#7784 details how rendering should be suppressed during a transition. We also need to ignore user input (irrespective of how rendering is suppressed) in this state. That's because the visual state of the Document displayed to the user doesn't align with the DOM state.

Note that the user agent may need to dispatch synthetic events to ensure the input stream observed by the developer makes sense. For instance, the user puts their finger down when rendering is suppressed which causes a touchstart event. If rendering is unsuppressed while the user finger is still down script would directly see a touchmove event. It makes sense to dispatch a synthetic touchstart event in this case. But this detail can be left up to the user agent.