Recursive counting

Well after success with my first recursive template I was all set to
make one of my own, but now shamefully am coming to the list for
advice over something that appears quite simple.

<options>
  <o type="A">who</o>
  <o type="A">what</o>
  <o type="A">when</o>
  <o type="B">how</o>
  <o type="B">nexus</o>
  <o type="B">triumph</o>
  <o type="C">alligator</o>
  <o type="C">spurn</o>
</option>

<people>
 <person pref="who" />
 <person pref="nexus" />
 <person pref="how" />
 <person pref="alligator" />
 <person pref="spurn" />
 <person pref="triumph" />
    .... etc ....
</people>

<!-- @count corresponds to number of times
the preference appeared among the list of <people> --->

 <out type="A" count="1" />
 <out type="B" count="3" />
 <out type="C" count="1" />