Thanks Larry to reply...
Yes, there is a reason why I need the parent form inside the _screen.
I am working on a "DataEnvironment Designer" and I´m trying to do something simial what we have in VFP - one main form and inside it we have n forms representing each one an existing CursorAdapter (according to SelectedForm.DE object)
If this main form is not in _Screen object, when I click in a Design Form Window or Properties Window (they are in VFP8 _screen), then, my DataEnvironment Designer goes back, behind the VFP Main Window.

The reason why I have to create a DataEnvironment Designer is because, I have some problems using VFP DataEnvironment Designer with CursorAdapters which have CursorSchema grater then 255 char. We implemented the CursorSchema in Init event but VFP DataEnvironment Designer doesn´t recognized it at design time.

I know that, another way to solve it is making a custom class to represent the CursorAdapters instead of form object. But, once it is ready using form I would like to know if is possible to have child forms inside a form that is in _screen.

Any idea?