title: Why does this css class have 3 different filter settings?
body: <p>Are these for cross browser reasons?</p>
  
  <p>Hoping someone can explain them to me:</p>
  
  <pre><code>opacity:.50;
  -ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";
  filter:alpha(opacity=50)
  </code></pre>