anchor.diff:        help: 'Check pub.dartlang.org for lasted packages and flag those that '
         'are outdated.');
   
  -const _FORMAT_ALLOWED = const ['html', 'dot'];
  -
   const _FORMAT_HELP = const {
     'dot': 'Generate a GraphViz dot file',
     'html': 'Wrap the GraphViz dot format in an HTML template which renders it.'
  
positive.code: ArgParser _getParser() => new ArgParser()
    ..addOption(_formatOption,
        abbr: 'f',
        allowed: _FORMAT_ALLOWED,
        defaultsTo: 'html',
        allowedHelp: _FORMAT_HELP)
    ..addOption(_ignoreOption,
  
negative.code:   var command = result.command;
  
    if (command == null) {
      print("Specify a command: ${parser.commands.keys.join(', ')}");
      _printUsage(parser);
      return;
    }
  