How to make a generated Editor into an editable GUI?

I have seen some Jucer projects where the ProcessorEditor.cpp is graphically editable. However, when I create a new plugin, I only get the C++ code. Is there some trick that I missed to convert the Editor? First I tried it by making a component as large as the editor, but that seems a weird route to me.

Thanks for any help

Have a look here and here.

Thanks! Already suspected it had to do with the meta data, I hope to fix it with this example.