How to make a file upload mandatory depending on the selected value in the list?

Question

Yii

There is a simple form for adding new information.
The form has a selection list and a file upload form. Now in the model it is indicated that files are an optional field, how to make it so that the mandatory presence of a file depends on the value selected in the list?

Answer 1

Figured it out myself.
Everything is in the docs - www.yiiframework.com/doc-2.0/guide-input-validatio... Conditional Validation section