#include <wctype.h> int iswdigit(wint_t wc);
The wide-character class "digit" is a subclass of the wide-character class "xdigit", and therefore also a subclass of the wide-character class "alnum", of the wide-character class "graph" and of the wide-character class "print".
Being a subclass of the wide character class "print", the wide-character class "digit" is disjoint from the wide-character class "cntrl".
Being a subclass of the wide-character class "graph", the wide-character class "digit" is disjoint from the wide-character class "space" and its subclass "blank".
Being a subclass of the wide-character class "alnum", the wide-character class "digit" is disjoint from the wide-character class "punct".
The wide-character class "digit" is disjoint from the wide-character class "alpha" and therefore also disjoint from its subclasses "lower", "upper".
The wide-character class "digit" always contains exactly the digits '0' to '9'.