msbuild: when in the build project is Microsoft.VisualBasic.Targets 'imported' by msbuild?

Question

Here's my situation: I'm trying to understand how msbuild works by looking at the build files located in the .NET framework install path:

C:\Windows\Microsoft.NET\Framework\v3.5>dir /s/b microsoft*
Microsoft.Build.Tasks.v3.5.xml
Microsoft.Build.xsd
Microsoft.Common.targets
Microsoft.Common.Tasks
Microsoft.CSharp.targets
Microsoft.Data.Entity.targets
Microsoft.VisualBasic.targets
Microsoft.WinFx.targets
MSBuild\Microsoft.Build.Commontypes.xsd
MSBuild\Microsoft.Build.Core.xsd

I'm assuming that msbuild starts with Microsoft.Common.Targets, and then at some point in the future msbuild 'looks' at my vb project file extension (.vbproj) and loads 'Microsoft.VisualBasic.targets'.

two questions:

1) Is my interpetation correct?

2) can you explain to me, where is the code that determines that this is a .vbproj file, and loads 'Microsoft.VisualBasic.targets' accordingly? Is the code locked away in an assembly somewhere, or is it visible in the build files listed above?

Answer 1

It "starts" with your .vbproj file. Take a look at that file, it will <Import> the Microsoft.VisualBasic.targets, which in turn will <Import> Microsoft.Common.targets.

Answer 2

In 4.0, which is currently available in Beta, there is a /preprocess switch which will make this all clear.