There are several (overlapping) categories of characters that have no formally associated type but that are nevertheless useful to name. They include graphic characters, alphabetic characters, characters with case (uppercase and lowercase characters), numeric characters, alphanumeric characters, and digits (in a given radix).
For each implementation-defined attribute of a character, the documentation for that implementation must specify whether characters that differ only in that attribute are permitted to differ in whether are not they are members of one of the aforementioned categories.
Note that these terms are defined independently of any special syntax which might have been enabled in the current readtable.
188.8.131.52 Graphic Characters
184.108.40.206 Alphabetic Characters
220.127.116.11 Characters With Case
18.104.22.168 Numeric Characters
22.214.171.124 Alphanumeric Characters
126.96.36.199 Digits in a Radix