title: How do they do this semi-transparent overlay effect in javascript/jquery?
body: <p>If you navigate to <a href="http://learn.knockoutjs.com/" rel="noreferrer">http://learn.knockoutjs.com/</a> you get a 'welcome' style screen which is a semi-transparent overlay that introduces users to the screen elements.  It's nifty.</p>
  
  <p>It looks a little like the jquery plugin BlockUI, but I think it's something a bit more fancy than that.  Fancybox comes close, but seems to only offer a single centre element.  Viewing source didn't help me much, I'm not a JS expert by any means.</p>
  
  <p>Does anyone know how this is done or how to do something similar on a page?</p>