code: func (o Options) sortedKeys() []int {
  	// Send all values for a given key
  	var codes []int
  	for k := range o {
  		codes = append(codes, int(k))
  	}
  
  	sort.Sort(sort.IntSlice(codes))
  	return codes
  }
docs: // sortedKeys returns an ordered slice of option keys from the Options map, for
  // use in serializing options to binary.