We've just released r0.2.0 of the Client-Server API specification. This release bundles up a number of clarifications and incremental improvements, as well as removing some outdated text relating to the pre-r0 event syncing APIs.
We've also taken the opportunity to make the license on the specifications explicit (we're using the Apache license), and have finally settled a long-running argument on what a user ID should look like.
As ever, the evolution of the spec has been helped tremendously by contributions and bug reports from the members of community - thanks to all those who have helped it on its way!