css/css-text/line-breaking/line-breaking-001.html

<!doctype html>
<html>
<meta charset="utf-8">
<title>CSS Text — line breaking around Zero With Space</title>
<meta name=assert content="When ‘white-space’ allows wrapping, line breaking behavior defined for the ZW line-breaking classes in [UAX14] must be honored.">
<link rel=help href="https://www.w3.org/TR/css-text-3/#line-break-details">
<link rel=match href="reference/line-breaking-001-ref.html">
<link rel=author title="Florian Rivoal" href="http://florian.rivoal.net">
<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
<style>
div {
    color:green;
    width: 1em;
    line-height: 1em;
    font-family: Ahem;
    white-space: normal;
    font-size: 20px;
}
.container {
    position: relative;
}
.fail {
    color: red;
    position: absolute;
    left: 0;
    top: 1em;
    z-index: -1;
}
</style>
<body>
    <p>There should be a green rectangle and no red.</p>
    <div class=container>
        <div>X&#x200B;X</div>
        <div class=fail>X</div>
    </div>
</body>
</html>