Up to this point, the sample application has been built as a PEF/CFM application which launches in Mac OS 9 and Mac OS X without Classic. However, Mach-O is the native executable format in Mac OS X. This step changes the development environment to build a Mach-O application bundle and is the first step to use an Xcode project as well as the legacy CodeWarrior project. For most applications, this should be a fairly simple step. However, if you rely on CFM libraries that aren't available in Mach-O, or if you have a plugin architecture to support, the move to Mach-O can be trickier.
This was also a good opportunity to do some cleanup and remove all of the Classic specific code. The menu handling code in ExamplePrefs.c in the 4_Mach-O folder has been simplified from step 3. The control activation and updating and window closing is now handled by the standard window handler in PrefsWindow.c