Reviving this thread, as @aris recently brought this up at Accents replacement with natural letter.
I was surprised to see it undocumented; I haven’t used it, but I’ve seen it discussed often enough to presume.
Anyhow, I don’t know the implications of what it does, so I’d like to use this thread to get feedback from someone with a clue, so we can move forward with documenting this config option.
The relevant docs issue is at https://github.com/gohugoio/hugoDocs/issues/94.