It looks like many of the links in the following product type docs are broken. They're supposed to point to classes but it seems like they just point to a 404 github page:

• https://github.com/magento-notes/magento2-exam-notes/blob/cd36d7e5f5df2365cef4122622a8337447fc34a8/7.%20Customizing%20the%20Catalog/1.%20Demonstrate%20ability%20to%20use%20products%20and%20product%20types.md