01·pyproject.toml — modern configuration

Why does build-backend.backend-path exist?

• Requires an absolute path to the Python interpreter.
• Configures the build environment PATH.
• Defines a path to backend binaries (gcc, clang).
• Allows using a build backend from a local project directory (in-tree backend) instead of from PyPI — e.g. a custom backend without publishing it to PyPI.