How to nest data in forms?

I would like to nest some data like this:

fields:

    header.title:
        type: text
        label: Title
        style: vertical
        autofocus: true
        validate:
            required: true

    header.place.address.street:
        label: Address - street
        type: text

    header.place.address.country:
        label: Address - country
        type: text

It does not work, but is it somehow possible?