[csswg-drafts] [css-page-3] clarification on whether "page" applies to (and propagates up from) "only-child" block-level elements (#7235)

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

== [css-page-3] clarification on whether "page" applies to (and propagates up from) "only-child" block-level elements ==
In css-page-3 section 8.1, "Using named pages: [page](https://www.w3.org/TR/css-page-3/#propdef-page)", defines its behavior in terms of **whether a box creates a [class A](https://www.w3.org/TR/css3-break/#btw-blocks) break points**.

Specifically, I'm looking at this quote:
> Applies to:  boxes that create [class A](https://www.w3.org/TR/css3-break/#btw-blocks) break points

Taken literally, this excludes block-level boxes that have no siblings.  Strictly speaking, such boxes do not create any Class A breakpoints, by definition (since Class A breakpoints are created **between siblings**; if there no siblings, there are no Class A breakpoints that were created).

Is this exclusion intentional?

This is important, because it impacts whether these elements propagate their `page` value to their parent box; and that impacts whether or not page breaks might get inserted between the parent box and its siblings (if the parent has class A breakpoints).  This is due to the wording here:
> The [page](https://www.w3.org/TR/css-page-3/#propdef-page) property works as follows:
> [...]
> A child propagates its own [start](https://www.w3.org/TR/css-page-3/#start-page-value) or [end page value](https://www.w3.org/TR/css-page-3/#end-page-value) if and only if the [page](https://www.w3.org/TR/css-page-3/#propdef-page) property applies to it.

Taken literally, this implies that an "only-child" block-level element would never propagate its used `page` value to its parent, because the `page` property "does not apply" to the "only-child" element, because it does not create any class A break points.

@fantasai does this make sense and do you recall whether it's intentional that we're excluding propagation from only-child elements here?

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/7235 using your GitHub account


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Received on Tuesday, 26 April 2022 23:28:56 UTC