When dealing with polymorphic data and using the remap functions it'd be nice to have a oneOf validator. It'd take as argument keys of the formGroup so it'd also be type safe.

Example here https://github.com/cloudnc/ngx-sub-form/blob/6ecdb2017e/src/app/main/listing/listing-form/vehicle-listing/vehicle-product.component.ts#L24-L25

And it could look like the following:

public getFormGroupControlOptions(): FormGroupOptions<YourPolymorphicForm> {
  return {
    validators: [NgxSubFormValidators.OneOf('prop1', 'prop2', 'prop3')],
  };
}