Defines the .NET runtime version of the task host that this task should be run in. Currently supported values: CLR2, CLR4, ...

Defines the .NET runtime version of the task host that this task should be run in.  Currently supported values:  CLR2, CLR4, CurrentRuntime, and * (any).  If Runtime is not specified, either the task will be run within the MSBuild process, or the task host will be launched using the runtime of the parent MSBuild process