[foo]
offsetExists(foo)
offsetGet(foo)
[bar]
offsetExists(bar)
offsetSet(bar,foo)
[null]
offsetExists(null)
offsetGet(null)
offsetSet(null,baz)
[foo][bar]
offsetExists(foo)
offsetGet(foo)
offsetExists(bar)
offsetGet(foo)
offsetSet(bar,abc)
[foo][bar]
offsetExists(foo)
offsetGet(foo)
offsetExists(bar)
offsetGet(bar)