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Revise for 6.0.0 Mathics3 API and current Mathics3 builtin standards described in `Guidelines for Writing
Documentation <https://mathics-development-guide.readthedocs.io/en/latest/extending/developing-code/extending/documentation-markup.html#guidelines-for-writing-documentation>`_.
This package has undergone a major overhaul. Modules have been split out along into logical groups following the documentation structure.
We have gradually been rolling in more Python type annotations and have been using current Python practices. Tools such as using ``isort``, ``black`` and ``flake8`` are used as well.
Evaluation methods of built-in functions start ``eval_`` not
``apply_``.
There is more refactoring more to do here, bugs that remain, functions needing adding or filling out.
We should assess the landscape for changes in modules that might be used here; there is probably something better maintained than ``langid``.