The proximity must show through when rendered to the user. I think the requirement in the area of this checkpoint could stand to be clarified. Ensure that the user has access to relationships between elements. Yes, then line by line explanation in the techniques document. Tables are so important that it's worth saying it directly.
Content includes metadata.
Yes, specialization of 2.1. Not sure if proposal is specific enough. And this is critical in the table area. It seems to hold some info not in 2.1. Priorities in WCAG may be disputed there as well.