[xsl] Count Ancestors Up To But Not Including a Given Type

Maybe it's the lateness of the hour but I'm finding myself stymied on 
what I hope is relatively simple check.
In DITA, as in many doctypes, you can have nested lists of the form:

<ol>
 <li>
  <ol>
   <li>
   </li>
  </ol>
 </li>
</ol>

As well as an intermixing of different list types, e.g.:

<ol>
 <li>
  <ul>
   <li>
    <ol>
     <li>


What I need to do is determine, for a given li, its depth of nesting 
within unbroken ancestry of a given list type.
Thus, int the first example, the deepest li is a level 2 because it has 
two ancestor <ol> elements with no intervening <ul> (or other non-list 
element that might occur within <li> and itself contain a list). In the 
second example, the deepest <li> is a level one because there is an 
intervening <ul> between the two <ol> ancestors.
I can't for the life of me figure out either a single expression or a 
recursive function that will return the correct answer.
What bit of logic am I failing to see? I am using XSLT 2.

Thanks,

ELiot

--
Eliot Kimber
Senior Solutions Architect
"Bringing Strategy, Content, and Technology Together"
Main: 610.631.6770
www.reallysi.com
www.rsuitecms.com

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