$re = '/^\s{4}\(bingo\).*\s/m';
$str = '(
(text
(bingo) <-- keep this (level=3)
text)
(text)
(bingo) <-- kick this (level=2)
(text)
)';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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