Смотри PFC:

powerobject lpo_parent

//Loop getting the parent of the object until it is of type window!
lpo_parent = this.GetParent()
do while IsValid (lpo_parent)
If lpo_parent.TypeOf() = window! Then Exit
lpo_parent = lpo_parent.GetParent()
loop

if not IsValid (lpo_parent) then
setnull(aw_parent)
return -1
end If

aw_parent = lpo_parent
return 1