# Immersive vs Fullscreen

Immersive mode and Fullscreen mode is a similar concept in Chromebook but slightly different.
Immerisve mode hides the top header and button bar to allow users have an immersive experience.
Full screen mode on the other hand shows a window on fullscreen.

In most cases, immersive mode and fullscreen mode have the state, both enabled or both disabled.
However there are several cases where one of them is enabled and the other is disabled.
Let's check such case.

## How it behaves
To summarize in the figure, it works like this:
| | Immersive | No immersive |
| -------- | -------- | -------- |
| Fullscreen | Usual immersive fullscreen | Locked fullscreen / Kiosk |
| No fullscreen | non tabstrip on tablet mode | normal window |

### Why not immersive
Locked fullscreen is the fullscreen where the user is not allowed to exit. This is used for education purpose. For example, the teacher gives a test to students by Google Form and the teacher don't want students to use Google Search nor other cheeting. In such case, the teacher provides students a quiz with LockedFullscreen so that students won't be able to exit until the test ends.
Usually, we aim to allow users to do whatever they want, so when the window is fullscreen we must give a way to exit it. Imemrsive mode allows user to use captions and observers tab list by swiping down gesture, so immerisve mode should be enabled together with fullscreen. However, the above case (teacher and student) is one of the exceptions, we don't want to allow features to users. So we disable immersivde mode not to give a hacky way to exit.

Kiosk app is also in this group, but this is simply because Kiosk app does not yet support immersive feature. (Not sure whether it will be supported in the future).

### Why not fullscreen
Non tabstrip window with tablet mode is the only example where it's immersive but not fullscreen.
The reason is very simple, because it's not fullscreen.

Immersive mode implies that the top header is hidden.
As for non tabstrip window, there is nothing useful on top. Tabstrip window shows urls, extensions and so on which are useful. But non tabstrip window only shows a caption such as close button, maximize button and minimize button.
These buttons are not needed especially in the tablet mode, so it's natural that thoes are hidden. On the other hand, it's not necesaraly fullscreen. The window can be snapped (occupies half of the screen). Still we want to hide the toolbar so it's marked as immersive but not fullscreen.