title: Folded menu navigation with KnpMenu
body: <p>I want to use KnpMenu for a current project to handle my navigation tree logic. 
  I have build a menu tree like this:</p>
  
  <pre><code>use Knp\Menu\Matcher\Matcher;
  use Knp\Menu\MenuFactory;
  use Knp\Menu\Renderer\ListRenderer;
  
  $factory = new MenuFactory();
  $menu = $factory-&gt;createItem('my_menu');
  
  $menu-&gt;addChild('home', array('uri' =&gt; '/', 'label' =&gt; 'Home'))
       -&gt;addChild('about', array('uri' =&gt; 'about', 'label' =&gt; 'About'));
  
  $cat1 = $menu-&gt;addChild('category_1', array('uri' =&gt; 'category_1', 'label' =&gt; 'Category 1'));
  $cat1_1 = $cat1-&gt;addChild('category_1_1', array('uri' =&gt; 'category_1_1', 'label' =&gt; 'Category 1.1'));
  $cat1_1-&gt;addChild('category_1__1', array('uri' =&gt; 'category_1_1_1', 'label' =&gt; 'Category 1.1.1'));
  $cat1_1-&gt;addChild('category_1_1_2', array('uri' =&gt; 'category_1_1_2', 'label' =&gt; 'Category 1.1.2'))-&gt;setCurrent(true);
  $cat1-&gt;addChild('category_1_2', array('uri' =&gt; 'category_1_2', 'label' =&gt; 'Category 1.2'));
  
  $renderer = new ListRenderer(new Matcher());
  echo $renderer-&gt;render($menu);
  </code></pre>
  
  <p>I was wondering if it is possible to render a folded menu tree where only the currently active menu items are displayed. The other items should not be displayed.
  In the documentation I haven't found a way to accomplish this. </p>
  
  <p>Does anyone have a solution?</p>
  
  <p>Thank you</p>