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chromium/third_party/blink/web_tests/fast/multicol/dynamic/spanner-becomes-float.html 

<!DOCTYPE html>
<p>Set the float property on a spanner so that it ceases to be a spanner.</p>
<p>There should be three blue <em>squares</em> below.</p>
<div style="-webkit-columns:3; -webkit-column-gap:0; width:600px;">
    <div id="elm" style="-webkit-column-span:all; width:100px; height:300px; background:blue;"></div>
</div>
<script>
    document.body.offsetTop;
    document.getElementById("elm").style.cssFloat = "left";
</script>