'foo', 'fool', 'fool', 'bar', 'barl', 'barl'
    -or-
'foo', 'fool', 'fool', 'fool', 'bar', 'barl'
    -or-
undef, undef, 'bar', 'barl', 'foo', 'fool'
    -or-
...

(depending on the order the keys are returned)