Handling with nested IF's at screen level could be a headache. Here are some suggestions to make it easy to understand where you are.
"Then" or "Else" parts
When you have nested IF's in a Web Screen, it might be dificult to know whether you're in the "then" or "else" part.
It would be nice if these parts could have borders with different colors, or some other way to tell one from another.
IF widgets at screen frows could have labels just like in action flows
Breadcrumbs / Widget selector
Widget selector should also help to understand whether you're in the "then" or "else" part. Putting the mouse over an IF wigdet should present the widget's label, name or condition