When documents use different constraints, conref and generalization processors may examine the @domains to verify compatibility between the document instances.
To determine compatibility between two document instances, a conref processor can check the @domains attribute to confirm that
Similarly, to determine compatibility between a document instance and a target document type, a generalization processor can use the @domains and @class attributes for the document instance and the @domains attribute for the target document type to determine how to rename elements in the document instance. For each element instance, the generalization processor:
If a module is found in the target document type, that module becomes the minimum threshhold for the generalization of contained element instances.
If a module is not found, the document instance cannot be generalized to the target document type and, instead, can only be generalized to a less constrained document type.
Note that a document instance can always be converted from a constrained document type to an unconstrained document type merely by switching the binding of the document instance to the less restricted schema (which would also have a different @domains attribute declaration). No renaming of elements is needed to remove constraints.