title: what does this selector select "#dialog:ui-dialog"?
body: <p>This selector is refered in <a href="http://jqueryui.com/demos/dialog/#modal-confirmation" rel="nofollow">http://jqueryui.com/demos/dialog/#modal-confirmation</a> (source code). </p>
  
  <pre><code>$( "#dialog:ui-dialog" ).dialog( "destroy" );
  </code></pre>
  
  <p><code>#dialog</code> is fine, how does <code>:ui-dialog</code> gets interpreted, i did not find it anywhere in docs.</p>
  
  <p>Could anyone shed some light? </p>