Explicitly tell the view that we're using XHTML, so it outputs valid XHTML.

library/App/Controller/Action.php

@@ -6,6 +6,7 @@ class App_Controller_Action extends Unl_Controller_Action
     {
         parent::init();
         $this->view->addHelperPath(dirname(__FILE__) . '/../View/Helper', 'App_View_Helper');
+        $this->view->doctype()->setDoctype(Zend_View_Helper_Doctype::XHTML1_TRANSITIONAL);
         // Zend_Controller_Action_HelperBroker::addPrefix('App_Controller_Helper');
     }
 }