A package that includes convenience helpers to assist with building Python
packages with compiled C/Cython extensions. It is developed by the Astropy
project but is intended to be general and usable by any Python package.

This is not a traditional package in the sense that it is not intended to be
installed directly by users or developers. Instead, it is meant to be accessed
when the setup.py command is run and should be defined as a build-time
dependency in pyproject.toml files.