https://drafts.csswg.org/css-break/

If we have an empty, zero-height block, and it occurs exactly at a fragmentainer boundary, where should it end up? In the former fragmentainer, or in the latter?

<div style="columns:2: column-fill:auto; height:100px;">
    <div style="height:100px;"></div>
    <div id="empty"></div>
    <div style="height:50px;"></div>
</div>

Is #empty in the first or second column? If the answer is "second", then how about:

<div style="columns:2: column-fill:auto; height:100px;">
    <div style="height:100px;"></div>
    <div id="empty"></div>
</div>

Should we establish a second column just to hold an empty fragment?

This may not matter for painting and hit-testing, but it's exposable via e.g. getClientRect().