What happens in a .Net 4 app when referencing .net 2 assemblies?

I have an application I want to upgrade to .NET 4, but I have a couple 3rd party assemblies that reference the .NET 2 BCL.

I seem to remember reading something that says they should play nice, but I can't find any docume开发者_高级运维ntation on the subject. ( I think my question posed to Google is just too broad, with not enough .Net 4 material out there yet )

Can anyone help me find documentation on what will happen in this case?

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If I'm reading Scott Guthrie's post, Multi-Targeting Support (VS 2010 and .NET 4 Series), correctly then that will work fine.

Of Interest?: .NET 4.0 project reference 2.0 assembly

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The .NET Framework 4 works side by side with older Framework versions. Applications that are based on earlier versions of the Framework will continue to run on the version targeted by default.

http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=0a391abd-25c1-4fc0-919f-b21f31ab88b7

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I wanted to reference StructureMap in one of my class libraries. Orginally it was created by VS2010 to use the .NET 4 client profile. Turns out, I had to changed this to the full .NET 4 framework, otherwise structuremap would not be recognized.