The iswalnum function is the wide-character equivalent of the
isalnum function. It tests whether wc is a wide character
belonging to the wide character class "alnum".
The wide character class "alnum" is a subclass of the wide character class
"graph", and therefore also a subclass of the wide character class "print".
Being a subclass of the wide character class "print", the wide character class
"alnum" is disjoint from the wide character class "cntrl".
Being a subclass of the wide character class "graph", the wide character class
"alnum" is disjoint from the wide character class "space" and its subclass
"blank".
The wide character class "alnum" is disjoint from the wide character class
"punct".
The wide character class "alnum" is the union of the wide character classes
"alpha" and "digit". As such, it also contains the wide character class
"xdigit".
The wide character class "alnum" always contains at least the letters 'A'
to 'Z', 'a' to 'z' and the digits '0' to '9'.
