anchor.diff:      parser.addFlag('help',
           abbr: 'h',
           negatable: false,
  -        help: 'show command help');
  +        help: 'show command help',
  +        callback: (help) {
  +          if (help) {
  +            _printUsage(parser);
  +          }
  +        });
  +
  +    parser.addFlag('verbose', abbr: 'v',
  +        help: 'Output more logging information.', negatable: false,
  +        callback: (verbose) {
  +          if (verbose) {
  +            Logger.root.level = Level.FINEST;
  +          }
  +        });
  +
       parser.addOption(
           'sdk',
  -        abbr: 's',
  -        help: 'Path to the sdk. Required.');
  +        help: 'Path to the sdk. Required.',
  +        defaultsTo: null);
   
       // Should be run in one of two modes
       //
  
positive.code: import "dart:async";
  
  import 'package:args/args.dart';
  import 'package:logging/logging.dart';
  
negative.code:     // and publish them to pub.dartlang.org.
      parser.addFlag(
          'daemon',
          help: 'run in daemon mode',
          callback: (mode) {
            serverMode = mode;
            if (clientMode && serverMode) {
              print("You must choose `daemon` or `client` modes to run in. Cannot choose both.");
              _printUsage(parser);
            }
          });
  
      parser.addFlag(
          'client',
          help: 'run in client mode',
          callback: (mode) {
            clientMode = mode;
            if (clientMode && serverMode) {
              print("You must choose `daemon` or `client` modes to run in. Cannot choose both.");
              _printUsage(parser);
            }
          });
  
      //
      // Daemon options
      //
      parser.addOption(
          'sleep-interval',
          help: 'Time requred to sleep in seconds before polling for new packages on pub.dartlang.org',
          defaultsTo: null);
      parser.addOption(
          'max-clients',
          help: 'Max number of possible client instances to fire up.',
          defaultsTo: null);
  
      //
      // Client options
      //
      parser.addOption(
          'package',
          help: 'Package to generate documentation for.', defaultsTo: null);
      parser.addOption( // TODO(adam): support possible version constraints for package generation.
          'version',
          help: 'Version of package to generate.', defaultsTo: null);
  
      return parser;
  }
  
  