[plugin: Redirection] replacement regex?

I’ve not been able to find an example of the types of regex the redirection plugin uses in the replacement string.

trying to use one rule in the plugin (not htaccess) to fix a spelling error across 15 URL’s, I have regex box turned on, and:
^(.*)lonliness(.*)$

to be replaced by
$1loneliness$2

but that fails, giving me results like /experiencing-/loneliness/-during-the-holidays/
(Note the unwanted added slash before and after loneliness). Does anyone know how to prevent the $1$2 etc from adding a slash whereever I do my backreference?

https://www.ads-software.com/extend/plugins/redirection/