code: func (vs *VSphere) collapseZonesInRegion(ctx context.Context, zones []cloudprovider.Zone) ([]cloudprovider.Zone, error) {
  	// first create a map of region -> list of zones in that region
  	regionToZones := make(map[string][]string)
  	for _, zone := range zones {
  		fds, exists := regionToZones[zone.Region]
  		if !exists {
  			fds = make([]string, 0)
  		}
  		regionToZones[zone.Region] = append(fds, zone.FailureDomain)
  	}
  
  	// Join all fds in same region and return Zone instances
  	collapsedZones := make([]cloudprovider.Zone, 0)
  	for region, fds := range regionToZones {
  		fdSet := sets.NewString(fds...)
  		appendedZone := volumehelpers.ZonesSetToLabelValue(fdSet)
  		collapsedZones = append(collapsedZones, cloudprovider.Zone{FailureDomain: appendedZone, Region: region})
  	}
  	return collapsedZones, nil
  }
docs: // collapse all zones in same region. Join FailureDomain with well known separator