There is a new pull request by cinerea0 against master on the void-packages repository

https://github.com/cinerea0/void-packages mdb
https://github.com/void-linux/void-packages/pull/38407

mdBook: update to 0.4.21
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#### Testing the changes
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A patch file from https://github.com/void-linux/void-packages/pull/38407.patch is attached