Great code needs no comments. Sure it does. « The simple and obvious way to do this misses important edge cases X, Y and Z. » « This is to work around a bug

Great code needs no comments. Sure it does. « The simple and obvious way to do this misses important edge cases X, Y and Z. » « This is to work around a bug in the framework we're using; see http://.. http://... . » « This is deliberately wrong, for compatibility with ABC system. »