This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
Remember, overridding methods can always be less restrictive than their parent methods. The one exception are private methods, which of course can't be overridden because they can't be seen by the subclass.