Determines whether a character is alphanumeric.
Unlike the standard C library
isalnum() function, this only
recognizes standard ASCII letters and ignores the locale,
FALSE for all non-ASCII characters. Also, unlike
the standard library function, this takes a char, not an int,
so don’t call it on
EOF, but no need to cast to #guchar before
passing a possibly non-ASCII character in.
Available since: 2.0
This function is not directly available to language bindings.