There isn't much. It's an old protocol, and very simple. But it's simple to the point of naivete and networks only really function with a bunch of ad-hoc extensions on top of it, but there's very little standardisation of those, and that's basically to get things like the concept of having a persistent identity that can't just be hijacked by anyone else on the server, let alone something like persistent message history, media sharing, or end-to-end encryption.