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Game Objects (GOs) opt-in to services by implementing the "marker" interface for each one it wants.
GOs enter the system via Install Pipeline, an asynchronous "standard" implementation that keys on the marker interfaces and performs the "protocol" for that marker. There are also Event and Uninstall pipelines.
Reference by name is encouraged. A trip through the pipeline includes a Bind Name List; allows GO to connect to interfaces in other GOs on the other End.