title: Creating a transparency mask for html
body: <p>Has anyone come across an effective way to mimic Webkit's </p>
  
  <pre><code>-webkit-mask-box-image: url(filename.png)
  </code></pre>
  
  <p>functionality?</p>
  
  <p>I'm trying to use non-square animated elements, and would prefer not having to do the masking on server-side.</p>
  
  <p>I'm set on supporting at least Gecko and Webkit, but if I can manage Opera and IE, that would be a bonus.</p>