Regex in tagger script

MusicBrainz Picard
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1

I am trying to use tagger script to create a sort tag. The usual way of doing this is by swapping two matching groups in regex, e.g. (.)\s(\w)$ => $2, $1
However I can’t find a way to do this with $rreplace() - is it possible to access matching groups in the “replace” parameter and if so, how?

2
3

Ah, thanks - I did search but didn’t find that. \2,\1