Configuring a subdomain with subdirectories for each project’s documentation

Continuing the discussion from How do I publish documenter.jl-generated docs to a subdirectory of a custom subddomain?:

I am trying to replicate this, and I’m confused about what “custom domain” I should use in my GitHub Pages settings for each repository. Say I have the username “user” at GitHub, and I own the name “”. My website is a GitHub project called “example.repo”. My github pages defaults to I can go into settings in GitHub, and serve my top-level website (“example.repo”) to the custom domain “”. Then I go to my DNS provider and create a CNAME which points “” to “”. This works great!

Now I want to create a subdomain: “”. I want each of my projects (A.jl, B.jl, C.jl) to have their documentation hosted at “”, etc.

How can I do so?