Extreme Clarity

The property of a program such that the source code exhibits everything about the system that anyone needs to know, immediately to hand, clear at a glance, accurate to six places.

Practices like RefactorMercilessly, limited MethodCommenting and TreatCommentsWithSuspicion lead in the direction of ExtremeClarity.

Never attained, ExtremeClarity can only be approached. But since TheSourceCodeIsTheDesign, the closer you approach, the better your world can be.

What are the differences (if any) between ExtremeClarity and SimplyUnderstoodCode? Or ExtremeNormalForm?