code: func (r *Router) RemoveArea(areaID types.AreaID) error {
  	r.Lock()
  	defer r.Unlock()
  
  	area, ok := r.areas[areaID]
  	if !ok {
  		return fmt.Errorf("area ID %q does not exist", areaID)
  	}
  
  	// Remove all of this area's managers from the index and shut them down.
  	for datacenter, info := range area.managers {
  		r.removeManagerFromIndex(datacenter, info.manager)
  		close(info.shutdownCh)
  	}
  
  	delete(r.areas, areaID)
  	return nil
  }
docs: // RemoveArea removes an existing network area from the router.