protected override object OnGet(Engine engine)
 {
     engine.SetReturnFrame();
     if (Body == null) return null;
     engine.ExecuteScript(Body, CodeTree);
     return engine.GetAndResetReturnValue();
 }
 protected override object OnGet(Engine engine)
 {
     engine.SetReturnFrame();
     Body.Execute(engine);
     return engine.GetAndResetReturnValue();
 }