tooltip on <s:textfield>

How is this supposed to work?

I get this at the bottom of the form, but for me it maps to an invalid url?

<!-- javascript that is needed for tooltips -->
<script type="text/javascript" src="/static/domTT.js">
</script>
<link rel="stylesheet" type="text/css" href="/static/domTT.css"/>

http://www.xx.xx/static/domTT.js

Is there some js that is supposed to take care of this?

https://struts.apache.org/tag-developers/textfield-tag does not mention 
anything.