Describes the combined set of all letters in the alphabet and the numbers 0 through 9. It is useful to group letters and numbers together because many
programs treat them identically, and differently from
punctuation characters. For example, most
operating systems allow you to use any letters or numbers in
filenames but prohibit many punctuation characters. Your
computer manual would express this rule by stating: "Filenames may be composed of alphanumeric characters."
Sometimes additional characters are considered alphanumeric. For example, on IBM mainframes the characters @, #, and $ are considered alphanumeric characters.
