Does CSS have any concept of <area>?

[tomhodgins]

If I'm using Intersection Observer and observing the intersection ratio, I'm not sure how this works for non-rectangular elements but I assume it's calculating the total surface area of the element (area = width * height for rectangles), so how would I describe how to apply a style when the observed area is half present:

div::observer {
  observe-intersection-ratio: half ???;
}

• I can think of how I'd describe that as a <number>, 0.5 or .5.

• I can think of how I'd describe it as a <ratio>, 1/2.

• And I can think of how I'd describe it as a <percentage>, 50%, but I'm not sure what percentage type that matches

It's not <length-percentage> because it's not a length. It feels like there should be an <area-percentage> but that would require there to be a concept of <area>. How should we describe this?

[bkardell]

I would think here these would be mapped to thresholds since they map very well to this mental model.. My understanding of this is that it is always based on the clientRects, so, there wouldn't be a concept of non-rectangular things by this definition (I think).