Where does Visual Studio identify its version. E.g. As Express, Standard, Professional, etc?
For example, the Express version does not support extensibility through add-ons. How do add-on authors prevent against their product being integrated with the Express version?
They don’t need to. Microsoft have disabled the functionality that looks for plugins. So even if it gets installed the Express version doesn’t go looking.
There may well be hacks you can do to get the Express versions to load plugins, but if that’s the case people will probably try to hack your plugin too.