Looks like Common Lisp's pathnames. In practice, though, they are *too* general, and you need an implementation-dependent parser and unparser which understands only the native format. Python, and my variant of it, deal only with Posix and Windows, which is all that are needed in practice nowadays, and provides portable parser/unparser pairs for each.
I never used TOPS-20, but I did use versioned files on VMS. I normally set the versioning limit to keep only the current and the one before that. IMO, version control systems and journaling file systems eliminate the need for versioning in the file system.