2.1.2 [W3C-WEBIDL1] Section 3.10.17 USVString
V0002: The USVString type is not supported
The specification states:
3.10.17 USVString The USVString type corresponds to the set of all possible sequences of Unicode scalar values, which are all of the Unicode code points apart from the surrogate code points.
IE11 Mode, IE10 Mode, and IE9 Mode (All versions)
USVString type is not