Xslt Doubt

I have an article xml file which consists of reference tagging as follows:


<mixed-citation publication-type="journal">
<string-name>
<given-name>Jennifer<given-name>
<surname>Piggy</surname>
</string-name>,
<string-name>
<given-name>Mark.<given-name>
<surname>Nicholas</surname>
</string-name>,edited by
<string-name>
<given-name>A<given-name>
<surname>Casti</surname>
</string-name>,
<string-name>
<given-name>John.<given-name>
<surname>Zakaris</surname>
</string-name>
</mixed-citation>

I have four string-name nodes, 2 nodes  before edited by and 2 nodes
after edited by
 I want to match template mixed-citation and pass elements in such a
way that initial 2 string-name nodes are given separate tagging than
final two string-name nodes.

such as
<naming>....</naming>,<naming>.....</naming>, edited by
<after-naming>....</after-naming>,<after-naming>.....</after-naming>
Any Idea?


--
Regards,
Chirag Matkar