Support for Versioning and Extensibility

The format designer shall not specify and the format producer shall not create Core Properties that use the Markup Compatibility namespace as defined in Annex F, “Standard Namespaces and Content Types”. A format consumer shall consider the use of the Markup Compatibility namespace to be an error. [M4.2] Instead, versioning and extensibility functionality is accomplished by creating a new part and using a relationship with a new type to point from the Core Properties part to the new part. This Open Packaging specification does not provide any requirements or guidelines for new parts or relationship types that are used to extend core properties.