@Override
 public Token clone() {
   final Token t = (Token) super.clone();
   if (payload != null) {
     t.payload = payload.clone();
   }
   return t;
 }
 @Override
 public void copyTo(AttributeImpl target) {
   super.copyTo(target);
   ((FlagsAttribute) target).setFlags(flags);
   ((PayloadAttribute) target).setPayload((payload == null) ? null : payload.clone());
 }