// using the semantics of fs.FS.Open:
// paths are always slash separated, with no
// leading / or ../ elements.
func (r *Reader) Open(name string) (fs.File, error) {
	r.initFileList()

	if !fs.ValidPath(name) {
		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrInvalid}
	}
	e := r.openLookup(name)
	if e == nil {
		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
	}