Add hover and leave methods for Slot elements. Try out the following test snippet.

Shoes.app do
  f = flow width: 0.4 do
    background green
    para 'hello ' * 30
  end
  s = stack width: 0.6 do
    background yellow
    tagline 'shoes ' * 20
  end
  f.leave{p 'left'}
  s.hover{p 'hovered'}
end