[csswg-drafts] [css-inline-3] leading-trim through to descendant line boxes (#5237)

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

== [css-inline-3] leading-trim through to descendant line boxes ==
The current definition of `leading-trim` relies on the concept of “first formatted line”. This was done for two reasons:
- it drills down through unstyled block boxes, which is helpful to the author and absolutely necessary given the way we generate anonymous block boxes
- it correctly aborts on nested formatting contexts, replaced elements, etc.

However, it might be a bit too aggressive. Consider

```
  <section style="leading-trim: start">
     <div class="warning" style="border: solid 10px; padding: 0.2em">...</div>
     <p>Whatever normal paragraph.</p>
  </section>
````

The .warning would probably be a bit surprised if the section trimmed its half-leading when it didn't request such trimming itself.

I think we might want to borrow the logic from margin collapsing, and not drill into boxes with non-zero padding/border. Whether or not the margins could have collapsed seems closely related to whether or not this block’s own content edge is adjacent to its descendant's first/last line box and therefore whether it should be controlling the leading on that line.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5237 using your GitHub account

Received on Thursday, 18 June 2020 05:35:08 UTC