$re = '~( # Group 1
\( # Opening bracket
( # Group 2
(?: # Non-capturing group
[^()] # Match anything except opening or closing parentheses
| # Or
(?1) # Repeat Group 1
)* # Repeat the non-capturing group zero or more times
) # End of group 2
\) # Closing bracket
)~x';
$str = '(user email ends with "@email.com" and user name is "John") or ((user email ends with "@domain.com" and user name is "Bob") or (user id is 5))';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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