The iswalpha function is the wide-character equivalent of the
isalpha function. It tests whether wc is a wide character
belonging to the wide character class "alpha".
The wide character class "alpha" is a subclass of the wide character class
"alnum", and therefore also a subclass 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
"alpha" is disjoint from the wide character class "cntrl".
Being a subclass of the wide character class "graph", the wide character class
"alpha" 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
"alpha" is disjoint from the wide character class "punct".
The wide character class "alpha" is disjoint from the wide character class
"digit".
The wide character class "alpha" contains the wide character classes "upper"
and "lower".
The wide character class "alpha" always contains at least the letters 'A'
to 'Z' and 'a' to 'z'.
