If you've got time, would you be able to create a PR to update the bits of documentation you were using? That way you'll be able to help the next guy who's struggling with the doc_spotlight feature.
I don't know exactly which sources this documentation is built from. I only found that documentation in rust repo by checking out branch to-be-dev-nightly, but that branch doesn't exist anymore. Do you know what was the purpose of that branch?
That's the version that ships with the stable toolchain, so it currently shows the documentation from Rust 1.42.0. It's updated every six weeks, when a new version of Rust is released.
Perhaps for the unstable book specifically, the web site should link to the nightly version instead of the stable version.