Go forward to iswctype
Go backward to iswupper
Go up to Ctype
Go to the top op libc

`iswxdigit'--hexadecimal digit wide-character test

     #include <wctype.h>
     int iswxdigit(wint_t C);
`iswxdigit' is a function which classifies wide-character values that
are hexadecimal digits.
`iswxdigit' returns non-zero if C is a hexadecimal digit wide-character.
`iswxdigit' is C99.
   No supporting OS subroutines are required.