Where does Core Schema Live in a federated graph?

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I am trying to understand what direction Apollo is headed with core schemas, specifically in a federated environment. I think I understand its purpose, versioning directives and enums. But I am unclear where the CoreSchema package and directives are to be used. Should they be added to the supergraph schema or the subgraphs individually? It seems like the core-schema is still work in progress, is it going to be part of the AF2 release?