Why use binary VM instructions with a VM written in JS instead of just straight binary data? Why does it even need to be instructions in the first place?
It needs to be instructions because the views aren't static. They are reactive. So some of the content is static, some might change due to user interaction. The VM understands this fundamentally and optimizes for that.
I'm not clear on where the logic is needed. Even if there are cells or boxes that need to be a percentage of their parent and/or have min and max sizes etc, that can still just be binary data.
