anchor.diff:                  [autoDismiss]="focusContents"
                   [class]="popupClassName"
                   [source]="popupSource"
  +                (autoDismissed)="onClose()"
                   role="tooltip">
     <div class="paper-container"
  +       tabindex="-1"
  +       [attr.aria-label]="title"
          [autoFocus]="focusContents"
          (mouseover)="onMouseOver()"
          (mouseleave)="onMouseLeave()">
  
positive.code:   @Input('offsetY')
    int offsetY = 0;
  
    bool get showPopup => _showPopup;
  
    final StreamController<bool> _visibleCtrl =
  
negative.code: 
    void onMouseLeave() {
      _tooltipController.deactivate(this);
    }
  
    /// Set focus back to the popupSource if focus was moved to the tooltip with
    /// [focusContents].
    void onClose() {
      if (focusContents && popupSource is ElementPopupSource) {
        Future(() => (popupSource as ElementPopupSource)?.sourceElement?.focus());
      }
    }
  
    // Proxy control of this tooltip via the tooltip controller.
  