should `missing_value` be at the top level inside a variable, or at the lower level as part of `attributes`?

[aportagain]

This came up in a discussion between Ulrich and myself recently. The current 0.2 spec says in the text

Missing data can either be expressed as null or given a specific missing_value numeric or string value which is defined in the attributes.

And in the example shows missing_value at the top level inside a variable (same level as data and shape):

{
    ...
    "variables": {
        "tmp2m": {
            "shape": ["time","latitude","longitude"],
            "missing_value": -9999,
            "data": [
                [[1.2,3.4,-9999 ...],
                [2.3,-9999,8.7 ...],
             ...
            ],
        ]
    ...
}

From just reading the text, I'd say missing_values should be inside attributes, but that obviously doesn't match the example... :)