I can't believe this hasn't been asked for.
I read the Wishlist a few times, and it's not there, and searched all open forums at least a dozen times, trying several different strings, and nothing came up, and so I'm forced to conclude that no one has bothered to ask for this. Which really surprises me, because to me it's a pretty important feature, and I can't be the only person who would use it. So here goes:
The ID3v2 standard has a tag it calls "Position in Media Set", but iTunes recognizes it and just calls it "Disc". It's just a number, like 1 or 2, that represents the CD# it is, like the second CD of a 4-CD set. (It can also be recognized as 3/4, where the second digit is the total number of CDs).
iTunes recognizes it, and so does my iPod, and I love it, because it saves me from having to write "(Disc 1)" in the Album tag, which is how I did it back in ID3v1. But that looks ugly, and also leads to a lot of directories if you put each album in its own directory (as I do).
So when is Winamp going to recognize this tag, that sits right next to the track number tag? Even better, when will I able to use it in the advanced title formatting? Right now, it's impossible to sort multi-CD sets correctly inside the Media Library.
Come on, I can't be the only one who uses this tag, especially not with iTunes out and using it completely.