When 8 bit ASCII is enabled, the following system characteristics change:
Character codes 128 to 254 are marked as :constituent in the readtable. This means that any of the new characters (except for the nonprinting character 255) can be symbol constituent. Alphabetic characters which appear in both cases, such as é and É, are considered to be alphabetical for purposes of symbol case control, while characters such as á that have no coresponding upper case are not considered to be alphabetical.
The reader is extended for the character data type to allow all the additional characters (except code 255) to be entered literally, for instance "#\é". These characters are also printed literally, rather than using the "M-" construct. Code 255 must still be entered as, and will be printed as, "#\M-Rubout".
Likewise strings do not need and will not use the backslash escape mechanism for codes 128 to 254.
The functions alphanumericp, alpha-char-p, upper-case-p, and lower-case-p perform as would be expected on the extended characters, treating the diacritic characters as their unadorned counterparts. As per the Common Lisp definition, both-case-p will only indicate T for characters available in both cases.