Light document is exactly how I do it. I do mostly backend and API design, and usually when it is up to me I flesh out a spec (one page, after discussion with the main client, being mobile devs, web devs, and so on) then have all stakeholders ok it. Surprisingly when its a one page prose everyone reads it pretty quickly. As long as the end result code matches that spec the other technical comments are not that hard to deal with and usually easily reversible should I merge then realize there was a mistake.