Regular Expressions 101

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/
(?:\w+)?\((?:[^()]*|\((?:[^()]*|\([^()]*\))*\))*\)
/
g
Non-capturing group
(?:\w+)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\w
matches any word character (equivalent to [a-zA-Z0-9_])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
Non-capturing group
(?:[^()]*|\((?:[^()]*|\([^()]*\))*\))*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
1st Alternative
[^()]*
Match a single character not present in the list below
[^()]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
()
matches a single character in the list () (case sensitive)
2nd Alternative
\((?:[^()]*|\([^()]*\))*\)
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
Non-capturing group
(?:[^()]*|\([^()]*\))*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
1st Alternative
[^()]*
Match a single character not present in the list below
[^()]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
()
matches a single character in the list () (case sensitive)
2nd Alternative
\([^()]*\)
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
Match a single character not present in the list below
[^()]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
()
matches a single character in the list () (case sensitive)
\) matches the character ) with index 4110 (2916 or 518) literally (case sensitive)
\) matches the character ) with index 4110 (2916 or 518) literally (case sensitive)
\) matches the character ) with index 4110 (2916 or 518) literally (case sensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/
g

Test String