Visibility options control when a virtual file may be "seen" by its hosting application.
Visbility may be changed using the right-click menu from the project file list.
By default, Virtual files are invisible to Shell components such as the File Open Dialog and Explorer tree controls. This keeps files hidden from the user's view, as most likely virtual files are intended to be used solely by the application, not the user.
By default Virtual files are visible to search/enum request by the application. For example, the file will be located through calls to Windows API functions FindFirstFile and SearchPath. If you make the file invisible to search request, it can still be opened and read using normal file I/O functions, but it will not show up in directory listings.