title: Permanently protected text in RichTextBox
body: <p>I want to make some selected text protected in RichTextBox. I tried something like this:</p>
  
  <pre><code>MouseClickEvent(...)
  {
     if(e.Button == MouseButtons.Middle)
     {
        SelectionProtected = true;
     }
  }
  </code></pre>
  
  <p>When I do this, it protects selected text until the selection is cleared. How can I make this protection permanent?</p>