anchor.diff:        defaultsTo: _CLOSURE_DEFAULT)
     ..addFlag('force-compile',
         help: 'Compile code with static errors', defaultsTo: false)
  -  ..addOption('log', abbr: 'l', help: 'Logging level (defaults to severe)')
  +  ..addOption('log', abbr: 'l', help: 'Logging level (defaults to warning)')
     ..addFlag('dump-info',
         abbr: 'i', help: 'Dump summary information', defaultsTo: null)
     ..addOption('v8-binary',
  
positive.code:   if (enableHashing == null) {
      enableHashing = serverMode;
    }
    // TODO(jmesserly): shouldn't level always default to warning?
    var logLevel = serverMode ? Level.WARNING : Level.SEVERE;
    var levelName = args['log'];
    if (levelName != null) {
      levelName = levelName.toUpperCase();
  
negative.code:       this.useColors: true,
        this.help: false,
        this.version: false,
        this.logLevel: Level.WARNING,
        this.serverMode: false,
        this.enableHashing: false,
        this.widget: true,
  