React Guideline: ErrorHandling — Use error boundaries. Description: Catch JavaScript errors in component tree. Do: ErrorBoundary wrapping sections. Don't: Let errors crash entire app. Good Example: <ErrorBoundary><App/></ErrorBoundary>. Bad Example: No error handling. Severity: High. Docs: https://react.dev/reference/react/Component#catching-rendering-errors-with-an-error-boundary.