title: filter: progid:DXImageTransform fails W3C CSS validation
body: <p>I am using the following three lines in CSS to enable smooth transitions between "slides", but line #1 fails W3C CSS validation.  </p>
  
  <pre><code>filter: progid:DXImageTransform.Microsoft.alpha(opacity=100);
  -moz-opacity: 1;
  opacity: 1;  
  </code></pre>
  
  <p>Is there a way to reformulate the same intent (smooth transitions through alpha blending) but with methods that won't fail validation?</p>