How about Cocoon/Axkit?

Switching to Cocoon for your web application environment may be way off, but the following got my attention...

Thinking about it though, I find that I've got to add in a whole new set of directives for handling API calls (that I create) as well as integrating with any XML processor.

...for what the cocoon project calls "logic sheets" or "taglibs": pre-defined functions done in xml, which may then be included in any source document (xml) by inserting a specific "tag".

The advantage is full separation of content, presentation and logic and using standards (xml and xslt in this case).

Besides Cocoon you may want to look into AxKit, similar structure but all done under mod_perl. Perl.com has a good article about using your own taglibs with axkit.

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Cheers, Joe