No files under site.collections

Hi, I am trying to create a collection and iterate over it to list all my files but when I print site.collections
it shows nothing under files:


Although I haves 4 files within the Binary_systems folder.
This is my config:

collections_dir: book
output: true
output: true

any formatting you may have is stripped when you post code without using backticks to mark it as code. There is also the </> code button in the editor to mark stuff as code.

Do you have a link to the repo?

I think collections are supposed to start with an underscore in the file system.