[tremon]

I have similar reservations about custom tags. My collection makes heavy use of non-standard tags, such as performer:<instrument>, opus, key, subtitle, or style. I can't find anything in the documentation about which tags are supported, or for which formats (I keep A/V registrations in Matroska containers, using the same tagging convention -- like using performer:<role> to save actor credits).

There is value for me in having a central database for this data, for example to find misspellings of the same name. But the fear of having 20 years of custom data entry destroyed by an overzealous tool makes me very hesitant to even try a solution like this.