[css-overflow] How does max-lines interact with hidden content?

[Loirooriol]

<div id="a" style="width: 0; max-lines: 2">
  <div id="b" style="max-lines: 1">Lorem ipsum</div>
  dolor
</div>

Due to #b's max-lines: 1, only Lorem is displayed and ipsum is discarded.

But #a has max-lines: 2. Does ipsum still count as one line, and thus dolor is discarded?

[frivoal]

Excellent question. I think we should only count the lines that are actually there, and therefore not count ipsum and not discard dolor. Otherwise:

• We have to fake-layout the discarded content for the sole purpose of counting the lines in it
• We would get the wrong number of lines from the users's point of view.

I think that is actually what the spec says already, since we're only counting line boxes, and ipsum isn't in a line box, but a clarifying note would certainly not hurt.

@fantasai, do you agree?

[Loirooriol]

We would get the wrong number of lines from the users's point of view.

Yes, but this objective is hard to generalize. What if I use max-height: 1lh; overflow: clip instead of max-lines: 1? Visually it would be the same, but now both lines would be counted...

[frivoal]

The "what about lines in overflow:clip` part question solves itself if:

• we decide in [css-overflow] Is the box a scroll container if only one of 'overflow-x' or 'overflow-y' is 'clip'? #1971 that overflow:clip creates a BFC, and
• we decide in #[css-overflow] Which descendants are skipped in max-lines? #2429 that max-lines skips counting lines in descendant BFCs.

I am not expressing either being for or against either of these, but they're dependencies, so we should look into this issue after we look into these.

[frivoal]

Given that we've resolved #2429 to make max-lines skip counting lines in descedant BGCs, but #1971 to say that overflow:clip does not create a BFC, the question remains open for overflow:clip.

I don't think there's any technical reason to make max-lines skip the descendants of overflow:clip, so we could close this as no change. On the other hand, maybe it is counter intuitive that we'd be counting invisible lines.

[heycam]

I agree that overflow: clip shouldn't affect whether a line is counted for max-lines. overflow: clip to me is mostly a visual effect (and I think the name "clip" suggests that too). You can also have lines partially visible when using overflow: clip, another indication that it is working visually rather than fragmenting away content that is overflowing.

[frivoal]

Right. We should close this as no change.

[Loirooriol]

So max-lines: 1 moves the second line to another region and it's not counted, and max-height: 1lh; overflow: clip counts it?

Some clarification would be useful, maybe a note or example.

[anjia]

Yeah, I agree there is no change.

max-lines:1 makes ipsum discarded, because max-lines does the layout.
max-height: 1lh; overflow: clip makes ipsum counted, because max-height does the layout and overflow just does a visual effect.