It's less a spec and more of, choose the tool that fits the job. A lot of these documents fit the overall structure of "high-level situation & recommendation; industry / product / customer context; more depth on recommendations considered; FAQ"
I don't have any examples, anymore (I left Amazon some years ago), but here are a couple of links that have reasonable takes on the structure and guidelines:
Bottom line: the purpose of the document is to drive a high-quality decision, so include what will help, and leave out anything extraneous. (I know, that's not very actionable.)