is Unlabelled Fallback

This can be marked 'true' to indicate that some published DeliveryTimeSettings or ShippingRateSettings are intended to apply to all OfferShippingDetails published by the same merchant, when referenced by a shippingSettingsLink in those settings. It is not meaningful to use a 'true' value for this property alongside a transitTimeLabel (for DeliveryTimeSettings) or shippingLabel (for ShippingRateSettings), since this property is for use with unlabelled settings.