1. UploadedFile::getInstances($model, 'file'); sees only one file if not set ```'file[]'```
```php
<?= $form->field($model, 'file[]')->fileInput(['multiple' => '']) ?>
```
2. ```$form->errorSummary(..)``` not return all errors of file attribute, but only the last.
So I had to invent.
```php
if ($model->hasErrors()) {
echo '<pre>';
print_r($model->getErrors());
echo '</pre>';
}
```
So it should be?
