Nice little minor-mode that will make your buffer all nice and flashy when you break some formatting rules, that is, it makes great reason to start TabsAndSpacesDiscussion all over again ;)

Available at: http://www.jpl.org/ftp/pub/elisp/develock.el.gz or at your near Debian repo (that's the way I actually learned about it, Debian packagers keep amazing me :)

* Does anyone find this useful?  It seems that this is just the kind of annoying highlighting that cperl does (and I turn off);  I rely on {()} balancing going out of whack to know when I've made a syntax mistake. --ErikBourget

* I tried it in Lisp mode and it filled my buffer with so much ketchup and mustard I nearly fell off my chair.

* This mode makes the whitespace pedant in me very, very happy.  --MichaelOlson

* I find it helpful. I'm trying to figure out how to activate it for !ProofGeneral's !CoqMode --SamuelBronson

* I personally like how it highlights text that goes past column 79, as well as trailing space.  To the ketchup and mustard guy: move point to ketchup and/or mustard; M-x customize-face; remove background color or make more subtle; done!  --DarrenEmbry

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ProgrammingModes