anchor.diff:        EventBusService newEventBusService)
         : super(newTextProcessingService, newTextareaDomService, newThemeService,
               newEventBusService) {
  -    eventBusService.subscribe('ShowMarkdownPreview', () => active = true);
  +    eventBusService.subscribe('ShowMarkdownPreview', () {
  +      active = true;
  +      updatePreview();
  +    });
       eventBusService.subscribe('HideMarkdownPreview', () => active = false);
     }
   
  
positive.code:   bool active = false;
  
    ngOnChanges(Map<String, SimpleChange> changes) {
      updatePreview();
    }
  
    void updatePreview() {
      _htmlDiv ??= querySelector('#previewPane');
  
      _htmlDiv.setInnerHtml(textProcessingService.convertMarkdownToHtml(content),
          treeSanitizer: _nullSanitizer);
    }
  
negative.code:     selector: 'markdown-preview',
      templateUrl: 'markdownpreview.html',
      directives: [NgModel, NgStyle, NgClass])
  class MarkdownPreview extends EditorComponentBase
      implements AfterContentInit, OnChanges {
    final _nullSanitizer = NullTreeSanitizer();
  
    DivElement _htmlDiv;
  