Revenue Recognition We recognize revenue from our services rendered when the following four revenue recognition criteria are met: persuasive evidence of an arrangement exists, services have been rendered, the price is fixed or determinable, and collectability is reasonably assured. Deferred revenue, which primarily relates to our subscription-based and commission based arrangements, is recorded when payments are received in advance of our performance as required by the underlying agreements. Click-based advertising and transaction revenue . Click-based revenue is derived primarily from click-through fees charged to our travel partners for traveler leads sent to the travel partners website. We record revenue from click-through fees in the same period as when the traveler makes the click-through to the travel partners website. Our instant booking transaction model revenue is comprised of commissions earned on all valid instant booking reservations. In a transaction model, our instant booking commission revenue is recorded at the time a traveler books a hotel transaction on our partners site where we, as facilitator for such booking, do not assume associated cancellation risk. Under the other instant booking model, called the consumption model, we assume cancellation risk associated with booking, and we record that revenue when the travelers stay at a hotel occurs. We have no post-booking service obligations for all instant booking transactions, regardless of the model chosen. Display-based and subscription-based advertising . We recognize display-based advertising revenue ratably over the advertising period or upon delivery of advertising impressions, depending on the terms of the advertising contract. Subscription-based advertising revenue is recognized ratably over the related contractual period over which service is delivered. Attractions . We work with local operators, or merchant partners, to provide travelers with access to tours and activities in popular destinations worldwide, earning a commission for s