im currently trying to create my own GUI, but its hard and not really documented

So 2 questions:
1. How to instantiate a Filler? Those lined things, that are in the normal uis, where the ui can be dragged. Those agui:Filler objects.
https://pasteboard.co/IgI1sGA.png
2. Is it possible to change things in the "Production Statistics" and the "Trains-Overview" UI? I want to add additional information and dont find a way to manipulate those UIs.