-foo => 'food',
-bar => 'bard'

##</code><code>##

'foo', undef, 'bar', undef
    -or-
'bar', undef, 'foo', undef

(depending on the order the keys are returned)

##</code><code>##

-foo => 'food',
foo  => 'fool',
-bar => 'bard',
bar  => 'barl'

##</code><code>##

'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)

##</code><code>##

'foo', 'food', 'bar', 'bard'
    -or-
'bar', 'bard', 'foo', 'food'

(depending on the order the keys are returned)