class CompositeElement : public Element {
public:
  virtual void Accept(Visitors);
private:
  List<Element*>* _children;
};
void CompositeElement::Accept (Visitors v) {
  ListIterator<Element*> i(_children);
  for (i.First(); !i.IsDone(); i.Next() {
    i .Currentltem()->Accept(v) ;
  }
  v.VisitCompositeElement(this);
}