// Sub returns an FS corresponding to the subtree rooted at fsys's dir.
//
-// If fs implements SubFS, Sub calls returns fsys.Sub(dir).
-// Otherwise, if dir is ".", Sub returns fsys unchanged.
+// If dir is ".", Sub returns fsys unchanged.
+// Otherwise, if fs implements SubFS, Sub returns fsys.Sub(dir).
// Otherwise, Sub returns a new FS implementation sub that,
-// in effect, implements sub.Open(dir) as fsys.Open(path.Join(dir, name)).
+// in effect, implements sub.Open(name) as fsys.Open(path.Join(dir, name)).
// The implementation also translates calls to ReadDir, ReadFile, and Glob appropriately.
//
// Note that Sub(os.DirFS("/"), "prefix") is equivalent to os.DirFS("/prefix")