cases:
  - valid: true
    value:
      id: diagram
      source: assets/diagram.svg
      alternates:
        - source: assets/diagram-described.svg
          purpose: accessible_alternative
          language: en
          media_type: image/svg+xml
          description: Diagram with expanded labels.
  - valid: false
    value:
      id: diagram
      source: assets/diagram.svg
      alternates:
        - source: assets/diagram-small.svg
  - valid: false
    value:
      id: diagram
      source: assets/diagram.svg
      alternates:
        - source: assets/diagram-small.svg
          purpose: unknown