code: func Check(appID string, opts Options) (Response, error) {
  	var req, err = checkRequest(appID, &opts)
  
  	if err != nil {
  		return Response{}, err
  	}
  
  	return doCheckRequest(opts, req)
  }
docs: // Check communicates with an Equinox update service to determine if
  // an update for the given application matching the specified options is
  // available. The returned error is nil only if an update is available.
  //
  // The appID is issued to you when creating an application at https://equinox.io
  //
  // You can compare the returned error to NotAvailableErr to differentiate between
  // a successful check that found no update from other errors like a failed
  // network connection.