Those parts of matrix needed for interop need to go through the spec change proposal process to land in the spec. But namespacing is used extensively. The spec

Those parts of matrix needed for interop need to go through the spec change proposal process to land in the spec. But namespacing is used extensively. The spec reserves the 'm.' prefix, e.g. 'm.text', but everyone is encouraged to extend using reverse dns namespacing, e.g. 'com.ycombinator.news.our.extension'.