The manual will tell you not to overfill, as would a speed sign state not to exceed the limit.
The truth is, manufacturers these days tolerate margin for errors. Fuel tank, oil tank, master cylinder etc. The marks are there for factory requirements and as a precaution, they are not there to imply danger by excess.
Sure, my brake fluid, coolant, engine oil all sit on the mark. But that's just pure measuring chance! I've never aimed to be accurate, rather I've aimed for the mark more or less. But more is better than less :-)