null: dom4j does not provide any information about attribute types.
public static org.dom4j.Branch searchForParent(org.dom4j.Branch subtree,
DOM4J does not guarantee to provide the parent of a node, but XDM requires this. In extremis,
if we need the parent of a node and it is not known, we search the document looking for it.
This is (fortunately!) very rarely necessary. One situation where we know it is needed is to find the parent of a
processing instruction whose parent is in fact the document node.
subtree - the root of a subtree to be searched
node - a node to be sought within this subtree
the parent of the sought node if it is found; otherwise null