anchor.diff:          defaultsTo: false, help: 'verbose output', negatable: false)
       ..addFlag('help', defaultsTo: false, negatable: false);
   
  -  var options = parser.parse(args);
  +  ArgResults options;
  +
  +  try {
  +    options = parser.parse(args);
  +  } on FormatException catch (e) {
  +    stderr.writeln(e);
  +    print(parser.usage);
  +    exitCode = 64;
  +    return;
  +  }
   
     if (options['help']) {
       print(parser.usage);
  
positive.code: import 'dart:io';
  import 'dart:mirrors';
  
  import 'package:args/args.dart' show ArgParser;
  import 'package:collection/collection.dart';
  import 'package:html/dom.dart' as dom;
  import 'package:html/parser.dart' show parseFragment;
  
negative.code:   var updateFiles = options['update-files'] as bool;
  
    if (updateFiles && (raw || verbose || (specifiedSection != null))) {
      stderr.writeln('The `update-files` flag must be used by itself');
      print(parser.usage);
      exitCode = 64; // unix standard improper usage
      return;
  