title: How do I bind text of checkbox to Header of Expander
body: <p>I have an Expander that contains 3 checkbox.</p>
  
  <pre><code>&lt;Expander Header="Bind Here" Grid.Row="3" Grid.ColumnSpan="2"&gt;
       &lt;StackPanel &gt;
            &lt;CheckBox&gt;Test 1&lt;/CheckBox&gt;
            &lt;CheckBox&gt;Test 2&lt;/CheckBox&gt;
            &lt;CheckBox&gt;Test 3&lt;/CheckBox&gt;
       &lt;/StackPanel&gt;
  &lt;/Expander&gt;
  </code></pre>
  
  <p>I want to append the text of a checked checkbox to the Header of the expander.</p>
  
  <p>Is it possible using binding?</p>