code: func (s *Registry) Save(w http.ResponseWriter) error {
  	var errMulti MultiError
  	for name, info := range s.sessions {
  		session := info.s
  		if session.store == nil {
  			errMulti = append(errMulti, fmt.Errorf(
  				"sessions: missing store for session %q", name))
  		} else if err := session.store.Save(s.request, w, session); err != nil {
  			errMulti = append(errMulti, fmt.Errorf(
  				"sessions: error saving session %q -- %v", name, err))
  		}
  	}
  	if errMulti != nil {
  		return errMulti
  	}
  	return nil
  }
docs: // Save saves all sessions registered for the current request.