I spent a while scratching my head reading the text in $rsearch trying to work out the examples. So many solidi
Anyway, the second example is a bit misleading as it doesn’t actually contain a matching group at all, insofar as there are no grouping parentheses. It seems that a group isn’t required for this function to work.
I think the examples could also be simpler while referring the reader to the rules on escaping.
As a side note, I used the function to create artistsort tags (albeit crudely):
$set(_surname,$rsearch(%artist%,.* \(.*\))) $set(_name,$rsearch(%artist%,\(.*\) )) $if(%artistsort%,,$if($ne(%_surname%,%_name%),$set(artistsort,%_surname%\, %_name%),$set(artistsort,%artist%)))