> What do you mean by "correct"? I mean this from the standard: "Nonspacing combining marks used by the Unicode Standard may be exhibited in apparent isolation

> What do you mean by "correct"? I mean this from the standard: "Nonspacing combining marks used by the Unicode Standard may be exhibited in apparent isolation by applying them to U+00A0 no-break space. " You can have valid Unicode that doesn't do this. But it's not intended to represent the character as some kind of textual thing. It's intended so that you can build up Unicode strings sensibly. Same idea as allowing mis-matched surrogates.