Javascript: In the <head>

  
<html>
<head>
  <script type="text/javascript">
  <!--
  alert("hello javascript world");
  -->
  </script>
</head>
<body>
</body>
<html>

Notice that the javascript code is surrounded with HTML comment markup. This keeps the validator from barfing all over our page. If we didn't "comment out" out JS the validator would attempt to read it as HTML not Javascript.