Breaking Boxes With CSS Fragmentation — Smashing Magazine
widowsproperties deal with how many lines should be left before or after a break (either caused by a column or a new page). For example, if I want to avoid a single line being left at the end of a column, I would use the orphans property, as in typography, an orphan is the first line of a paragraph that appears alone at the bottom of a page with the rest of the paragraph broken onto another page. The property should be added to the same element which is fragmenting (in our case, the multicol container).
D’après CanIUse, c’est très largement implémenté (sauf Firefox).