First, I just want to thank everyone who has worked on MP3TAG since its amazing.
Most of the music I get is multiple disc compilations. Generally, either the file name has 3 number in the beginning of the file name to identify this (###). I figured out I can use the filter to test some RegEx and got [1-9][0-9][0-9] working on finding these tracks.
The bad stuff is when the filename only has two number but still part of a multi disc set. In this case there is usually one of the following strings in the %album% field: "Disc #", "CD #", "Volume #", "Vol. #", or "Vol #". These can also vary with either having (or not having) spaces and underscores.
What I want to do is create an action / script that would first check for the 3 numbers in the filename. If not found, it would check for the string's in the %album% field. If it does find 3 numbers, it would have to export the first digit to a %disc% field that I have to store the disc number. If it goes the string route, it would have to export that appropriate digit to the %disc% field.
The entire process should leave the file exactly as it was unless the file is part of a multi disc set where it would add the disc number information.
I'm going to fool around and see what I can get figured out, but unfortunately I've never used RegEx before.