==== AC4_descriptor

Defined by DVB in <<ETSI-300-468>>.

Because of the possible introduction of an ATSC version of the `AC4_descriptor`,
the XML name for the DVB version is `<DVB_AC4_descriptor>`.
For compatibility, `<AC4_descriptor>` is still accepted.

[source,xml]
----
<DVB_AC4_descriptor
    ac4_dialog_enhancement_enabled="bool, optional"
    ac4_channel_mode="uint2, optional">
  <ac4_dsi_toc>
    Hexadecimal content, optional
  </ac4_dsi_toc>
  <additional_info>
    Hexadecimal content, optional
  </additional_info>
</DVB_AC4_descriptor>
----
