Re: [csswg-drafts] [css-grid-3][masonry] Handling baseline shim for multi-span items in intrinsic track sizing (#13530)

> It should give exactly the same results as in Grid.

@fantasai I'm not sure what you mean by this. In grid, we know item placement up front; in grid lanes we don't, so we apply item contributions into every possible track they could be placed. Ignoring baselines or this issue, we can easily get different track sizing results than grid (unless of course the track sizes are definite up front).

In either case, the baseline shim is part of an item's contribution during track sizing. The question here is how to determine that shim if items that should be in the same shared baseline group end up in different virtual item groups (because they have a different span and/or placement).

As @yanlingwang23 illustrated in her example, items that should be in the same baseline sharing group can end up in different virtual item groups, which means the baseline shim calculation can be incorrect, and thus, the track sizing algorithm will not have accurate item contributions to accommodate baseline alignment.

I would be supportive of going with option 3 given that is more efficient and avoids side effects of the other two options. Although it can produce larger track sizes than needed, we already can produce larger track sizes in grid lanes as a result of the fact that we place every item in every possible position.

I don't think baselines will be a common use case in grid lanes, so option 3 seems like it makes a reasonable trade off to me.

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Received on Friday, 27 March 2026 20:51:19 UTC