code: func (pdb *BytesBrokerWatcherEtcd) Watch(resp func(keyval.BytesWatchResp), closeChan chan string, keys ...string) error {
  	for _, key := range keys {
  		err := watchInternal(pdb.Logger, pdb.watcher, closeChan, key, resp)
  		if err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // Watch starts subscription for changes associated with the selected <keys>.
  // KeyPrefix defined in constructor is prepended to all <keys> in the argument
  // list. The prefix is removed from the keys returned in watch events.
  // Watch events will be delivered to <resp> callback.