title: W3C validator shows new error: "Meta requires 'name' attribute"
body: <p>The w3C validator was all fine with this code:</p>
  
  <pre><code>&lt;meta property="og:site_name" content="--Sitename--" /&gt;
  </code></pre>
  
  <p>If I replace the <code>property</code> attribute with <code>name</code>, the validator says <code>og:site_name</code> is not registered.</p>
  
  <p>All of a sudden today it displayed this error:</p>
  
  <blockquote>
    <p>Error Line 7, Column 66: Element <code>meta</code> is missing required attribute <code>name</code>. </p>
  </blockquote>
  
  <p>Nothing is changed but this error popped up.</p>
  
  <p>Anyone knows why, and the solution for that?</p>