Treating it declaratively is what I initially thought it would be, but what happens when the user needs to tweak the layout for some unique requirement? My guess is what would happen is it would force them to completely eject from your declarative approach, similar to how if you build software on low-code tools, and need to tweak something, you typically have to completely eject. The low-code thing has no understanding to render your custom thing.

Idk maybe this can be solved, but seems problematic to describe layouts like SQL then rely on query planners to deliver the perfect execution.