Google's earlier Alternate Masonry Proposal—which didn't allow for mixed track sizing and constrained all content-sized tracks to be the same size—allowed repeat(auto-fill, auto) as a track listing, computing auto as the largest [item size]/[span size].

This definition doesn't work with mixed track sizes, because the amount that an item contributes to each track can differ based on what it's spanning. Filing this issue to ask if we can still add this value, and if so, what does it mean? Does it also work in grid layout?

Note: There's a separate, but related, issue about what the initial track listing should be, and whether it should be this.