The point is not in the mistake the user made, but how that error manifests. Subsequent punctuation characters that were not intended to be displayed in a diff

The point is not in the mistake the user made, but how that error manifests. Subsequent punctuation characters that were not intended to be displayed in a different font are not kept as-is, nor do they trigger warnings like "character not present in font", but are instead substituted by random other characters. This is 1970s' "you're holding it wrong" error-handling philosophy, same one as C's. And yet Knuth seems to regard Unicode not as a basic building block of interoperability, but as useless bells-and-whistles, judging by his satirical "iTeX" presentation.