Re: [csswg-drafts] [css-grid-3][masonry] Baseline alignment in the masonry axis (#9530)

> we think it makes sense to use the highest first baseline and lowest last baseline, which would match how multicol calculates a first/last baseline

One clarification here:  I think we should restrict the search to only consider the {first,last} item in each track (or the items in the {first,last} tracks themselves, in the opposite axis).

For example, consider a masonry layout with the following terrible-pseudo-code, and suppose we're trying to establish the masonry container's last-baseline (in order to lay it out it in some external formatting context):
```
<masonry style="masonry with two roughly equal columns">
  <div style="limited height, giant font-size">A</div>
 <div style="medium font-size">B</div>
 <div>C</div>
```
Let's say that^ markup renders like this:

<img width="1920" height="1080" alt="Image" src="https://github.com/user-attachments/assets/579f0d8b-4c9e-418a-a962-ec32926674e8" />

What should we use for the masonry container's last-baseline in this example?

Intuitively, I'd expect us to derive the masonry-container's last baseline by comparing "C" and "B" (the last item in each masonry-column), and we should choose the one with the further-down baseline (which in this case is "C").  This is an interesting case because **technically item "A" has an even-lower baseline** since its text is giant and overflows beyond even the bottom of the "C" item; so if we were strictly saying to use "the lowest last-baseline [of *all* the items]" then we'd use that.  But I don't think we want to sign up for analyzing *every* item to find which one has the lowest last-baseline, right?

(I suspect this is the right thing to do for compat with multi-col, as well, but I haven't actually tested.)

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Received on Tuesday, 19 August 2025 18:10:36 UTC