In WiX files, what does Name="SourceDir" refer to?

From: https://robmensching.com/blog/posts/2010/1/26/stackoverflow-what-does-namesourcedir-refer-to/

Honestly, it's something that we should have hidden from the developer but didn't. Sorry. The truth of the matter is that the Windows Installer expects the Directory tree to always be rooted in a Directory row where the primary key (Directory/@Id) is "TARGETDIR" and the DefaultDir column (Directory/@Name) is "SourceDir".

During an install, TARGETDIR will default to the largest drive on the machine. SourceDir will be set to the location where the MSI is being executed. Now, SourceDir is tricky after the initial install because it won't be set unless the ResolveSource action is called. However, you don't want to explicitly call the ResolveSource action because it is likely to prompt you to provide the original source media (aka: insert the CD, please).

What we should have done in the WiX toolset is remove the need to specify the TARGETDIR/SourceDir pair and say "Any Directory element that has no parent will automatically be parented to TARGETDIR because that's what the MSI SDK says to do." Instead, you have to do it yourself... and some devs wonder what it all means.

None of this was really helpful for me. I found this thread wondering how to make a Debug build, where my source files (the ones going in the installer) could be pulled from either the "Release" build dir or the "Debug" build dir of the project I am trying to make an installer for.

After some grepping, I found the actual path in the wixproj file, there SourceDir is defined as:

<SourceDir>$(SolutionDir)distribution\Release</SourceDir>

which has really nothing to do with installation files and project files. I was able to add another PropertyGroup that mirrored the release group which now pointed to my debug files:

<SourceDir>$(SolutionDir)distribution\Debug</SourceDir>

Hope this helps someone. I know it's a little off topic, but hopefully it helps someone in the future. Not sure why the project plug-in does not expose this value? Or am I missing that?