This is only very basic help. You may insert/modify your Widgets within the above widgetTable. Once there is a valid x,y,w,h entry the rectangle with text will be shown. The type of the widget is defined by name.
You can "Move Widget" or "Scale Widget" with the arrow buttons. If name == Diagram then pvCairoTestDiagram(cr,x,y,w,h); from libpvcairo will be shown (example for a real widget).
You may click "Save Table" to store widgetTable.csv to disk. When you click "Show Mask2" the deployed design will be shown in that mask.