InstallMate sets this variable to the value of the /u command line option. This option signals to the installer that it is running in upgrade mode and prevents certain actions (such as delayed file removal) that are unsafe in this context.
You can refer to this variable as <TsuUpgrade>. In conditional expressions you can omit the brackets and use tests like TsuUpgrade to test for an upgrade installation or removal. This variable is initialized from the command line options and used internally by the installer.