With this week's iTunes' release of 18.104.22.168, iTunes is now writing "Grouping" values from its library out to a new ID3 frame "GRP1". Support of this new "iTunes Grouping" frame in Mp3tag would be a very useful alternative to the problematic "Work" / TIT1 frame to store mood & style keywords.
I've added support for the iTunes-specific ID3v2 grouping field (GRP1) as GROUPING with the current development build Mp3tag v2.80d.
I've decided against any automatic conversion, but instead for a dedicated tag field. If you have any grouping values stored at CONTENTGROUP which you want to use with the new GROUPING field, you can use the "Tag – Tag" converter or an "Format value" action to copy the values.
I am unable to find a field with the name GROUPING or GRP1 since updating to v2.80d. Is it named something else?
Good point. You can enter the name GROUPING simply at the extended tag dialog at [Alt+T] (and elsewhere). I'll add it to the field drop-down list.
AWESOME, thank you Florian!