The value of char-code-limit is a non-negative integer that is the upper exclusive bound on values produced by the function char-code, which returns the code component of a given character; that is, the values returned by char-code are non-negative and strictly less than the value of char-code-limit.

Common Lisp does not at present explicitly guarantee that all integers between zero and the value of char-code-limit are valid character codes, and so it is wise in any case for the programmer to assume that the space of assigned character codes may be sparse.