Add mask placeholders ?L and ?U which is non-ASCII lower and
upper case characters.

In CP737,
?l = abcdefghijklmnopqrstuvwxyzαβγδεζηθικλμνξοπρσςτυφχψωάέήϊίόύϋώ
?L = αβγδεζηθικλμνξοπρσςτυφχψωάέήϊίόύϋώ