anchor.diff:    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);
  
positive.code:   ..addOption('indent',
        abbr: 'i',
        help: 'Customizes the indention when pretty printing.',
        defaultsTo: '  ');
  
  void printUsage() {
    stdout.writeln('Usage: xml_pp [options] {files}');
  
negative.code: 
    for (final file in files) {
      final document = xml.parse(file.readAsStringSync());
      stdout.writeln(document.toXmlString(pretty: pretty, indent: indent));
    }
  }
  