Although Mp3tag has no concrete list oriented functions, like ItemCount or ItemExtract, there might be a trick to simulate such functionality.
"Format value" a temporary tag field e. g. MYFOLDERPATH with the value
$replace(%_FOLDERPATH%,'','\\')
This should split the folder path into its components and create multiple MYFOLDERPATH tag fields in extended tag view dialog.
Using scripting function $meta(MYFOLDERPATH,N) you can fetch the Nth item from the folder path.
Using scripting function $meta(MYFOLDERPATH,$sub($folderdepth(%_FOLDERPATH%),N)) you can fetch the Nth item (zero based) from the right side of the folder path.
After all is done you can remove the temporary tag field.
DD.20091113.0825.CET