Nesting - Drop Targets
Drop targets can be nested. IsOver is true for every target under the
pointer, while IsOverShallow (React DnD's isOver({ shallow: true }))
is true only for the innermost one. Drag the box over the nested squares to see the
difference.
Drag me into the nest
level 0
level 1
level 2
level 3
= shallow hover (innermost) = also over (ancestor)