$re = '/\([^)]*\)|\[[^\]]*\]/';
$str = '1. The (quick) brown [fox]
2. The (quick) (test) brown [fox] [more] (test) [test][test]
3. The (quick) brown [fox] The (quick) brown [fox] The (quick)
brown [fox] The (quick) brown [fox]
4. Hopefully, you [don\'t) have cases like (this].
5. Or this: (nesting (like this), need update to regex).
6. Or heterogeneous mixing: (Test [condition] )
If you have conditions 4, 5, 6. Please update your question!';
preg_match_all($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