title: url() function for HTML background
body: <pre><code>div {  background:url(smiley.gif) top left no-repeat }
  </code></pre>
  
  <p>What is this <code>url()</code>? I can't find documentation online.</p>
  
  <p>(See <a href="http://www.w3schools.com/cssref/css3_pr_background.asp">http://www.w3schools.com/cssref/css3_pr_background.asp</a>.)</p>