title: Enable peek/pop on links in XHTML pages
body: <p>On iPhone 6S and 6S Plus, 3D touching on a link will open a preview of the page, and pressing harder will open the page. This works for pages parsed as HTML.</p>
  
  <p>But a simple page like this:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"&gt;
      &lt;head&gt;
          &lt;meta name="viewport" content="initial-scale=1" /&gt;
          &lt;title&gt;3D Touch Test Page&lt;/title&gt;
      &lt;/head&gt;
      &lt;body&gt;
          &lt;p&gt;Link to &lt;a href="//apple.com"&gt;apple&lt;/a&gt;.&lt;/p&gt;
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>If served with the <code>Content-Type</code> as <code>application/xhtml+xml</code>, peek and pop on the test link won't work. It works perfectly with the same content served as <code>text/html</code>.</p>
  
  <p>How can I work around this to still have peek and pop work in an XHTML page? Am I doing something wrong here?</p>