- An Introduction to Programming in Emacs Lisp
https://www.gnu.org/software/emacs/manual/html_node/eintr/index.html
https://www.gnu.org/software/emacs/manual/pdf/eintr.pdf
https://github.com/RenWenshan/emacs-lisp-intro-solutions
- Emacs Lisp Reference Wiki
https://www.emacswiki.org/emacs/EmacsLispReference
- Learn Emacs Lisp
https://www.emacswiki.org/emacs/LearnEmacsLisp
- Emacs Lisp Cookbook
https://www.emacswiki.org/emacs/ElispCookbook
- Category Code
https://www.emacswiki.org/emacs/CategoryCode