public static function getAllPatternCacheSubkeys() : array
    {
        $subkeys = [];
        $chars = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'];

        foreach ($chars as $charOne) {
            foreach ($chars as $charTwo) {
                $subkeys[$charOne . $charTwo] = '';
            }
        }

        return $subkeys;
    }