The proposal is to add medium formats to represent the different data areas on DVD-Audio mediums and stems from the discussion here... https://community.metabrainz.org/t/sacd-release-missing-hi-def-stereo-tracks/487829

For DVD-Audio, the Hi-Res MCH audio files reside in a  separate folder (AUDIO_TS) than the content that can be read by a conventional DVD Player (VIDEO_TS).   Only a DVD-Audio player can play the HD audio content, although DVD Players support HD stereo and some DVD-Audio discs are authored with the HD stereo in the DVD content section).

DVD-Audio

•  DVD-Audio (HD audio)

•  DVD-Audio (DVD content)

This would also result in a few additions to the DualDisc Formats...

DualDisc (CD side)

DualDisc (DVD-Video side)

DualDisc (DVD-Audio side)

•  DualDisc (DVD-Audio side, HD audio)

•  DualDisc (DVD-Audio side, DVD content)