anchor.diff:      ..addFlag('version', abbr: 'v')
       ..addFlag('sourcemap', abbr: 'm')
       ..addOption('cssjanus-path')
  -    ..addOption('cssjanus-direction')
  +    ..addOption('cssjanus-direction', allowed: ['ltr', 'rtl', 'bidi'])
       ..addOption('load-path', abbr: 'I', allowMultiple: true)
       ..addOption('plugin-path', abbr: 'P')
       ..addOption('precision', abbr: 'p')
  
positive.code: 
      final cssjanusPath = results['cssjanus-path'];
      final cssjanusDirection = results['cssjanus-direction'];
      if (cssjanusPath != null) {
        if (cssjanusDirection != 'ltr' && cssjanusDirection != 'rtl') {
          throw 'Unexpected direction: "$cssjanusDirection"';
        }
      }
      return new SassCArgs(
          args.where((a) => !a.startsWith('--cssjanus-')).toList(),
          includeDirs: results['load-path'] as List<String>,
  
negative.code: import 'package:barback/barback.dart' show Asset;
  import 'package:quiver/check.dart';
  
  import '../css_mirroring/bidi_css_generator.dart';
  import '../css_mirroring/cssjanus_runner.dart';
  import '../image_inlining/main.dart';
  import '../utils/io_utils.dart';
  import '../utils/path_resolver.dart';
  