optional-dependencies
Domain: Python Packaging
🎯 Motivation
Extra packages for optional features, grouped under [project.optional-dependencies]. Users install them with pip install mypkg[extra].
📋 Concrete Example
Define dev = ["pytest", "ruff"] so pip install mypkg[dev] adds testing tools.
🔗 Analogy
Optional dependencies are add-ons at a restaurant — pay extra for cheese or dessert, the base meal still works.