Both. The book contains an explanation of how to derive the condition system from the primitive operators of Common Lisp, which should be useful both for users that try to gain some intuition or broaden their understanding of how the condition system works under the hood, and for people who want to implement a condition system in a programming language without one - be it Common Lisp or a different language.
Implementing a condition system in a Common Lisp implementation is actually a mostly solved problem, since one can use e.g. https://github.com/phoe/portable-condition-system or borrow some code from an already working Common Lisp implementation.
Implementing a condition system in a Common Lisp implementation is actually a mostly solved problem, since one can use e.g. https://github.com/phoe/portable-condition-system or borrow some code from an already working Common Lisp implementation.