Teach the lexer/parser to recognize and decode them in JSON5 mode. Teach the encoder to use them in JSON5 mode. Add another error message for bad hex digits. Test cases to show they work, and that the bad-digit check fires.
Teach the lexer/parser to recognize and decode them in JSON5 mode. Teach the encoder to use them in JSON5 mode. Add another error message for bad hex digits. Test cases to show they work, and that the bad-digit check fires.