nesting xml

I'm just starting to learn xml/xsl and am wondering if it's possible to use a sub or a function call in xsl.  I have an xml file that could possibly have near infinite depths, and i'm wondering how to parse that...a short example:

<?xml version="1.0"?>
<main>
  <item_type_1>
    <name>Joe</name>
    <occupation>Carpenter</occupation>
  </item_type_1>
  <item_type_2>
    <business_name>LALA Inc.</business_name>
    <founder>
      <item_type_1>
        <name>Bob</name>
        <occupation>Lawyer</occupation>
      </item_type_1>
    </founder>
  </item_type_2>
  <item_type_2>
    <item_type_1>
      <item_type_3>
        <item_type_4>
        </item_type_4>
      </item_type_3>
      <item_type_4>
      </item_type_4>
    </item_type_1>
  </item_type_2>
</main>

and well you get the idea...

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