GoView.OnDragOver override

How do I compute the bounds of the objects involved in a drag and drop operation from the DragEventArgs ?
I want to set the evt.Effect to DragDropEffects.None to prevent a drop based on some criterium.
For this I need to be able to compute the bounds of the collection that is baing dragged, e.g. from the Palette.
The mouse location included in the DragEventArgs does not take the extent of the collection into account.
The GoView Selection does not neccesarily contain the objects until after the drop, which is too late, so all I have are the DragEventArgs.

DragEventArgs.Data will give you that GoSelection being dragged.

If you know which GoView the drag is coming from, you could just look at its Selection.

GoSelection.HotSpot will tell you the offset from the GoSelection.Primary.Position to the mouse point where the drag started.