How does Visual Studio populate its Add References dialog?

Question

This is a deliberate repost of an earlier question. The reason why I'm posting a question that has already been answered is I beleive it wasn't answered completely.

My question is this: how does VS populate its Add References dialog for .Net objects? So far, I know about the following:

• The PublicAssemblies folder inside VS's installation path.
• The AssemblyFolders registry keys (for either 32-bit or 64-bit installations)

Unfortunately, both of the above do not explain how Add References manages to list assemblies from Unity or MS Office. Those assemblies' paths are not listed in registry and are not placed in PublicAssemblies folder. How does Visual Studio find them?

Any idea is appreciated. I am really stuck on this.