Added shadow directionality to the dir attribute algorithm

[meyerweb]

Closes #3699. See https://github.com/whatwg/html/issues/3699#issuecomment-951423468 for a summary of what the changes are meant to do.

• [ ] At least two implementers are interested (and none opposed):
  • Apple
  • Google
• [ ] Tests are written and can be reviewed and commented upon at:
  • Tests for directionality and shadow DOM
• [ ] Implementation bugs are filed:
  • Chrome: https://bugs.chromium.org/p/chromium/issues/detail?id=576815
  • Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1722762
  • Safari: https://bugs.webkit.org/show_bug.cgi?id=64861

(See WHATWG Working Mode: Changes for more details.)

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/dom.html ( diff ) /infrastructure.html ( diff ) /rendering.html ( diff )

[domenic]

@tabatkins could you also help review this? We're looking for someone who is more of an expert in layout-type stuff, which the HTML editors aren't :)

[meyerweb]

We should also loop in fantasai, but GitHub doesn’t seem to want to autocomplete her account here.

[fantasai]

Oh, and I might suggest dropping a link directly to https://github.com/whatwg/html/issues/3699#issuecomment-951423468 (and/or copy in its text) into the extended description part of the commit message. This is a pretty confusing area of HTML, and the discussion in 3699 is quite long, so it's probably helpful to have that info easily accessible in the version history.

[meyerweb]

Very interested in feedback from @annevk and @tabatkins, but happy to hear from anyone, on these latest changes from Elika! Hoping to have all feedback in and changes made before the next triage meeting, so that this can be merged and closed.

[tabatkins]

+1 to fantasai's suggested changes. As far as I can tell, they match the intent of her comment and generally describe a good behavior.

[meyerweb]

I believe this is ready to be merged.

[annevk]

There's a couple unresolved questions still. It also seems that this branch has merge conflicts. You want to rebase against main, resolve conflicts, and force push.

Also, I think we should have at least one other person look at this. Perhaps @smaug----?

[fantasai]

Editorial comment: We have a lot of <code data-x="attr-dir">dir</code> attribute is not in a defined state (i.e. it is not present or has an invalid value); can we extract out that parenthetical into a note or something before/after the entire list and not repeat it so many times?

[bkardell]

Closing in favor of an updated and reworked PR https://github.com/whatwg/html/pull/9166