Learning Metafont and CWeb lately. Along with that, I've been beating more on mmm-mode to support CWeb. There are a number of areas where mmm-mode doesn't do things the best way for cweb, so I'm doing a bit of hacking on its internals. CWeb looks like a good choice, because it's different enough from what mmm-mode handles already that by the time I get a submode class for it, mmm-mode should be able to handle almost anything easily.