How to do "C++ classes"?

[rempas via Digitalmars-d-learn]

I'm seeing in the page about "BeterC" and in the part about the 
[retained 
features](https://dlang.org/spec/betterc.html#retained), the #11 
says about "COM classes and C++ classes". What are the "C++ 
classes"? I tried to create a class using "extern(C++)" but this 
didn't worked. Can someone make an example on that?