code: func buildAux(aa []sam.Aux) (aux []byte) {
  	for _, a := range aa {
  		// TODO: validate each 'a'
  		aux = append(aux, []byte(a)...)
  		switch a.Type() {
  		case 'Z', 'H':
  			aux = append(aux, 0)
  		}
  	}
  	return
  }
docs: // buildAux constructs a single byte slice that represents a slice of sam.Aux.