title: Symfony2 twig code doesn't work in xml template as it works in html
body: <p>why twig code <code>{% set code = code(_self) %}</code> doesn't work in xml template.</p>
  
  <pre><code>&lt;!-- src/Acme/DemoBundle/Resources/views/Demo/hello.xml.twig --&gt;
  &lt;hello&gt;
      &lt;name&gt;{{ name }}&lt;/name&gt;
  &lt;/hello&gt;
  {% set code = code(_self) %}
  </code></pre>
  
  <p>like it works in html template.</p>
  
  <pre><code>{% extends "AcmeDemoBundle::layout.html.twig" %}
  
  {% block title "Hello " ~ name %}
  
  {% block content %}
      &lt;h1&gt;Hello {{ name }}!&lt;/h1&gt;
  {% endblock %}
  
  {% set code = code(_self) %}
  </code></pre>