public Object exec(List arguments) 
{
            Set names = new HashSet(arguments);
            List list = new LinkedList(nodes);
            Iterator it = list.iterator();
            while (it.hasNext()) {
                Object node = it.next();
                String name = null;
                if (node instanceof Element)
                    name = ((Element)node).getName();
                else if (node instanceof Attribute)
                    name = ((Attribute)node).getName();
                else if (node instanceof ProcessingInstruction)
                    name = ((ProcessingInstruction)node).getTarget();
                else if (node instanceof EntityRef)
                    name = ((EntityRef)node).getName();
                else if (node instanceof DocType)
                    name = ((DocType)node).getPublicID();
                if (name == null || !names.contains(name))
                    it.remove();
            }
            return createNodeListModel(list, namespaces);
}

 public boolean isEmpty() 
{
            return false;
}