openapi: 3.0.0
info:
  title: ACME
  version: 1.0.0

paths:
  /pets:
    get:
      operationId: listPets
      responses:
        "200":
          description: OK
          content:
            application/json:
              schema:
                allOf:
                  - type: object
                    properties:
                      prop1:
                        type: string
                  - type: object
                    properties:
                      prop2:
                        type: boolean
                  - type: object
                    properties:
                      prop3:
                        type: integer
