title: Is it possible to validate the xmlns:fb (Facebook) attribute?
body: <p>I have a Facebook Like button on my site and as such also have the <code>xmlns:fb</code> attribute on the <code>&lt;html&gt;</code> tag:</p>
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html lang=&quot;en&quot; xmlns:fb=&quot;http://www.facebook.com/2008/fbml&quot;&gt;
  </code></pre>
  <p>However, when running my site through the W3C validator, I get these errors:</p>
  <blockquote>
  <p>Line 2, Column 61: Attribute xmlns:fb not allowed here.</p>
  <p>Line 2, Column 61: Attribute with the local name xmlns:fb is not serializable as XML 1.0.</p>
  <p>Line 222, Column 72: Attribute fb:like:layout is not serializable as XML 1.0.</p>
  <p>Line 222, Column 72: Attribute fb:like:layout not allowed on element a at this point.</p>
  </blockquote>
  <p>It is my understanding that using the <code>xmlns:fb</code> attribute adds <code>fb</code> to the document namespace, so that using any <code>&lt;fb:</code> element is valid. Is that not the case? Is it a HTML5 issue?</p>
  <p>I also have similar validation errors with the Twitter button, is it possible to fix those as well?</p>
  <blockquote>
  <p>Line 223, Column 53: Attribute tw:via is not serializable as XML 1.0.</p>
  <p>Line 223, Column 53: Attribute tw:via not allowed on element a at this point.</p>
  </blockquote>