<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<style>
body { white-space: pre-wrap; width: 1ch; font-family: monospace }
body:first-line { }
</style>
<script>
function boom()
{
document.body.textContent = "\n\u202AX ";
document.documentElement.offsetHeight;
document.body.appendChild(document.createTextNode("Y"));
document.documentElement.offsetHeight;
}
</script>
</head>
<body onload="boom();"></body>
</html>