Help us invent CSS Grid Level 3, a.k.a. "Masonry" layout

I love the idea but I'm not quite sure what it has to do with the grid.

But then again, I don't really understand CSS grids at all, flexbox seems to be able to handle most of it.

Having it as a flex wrap mode would make sense to me, but I suspect it will just wind up as a grid option, which is fine, I'm just glad this feature exists at all.