Validate a password using preg_match with regular expression

validate_password_with_preg_match.php

<?php

declare(strict_types=1);

/*
A pattern with multiple conditions:
- at least one digit.
- at least one lowercase letter (including special Scandinavian characters).
- at least one uppercase letter (including special Scandinavian characters).
- at least one character that is not a letter or a number (including special Scandinavian characters).
- a total length of a string is at least 12 characters.

Passwords with Scandinavian characters: aÅ#123456789, öB#123456789, öb#123456789, AÅ#123456789
*/

$pattern = '/^(?=.*[0-9])(?=.*[a-zæøåäö])(?=.*[A-ZÆØÅÄÖ])(?=.*[^a-zA-Z0-9æøåäöÆØÅÄÖ]).{12,}$/u';
$password = 'aÅ#123456789'; 

if (preg_match($pattern, $password)) {
  echo 'Valid password';
} else {
  echo 'Invalid password';
}