anchor.diff:    Directory packageRootDir;
     if (args['package-root'] != null) {
       packageRootDir = new Directory(_resolveTildePath(args['package-root']));
  +  }
  +
  +  if (args.rest.isNotEmpty) {
  +    var unknownArgs = args.rest.join(' ');
  +    print('Error: detected unknown command-line argument(s): $unknownArgs');
  +    _printUsageAndExit(parser, exitCode: 1);
     }
   
     PackageMeta packageMeta = sdkDocs
  
positive.code:   String url = args['hosted-url'];
    String footerFilePath = _resolveTildePath(args['footer']);
    if (footerFilePath != null && !new File(footerFilePath).existsSync()) {
      print(
          "Warning: unable to locate the file with footer at ${footerFilePath}.");
      exit(1);
    }
    String headerFilePath = _resolveTildePath(args['header']);
    if (headerFilePath != null && !new File(headerFilePath).existsSync()) {
      print(
          "Warning: unable to locate the file with header at ${headerFilePath}.");
      exit(1);
    }
  
  
negative.code: 
    var readme = args['sdk-readme'];
    if (readme != null && !(new File(readme).existsSync())) {
      print("Error: unable to locate the SDK description file at $readme.");
      exit(1);
    }
  
    Directory inputDir = new Directory(args['input']);
    if (!inputDir.existsSync()) {
      print("Error: unable to locate the input directory at ${inputDir.path}.");
      exit(1);
    }
  
  