Use of the new validationRules on repeatable and relation is not documented

[Polfo]

A nice new feature is the validationRules attribute for a field now, but how do we apply this to a repeatable field or a relation?

[Polfo]

Something like this works for repeatable, but please hint how to do this for relation.

CRUD::addFields($fields); // $fields includes `validationRules` for non-repeated fields
CRUD::setValidation();
CRUD::setOperationSetting('validationRules', CRUD::getOperationSetting('validationRules') + [
    'songs.*.name' => 'required',
    'songs.*.info' => 'required',
]);