Follow the links under the link. As I mentioned in my other comment, this is an optimization that enables (transparent) allocation of reference types on the stack. I.e. the compiler might be able to allocate the object that's created with 'new' on the stack.
What I understand is that this is stack allocating reference types, when the compiler can infer that it is safe to do so. Which I think is an optimization .net Core desktop doesn't yet do.
Also worth noting, I believe .net Core doesn't necessarily stack allocate value types either, seems a lot of conditions can make it unsafe as well, like a closed over value type that could escape the local scope, so value types arn't always stack allocated either. Only done when it is safe to do so.
I guess that's what they meant. However, that's a bit misleading, since the runtime doesn't care about that that's a value type captured in a closure, as it's a class field in IL already. And those are always allocated like their containing type.
