In the process of testing some medium complicated sort functions I needed to check out the intermediate results (nested ifs, etc).
I added a new Column "Test" with it's Value set to the function to be tested. I moved the column to be adacent to the source fields.
Now I can see the results of using and combining the various scripting functions.
I also use an external text editor to create the functions and then use the standard Ctrl-C, Ctrl-X, Ctrl-V to Copy, Cut, or Paste between the text editor and MP3Tag.
Great way to learn and test the scripting functions.