/**
* Returns a message about the difference between the nodes.
* If there is no difference, a null is returned.
*/
public String compareNodes(Node thisResult, Node oldResult){
MATCH v = thisResult.compareToNode(oldResult, false);
if(MATCH.match == v) {
// If this node matches, check all the children of this node.
if(thisResult.getTags()!= null){
for(int i=0; i < thisResult.getTags().size(); i++){
String r = compareNodes(thisResult.getTags().get(i),