php - context node in xpath problem
You have to use .//cf:image
to make it relative to the context node.
From http://www.w3.org/TR/xpath/#path-abbrev:
//para selects all the para descendants of the document root and thus selects all para elements in the same document as the context node
and
.//para selects the para element descendants of the context node
Also see http://bugs.php.net/bug.php?id=34413