[['bl'], 'file', 'extensions' => 'png, jpg, svg', 'maxFiles' => 2],
<?php $form = ActiveForm::begin(['options' => ['enctype' => 'multipart/form-data']]); ?>
<?= $form->field($model, 'title')->textInput(['maxlength' => true]) ?>
<?= $form->field($model, 'bl[]')->fileInput(['multiple' => true, 'accept' => 'image/*']) ?>
<div class="form-group">
<?= Html::submitButton('Сохранить', ['class' => 'btn btn-success']) ?>
</div>
<?php ActiveForm::end(); ?>