Based on the comment patch from Robert Kukla (roolku) (see http://www.rockbox.org/tracker/task/6301
) I created a patch to enable usage of the albumartist tag and the comment tag for both displaying in the WPS as well as using as filter and conditional in tagnavi.config.
If you set the albumartist tag e.g. to Various for all tracks of compilations and to the track artist for all tracks of non compilation albums you can easily create a "browse by albumartist" menu item in tagnavi.conf which shows only artists who have their own album (which usually reduces the length of the artist list a lot).
Example: "Album artist" -> albumartist ? albumartist != "Various" -> album -> title
You can also create a Compilation menu item with: "Compilations" -> album ? albumartist == "Various" -> title
For mp3 files you have to set the BAND tag (TP2/TPE2) which is commonly used for album artist.
Since for ogg vorbis and flac files no single standard tag exist, the patch reads the tags ALBUMARTIST, ALBUM ARTIST (with one space inbetween) and ENSEMBLE which are the most commonly used tags for album artist. Each of these tags will be recognized by the patch.
In tagnavi.config you have to use albumartist or ensemble as filter or in conditionals. album artist (with space) is not possible since spaces are used as delimiter between tags. Both of albumartist and ensemble will work in tagnavi.config, it doesn't matter whether you tag your ogg/flac files with an ALBUMARTIST, ALBUM ARTIST or ENSEMBLE tag.
In WPS the album artist can be displayed with %iA
The comment tag can e.g. be used for titles of classical pieces (like "Symphony Nr. 9") if more than one piece are on an album. In tagnavi.config simply use comment as filter or in a conditional. In WPS use %iC to display the comment. Of course you can use the comment tag to store whatever you want.
The patch can be downloaded from flyspray (http://www.rockbox.org/tracker/task/6638
). I hope you will enjoy the patch :-)