[wongarsu]

Maybe there should be a grid-template-masonry-direction? Just quickly surveying a couple of sites, "masonry" and "horizontal masonry" seem to be about equally common.

On the other hand horizontal masonry is constructed very differently: Flickr fits thumbnails into a row until it reaches some predefined total length, then scales everything down slightly so the total row width matches exactly (resulting in rows of different height). Deviantart does something similar, but shuffles the images for better fit so that the different row heights are barely perceptible.

[chuckadams]

Filling rows without any defined columns is more or less what flexbox already does.