I've implemented std::error, meeting the requirements laid out in [P1028
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1028r3.pdf>], and
based on this experience, have written up a paper outlining various design
decisions and concerns that came up during the implementation, particularly
with regard to how std::error might map to existing error mechanisms
(dynamic exceptions, std::error_code).

This is not a formal proposal right now. It is intended simply to further
discussion around the design, requirements and implementation details of
some future std::error specification.

https://charles-salvia.github.io/std_error_feedback.html