Where is the method EnsureMetaFields defined?

I'm following the tutorial to create a basic module and already the very first code example presents a problem. When inheriting from ModuleBase, according to the example my class should have a method EnsureMetaFields. But I don't think it does, and neither does Visual Studio.

It doesn't help that the documentation doesn't specify what assemblies to reference. 

So where is this method defined?

Thanks!

Never mind, it's a few pages ahead in the PDF, I just didn't notice it yet.