/* Is the UTF8-encoded byte 'c' the first byte of a two byte sequence? Use
* UTF8_IS_NEXT_CHAR_DOWNGRADEABLE() instead if the input isn't known to
/* Is the UTF8-encoded byte 'c' the first byte of a two byte sequence? Use
* UTF8_IS_NEXT_CHAR_DOWNGRADEABLE() instead if the input isn't known to