IXSomething vs ISomething

I stumbled upon a documentation where COM objects have two kinds of interfaces, one starting with I, second with IX. Documentation says that IX is derived from开发者_开发问答 IUnknown, and I is derived from IDispatch.

Is it better to use IX interfaces if I use C++? As far as I understand the I interfaces are designed for scripting languages in this case? Are there any other differences?

The X belongs to the next word. Feed vs XFeed. "Extended", version 2 of the API.