use it for the default in `set_config` and simplify and add more
flexibility to the the config processing, and potentially in other
options as well.
The reverse policy returns a vector but in reversed order from normal.
This is what we want in the config processing
Inspired by #862, and updated with recent code changes.
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Co-authored-by: Volker Christian <me@vchrist.at>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
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