Great to see you are diving in!
The DataSet contains the rows Universal currently has in view, so the current page of data.
Debugging, when you look a the source panel in the developer tools (I’m using Chrome here), you should note that the navigation panel is a tree. And you can traverse down it and actually find you’re own code and put a breakpoint in it.

The same is true for the console. At the top, there is a dropdown that will allow you to find you’re source and select it to see its output;

And updateState should be thought of as an event that happens when the state of the Universal GUI changes in a way where Universal itself would also get a different state. This event is directly linked to the State property. That itself can have 3 states;
- regular (all things are clickable for the user)
- editing (a lot of stuff should be blocked)
- locked (there is an actual model popup over the GUI)
Hope this helps!
Thanks @Sebastiaan Meijerink, didn't know about the ability to select source.