The default value of the common path if it is not already defined in the hosting process. Normally the hosting process will ...

                        The default value of the common path if it is not already defined in the hosting process.
                        Normally the hosting process will define these common paths, then re-wire the data when it is loaded.
                        For example, $(SolutionDir) will be re-written to the path of the currently loaded solution in Visual Studio.
                        These common paths help make DGML documents more portable.