<!DOCTYPE html>
<p>Trigger layout inside a clipped box inside a multicol container that has a spanner. Then trigger
    layout outside the clipped box, but still inside the multicol container. This tests that we
    don't perform any optimized subtree layout operations incompatible with multicol (which would
    typically cause assertion failures).</p>
<p>You should see a blue square below, and nothing else (no red, no "FAIL").</p>
<div id="multicol" style="-webkit-columns:2; line-height:2em;">
    <div style="width:5em; height:2em; overflow:hidden;">
        <div id="block" style="-webkit-column-break-inside:avoid; width:3em; height:2em; background:blue;"></div>
        <div style="-webkit-column-span:all; width:4em; height:2em; background:blue;"></div>
        <div style="background:red;">FAIL</div>
    </div>
</div>
<script>
    document.body.offsetTop;
    document.getElementById("block").style.width = "4em";
    document.body.offsetTop;
    document.getElementById("multicol").style.width = "50%";
</script>