nations of the packages can be created without the need to copy
    package names multiple times.

@var _EXTRAS_REQUIRE: C{extras_require} is a dictionary of items that can be
    passed to setup.py to install optional dependencies.  For example, to
    install the optional dev dependencies one would type::

        pip install -e ".[dev]"

    This has been supported by setuptools since 0.5a4.

@var _PLATFORM_INDEPENDENT: A list of all optional cross-platform dependencies,
    as setuptools version specifiers, used to populate L{_EXTRAS_REQUIRE}.

@var _EXTENSIONS: The list of L{ConditionalExtension} used by the setup
    process.

@var notPortedModules: Modules that are not yet ported to Python 3.
é