process.stdout.fd is mentioned in these 2 sections:

https://nodejs.org/api/async_hooks.html#async_hooks_printing_in_asynchooks_callbacks
https://nodejs.org/api/async_hooks.html#async_hooks_asynchronous_context_example

But it is not documented in process.stdout or in a section of any mentioned prototype (net.Socket, Duplex or Writable stream).

Should it be documented with process.stdin.fd and process.stderr.fd?