Ответ 1
Это псевдоним для combine.
Combine two paths, if the second path isAbsolute, then it returns the second.
Valid x => combine (takeDirectory x) (takeFileName x) `equalFilePath` x
Posix: combine "/" "test" == "/test"
Posix: combine "home" "bob" == "home/bob"
Windows: combine "home" "bob" == "home\\bob"
Windows: combine "home" "/bob" == "/bob"