Laravel 9.* validation rule to check that the format of a provided string matches the required format for Australian drivers licences.

AustralianDriversLicence.php

<?php

namespace App\Rules;

use Illuminate\Contracts\Validation\Rule;

class AustralianDriversLicence implements Rule
{
    /**
     * Determine if the validation rule passes.
     *
     * @param string $attribute
     * @param mixed $value
     * @return bool
     */
    public function passes($attribute, $value): bool
    {
        // 1. Max length 9 characters
        // 2. Alphanumeric characters only
        // 3. Must have at least 4 numeric characters
        // 4. Must have no more than 2 alphabetic characters
        // 5. The third and fourth character must be numeric
        return (
            strlen($value) <= 9
            && ctype_alnum($value)
            && preg_match_all('/[0-9]/', $value) >= 4
            && preg_match('/[0-9]{3}/', $value)
            && preg_match('/[0-9]{4}/', $value)
        );
    }

    /**
     * Get the validation error message.
     *
     * @return string
     */
    public function message(): string
    {
        return __('The provided drivers licence is not valid.');
    }
}