The installer sets this variable to the version of the Sxs.dll file if the installer runs on a system with support for side-by-side assemblies. If Sxs.dll is not present, this variable is not set.
You can refer to this variable as <MsiWin32AssemblySupport>. In conditional expressions you can omit the brackets and simply use MsiWin32AssemblySupport as a test for side-by-side assembly support. Set automatically by all installers.