title: Dublin Core and Metaname cause W3C Validation Issues in HTML5 page
body: <p>I use these tags in the head of an HTML5 page, but these cause problems in W3C Validation 
  <em>Keyword is not registered</em>.</p>
  
  <pre><code>&lt;meta name="viewport" content="width=device-width, minimum-scale=1.0, maximum-scale=1.0" /&gt;
  &lt;meta name="description" content="Sitename - My Website" /&gt;
  &lt;meta name="keywords" content="graphic, security," /&gt;
  &lt;meta name="author" content="My Name" /&gt;
  &lt;meta name="identifier-url" content="" /&gt;
  &lt;meta name="revisit-after" content="14 days" /&gt;
  &lt;meta name="robots" content="all" /&gt;
  &lt;meta http-equiv="content-language" content="en" /&gt;
  &lt;meta name="Language" content="en" /&gt;
  </code></pre>
  
  <p>Same problem also with Dublin Core</p>
  
  <pre><code>&lt;!-- Dublin Core --&gt;
  &lt;meta name="DC.Title" content="My Site"/&gt;
  &lt;meta name="DC.Subject" content="WebDesign; Analysis"/&gt;
  &lt;meta name="DC.Description" content="This is my site bla bla bla"/&gt;
  &lt;meta name="DC.Publisher" content="My Name"/&gt;
  &lt;meta name="DC.Rights" content="Allrights reserved."/&gt;
  &lt;!-- Fine Dublin Core --&gt;
  </code></pre>
  
  <p>How I could fix this issue? If I delete these parts obviously the site run but I lost useful keywords that could help to better indexing my page.</p>
  
  <p>Any suggestion?</p>