The <Alternate>YY</Alternate> tag is used to return the alternate validating carrier or optional validating carrier as follows:

• Alternate Validating Carrier – A marketing carrier who participates in the itinerary and returns the same fare solution as the default/primary validating carrier
• Optional Validating Carrier – Describes a condition when there are two or more neutral validating carriers that can be assigned to the same lowest fare solution. One of these carriers must be chosen as the validating carrier because a default validating carrier cannot be assigned by the system.

• Include Validating Carriers without BSP check – allows you to override local settlement validation method and IET validation.