<!DOCTYPE html>
<script>
    onload = function() {
        document.body.offsetTop; // trigger layout
        document.getElementById('elm').className = "x";
    }
</script>
<style>
    .x::after { display:block; -webkit-column-span:all; background:yellow; content:".........."; }
</style>
<p>Test adding an ::after pseudo element that's a spanner. The DOM node is followed by more content,
    so we need to split the existing column row into two.</p>
<p>There should be three rectangles with identical sizes below. The first and third one
should be blue with nothing inside. The second one should be yellow with some dots
inside.</p>
<div style="-webkit-columns:4; line-height:100px; background:blue;">
    <span id="elm">&nbsp;</span>
    &nbsp;
</div>