The self axis refers to
the context node. It's sometimes useful when making relative
links. For example, /self::node() selects the root
node of the document (which is not the same as the root element
of the document; that would be selected by
/child::* or, in this example,
/child::FAMILYTREE.) It can abbreviated by a single
period. However, this axis is rarely used in XPointers. It's
more useful for XSLT select expressions.