[css-scroll-snap-1] Clarify which writing-mode is used for scroll-snap-align, scroll container or snap position element?

[hiikezoe]

I've been thinking it's for sna-position element, but jfkthame thinks it's for scroll container.

Here is an example that the writing-mode for snap position element differs from scroll container's value;
https://codepen.io/anon/pen/vMyRVV

[fantasai]

Good question! I'm surprised we didn't spec this interaction. The box alignment properties use the container's writing mode, so I think it makes sense here to use the scroll container's writing mode (i.e. the writing mode of the alignment container). https://www.w3.org/TR/css-align-3/#positional-values

[fantasai]

(If in the future we want to use the element's own writing mode to resolve the logical values, we can add self-start/self-end keywords.)

[tabatkins]

Yes, given the container properties definitely use the container's writing mode, I think it's most useful to default the descendant's properties to use the same.

[majido]

I agree with the proposed solution. It makes sense to be consistent with box alignment properties and it feels most natural to me.

Having said that I don't think Chromium current implementation is correct. Here is a slightly modified version of the original example where I gave second container direction: rtl which I take it that with the proposed solution should interpret start as aligning the snap area to the right side of the scroll container. Which we don't at the moment. I will file a chromium bug for this.

[hiikezoe]

Having said that I don't think Chromium current implementation is correct. Here is a slightly modified version of the original example where I gave second container direction: rtl which I take it that with the proposed solution should interpret start as aligning the snap area to the right side of the scroll container. Which we don't at the moment. I will file a chromium bug for this.

Just FYI, Firefox has also the issue on the example. I filed bug https://bugzilla.mozilla.org/show_bug.cgi?id=1546835.

[tabatkins]

Agenda+ to confirm the conclusion.

[css-meeting-bot]

The CSS Working Group just discussed scroll-snap align vs writing-mode, and agreed to the following:

• RESOLVED: use the writing mode of the container

The full IRC log of that discussion

<fantasai> Topic: scroll-snap align vs writing-mode
<emilio> thanks dbaron :)
<fantasai> github: https://github.com//issues/3815
<florian> fantasai: the question is which writing-mode is used for scroll-snap-align:start and the container and the containee have different writing-modes
<florian> fantasai: the proposal is to use the writing-mode of the container
<florian> fantasai: because that's what we do for alignment properties
<florian> fantasai: we also have the self-start and self-end keywords if you want that
<florian> fantasai: that made more sense to align all things the same side in a single container
<florian> fantasai: this proposal is motivated by consistency with that
<florian> jen: sounds reasonable to me
<florian> plinss: me too. objections?
<florian> RESOLVED: use the writing mode of the container
<florian> jen: I wanted to thank the group for the great hard work to make specs understandable.
<bdc> (fully agree with jen)
<florian> jen: I have been at conferences, and after strugling with other specs, I really want to voice appreciation for doing it well as this group does.