anchor.diff:    ..addOption('indent',
         abbr: 'i',
         help: 'Customizes the indention when pretty printing.',
  -      defaultsTo: '  ');
  +      defaultsTo: '  ')
  +  ..addFlag('pretty',
  +      abbr: 'p',
  +      help: 'Reformats the output to be pretty.',
  +      defaultsTo: true);
   
   void printUsage() {
     stdout.writeln('Usage: xml_pp [options] {files}');
  
positive.code: 
    for (final file in files) {
      final document = xml.parse(file.readAsStringSync());
      stdout.writeln(document.toXmlString(pretty: true, indent: indent));
    }
  }
  
negative.code:   final files = <File>[];
    final results = argumentParser.parse(arguments);
    final indent = results['indent'];
    final pretty = results['pretty'];
  
    for (final argument in results.rest) {
      final file = File(argument);
  