USVString corresponds to the set of all possible sequences of unicode scalar values. USVString maps to a String when returned in JavaScript; it's generally only used for APIs that perform text processing and need a string of unicode scalar values to operate on. USVString is equivalent to DOMString except for not allowing unpaired surrogate codepoints. Unpaired surrogate codepoints present in USVString are converted by the browser to Unicode 'replacement character' U+FFFD, (�).