I want to be able to use outline-minor-mode to fold my use-package blocks at convenient points. Ideally, I want to be able to fold sections following :config, :init, :custom, etc. as well as definitions inside those blocks. The current value of outline-regexp when in emacs-lisp-mode is:

";;;;* [^ 	\n]\\|(\\|\\(^;;;###\\(\\([-[:alnum:]]+?\\)-\\)?\\(autoload\\)\\)"

I thought appending \\|[[:space:]]*:\\(init|config|custom\\) to this would work, but it doesn’t. Any help would be much appreciated.

(I see there’s a related post here, but I didn’t find anything there that helped me.)