yii\web\MultipartFormDataParser::addValue PHP Method

    private function addValue(&$array, $name, $value)
    {
        $nameParts = preg_split('/\\]\\[|\\[/s', $name);
        $current =& $array;
        foreach ($nameParts as $namePart) {
            $namePart = trim($namePart, ']');
            if ($namePart === '') {
                $current[] = [];
                $lastKey = array_pop(array_keys($current));
                $current =& $current[$lastKey];
            } else {
                if (!isset($current[$namePart])) {
                    $current[$namePart] = [];
                }
                $current =& $current[$namePart];
            }
        }
        $current = $value;
    }