$re = '/^(?=.*[A-Z])(?=.*[a-z])(?!.*[A-Z][A-Z])(?!.*[a-z][a-z]).{10,15}$/m';
$str = 'aA1234567890AA
aA1234567890A
aA1234567890aa
67890AaAaAaAaAa
123456789123
1234567891Aa
';
preg_match_all($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