I think it depends on who the documentation is intended for. I often let public facing documentation be the source of truth for expected behavior unless it's i

I think it depends on who the documentation is intended for. I often let public facing documentation be the source of truth for expected behavior unless it's infeasible to coerce the system to that behavior. If the latter does occur, the documentation gets updated. If the question is what does the software actually do, then of course the code, toolchain, and runtime are the authority.