public WebFormsPageCompositionElement(System.Web.UI.Page page)
        {
            _masterPage = page;

            var placeHolders = _masterPage.GetRootControl().GetDescendantControls <ContentPlaceHolder>();

            foreach (var nativePlaceHolder in placeHolders)
            {
                this.PlaceHolders.Add(nativePlaceHolder.ID, new RenderingsPlaceHolder(nativePlaceHolder.ID));
            }

            this.GlobalPlaceHolders.Add(GlobalLayoutPlaceHolderIds.Head);
            this.GlobalPlaceHolders.Add(GlobalLayoutPlaceHolderIds.Scripts);
            this.GlobalPlaceHolders.Add(GlobalLayoutPlaceHolderIds.InternalStateTracking);

            IsFromLayout = true;
        }