is this something new (interface function migration)?…ion/index.html

Why should I want to do this migration? wasn’t BP interfaces there for a good reason after all?

Edit: I wish entries in the documentation had update date…

Actually it does, you can check in the top right and see that it was tagged 4.9 which means it’s pretty old. I had no idea this existed though. From what I know BP interfaces still work fine, I think this is just a convenience thing for when you decide you didn’t need an interface but still want the functions added to the BP without a bunch of copy paste.

Exactly. The migration simply puts the function definition into the BP itself. Which means you need the concrete type of the Blueprint (instead of using an interface) if you want to call this function.