==== subtitling_descriptor

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

[source,xml]
----
<subtitling_descriptor>
  <!-- One per subtitle -->
  <subtitling language_code="char3, required"
              subtitling_type="uint8, required"
              composition_page_id="uint16, required"
              ancillary_page_id="uint16, required"/>
</subtitling_descriptor>
----
