function checkNewContainer(container, part, nextPart, toDelete) {
    if(container[part] === undefined) {
        if(toDelete) return false;

        if(typeof nextPart === 'number') container[part] = [];
        else container[part] = {};
    }
    return true;
}
make new sub-container as needed.
returns false if there's no container and none is needed
because we're only deleting an attribute