This is the source of the Reference Developer Guide, published at https://rust-lang.github.io/reference/dev-guide/. It is written in Markdown using mdbook. If you are editing these pages, the best way to view them is to run mdbook serve --open. This will start a web server on localhost that you can visit to view the book; it will automatically reload each time you edit a page.
This is published via GitHub Actions to GitHub Pages.