code: func (s *Set) ToStrings() []string {
  	if s.IsEmpty() {
  		return nil
  	}
  	if s.All {
  		return []string{"*"}
  	}
  	out := make([]string, 0, len(s.IDs)+len(s.Groups))
  	for ident := range s.IDs {
  		out = append(out, string(ident))
  	}
  	for group := range s.Groups {
  		out = append(out, "group:"+group)
  	}
  	sort.Strings(out)
  	return out
  }
docs: // ToStrings returns a sorted list of strings representing this set.
  //
  // See 'FromStrings' for the format of this list.