Module path 

Lexical path handling — normalization, and the guard that keeps a staged op inside the root it was applied against.

Purely lexical: nothing here touches the filesystem, so it holds for a path naming something that does not exist yet, and it is the same answer on every backend. Symlinks are consequently not resolved — a link inside the root pointing out of it is not something this can see. A backend that must defend against that has to refuse symlinks itself.

Functions

escapes_root

Whether path, resolved against a root, would land outside it.

normalize

Lexically normalize a relative path: drop . components and fold parent/.. pairs. Leading .. components (escaping the root) are kept — the caller decides whether that is an error, which is what escapes_root is for.