For example, when your mouse is over a button (known as the rollover state), someone has to show what this is going to look like. But it also gets a lot more complex because some pages have multiple actions that happen during a click, rollover, after a click. These can be things like notifications to the user, modal boxes (popups), and other changes to the ‘view’ of the page based on actions of users. This list is just the a small subset of the number of states that have to be considered by UX designers. They must consider these same states on every device type, screen size, input system (mouse, keyboard, screen reader, gesture, touch-system, etc.), and all of this paired with accessibility compliance.