As you're typing them they're in a live editing preview mode, but when you press enter they get applied "permanently".
(...) you don't have to hit enter or a button to make it execute, and you don't have to undo if it didn't do what you wanted it to. The code is continuously parsed and interpreted as it is edited (as long as it is valid). The function-invocations register themselves with the editor UI, which draws these visualisations and keeps state for them as long as the editing session exists and the function invocation is not removed. This lets the user tweak the code and make sure it works, as well as tweak the selections etc. Once the user is happy with the result, they can commit the changes.