I've recently made a change to Gantry::Conf which allows for the nesting of configuration variables. In this example I have defined a sample_instance where I want to pull in the correct site wrapping depending on uri location. However, I don't want to specify a wrapping for each location, because I'm lazy. I just want to specify the lowest, most common location and set the wrapping there. This is where the nesting helps out.
<instance sample_instance>
dbconn dbi:SQLite:dbname=app.db
template_wrapper customer_wrapper.tt
doc_rootp /static
<GantryLocation /admin>
template_wrapper admin_wrapper.tt
</GantryLevel>
<GantryLocation /admin/user>
template_wrapper user_wrapper.tt
</GantryLevel>
</instance>
/ (customer_wrapper.tt)
/admin (admin_wrapper.tt)
/admin/user (user_wrapper.tt)
/admin/some/other/location (admin_wrapper.tt)
/stats (customer_wrapper.tt)