Yes, today it is a little inappropriate. This is a managed declaration of type COM interface. Also, check out ComTypes.IExpando and InteropServices.UCOMIExpando. The main interfaces for runtime scripts for implementing property packages. In particular, for Javascript, check this thread .
Microsoft had high hopes for JScript, it was the main language supported on the side of C #, VB.NET and Managed C ++. This did not work.
Forgotten, but not completely dead. ExpandoObject Class Returns to .NET 4.0
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