allOf:
  - type: object

    required:
      - extra_service
      - tracking_events

    properties:
      extra_service:
        type: string
        enum:
          - certified
          - certified_return_receipt
        description: |
          Add an extra service to your letter. See [pricing](https://www.lob.com/pricing/print-mail#compare) for extra costs incurred.
            * `certified` - track and confirm delivery for domestic destinations. An extra sheet (1 PDF page single-sided or 2 PDF pages double-sided) is added to the beginning of your letter for address and barcode information. See here for templates: [#10 envelope](https://s3-us-west-2.amazonaws.com/public.lob.com/assets/templates/letter_certified_template.pdf) and [flat envelope](https://s3-us-west-2.amazonaws.com/public.lob.com/assets/templates/letter_certified_flat_template.pdf) (used for letters over 6 pages single-sided or 12 pages double-sided). You will not be charged for this extra sheet.
            * `certified_return_receipt` - request an electronic copy of the recipient's signature to prove delivery of your certified letter

      tracking_number:
        type: string
        description: >-
          The tracking number will be here immediately upon creation.

          Dummy tracking numbers are created in test mode.
        nullable: true

      tracking_events:
        description: >-
          An array of certified tracking events ordered by ascending `time`. Not populated in test mode.
        type: array
        items:
          $ref: "../../../shared/resources/tracking_events/models/tracking_event_certified.yml"

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

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