/
\(\?P<(\w+)> # named group (name captured as group 1): (?P<name>
( # matching pattern as group (2) in form: b(R1)a1...(R2)a2
[^)(]*+ # `b` (before) part - any not `)(` characters
(?: # non capturing group for repeated `(R)a`
\((?2)\) # `R` - reference to group 2 for possible nested braces
[^)(]*+ # 'a' (after) part - any not `)(` characters
)* # `(R)a` repetition is optional
) # end the group 2
\) # end of the named group to match
/
gx