Extending Border

Ive got a class 'A' that extends Border, with the following markup:

<wicket:border>
<div>
<h1><span wicket:id="header"></span><span
class="close"><a>X</a></span></h1>
<wicket:body></wicket:body>
</div>
</wicket:border>

This all works fine. Can I extend class A? If so what should the markup of
class B look like (i.e. how do I get the child markup dropped in to the
<wicket:body> section)?

I'm currently hitting:

B.html: Unable to find <wicket:border> tag in associated markup file for
Border: [B [Component id = bPanel]] MarkupStream: [unknown]

Regards

Nick