-   kind: map
    keys: {kind: mixed}
    values: {kind: mixed}
    id: [objects, X]
-   kind: record
    fields:
    -   name: y
        value:
            kind: map
            keys: {kind: mixed}
            values: {kind: mixed}
        required: true
    id: [objects, Y]
-   kind: record
    fields:
    -   name: z
        value:
            kind: map
            keys: {kind: mixed}
            values: {kind: mixed}
        required: true
    id: [objects, Z]