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Re: [csswg-drafts] [css-contain-2] Clarify whether content-visibility: auto subtree elements are visible in accessibility (#5857)

From: Alice via GitHub <sysbot+gh@w3.org>
Date: Mon, 11 Jan 2021 22:54:12 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-758275810-1610405650-sysbot+gh@w3.org>
It would be worth hearing from AT users and other experts on this.

My sense is that the actual user impact of exposing `visibility: hidden` and `display: none` elements (including `<script>` and `<style>` elements) inside `content-visibility: auto` areas to AT will be minimal.

Firstly, I'm imagining it will typically be used on blocks which contain only content - scripts and styles would not tend to be in content which should be rendered on-demand.

Secondly, even if they are in that content, they aren't going to be exposed to users of AT while they're not in or near the visible viewport, because AT doesn't typically provide a way to explore off-screen content in depth, since a majority of users of AT can access the visible content in some way.

The only scenario I can immediately think of where it might be an issue for users is AT find-in-page, which could find content inside of offscreen `<script>` or `<style>` elements, cause them to be scrolled into view, and thus cause their styles to be resolved and those elements to be hidden.

I _think_, given the unlikelihood of this actually happening frequently, it's a reasonable trade-off against the other options we could think of, namely:

- resolve style for all `content-visibility: auto` elements if AT APIs are being accessed, or
- the current implementation, which effectively doesn't expose `content-visibility: auto` elements (including headings and landmarks) to AT (since they are exposed as "hidden", analogous to how `aria-hidden` regions are exposed).

I guess a final option might be to _only_ expose nodes matching a safelist of computed roles, but that sounds like a bit of a can of worms potentially.

@cookiecrook any thoughts? Anyone else to tag in?

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