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The intersection of @following and @followers should be @friends.
Proposal: Group ID Registry
We should treat Group IDs in a manner similar to other kinds of label-type extension points (e.g. link relations) and have a Registry of Common Group IDs. We would define an initial collection of well-known group identifiers (e.g. @self, @all, @summary, @manager, etc) and define their specific meaning within OpenSocial applications. Implementations would be free to implement the specific group ID's they need, as well as define additional group ID's as needed. When id's become common in use, they can be added to the registry. The Registry would be maintained on the OpenSocial Wiki.