Re: [csswg-drafts] [css-break] Clarify the expections of monolithic boxes that fits but has descendants which overflow (#6056)

Would be great to have this clarified. We should revert that change in Blink if it's the wrong interpretation, or even just for the sake of interop.

Here's some more input to the discussion, which is somewhat related, although in this case it's about a *non-monolithic* box that has monolithic overflow. We have this test in Chromium:
https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/fast/multicol/tall-line-in-short-block.html;l=1;drc=77578ccb4082ae20a9326d9e673225f1189ebb63

It passes in Gecko, EdgeHTML, and legacy Blink, but not with LayoutNGBlockFragmentation (that feature is tracked by http://crbug.com/829028).

This test passes for various reasons in various browsers, but Gecko seems to have the most reasonable reason. It goes something like this: If the containing block has a specified block-size (or max-block-size or whatever) that would fit in the current fragmentainer, fit the first piece of monolithic content (such as a line box) in the current fragmentainer as well, even if it overflows the fragmentainer.

```html
<!DOCTYPE html>
<style>
  .multicol {
    columns: 2;
    column-fill: auto;
    height: 150px;
    line-height: 20px;
    column-rule: solid;
    orphans: 1;
    widows: 1;
    background:yellow;
  }
  .filler {
    height: 100px;
  }
  .linecontainer {
    height: 20px;
  }
  .tall {
    display: inline-block;
    width: 100px;
    height: 100px;
    background: blue;
  }
</style>
<p>There should be a blue square in the first column, and the word "second" in
  the second column.</p>
<div class="multicol">
  <div class="filler"></div>
  <div class="linecontainer">
    <div class="tall"></div><br>
    second
  </div>
</div>
```

fast/multicol/tall-line-in-short-block.html was added because Google Docs depended on that behavior, and I believe that's still the case. But is this valid? And why? Why shouldn't we push .linecontainer to the next column, where everything would fit?

cc @fantasai @atanassov 

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Received on Tuesday, 26 October 2021 09:46:09 UTC