There are lots of WWDC 2011 video in apple's developer website. And in the video, there are some demo about coding in xcode.
The magic thing is: In these demo, the speakers didn't type the sample code one by one. They just press some keys in xcode, then the codes existed in xcode.
I think it's a good way to do the demo, so I want know what technique did apple use. I've do some research on the demo, it is not a simple "cmd+z" or "cmd+shift+z" method.
It's an app called Demo Monkey. Apple actually provides it as a sample code project.
From the description:
The example is a document-based application which serves as a "typing assistant". Each document contains a collection of text snippets which you can insert in turn into another application using a service. When creating a document, you can import text snippets also using a service.