Select for empty field in indexTags?

[Airman]

I use the CATEGORY field to separate large or special libraries in my collection, and I leave CATEGORY empty for most of my non-classical music in order to avoid adding an extra tag for my general music collection.

I learned today that I can set "CATEGORY=Classical:Classical Library" under indexTags so that I can browse my classical collection directly.

But is there a way to do something like "CATEGORY=<none>:Non-Classical Library", so that it only selects files that lack that field?

Also, I have another question about multidisc album sorting, but I'm not sure whether the answer is on the library end or the control point end:

Is it possible to make DISCSUBTITLE separations on album tracklists expandable, and show up as collapsed by default?

I have some large classical anthologies, some with over 100 CD's, and right now the only options I know of are to give each disc a different album tag (frustrating for browsing all albums by a composer), or to tag the collection as a single album with many discsubtitle fields, which results in long track listings for that anthology which are difficult to browse.

If the album tracks started as a collapsed list with discsubtitle as the headers, it would be much easier to browse through the contents of these large anthologies.

Thanks in advance.