==== service_group_descriptor

Defined by ARIB in <<ARIB-B10J>>.

[source,xml]
----
<service_group_descriptor service_group_type="uint4, required">

  <!-- One per service when service_group_type == 1 -->
  <service primary_service_id="uint16, required"
           secondary_service_id="uint16, required"/>

  <!-- Optional private data for other group types -->
  <private_data>
    Hexadecimal content
  </private_data>

</service_group_descriptor>
----
