Shutil.unpack_archive cannot extract files with filename contains ".."

There is a file named “a…txt” in folder a, which cannot be decompressed by shutil after compression…
I found this code in

# don't extract absolute paths or ones with .. in them
if name.startswith('/') or '..' in name:

I want to know the reason

There is an open bug against cpython regarding this behavior: behavioral differences between shutil.unpack_archive and ZipFile.extractall · Issue #65106 · python/cpython · GitHub

As a workaround, you can use zipfile or tarfile instead.

The claim is that a path with … as a directory is skipped.
But that is not what that code does. It is not looking a whole directory names in the path.

So a…txt should be fine, but foo/…/etc/passwd should be rejected.
A new bug saying this is not a duplicate of the one above as far a I read it.