Do you know a simple way to tell GNU Emacs to recognize LaTeX \iffalse ... \fi blocks and to display them in a special way, e.g., using a lighter font, or using font-lock-comment-face. Is there a LaTeX style package that already knows how to do this?

I understand that correctly recognizing valid \iffalse's and their matching \fi's in arbitrary LaTeX source file is a non-trivial problem, but I am happy with an approximate solution that works in most easy cases, e.g., that assumes no nesting of \if\fi's and requires these commands to appear alone on their source line.

  • I've little idea how to do this, but I believe AUCTeX would could/would be useful here---is its use allowed, or should it stick to normal tex-mode? – Sean Allred Jul 30 '13 at 17:08
  • A solution with AUCTeX is fine with me. – phs Jul 31 '13 at 7:48

This solution does not require AUCTeX to the best of my knowledge.

Add the following to your .emacs:

(add-hook 'TeX-mode-hook
  (lambda ()
    (font-lock-add-keywords nil '(
      ("\\\\iffalse\\(\\(.\\|\n\\)*?\\)\\\\fi" 1 font-lock-comment-face)))))


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