code: func New(ls ...Label) Labels {
  	set := make(Labels, 0, len(ls))
  	for _, l := range ls {
  		set = append(set, l)
  	}
  	sort.Sort(set)
  
  	return set
  }
docs: // New returns a sorted Labels from the given labels.
  // The caller has to guarantee that all label names are unique.