Looking more into this, I found this document with details about the popularity of different alternative directory names: “Project Layout - Survey Results and Updates” https://vector-of-bool.github.io/2018/09/16/layout-survey.ht...

There is also a separate proposal from around the same time, dated one month later and very focused on C++ which I find less useful for C: “Canonical Project Structure” https://open-std.org/JTC1/SC22/WG21/docs/papers/2018/p1204r0...