How to reference services defined in a Docker provider from a Traefik config file?

Labels in docker-compose are not updatable at runtime so I'd like to keep most of my rules and other Traefik configuration outside of docker-compose, ideally setting only a "traefik.enable=true" label there.
Using v2.0-beta, I tried declaring routing rules in traefik.toml/traefik.yml, guessing various permutations of namespace (eg, 'http.routers.someName') and service name as displayed in http://localhost:8080/api/http/services (eg, 'sinatra-api_webstack@docker') but nothing works and I can't find documentation explaining conventions or syntax.
If possible, can you please share an example or explain the syntax?
Please let me know if the answer would differ for v1.7--I'll likely downgrade versions later today. (Because it's easier to find full examples from third parties.)

Cross provider reference was not possible in the 1.7, this is a new functionality of the v2, and the only thing you have to do, is to reference the full qualifier of you're service created in docker.

So for example in the provider file you need to create a router like this.

  rule = "PathPrefix(`/`)"
  service = "sinatra-api_webstack@docker"

It should work, and if it doesn't work could you share your docker-compose, your traefik.toml and the debug log?

Thanks. I thought I tried that (with yml though) but haven't had a chance to revisit--will try again after I finish an active project and write again.