$re = '/\b(?:\d{11}|(?=\d{0,5}[A-Z])[A-Z0-9]{6})(?:[\s\.]|$)/m';
$str = '12345678901
123456
123F56
A12345
123456.4
123456.B';
preg_match_all($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