private void OnTabItemGotFocus(object sender, RoutedEventArgs e)
 {
     if (sender == tabDrawing)
     {
         if (_drawingPage != null)
         {
             _drawingPage.PageSelected(true);
         }
     }
     else if (sender == tabXamlOutput)
     {
         if (_xamlPage != null)
         {
             _xamlPage.PageSelected(true);
         }
     }
     else if (sender == tabSvgInput)
     {
         if (_svgPage != null)
         {
             _svgPage.PageSelected(true);
         }
     }
 }