JSON_CHECK_NEGATIVE([bad escape in quoted string],
[[["\x12"]]],
[error: bad escape \x])
-JSON_CHECK_NEGATIVE([\u must be followed by 4 hex digits],
+JSON_CHECK_NEGATIVE([\u must be followed by 4 hex digits (1)],
[[["\u1x"]]],
+ [error: quoted string ends within \u escape])
+JSON_CHECK_NEGATIVE([\u must be followed by 4 hex digits (2)],
+ [[["\u1xyz"]]],
[error: malformed \u escape])
JSON_CHECK_NEGATIVE([isolated leading surrogate not allowed],
[[["\ud834xxx"]]],