Register_raw is like Register except you get to deal with the whole pipe. This is useful if, e.g., your model_of_response function can fail, so that you'd like to filter items out from the result pipe.
Register_raw
Register
model_of_response
Version_i : sig ... end
val rpc : (Version_i.query, Version_i.response, Version_i.error) Async_rpc_kernel.Rpc.Pipe_rpc.t