This variable contains the product code of the main product for an add-on installer. InstallMate sets this variable when the installer is built, but only if the Add-on/Upgrade for product attribute is set on the Product info project page.
Used internally by InstallMate. You can refer to this variable as <MainProductCode>. Do not set this variable directly; it is set automatically when you build the installer, using information from the Product info project page.