'2D Viewport To World' example doesn't follow API docs recommendation

[AccessViolation95]

How can Bevy's documentation be improved?

https://bevyengine.org/examples/2d-rendering/2d-viewport-to-world/

This example adds an input handling system like so: .add_systems(FixedUpdate, controls).
It uses the FixedUpdate schedule for this. However, the documentation for the Update schedule suggests that it should be used for input handling functions instead. Furthermore, the FixedUpdate documentation links to Update for "examples of systems that should not use this schedule," so this might cause some confusion.

I'm assuming the API documentation is correct but I don't know whether the example is. I suggest one of these changes:

• If the example's choice of schedule for this system is indeed the preferred option, it should explain why it chooses to deviate from the recommended usage of the schedules per the API docs in a code comment.
• If the example's choice of schedule for this system is incorrect or inconsequential, it should follow the recommendations of the API docs for consistency.

[janhohenheim]

IMO Update should not contains this hint, as it is a footgun when doing physics in fixed update schedules. This would cause input to lag behind by a frame or more, depending on whether the input is accumulated or not, leading to unresponsive movement!
Better to direct the users to PreUpdate or, better yet, RunFixedMainLoop, in_set(RunFixedMainLoopSystem::BeforeFixedMainLoop), which has a really really intimidating name unfortunately.

See our other documentation which already points away from Update:

• https://bevyengine.org/examples/movement/physics-in-fixed-timestep/
• https://docs.rs/bevy/latest/bevy/prelude/enum.RunFixedMainLoopSystem.html#variant.BeforeFixedMainLoop

Note that I think it's totally fine to leave inputs in Update for examples. No need to overcomplicate things there! I would just wish the documentation wouldn't let users run into a footgun without warning 😅