$re = '/^[a-z\d+]\.(\d+)?\.?(\d+)?(\s\(.*\)\s)?\s+/m';
$str = '
c.2 Employed population below international poverty line, by sex and age (%) Age: 15+
b.1 Employed population below international poverty line, by sex and age (%) Age: 15+
a.1 Employed population below international poverty line, by sex and age (%) Age: 15+
1. Employed population below international poverty line, by sex and age (%) Age: 15+
1.2 Employed population below international poverty line, by sex and age (%) Age: 15+
1.1.1 Employed population below international poverty line, by sex and age (%) Age: 15+
5.6.2 (S.1.C.1) Employed population below international poverty line, by sex and age (%) Age: 15+
5.6.2 (S.3) Employed population below international poverty line, by sex and age (%) Age: 15+
5.6.2 (S.4.C.13) Employed population below international poverty line, by sex and age (%) Age: 15+';
preg_match_all($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