I cannot validate this blank HTML page to XHTML 5.1
<p>I cannot validate this blank page to XHTML 5.1.</p>

<pre><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;
  &lt;head&gt;
    &lt;meta charset="utf-8" /&gt;
    &lt;title&gt;XHTML 5.1 blank page&lt;/title&gt;
  &lt;/head&gt;

  &lt;body&gt;
    &lt;h1&gt;Blank page&lt;/h1&gt;
    &lt;p&gt;Text here.&lt;/p&gt;
  &lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>All tags are well-closed and I specific the DOCTYPE, what I'm wrong?</p>