>   (rx "("
>       (* whitespace)
>       (? (regexp ert-font-lock--face-symbol-re)
>          (* (+ whitespace)
>             (regexp ert-font-lock--face-symbol-re))
>          (* whitespace))
>       ")")
>
> instead. Not as pretty but should actually work.
>

Yeah, somewhat cleaner. Added to the patch.

Not sure using rx-define et al makes sense for 3 regular expressions I
need to test directly.

Here's patch v2.

--
Regards,

Vladimir Kazanov