Passengers with e-tickets are required to check-in at the airport for a flight in the usual manner, except that they may be required to present an e-ticket itinerary receipt or personal identification, such as a passport, or credit card. They can also use the Record locator, often called booking reference, a code of six letters and digits. Producing a print-out of an e-ticket itinerary receipt may be required to enter the terminal of some airports or to satisfy immigration regulations in some countries.[citation needed]