If I understand it correctly customize-set-variable can be used for
those who prefer to edit .emacs rather than use the custom interface.
The two I know of are custom-set-faces and custom-set-variables. They
are put automatically into an initialization file by the Custom user
interface (that is how I discovered them) and can be edited manually.
Their expressions look like this (from my .emacs file):
(custom-set-variables '(Info-fontify t))
(custom-set-faces
'(font-lock-comment-face
((((class color) (background dark)) (:foreground "yellow")))))
If so should not this be documented in Info?
Yes, they should; I did not realize they weren't!