
PASS Root margin with explicit root. 
PASS First rAF 
PASS document.scrollingElement.scrollTop = window.innerHeight. 
PASS root.scrollTop = 50, putting target into root margin 
PASS document.scrollingElement.scrollTop = 0. 
PASS root.scrollTop = 0 
PASS root.scrollTop = 50 with root scrolled out of view.