A composer tag
The composer tag should be on the Tags page, so long as at least one file is tagged with it. It should appear under "Choose columns".
Peter Schneider commented
Yes, please make it a display item in the tags UI (why is it missing in the first place?). Having the composer tag editable would be extremely convenient for manually correcting tags in classical music. This is the only thing that keeps me from buying bliss...
Thanks... but what should be done with it? Do you mean automatic population of the tag? Simply displaying it in the bliss UI?