Improve comments, add an error throw that shouldn't happen
Improve comments, add an error throw that shouldn't happen

Ignore-this: 7675070826b3c53499e4352e692d6036

darcs-hash:20120826085426-c3db2-648c1b82565fa87710737b641c8159ea257011d9

yzhou61/xmonad-contrib,yzhou61/xmonad-contrib,yzhou61/xmonad-contrib