anchor.diff:        help: "Assume that the transformer is in use, so name and args "
             "don't need to be specified for messages.");
   
  +  parser.addOption("locale",
  +      defaultsTo: null,
  +      callback: (value) => locale = value,
  +      help: 'Specify the locale set inside the arb file.');
     parser.addOption("output-dir",
         defaultsTo: '.',
         callback: (value) => targetDir = value,
  
positive.code:     exit(0);
    }
    var allMessages = {};
    for (var arg in args.where((x) => x.contains(".dart"))) {
      var messages = extraction.parseFile(new File(arg), transformer);
      messages.forEach((k, v) => allMessages.addAll(toARB(v)));
  
negative.code:   bool transformer;
    var parser = new ArgParser();
    var extraction = new MessageExtraction();
    String locale;
    parser.addFlag("suppress-warnings",
        defaultsTo: false,
        callback: (x) => extraction.suppressWarnings = x,
  