)?(\d{0,3}|[a-z]{1,3})(?:<\/\2>)?(\.)?\)|\[(?:<([a-z])>)?(\d{0,3}|[a-z]{1,3})(?:<\/\2>)?(\.)?\])\s*(.*)/i'; $result = preg_match($regex, $string); if($result) { return preg_replace($regex, '%%$1|$8', $string); } else { $regex = '/^(\d{0,3}|[a-z]{1,3})\.\s*(.+)$/i'; $result = preg_match($regex, $string); if($result) { return preg_replace($regex, '%%$1.|$2', $string); } else { return $string; } } } $strings = array( '(1)blahblah', '(iv.) blahblah', '[b]  some stuff', '25. blahblah', 'A. some other stuff. one', 'blah. some other stuff', 'text (1) text', '2008. blah', '[123) <-- mismatch' ); foreach($strings as $string) echo do_replace($string) . PHP_EOL; ?>