title: Use checkbox as togglebutton in expander
body: <p>Im quite new to wpf and have to following problem.</p>
  
  <p>I need to create a List (i am using a listbox) of items that can be expanded (expander).
  The problem is, that they can be expanded, only if they have been 'selected'. 
  Each listboxitem should have a checkbox and some text.</p>
  
  <p>So very basic example to illustrate what i mean:</p>
  
  <pre><code>&lt;listbox&gt;
  &lt;item&gt;(checkbox) John Doe&lt;/item&gt;
  &lt;item&gt;(checkbox) Mike Murray&lt;/item&gt;
  &lt;/listbox&gt;
  </code></pre>
  
  <p>If any (so multiple is allowed) of the checkboxes in the listbox are checked, then 
  the item expands showing more data.</p>
  
  <p>Again an example:</p>
  
  <pre><code>&lt;listbox&gt;
  &lt;item&gt;
     (checkbox-checked) John Doe
     Some extra data shown in expanded area
  &lt;/item&gt;
  &lt;item&gt;
     (checkbox-unchecked) Mike Murray&lt;/item&gt;
  &lt;/listbox&gt;
  </code></pre>
  
  <p>I cant get a expander to use a checkbox as 'togglebutton'.</p>
  
  <p>Could anyone help me out? Some example code would be very welcome...</p>