Use Case:
There are shared process definitions which models the default process. Each tenant can provide a custom definition to override the default one. When a process instance arrives a call activity then it should create an instance of the overridden process definition instead of the default one. If there is no custom definition then it should use the default process definition.

AT:

• provide a predefined method of the tenant id provider (calledElementTenantId attribute on call activity) to use the overridden process definition of a tenant