Nope, that actually 404's. It may appear to work, because most browsers will apply some equivalent to the `__fdio_cleanpath()` function mentioned in the article

Nope, that actually 404's. It may appear to work, because most browsers will apply some equivalent to the `__fdio_cleanpath()` function mentioned in the article, resolving the traversal locally. You can verify this as follows: curl -I --path-as-is 'https://github.com/fuchsia-mirror/docs/blob/master/the-book/../../master/the-book/dotdot.md'