Bingo. That's why I used the "effectively" qualifier - if my toolchain says "oh this is UTF-8," then I should be able to trust that it's for-real, honest-to-goo

Bingo. That's why I used the "effectively" qualifier - if my toolchain says "oh this is UTF-8," then I should be able to trust that it's for-real, honest-to-goodness, spec-compliant UTF-8. If it's "oh this is the part of UTF-8 that was easy to implement " instead, then that tool has lied to me. I shouldn't have to read the documentation to find out that something is not what it claims to be. Bonus points for the documentation brazenly ignoring that they're implementing something that's not spec-compliant and naming it like it is.