“One of the great advantages of Cocoa is getting a lot of functionality with little code. There are classes in the Cocoa Framework that handle much of the necessary work in creating applications that have multiple documents.
NSDocument and its closely related cohort
NSWindowController combine to give you a powerful starting point when building your own multiple document applications. The best way to illustrate the power that these classes offer is with an example; that’s how HTMLEditor.app was born. HTMLEditor is a basic text editor that has file associations for HTML. No big deal right? Well, over the next month or so, HTMLEditor will be extended to include a number of additional features, forming the basis of a series of articles.” Read the rest of the MacOSX Cocoa/Project Builder step-by-step tutorial at StepWise.