code: func setOSArch(labels map[appctypes.ACIdentifier]string, os, arch string) error {
  	// Translate arch tuple into the appc arch tuple.
  	appcOS, appcArch, err := appctypes.ToAppcOSArch(os, arch, "")
  	if err != nil {
  		return err
  	}
  
  	// Set translated labels.
  	setLabel(labels, "os", appcOS)
  	setLabel(labels, "arch", appcArch)
  	return nil
  }
docs: // setOSArch translates the given OS and architecture strings into
  // the compatible with application container specification and sets
  // the respective label entries.
  //
  // Returns an error if label translation fails.