatible regarding data format for requests and responses. To achieve this, namespace schema versioning is used in the request for webservices, indicating which version the client is on and what data-format the client expects in the result. For REST, versioning is defined as part of endpoint itself.
Important: All clients must accept new (unknown) elements in the response. E.g. unknown elements should be ignored. Also, new error codes and warning codes could be added as well. The client framework used by client must not crash when unknown elements or new code values are are encountered.
When incompatible changes in the schema are made (other than addition of new elements), the namespace versioning will be updated accordingly. The new schema is used at the same endpoint URL as before for webservices. Old schema versions will be shut down some time in the future, so its recommended always updating to the latest version.