external-refs elaboration requested

[Terrence Brannon]

I found the docs on external refs to be a bit terse. Given the external refs in the sample site.xml:

 <external-refs>
    <forrest href="" href="http://forrest.apache.org/">http://forrest.apache.org/ ">
      <linking href="">      <validation href="">      <webapp href="">      <dtd-docs href="" docs.html"/>
    </forrest>
    <cocoon href="" href="http://cocoon.apache.org/">http://cocoon.apache.org/"/>
    <xml.apache.org href="" http://xml.apache.org/"/>
  </external-refs>

I would like to know how to form ext: elements these:
 
* http://forrest.apache.org/docs/validation.html
* http://cocoon.apache.org/
* http://cocoon.apache.org/2.1/features.html

Thanks,
Terrence