If your ObjectARX application uses global functions acedCommand() or acedCmd() or AcApDocManager functions to create, close or activate documents, or your LISP *error* handlers use the (command) function, then these migration requirements pertain to you.
The fiber facility is unique to the Windows operating system. It has been available In all Windows versions since NT, including Windows 7. There is no comparable facility on MacOS, so all LISP and ObjectARX applications being ported to AutoCAD 2011 for Mac must adhere to these migration requirements, if applicable.