"Reality is not a collection of things, it’s a network of processes."


+facebook_is_better_than_bonfire boundaries and circles are integrated in topics, so you were able to add this sub-topic because the parent topic has open boundaries (public), but you can create topics where only some circles can publish (in which case things they tag end up in the Submitted tab and don't appear in the feeds of topic followers) or create sub-topics, etc