> It's a system to display text and a couple of images on a 2D plane

And how is that different from a UI framework?

> Almost every single interaction and change requires the browser to recalculate the layout of the entire page and to redraw it.

What UI frameworks don't do this?

> And how is that different from a UI framework?

In none of them text is primary and all other incidental?

> What UI frameworks don't do this?

In which UI framework actions like "set focus on an element" triggers a full page re-layout?

Also, in which UI framework there's even a discussion of "try to not trigger re-paint/re-flow"?

And yes, I know about immediate mode UI where the entire layout is re-calculated every frame. But then they can usually render thousands of elements at 60fps.