definitions:
  ServerStatus:
    type: string
    enum: [OK, Not OK]

  Server:
    type: object
    properties:
      Name:
        type: string
      Status:
        $ref: '#/definitions/ServerStatus'
      # introduce a circular ref here
      SiblingServer:
        $ref: '#/definitions/Server'
      # introduce a nest ref here
      RemoteProps:
        $ref: 'definitions-31.yaml#/definitions/RemoteProperty'
        # TODO: same with absolute ref (e.g. http://...)