xpointer(/child::FAMILYTREE/child::PERSON[position()=3])
The location path of this XPointer is
/child::FAMILYTREE/child::PERSON[position()=3]
.
It is built from two location steps:
/child::FAMILYTREE
child::PERSON[position()=3]
It identifies the single node:
<PERSON ID="p3" FATHER="p2" MOTHER="p1">
<NAME>Elodie Bellau</NAME>
<BORN>11 Feb 1858</BORN>
<DIED>12 Apr 1898</DIED>
<SPOUSE IDREF="p4"/>
</PERSON>