docs: public static Request registerRequest(Request req) {
      assert req.supportedVersions().length > 0;
      for (API_VERSION ver : req.supportedVersions()) {
        String href = req.href(ver);
        assert (! _requests.containsKey(href)) : "Request with href "+href+" already registered";
        _requests.put(href,req);
        req.registered(ver);
      }
      return req;
    }