The only semblance of Rust documentation policy/guidelines can be found in src/book/documentation.md, which I think should be moved elsewhere, perhaps to Style guidelines or own file. The chapter can remain in the book, but should only explain how stuff is done, not mandate policy (e.g. “The first line of a documentation comment should be a short summary of its functionality”).
One other thing: if we do create documentation policy/guidelines, should it be universal to Rust projects, or just the rust-lang/rust? I suggest we create “Documentation Guidelines”, either as a stand-alone document or as a chapter of “Style Guidelines” document, and have contributions to rust-lang/rust documentation follow those guidelines.
Not to be a downer, but there has been a great rush to institute new ‘policy’ lately, and it’s kind of grinding on me. Maybe we can focus on writing software for a while and not doing politics.
Ideally, we'd come up with these guidelines, but until we have enough people doing lots of docs to make a documentaiton team, I don't think that it's worth it to do more. These kinds of RFCs are high, high, high effort.