What do you mean by "outside the code" Erik ? Before I get on my high horse.
If you do, please do not ride into the sunset.

Anyhow, "outside the code" means outside the file(s) where the code reside.

I have seen, I don't know how many, "documentations" in separate binders where "the slight difference due to code updates forgotten in the documentation" led to some poor sod running around in circles for days because of relying on understandable documentation instead of non-understandable code.

Another reason for the argument is that, if outside documentation exist, you have the perfect excuse for not commenting your code to a reasonable level.

Erik