code: func (reg *WatchDataReg) Register(resyncName, keyPrefix string) error {
  	reg.adapter.access.Lock()
  	defer reg.adapter.access.Unlock()
  
  	for resName, sub := range reg.adapter.subscriptions {
  		if resName == resyncName {
  			// Verify that prefix does not exist yet
  			for _, regPrefix := range sub.KeyPrefixes {
  				if regPrefix == keyPrefix {
  					return fmt.Errorf("prefix %q already exists", keyPrefix)
  				}
  			}
  			sub.KeyPrefixes = append(sub.KeyPrefixes, keyPrefix)
  			return nil
  		}
  	}
  	return fmt.Errorf("cannot register prefix %s, resync name %s not found", keyPrefix, resyncName)
  }
docs: // Register starts watching of particular key prefix. Method returns error if key which should be added
  // already exists