C# and Microsoft Visual Basic support extension methods that let you add functionality to another class and use a familiar dotted style to access them. WinRT doesn't currently support them so you need to write a separate .NET library in addition to your WinRT component to expose them. Extension methods can be used as standard static methods so usage from languages that don't support extension methods such as C++ will be similar to calling a static method but for the languages that do support them, it can be used as extension methods. This could be implemented as an attribute as well which then can be used by CsWinRT to project it as an extension method.
C# and Microsoft Visual Basic support extension methods that let you add functionality to another class and use a familiar dotted style to access them. WinRT doesn't currently support them so you need to write a separate .NET library in addition to your WinRT component to expose them. Extension methods can be used as standard static methods so usage from languages that don't support extension methods such as C++ will be similar to calling a static method but for the languages that do support them, it can be used as extension methods. This could be implemented as an attribute as well which then can be used by CsWinRT to project it as an extension method.