code: func (a *API) FetchMetricCluster(cid CIDType, extras string) (*MetricCluster, error) {
  	if cid == nil || *cid == "" {
  		return nil, fmt.Errorf("Invalid metric cluster CID [none]")
  	}
  
  	clusterCID := string(*cid)
  
  	matched, err := regexp.MatchString(config.MetricClusterCIDRegex, clusterCID)
  	if err != nil {
  		return nil, err
  	}
  	if !matched {
  		return nil, fmt.Errorf("Invalid metric cluster CID [%s]", clusterCID)
  	}
  
  	reqURL := url.URL{
  		Path: clusterCID,
  	}
  
  	extra := ""
  	switch extras {
  	case "metrics":
  		extra = "_matching_metrics"
  	case "uuids":
  		extra = "_matching_uuid_metrics"
  	}
  
  	if extra != "" {
  		q := url.Values{}
  		q.Set("extra", extra)
  		reqURL.RawQuery = q.Encode()
  	}
  
  	result, err := a.Get(reqURL.String())
  	if err != nil {
  		return nil, err
  	}
  
  	if a.Debug {
  		a.Log.Printf("[DEBUG] fetch metric cluster, received JSON: %s", string(result))
  	}
  
  	cluster := &MetricCluster{}
  	if err := json.Unmarshal(result, cluster); err != nil {
  		return nil, err
  	}
  
  	return cluster, nil
  }
docs: // FetchMetricCluster retrieves metric cluster with passed cid.