One sort of weird case is if I have an image key (sha-based) and want to store thumbnail sizes: 'bae6ff187e4c491e5de9cfa3b039ce7da8255798' makes sense as a base key, but really I want bae6ff187e4c491e5de9cfa3b039ce7da8255798/400x400 for thumbnails rather than storing individual thumbnail shas, hah.