default := {
    "foo" : 2,
    "bar" : true
};

overridden := default << {
    "foo" : 0,
    "enabled" : false,
    "window" : null
};

window := {
    "width" : 640,
    "height" : 480
};

foobar := {
    "child" : overridden << {
        "window" : window
    } << {
        "enabled" : true
    }
};