Comment by WalterBright

> But these characters only look identical in some fonts.

That's a problem with the fonts.

> And what about the round-trip rule?

Print Unicode on paper, then ocr it, and you'll get different Unicode. Oh, and normalization.

> ligatures

Generally an issue with rendering.

> semantic distinction

Unicode isn't about semantics (or shouldn't be). Consider 'a'. It's used for all kinds of meanings.