Note: this is not a policy doc. At least, not yet.
This is a pile of notes that should probably be integrated into the rustc-dev-guide at some point. These roles, at least for me, inform where and how I've designed features and pages in rustdoc.
With these roles written down, I'm going to try to avoid referring to a "rustdoc user" most of the time, because that's not usually specific enough. Rustdoc has three interfaces, with three different audiences, who, sometimes, overlap.