anchor.diff:  
       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>,
  
positive.code:     ..addFlag('version', abbr: 'v')
      ..addFlag('sourcemap', abbr: 'm')
      ..addOption('cssjanus-path')
      ..addOption('cssjanus-direction')
      ..addOption('load-path', abbr: 'I', allowMultiple: true)
      ..addOption('plugin-path', abbr: 'P')
      ..addOption('precision', abbr: 'p')
  
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';
  