The DRY principle states that the logic and data should not repeat itself in

• Code
• Documentation
• Data structures

Change in the field/logic in one part of the program or data store should not result in changing it in multiple points of program/data store. Similarly in same for documentation. Try to maintain single source of truth.

Commenting

• Restrict non-API commenting.
  • As code already shows how it is done.

Also see

1. Comments