title: How can I prevent a panel from being closed?
body: <p>I am using AvalonDock (V2) with a DocumentsSource:</p>
  
  <pre><code>&lt;a:DockingManager DocumentsSource="{Binding Items}"/&gt;
  </code></pre>
  
  <p>I would like to disable the possibility to close a panel using a Style or something that works with a DocuemntsSource.</p>
  
  <p>If possible I would like to have the closing Element to dock in a collapsed manner to the DocumentManager instead of closing.</p>