Whether c is a letter or a number (0 .. 9, a .. z, A .. Z).
1 assert( isAlphaNum('A')); 2 assert( isAlphaNum('1')); 3 assert(!isAlphaNum('#')); 4 5 // N.B.: does not return true for non-ASCII Unicode alphanumerics: 6 assert(!isAlphaNum('á'));
See Implementation