Comment 2 for bug 1697212

that's a good question!

I'm not a Microsoft specialist, so I do not really know where to search for. but, if I remember right, Microsoft requires only the uninstall keys, and in the list of uninstall keys, there is one named "InstallLocation".

the key used in the install section might be optional, to help applications like IDEs to identify existing software.

if you do not find the exact specs, you may look inside an actual registry for some more or less standard Microsoft applications, I guess you will find "InstallLocation".