The documentation and the Composite NodeStore implementation are a work-in-progress. Please ask on oak-dev for things that are missing or unclear.
The Composite NodeStore mounts various other node stores in read-only mode. Since the read-only mode is not enfored via permissions, it may not be queried via Session.hasPermission. Instead, the read-only status is surfaced via Session.hasCapability. See OAK-6563 for details.
