title: How to make the content of Expander visible to VisualTreeHelper
body: <p>I've put an Expander onto a Page. Within the expander there is a Label. After the page is loaded, the expander is not yet expanded. At this point, I inspect the Expander using VisualTreeHelper, I got a structure like this:</p>
  
  <pre><code>  Expander
      Border
        DockPanel
          ToggleButton
            Border
              Grid
                Ellipse
                Ellipse
                Path
                ContentPresenter
          ContentPresenter
  </code></pre>
  
  <p>where there is no Label under the last ContentPresenter.</p>
  
  <p>However, Once the expander is expanded and then collapsed, I got the a different structure using VisualTreeHelper:</p>
  
  <pre><code>  Expander
      Border
        DockPanel
          ToggleButton
            Border
              Grid
                Ellipse
                Ellipse
                Path
                ContentPresenter
          ContentPresenter
            Label
              Border
                ContentPresenter
  </code></pre>
  
  <p>This time, the Label appears under the ContentPresenter.</p>
  
  <p>It seems that as long as the expander has been expanded, VisualTreeHelper will know the contents within the Expander. But is there a possible way to make VisualTreeHelper be aware of Expander's contents without expanding it?</p>
  
  <p>Thanks.</p>