It is very bold statement. Code models some real-world entities (domain). Code (completely with comments and documentation) cannot and should not document fully

It is very bold statement. Code models some real-world entities (domain). Code (completely with comments and documentation) cannot and should not document fully domain. It is context, which is needed to understand code. Yes, simple CRUD application can have all context encapsulated, but what's about some code which models, say, some aspect of chemistry? Should this code have enough context which includes several post-grad university courses? Or «simpler» example from my current $Job: we have a lot of code to build some models of derivative stock exchange instruments (options, futures, etc). Enough context for this code is, like, full shelf of 1000 page books. Good luck to review this code for everything but off-by-one errors if you don't work in this area for 5+ years.