better custom code support

As soon as I migrate a Div element into custom code I cannot drag'n'drop other components on it anymore. However you might be able to recognize an opening xml tag and a matching closing xml tag in my custom code. I think this is sufficient to make the custom code able to receive dropped elements:

  whatever I wrote
  <!-- this is where the dropped element goed -->

Maybe you also need to add an attribute so select whether the dropped elements will be blaced at the end (as shown here) or at the beginning (before "whatever I wrote").

Custom code won't support drag and drop as devs have said so in past