I'm trying to extract %GUEST ARTIST% from the following %title%:
Keep On Movin' (feat. Inga Lühning)
[#0] T=5 F=GUEST ARTIST 1=$regexp(%title%,(^.*)feat\\\\. (.*?)\\\\),$2)
In Notepad++, the regexp (^.)feat. (.?)) returns (via $2): Inga Lühning
However, under mp3tag's format value action for %GUEST ARTIST%, $regexp(%title%,(^.)feat. (.?)),$2) it returns: ,$2)
It is the same when the regexp is encased in quotation marks.
The problem with Guess Value is that the term "feat." can be variable like "ft.", "featuring", etc. I can use "|" in regexp to enable lookup of such variations of "feat." To my understanding, this is not possible with guess value.