anchor.diff:      header.addComponent(new Spacer()..percentWidth = 100.0..percentHeight = 100.0.._className = 'floating-window-header-spacing');
       header.addComponent(closeButton);
       
  -    footer.addComponent(new Spacer()..percentWidth = 100.0..percentHeight = 100.0);
  +    if (!hasFooterElements) footer.addComponent(new Spacer()..percentWidth = 100.0..percentHeight = 100.0);
       footer.addComponent(resizeHandleGroup);
       
       super.addComponent(header);
  
positive.code:       ..height = 10
        ..onControlChanged.listen((FrameworkEvent<Element> event) => _addResizeListeners(event.relatedObject));
      
      if (_pendingHeaderElements.isNotEmpty) {
        _pendingHeaderElements.forEach((BaseComponent E) => header.addComponent(E));
        
        _pendingHeaderElements.clear();
  
negative.code:       _pendingContentElements.clear();
      }
      
      if (hasFooterElements) {
        _pendingFooterElements.forEach((BaseComponent E) => footer.addComponent(E));
        
        _pendingFooterElements.clear();
  