David Chisnall has in-depth knowledge of Cocoa as both implementer and developer. As co-founder of the Étoilé project to build an open source desktop environment atop GNUstep, he has created a new Objective-C runtime library, contributed code to the Objective-C front end for the LLVM compiler, and published many papers on Objective-C. He wrote an extremely popular series of articles on Objective-C and Cocoa for InformIT, and authored The Definitive Guide to the Xen Hypervisor.