The Selection which triggered the application of this discount.
| quantity | number <double>  The amount of the selection used to trigger the applied discount. | 
| object (ExternalReference)  A wrapper object with fields that allow reference to a Toast entity by Toast GUID. | 
{- "selection": {- "guid": "string",
- "entityType": "string",
- "externalId": "string"
 },
- "quantity": 0
}