public void visit(final NodeListOptional n, final A argu) {
   if (n.present()) {
     for (final Iterator<INode> e = n.elements(); e.hasNext(); ) {
       e.next().accept(this, argu);
     }
     return;
   } else return;
 }
 public void visit(final NodeSequence n, final A argu) {
   for (final Iterator<INode> e = n.elements(); e.hasNext(); ) {
     e.next().accept(this, argu);
   }
   return;
 }