Strategy for safely understanding and modifying unfamiliar or legacy codebases: trace down from entry points, learn up from primitives, characterize before changing. Use when working in a codebase for the first time, before modifying code whose behavior is unclear, or when the user says レガシー, 初めて触るコード, 引き継いだコード, このコードどうなってる. Not for diagnosing a specific bug (use systematic-debugging).
