I've noticed something odd about the font-locking in Emacs Lisp mode and Lisp mode - keyword args are highlighted using the font-lock-builtin-face and constructs like &optional are highlighted using font-lock-type-face. I guess this was was done way back and hasn't been updated in a while, but I think it might a good idea to revise this. Pretty sure those font faces are intended for different usage. I think it would be great if all Emacs programming modes used the built-in font-lock faces consistently, so that the meaning of certain faces doesn't change from mode to mode. I guess that the two modes might also start using the font-lock-built-in face to highlight their core functions (like car, cdr, mapcar, mapc, etc) - as Clojure mode does. Personally I feel that uses of the keyword face for things that are not special forms (like the when macro) should be replaced with uses of the built-in face.
I've posted this to devel a while back (http://lists.gnu.org/archive/html/emacs-devel/2013-07/msg00592.html) and Michael Heerdegen suggested reporting it as a bug as well.


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Cheers,
Bozhidar