Input backend options for UI Toolkit events at runtime.
| Default | The initial configuration on UI Toolkit start up. This is equal to InputSystemCompatibleBackend. This option will use the Input System package is available, and the old Input Manager if not. |
| InputSystemCompatibleBackend | The new Input System compatible backend allows the Input System package to send its input to UI Toolkit directly, removing the need for an UnityEngine.EventSystems.EventSystem in the user scene. This option will use the Input System package is available, and the old Input Manager if not. |
| LegacyBackend | The legacy backend relies on the Input Manager UnityEngine.Input class only and is not compatible with the Input System package. This option will always try to use the old Input Manager. If the Input Manager is not enabled as an active input handler, UI Toolkit runtime events will not work. |