Thanks everybody for your insightful comments. I’m catching up and like the others wasn’t entirely sure about contiguity at first but David’s example and your comments helped to clarify that. I’m still not entirely sure about violation of temporal contiguity: would that refer to when, for example, a diagram is shown on one slide but it is commented on somewhere else? I also wonder whether the actual application of these principles depends on the discipline.
In terms of L2 speakers, I agree that redundancy/modality may need some re-thinking.