code: @Override
      public void visit(NodeVisitor v) {
          if (v.visit(this)) {
              for (AstNode e : getElements()) {
                  e.visit(v);
              }
          }
      }
docs: Visits this node, then visits its element expressions in order.
  Any empty elements are represented by {@link EmptyExpression}
  objects, so the callback will never be passed {@code null}.