Thank you both.
Yes I am trying to export a catalogue which means a list of my albums along with the artists, composers etc. information to an external software, say Excel. If you have more than one composer in an album it just gives you the value '[varies]' which is really unfortunate. Nobody would understand anything about this kind of album list, if the composer (or whatever) field is just '[varies]'. I need all composers to be listed instead of '[varies]'.
Listbuild(), I think, will not do the job since it works track by track basis by just taking a delimiter into account. I need some kind of loop to sweep all tracks in an album, collect the composer information and write this down in a column.
To tell the truth, I am actually a bit disappointed about JRiver. Such a fundamental feature should have already been implemented in the software and any custom functions should not have been necessary. Furthermore, nobody can find a solution. Strange....