[css3-page] [css3-multicol] paginating for zero-height pages/columns

Melinda and I discussed this problem a few times, but didn't manage to come
up with any clever answers. Question: What should be the expected rendering
of continuous content (e.g. a fixed-height div) when painted into zero-height
pages or columns?

If we had lines of text, we could invoke the "don't break line boxes" rule
and force at least one line box per page, even if it wound up getting clipped
entirely. But with something that has no discrete units, what should the UA
do?

~fantasai