I'm glad to see people experimenting with alternative document/object representations, but this one might be a hard sell: based on the README[1], it only has Python, Zig and Janet implementations so far. One of the nice things about YAML (and JSON, TOML, etc.) is that they have decently mature C, C++, or Rust libraries that other languages bind to.

[1]: https://github.com/KenKundert/nestedtext