$plural_rules = array(
            '/(quiz)$/'                => '\1zes',      // quizzes
            '/^(ox)$/'                 => '\1\2en',     // ox
            '/([m|l])ouse$/'           => '\1ice',      // mouse, louse
            '/(matr|vert|ind)ix|ex$/'  => '\1ices',     // matrix, vertex, index