PHP json_encode json与数组的变化。 JSON有时不会作为JSON出现在firebug中

Does JSON like any specific array structure?

when it is used in

$value['date'][0] = "12-21-2012";
$value['name'][1] = "Joe";
echo json_encode($value);

it seems to detect JSON under firebug

however, when it is switched around firebug does not seem to see it as JSON

$value[0]['date'] = "12-21-2012";
$value[1]['name'] = "Joe";
echo json_encode($value);

is it behaving normally?