// 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}
	}

pkg io/fs, func ReadDir(FS, string) ([]DirEntry, error)
pkg io/fs, func ReadFile(FS, string) ([]uint8, error)
pkg io/fs, func Stat(FS, string) (FileInfo, error)
pkg io/fs, func Sub(FS, string) (FS, error)
pkg io/fs, func ValidPath(string) bool
pkg io/fs, func WalkDir(FS, string, WalkDirFunc) error
pkg io/fs, method (*PathError) Error() string
pkg io/fs, method (*PathError) Timeout() bool
pkg io/fs, method (*PathError) Unwrap() error