How to attach webform block as views slideshow attachment

Hello,

I created a views slideshows block and a webform block. When I edit the views, I click Add > Attachment, I did not see any option to select the webform block. How can I have the block as an attachment of the views slideshows?

Thanks.

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/22/feed