One way to visualize the flow of the game screens would be to picture a finite state machine of all the screens and how they trigger each other's appearance. However, while that works and is logically accurate, we broaden the concept of the active state into a stack.
Note
Finite State Machine (FSM): While this is a well known concept across the world of computation, we will shortly describe the state machine as a collection of states that ensures that only one state is active at any given time. The transition of the current state into a new one is always triggered by a condition or a timer. So, for any state of the FSM, there will be a determined set of triggers that will activate new states when appropriate.
Now, turning the active state into a stack essentially means that the current state is not an individual piece anymore, but rather a stacked group of pieces, when necessary. Usually, the state mechanism will only have one state active at a time, and while this is true...