anchor.diff:        results["update-cfe"] as bool ||
         results["update"] as bool;
   
  +  var nnbd = results["nnbd"] as bool;
  +
     if (!removeAnalyzer && !removeCfe && !insertAnalyzer && !insertCfe) {
       _usageError(
           parser, "Must provide at least one flag for an operation to perform.");
  
positive.code:           removeAnalyzer: removeAnalyzer,
            removeCfe: removeCfe,
            insertAnalyzer: insertAnalyzer,
            insertCfe: insertCfe);
      }
    }
  }
  
negative.code:       help: "Replace analyzer error expectations.", negatable: false);
    parser.addFlag("update-cfe",
        help: "Replace CFE error expectations.", negatable: false);
  
    parser.addSeparator("Other flags:");
    parser.addFlag("nnbd",
        help: "Analyze with the 'non-nullable' experiment enabled.",
        negatable: false);
  
    var results = parser.parse(args);
  
  