No, but clearly indicated, in the equivalent code, is the fact that each module name is held as a key in %INC i.e. the underlying OS is responsible only for returning the/a requested file - thus only on a case-sensitive OS will require Foo; and require FoO; equate to different module implementation files being included i.e. on a case-insensitive OS, both require Foo; & require FoO; equate to the same module implementation file being included.