WIX: Howto set the name of the msi output file dynamically

Question

I want to include some dynamic part in the filename of the msi file my wix projects produce. This dynamic part should be controlled by variables which are part of my wix project

Answer 1

Do the variables have to be defined in WiX? I'm building my setup binaries from MSBuild, and I've simply set the output file name to MyProject_$(Platform) -- I expect that any MSBuild variable substitution will work equally well.