I tested following strings with invalid surrogate pair and unpaired surrogate in files:

1. `"a\uD800\uD800x"`
2. `"a\uD800x"`

The error messge was: "... invalid string: surrogate U+DC00..U+DFFF must be followed by U+DC00..U+DFFF; ..."

I think it must be: "... invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF; ..."