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<!DOCTYPE HTML>
<html>
<head>
<style>
#target5 {
position: absolute;
top: 0px;
left: 0px;
width: 20px;
height: 20px;
background: #f00;
}
</style>
<body>
<div id="target"></div>
<script>
var io = new IntersectionObserver(function(records) {
var viewportWidth =
document.documentElement.clientWidth || document.body.clientWidth;
var viewportHeight =
document.documentElement.clientHeight || document.body.clientHeight;
var result = records.length === 1 &&
records[0].rootBounds.top === 0 &&
records[0].rootBounds.left === 0 &&
records[0].rootBounds.right === viewportWidth &&
records[0].rootBounds.width === viewportWidth &&
records[0].rootBounds.bottom === viewportHeight &&
records[0].rootBounds.height === viewportHeight;
if (!result) {
result = [records.length,
records[0].isIntersecting,
records[0].rootBounds.top,
records[0].rootBounds.left,
records[0].rootBounds.right,
records[0].rootBounds.width,
records[0].rootBounds.bottom,
records[0].rootBounds.height,
viewportWidth,
viewportHeight].join(',');
}
window.opener.postMessage(result, '*');
});
io.observe(document.getElementById("target"));
</script>
</body>
</html>