@Poppa Mintin
My goal is; to create a control( parented to a Panel) that, in design-Mode,
when a user drags an item onto it, creates an other item and adds that also as a child.
So, drag (for instance) a panel on the control, and the result will be that the control has two panels as children.
I can code that. But the custom designer, I have added to the control,( so the user can choose some properties of the added item( by smart-tags)), does not notice the second created item.
I could have the user just add two items, but that doesn't feel intuitive.