​x
 
<!DOCTYPE html>
<html>
<head>
  <style>
    .full { border: 1px solid red; }
  </style>
  <script type="text/javascript" src="/jquery/jquery.js"></script>
</head>
​
<body>
<ul><li>Does the UL contain an LI?</li></ul>
​
<script>
  $("ul").append("<li>" + ($("ul").has("li").length ? "Yes" : "No") + "</li>");
  $("ul").has("li").addClass("full");
</script>
​
</body>
</html>
​