Regular Expressions 101

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/
(?<name>\w+)\s*\(\K (?<e> [^()]+ | [^()]* \((?&e)\) [^()]* )* (?=\))
/
gmx
Named Capture Group name
(?<name>\w+)
\w+
matches any word character (equal to [a-zA-Z0-9_])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
\s*
matches any whitespace character (equal to [\r\n\t\f\v ])
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\( matches the character ( literally (case sensitive)
\K resets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
Named Capture Group e
(?<e> [^()]+ | [^()]* \((?&e)\) [^()]* )*
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
1st Alternative
[^()]+
Match a single character not present in the list below
[^()]+
2nd Alternative
[^()]* \((?&e)\) [^()]*
Match a single character not present in the list below
[^()]*
\( matches the character ( literally (case sensitive)
(?&e) recurses the subpattern named e
\) matches the character ) literally (case sensitive)
Match a single character not present in the list below
[^()]*
Positive Lookahead
(?=\))
Assert that the Regex below matches
\) matches the character ) literally (case sensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
x modifier: extended. Spaces and text after a # in the pattern are ignored
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gmx

Test String