Per my action item from the last conference call, I've cleaned up the Swagger API spec to add fuller descriptions of requests, responses and parameters. I also cleaned up the model names, added finer grained response codes and tried to address a concern about the non-RESTful use of verbs for collection operations by putting these at a subpath (which I know is still not perfect, and I welcome other suggestions!)
You can explore the updated API in the Swagger UI at http://rdacollectionswg.github.io/apidocs/#
Or you can just look at the spec directly in your preference of JSON or YAML:
We obviously still have work to do here, both on the model objects and the operations, but hopefully it's a step closer to where we want to be.