Magento 2 Import: "Check Data" and "Import" Button. What php method is called?

Question

I have two similar questions regarding the import in Magento 2:

1. what class method is called when the Check Data button is clicked?

The button has this attribute onclick="varienImport.postToFrame();", but I am not able to figrure out what php file is called ultimatley.

2. What class method is called when the subsequent Import button is clicked?

Answer 1

1) Ajax validation will be called: vendor/magento/module-import-export/Controller/Adminhtml/Import/Validate.php

2) vendor/magento/module-import-export/Controller/Adminhtml/Import/Start.php

What class method is called when the subsequent "Import" button is clicked?