> But I'm not sure how simple it would be to explain to a non-technical user why size_5, size_10 and size_15 are in order but size_0.25, size_0.5 and size_0.75

> But I'm not sure how simple it would be to explain to a non-technical user why size_5, size_10 and size_15 are in order but size_0.25, size_0.5 and size_0.75 are out-of-order. You don't have to explain it if the situation never comes up. I'd bet 99.9% of computer users don't have any files which would trigger this edge case in a situation they would actually notice. Decimals just aren't that commonly used in this context, and even if you do have decimals the sorting will still work a lot of the time. For the remaining 0.5%, chalk it up to a bug. I literally had to test this on my Mac just now because I never realized it was broken.