I'm trying to add functionality found in some other code editors to my Emacs configuration, whereby C/C++ code within #if 0...#endif blocks is automatically set to the comment face/font. Based on my testing, cpp-highlight-mode does something like what I want, but requires user action. It seems like tying into the font-lock functionality is the correct option to make the behavior automatic. I have successfully followed examples in the GNU documentation to change the face of single-line regular expressions. For example: (add-hook 'c-mode-common-hook (lambda () (font-lock-add-keywords nil '(("\\<\\(FIXME\\|TODO\\|HACK\\|fixme\\|todo\\|hack\\)" 1 font-lock-warning-face t))))) works fine to highlight debug related keywords anywhere in a file. However, I am having problems matching #if 0...#endif as a multiline regular expression. I found some useful information in this post (How to compose region like ""), that suggested that Emacs must be told specifically to allow for multiline matches. But this code: (add-hook 'c-mode-common-hook (lambda () '(progn (setq font-lock-multiline t) (font-lock-add-keywords nil '(("#if 0\\(.\\|\n\\)*?#endif" 1 font-lock-comment-face t)))))) still does not work for me. Perhaps my regular expression is wrong (though it appears to work using M-x re-builder), I've messed up my syntax, or I'm following the wrong approach entirely. I'm using Aquamacs 2.1 (which is based on GNU Emacs 23.2.50.1) on OS X 10.6.5, if that makes a difference. Any assistance would be appreciated!