Thanks @LeonidS !

I managed to make all that work. Once you understand the logic of the content, it's indeed quite rational and no-nonsense. Being a dev myself, I can guess the architecture of the object-oriented backend used to make it happen.

However, the GUI is not helping and even misleading. Navigating the parents and children attached to each display/form/etc. is cumbersome and needs several tries to get it right even with the doc. This is definitely a place where I would prefer to directly interact with PHP snippets (and read a flat list of commands/declarations) rather than a multi-tray, nested list of widgets that you have to chase through several pages.