I'm wondering how to create Parts for bookdown projects. I first thought I was looking for Sections, but that language seems in Bookdown to refer to parts of chapters, but this would be a higher level organization. Examples I can see of this having been done create part headings that can't be navigated to directly but at least provide an organizational scheme:
Irrizary's Introduction to Data Science with parts
II Data Visualization
Xie, Allaire, Grolemund R Markdown: The Definitive Guide with parts:
I Getting Started
II Output Formats
Lovelace, Nowosad, Muenchow Geocomputation with R after chapter 1 there's
I imagine this might use something in the _bookdown.yml file, but I don't have a clue what it would be.