The installer sets this variable to a nonzero value if the target system is running a core (non-UI) version of Windows. Currently, only Windows Server 2008 has Core installations (in addition to full installations).
Windows Core versions do not have a graphical user interface shell, but only a command line interface. As such, they do not support all shell-oriented Windows features. However, the InstallMate 9 Setup.exe program runs normally on these systems and can be used both in interactive and in silent mode.
You can refer to this variable as <WindowsCore>. In conditional expressions you can omit the brackets and simply use WindowsCore as a test for a Windows core installation. Set automatically by all installers.