allOf:
  - type: object

    properties:
      tracking_events:
        description: An array of tracking events ordered by ascending `time`.
        type: array
        items:
          $ref: "../../../shared/resources/tracking_events/models/tracking_event_normal.yml"

      cards:
        description: An array of cards associated with a specific letter
        type: array
        items:
          $ref: "../../cards/models/card.yml"
        nullable: true

      return_address:
        $ref: "../attributes/return_address.yml"

  - $ref: "letter_base.yml"
  - $ref: "letter_generated_base.yml"