Some fun with Internet Explorer and general stupidity with the <script> tag and various standard attributes.
<script><!--
document.writeln("It worked!"); //--></script>
Did it work?
<script language="JavaScript"><!--
document.writeln("It worked!"); //--></script>
Did it work?
<script type="text/javascript"><!--
document.writeln("It worked!"); //--></script>
Did it work?
<script type="application/x-javascript"><!--
document.writeln("It worked!"); //--></script>
Did it work?
After each "Did it work?", if the script actually ran, you would see "It worked!". Otherwise, the script was ignored.