Oh, failure is way better. But a lot of the original APIs didn't have failures, they just returned a value, and MS doesn't like to break backwards compatibility

Oh, failure is way better. But a lot of the original APIs didn't have failures, they just returned a value, and MS doesn't like to break backwards compatibility even when it'd be easier for everyone if they did. For "they", I mean MS could have made BestFit work as follows: if an input string contains characters not in the user's code page, then return a new string with characters replaced by with the name of that code point as assigned by the Unicode consortium (and maybe also the textual code point number U+<number>). This requires a new allocation and copies of the parts of the string not needing replacement, but loses no information and creates no security holes.