public Object exec(List arguments) throws TemplateModelException 
{
            if (arguments == null || arguments.size() == 0)
                throw new TemplateModelException("_type expects exactly one argument");
            String arg = (String)arguments.get(0);
            boolean invert = arg.indexOf('!") != -1;
            // NOTE: true in each of these variables means 'remove', not 'keep'
            // This is so we don't invert their values in the loop. So,
            // a is true < -- > (a is not present in the string) xor invert.
            boolean a = invert != (arg.indexOf('a") == -1);
            boolean c = invert != (arg.indexOf('c") == -1);
            boolean d = invert != (arg.indexOf('d") == -1);
            boolean e = invert != (arg.indexOf('e") == -1);
            boolean n = invert != (arg.indexOf('n") == -1);
            boolean p = invert != (arg.indexOf('p") == -1);
            boolean t = invert != (arg.indexOf('t") == -1);
            boolean x = invert != (arg.indexOf('x") == -1);
            LinkedList list = new LinkedList(nodes);
            Iterator it = list.iterator();
            while (it.hasNext()) {
                Object node = it.next();
                if ((node instanceof Element && e)
                    || (node instanceof Attribute && a)
                    || (node instanceof String && x)
                    || (node instanceof Text && x)
                    || (node instanceof ProcessingInstruction && p)
                    || (node instanceof Comment && c)
                    || (node instanceof EntityRef && n)
                    || (node instanceof Document && d)
                    || (node instanceof DocType && t))
                    it.remove();
            }
            return createNodeListModel(list, namespaces);
}

 public boolean isEmpty() 
{
            return false;
}