There isn't a single thing, we tune it on a regular basis. It usually considers things like freshness (don't show days old posts), engagement (do people actually find the post interesting), did the poster contribute to the community, is it repetitive, etc. There's a few more improvements we need to do, to give everyone a fair chance and all that, but the big idea is that it's a valuable digital real estate and we want to give everyone a chance, especially those that contribute to other people's posts and keep it interesting and fresh.