[csswg-drafts] [css-gaps-1] `overlap-join` with `between` rule visibility (#13697)

kbabbitt has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-gaps-1] `overlap-join` with `between` rule visibility ==
This came up while @oSamDavis @jav099 and I were discussing implementation of `rule-inset: overlap-join` which we resolved to add in #13137.

The intent of that value is to give authors an easy way to join decoration segments neatly with each other. Where two perpendicular segments meet, it's equivalent to `rule-inset: calc( -(50% + crossing_decoration_width/2) )` or in English, "halfway into the intersection, plus enough to cover the remaining width of the crossing decoration":

<img width="219" height="223" alt="Image" src="https://github.com/user-attachments/assets/8e3e640b-cd15-4433-a1db-e17112d15983" />

But there's an edge case that arises when this value is used with `rule-visibility-items: between`. That value causes us to paint decorations only where there are items on both sides of the gap. The `calc()` treatment above would lead to decorations still protruding into intersections even when there's no crossing decoration for it to join:

<img width="757" height="382" alt="Image" src="https://github.com/user-attachments/assets/44231884-6cc1-45a3-bc51-4a7c99a9ae0d" />

My initial reaction was that we should not do that and instead leave such decorations flush with the adjacent items, which would be equivalent to an inset of `0` at those specific endpoints. But I'm somewhat worried that behavior might be too magical. What do folks think?


Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13697 using your GitHub account


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Received on Friday, 20 March 2026 23:19:08 UTC