[resize-observer] Why does ResizeObserver not fire on non-replaced inline elements?

[trusktr]

The resize-observer spec says

Observations do not fire for non-replaced inline Elements.

I am guessing this is because such elements are split into pieces (rows).

I see that the latest ResizeObserver spec allows it to return an array of sizes when content is split across columns. Based on this, it seems feasible to also have it give us an array of the sizes of the pieces of a non-replaced inline element's rows.

Or it could just give us the size of the bounding box, but this would make the use cases more limited, though the limited use cases could still be useful.

Is it simply that nothing has been decided on how to handle multiple pieces of a non-replaced inline element?

[Loirooriol]

getClientRects() has no problem returning the actual sizes of a non-atomic inline, so I think that ResizeObserver should just stop pretending that the size is zero and just populate the arrays with the fragment sizes.

It may be fine (or even required by compat) to keep contentRect being an empty rect or something special, but populating borderBoxSize, contentBoxSize and devicePixelContentBoxSize as normal seems useful.