code: func (cs Set) Split() (domain, target, ref string) {
  	switch p := strings.SplitN(string(cs), "/", 3); len(p) {
  	case 1:
  		return p[0], "", ""
  	case 2:
  		return p[0], p[1], ""
  	default:
  		return p[0], p[1], p[2]
  	}
  }
docs: // Split splits a Set into its domain, target, and ref components.