Thanks. I get it now, but never would have guessed that's what it meant. There's a tradeoff here between conciseness and clarity in this display format. If I were going for the briefest form possible, I would write my example like this:
ID3v2.3 APEv2 Lyrics3v2 ID3v1.1
This would show the presence and order of tags, and which one was read (bold), with the bolded text having a mouseover tooltip saying "Data is being read from this tag only."
Sure, and I agree about one tag, to the extent that it's covering general metadata. But like I said, you don't always know what's in each tag. Sometimes they have redundant data, but sometimes they have unique pieces of info you want to keep. I've seen pretty much every combination.
In the file that I was working with, I want to fix some things in the metadata in the ID3v2 tag, and I also want to keep the ReplayGain (including MP3Gain undo info) which lives in the APE tag. The Lyrics3v2 and ID3v1 tags are redundant this time, so they can go, but I've seen cases where they were including info that wasn't in the ID3v2 tag. And although it wasn't the case this time, there are times when the APE tag has more robust metadata than the ID3v2 tag.
So I feel Mp3tag ought to provide a way to switch the data view from tag to tag from the main UI. I can see how that would get complicated, though.