Agreed. Even basic things like detecting if the installer is making a fresh install or upgrading existing installation require arcane condition checks: https://stackoverflow.com/questions/320921/how-to-add-a-wix-... And worst of all, all sources I've ever found (including the linked answers) contain at least a few mistakes or unhandled cases, so I'm not confident enough to make any improvements. Documentation could really use battle-tested examples from people who understand MSI installers very well.