Subscription price markup

schema.org can express a recurring price, but it has no single billing-period field. UnitPriceSpecification carries the price, with referenceQuantity and unitCode (a UN/CEFACT common code or a URL) for the unit the price applies to. billingDuration gives how long the price is billed (for example, a subscription's contractual duration), billingStart gives when the price becomes valid and billing starts, and priceType separates list and sale prices. Google's SoftwareApplication rich result requires only name, offers.price (0 for a free app) and a rating or review, and it documents no subscription or billing-period properties. So the billing period an agent needs to compare plans has to be stated in the visible pricing table as well.