title: rel="canonical" html5 unable to validate
body: <p>Should the link attribute <code>rel="canonical"</code> validate against html5?</p>
  
  <p>It is the first time I am using this and I am getting the following validation errors:</p>
  
  <p>"Bad value canonical for attribute rel on element link: Keyword canonical is not registered."</p>
  
  <p>It kind of suggests it shouldnt although I cant find any concrete documentation on this.</p>
  
  <p>Edit - Here is the line that is throwing the validator off:</p>
  
  <pre><code>&lt;link rel="canonical" href="http://dev.local/" /&gt;
  </code></pre>
  
  <p>I have  tried it with and  without the closing slash</p>