intersection-observer/resources/same-origin-grand-child-iframe.html - external/github.com/web-platform-tests/wpt - Git at Google

 <!DOCTYPE html>
 <div id="target"></div>
 <script>
 const observer = new IntersectionObserver(records => {
   window.top.postMessage(records[0].rootBounds, "*");
 }, {});
 observer.observe(target);
 </script>
	<!DOCTYPE html>
	<div id="target"></div>
	<script>
	const observer = new IntersectionObserver(records => {
	window.top.postMessage(records[0].rootBounds, "*");
	}, {});
	observer.observe(target);
	</script>