title: What is the correct usage of CSS attr function?
body: <p>Since this function is implemented in IE8, I wanted to see exactly what I could do with it, but I'm having trouble getting it to work anywhere other than the :before and :after css pseudo-elements.  Should the following be allowed?</p>
  
  <pre><code>span[color] { color: attr(color); }
  </code></pre>
  
  <p>I tried it in Google Chrome too, but it didn't work.  Also, what about more dynamic things like:</p>
  
  <pre><code>input[value=attr(default)] { color: gray; }
  </code></pre>