title: checking if element is in list in gae template
body: <p>I have class:</p>
  
  <pre><code>class Article(db.Model):
       visitedBy = db.ListProperty(int)
  
  context = {
      "article": Article(),
      "id": 3
  }
  </code></pre>
  
  <p>In template I try do it:</p>
  
  <pre><code>{% if id in article.visitedBy %}
       &lt;p&gt;Eureka&lt;/p&gt;
  {% endif %}
  </code></pre>
  
  <p>But I got error:</p>
  
  <pre><code>TemplateSyntaxError: 'if' statement improperly formatted
  </code></pre>
  
  <p>My question is how can I check in template if some item is in list?</p>