<!DOCTYPE html>
<html>
<head>
<style>
nav {
    float: left;
}
section {
    clear: both;
    position: relative;
}
</style>
</head>
<body>
<section>
<nav>This floats</nav>
<div>This doesn't</div>
</section>
<section>
<nav>This floats</nav>
<div style="overflow: hidden;">This is a block formatting context</div>
</section>
<section>
<nav>This floats</nav>
<div style="position: absolute; top: 0; left: 0; width: 100px; height: 100px;">
    This is abspos
</div>
</section>
</body>
</html>

