Proper ID3 tag for "part of" reference (not to be confused with TPOS)

I noticed on MusicBrainz some tracks have a part of association to them, such as the first track here Release “Bites” by Skinny Puppy - MusicBrainz

I want to tag my files with this part of reference (as a multi value field), but I am unsure what the proper ID3 tag for this is, or if such a tag exists (in which case I’ll have to create a custom tag). Any ideas? If not any ideas as to what I should call this if it’s going to be a custom tag?