Regular Expressions 101

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/
\(([^()]|(?R))*\)
/
g
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
1st Capturing Group
([^()]|(?R))*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
1st Alternative
[^()]
Match a single character not present in the list below
[^()]
()
matches a single character in the list () (case sensitive)
2nd Alternative
(?R)
(?R) recurses the entire pattern
\) 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.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
g

Test String

Code Generator

Generated Code

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Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report.
For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php