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[css-break] Clarify definition of widow and orphans. #1823

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frivoal opened this Issue Sep 18, 2017 · 2 comments

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frivoal commented Sep 18, 2017

The section on orphans, widows in css-break says this:

The orphans [resp. widow] property specifies the minimum number of line boxes in a block container that must be left in a fragment before [resp. after] a fragmentation break.
[...]
If a block contains fewer lines than the value of widows or orphans, the rule simply becomes that all lines in the block must be kept together.

While it is clear to me what this is supposed to do if the block container only contains inline-level content, the meaning is less obvious when it has block level descendants.

Take this example:

<style>div {  widows: 3; }</style>
<div>
  <p>
    line 1<br>
    line 2
  </p>
  <p>
    line 3<br>
    line 4
  </p>
</div>

https://www.w3.org/TR/css-display-3/#block-container is pretty clear that block containers can either contain online inline-level boxes or block level boxes, but the terminology isn't 100% clear (as far as I can tell) about whether a block container that contains block level elements can still be said to have "line boxes in it” (indirectly, via its block level children that themselves are block containers containing inlines), or if it should be considered not to have "line boxes in it”.

  1. If the above spec prose is to be interpreted as applying only to line boxes that are direct children of block containers that establish an inline formatting context, then widows:3 forbids breaks inside both <p>, but does not prevent breaks between line 2 and 3:

If a block contains fewer lines than the value of widows or orphans, the rule simply becomes that all lines in the block must be kept together.

The block has no (direct) lines, there's nothing to keep together, and the break is allowed.

  1. If the above prose is meant to apply to line boxes that are descendants of the block container, at any depth (but presumably within the same BFC), the the break between line 3 and 4 would be forbidden.

I think the spec intends the first one. If that is the case, I suggest clarifying by changing the "Applies to" line to "Block container boxes that establish new inline formatting contexts" and/or by adding the following prose: “The widows and orphan properties have no effect on block container boxes that contains only block-level boxes”.

@frivoal frivoal added the css-break-3 label Sep 18, 2017

@frivoal frivoal self-assigned this Sep 18, 2017

@frivoal frivoal added the Agenda+ label Sep 26, 2017

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The Working Group just discussed Clarify definition of widow and orphans., and agreed to the following resolutions:

  • RESOLVED: We want the interpretation to be the first option in issue 1832
The full IRC log of that discussion <dael> Topic: Clarify definition of widow and orphans.
<dael> github: https://github.com/w3c/csswg-drafts/issues/1823
<dael> florian: I realized there was ambig. in the definition. [reads from spec]
<TabAtkins> (this is probably related to how line-clamp needs to work)
<dael> florian: The reaosn I think this is ambig is that line boxes in a block container isn't clear if they must be direct children or indirect descendants. I don't think it intends indirect. If it did if you had a div with two paragraphs with widows and you'd end up glueing them together.
<dael> florian: I think we clarify that we only mean direct children.
<dael> TabAtkins: THe usual intent is to set on a page box, correct?
<dael> fantasai: No, this is about paragraphs, not page boxes.
<dael> fantasai: The definion is about block containers with line boxes. You must have a min number of line boxes in each fragment. I thought that was clear, but if it's not we can clarify. This is only line boxes. And property inherits. If there's a block in your block that's a child. But you can break at the boundary.
<dael> fantasai: You can always say break after at a block. Usually that's not an issue because a block inside a block is sep. content.
<dael> astearns: Intent is closer to v1 in the example.
<dael> dauwhe: v2 in the example would be bad.
<dael> dauwhe: abs v1
<dael> florian: I think there are rare cases where you might want v2 but you should control that seperately.
<dael> astearns: If there is a case where you want v2 you would structure html differently.
<dael> florian: prob
<dael> dauwhe: Or the thing you're trying to fix would not be a widow.
<fantasai> s/a child/a child to which widows can also apply/
<dael> florian: I think we can address the rarity of v2 another time if we can resolve on meaning v1. An editor can change or I send a PR.
<dael> astearns: I'm not certain an edit is req but that may be because I"m interp in a particular way.
<dael> Bert: If florian finds it's unclear it prob is. I didn't imagine it in another way, but if florian reads it another way it needs clarification
<dael> astearns: florian you'll do a PR to fix the wording?
<dael> florian: Yes
<dael> astearns: Okay, we'll then look at wording and decide to take the change
<dael> florian: Or resolve on intent
<dael> astearns: Resolve that we want the interpretation to be the first one in your client and then you write the pull. Obj?
<dael> TabAtkins: Nope.
<dael> RESOLVED: We want the interpretation to be the first option in issue 1832
Member

css-meeting-bot commented Oct 11, 2017

The Working Group just discussed Clarify definition of widow and orphans., and agreed to the following resolutions:

  • RESOLVED: We want the interpretation to be the first option in issue 1832
The full IRC log of that discussion <dael> Topic: Clarify definition of widow and orphans.
<dael> github: https://github.com/w3c/csswg-drafts/issues/1823
<dael> florian: I realized there was ambig. in the definition. [reads from spec]
<TabAtkins> (this is probably related to how line-clamp needs to work)
<dael> florian: The reaosn I think this is ambig is that line boxes in a block container isn't clear if they must be direct children or indirect descendants. I don't think it intends indirect. If it did if you had a div with two paragraphs with widows and you'd end up glueing them together.
<dael> florian: I think we clarify that we only mean direct children.
<dael> TabAtkins: THe usual intent is to set on a page box, correct?
<dael> fantasai: No, this is about paragraphs, not page boxes.
<dael> fantasai: The definion is about block containers with line boxes. You must have a min number of line boxes in each fragment. I thought that was clear, but if it's not we can clarify. This is only line boxes. And property inherits. If there's a block in your block that's a child. But you can break at the boundary.
<dael> fantasai: You can always say break after at a block. Usually that's not an issue because a block inside a block is sep. content.
<dael> astearns: Intent is closer to v1 in the example.
<dael> dauwhe: v2 in the example would be bad.
<dael> dauwhe: abs v1
<dael> florian: I think there are rare cases where you might want v2 but you should control that seperately.
<dael> astearns: If there is a case where you want v2 you would structure html differently.
<dael> florian: prob
<dael> dauwhe: Or the thing you're trying to fix would not be a widow.
<fantasai> s/a child/a child to which widows can also apply/
<dael> florian: I think we can address the rarity of v2 another time if we can resolve on meaning v1. An editor can change or I send a PR.
<dael> astearns: I'm not certain an edit is req but that may be because I"m interp in a particular way.
<dael> Bert: If florian finds it's unclear it prob is. I didn't imagine it in another way, but if florian reads it another way it needs clarification
<dael> astearns: florian you'll do a PR to fix the wording?
<dael> florian: Yes
<dael> astearns: Okay, we'll then look at wording and decide to take the change
<dael> florian: Or resolve on intent
<dael> astearns: Resolve that we want the interpretation to be the first one in your client and then you write the pull. Obj?
<dael> TabAtkins: Nope.
<dael> RESOLVED: We want the interpretation to be the first option in issue 1832
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frivoal commented Oct 12, 2017

@frivoal frivoal added the Agenda+ F2F label Nov 3, 2017

@astearns astearns removed the Agenda+ F2F label Nov 6, 2017

@frivoal frivoal closed this in #1864 Nov 6, 2017

fantasai added a commit that referenced this issue Aug 23, 2018

[css-break-3] Apply clarification requested in #1823, widows/orphans …
…apply to block containers that directly contain line boxes (only)
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