anchor.diff:  @anonymous
   class GtagException {
     external factory GtagException({
  -    String description,
  -    bool fatal,
  +    String? description,
  +    bool fatal = false,
     });
   
     external String get description; // Description of the error.
  
positive.code: // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // @dart=2.9
  
  @JS()
  library gtags;
  
negative.code: @anonymous
  class GtagEvent {
    external factory GtagEvent({
      String? event_category,
      String? event_label, // Event e.g., gaScreenViewEvent, gaSelectEvent, etc.
      String? send_to, // UA ID of target GA property to receive event data.
  
      int value = 0,
      bool non_interaction = false,
      dynamic custom_map,
    });
  
  