Remove UA styles for h1 in article, aside, nav, section

[zcorpan]

Fixes #7867

• At least two implementers are interested (and none opposed):
  • Gecko
  • Chromium Remove UA style for h1-h6 in section (et. al.) and hgroup #7867 (comment)
  • WebKit Remove UA style for h1-h6 in section (et. al.) and hgroup #7867 (comment)
• Tests are written and can be reviewed and commented upon at:
  • HTML: Remove UA styles for h1 in article, aside, nav, section web-platform-tests/wpt#51673
• Implementation bugs are filed:
  • Chromium: https://issues.chromium.org/issues/394111284
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1885509
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=292765
• Corresponding HTML AAM & ARIA in HTML issues & PRs: N/A
• MDN issue is filed: Suggest specifying font-size and margin-block on h1 mdn/content#37827 and Update "Specifying a uniform font size for h1" mdn/content#39582 (MDN page)
• The top of this comment includes a clear commit message to use.

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

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/rendering.html ( diff )

[domenic]

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[zcorpan]

I think we can land this, see #7867 (comment)

[annevk]

So Chrome will only follow once it's been 100% in Firefox stable for some time and apart from the warning hasn't experimented with this yet? If so I'd like to defer merging to @domenic. We might need a better way to decide these things. The main thing I'm concerned about is wasting cycles of people on the outside who assume it's happening based on a change to the HTML standard when we're in fact not that certain.

[AtkinsSJ]

The main thing I'm concerned about is wasting cycles of people on the outside who assume it's happening based on a change to the HTML standard when we're in fact not that certain.

That's much appreciated!

[mfreed7]

So Chrome will only follow once it's been 100% in Firefox stable for some time and apart from the warning hasn't experimented with this yet?

That's roughly right, yes. We've had the deprecation warnings going for several milestones and haven't heard any issues. But I'd like to wait until this is shipped at 100% for at least a milestone in Firefox before we start the process in Chromium. Having said that, it looks pretty likely to go ahead, at least to me.

[domenic]

We do have a few of these sorts of things recently, where everyone's on board but is unsure on the compat implications. (whatwg/webidl#1465 is another.) My tendency is to be more aggressive about merging, but I'm hearing hesitation from others... so I don't really know where that leaves us.

[zcorpan]

I'm OK with waiting here until another browser has decided to ship. But yeah, it seems we should discuss the meta issue.

[annevk]

Maybe something along these lines:

1. If multiple browsers are landing patches and little fallout is expected, as was the case with escaping < and > in attribute values near the end, let's proceed and align the standard assuming success.
2. If other browsers are wary but supportive, let's wait until one browser has actually shipped the new behavior before aligning the standard. (Which means once Firefox 140 ships we'd land this PR and assume eventual success.)

[mfreed7]

Maybe something along these lines:

1. If multiple browsers are landing patches and little fallout is expected, as was the case with escaping < and > in attribute values near the end, let's proceed and align the standard assuming success.
2. If other browsers are wary but supportive, let's wait until one browser has actually shipped the new behavior before aligning the standard. (Which means once Firefox 140 ships we'd land this PR and assume eventual success.)

+1 to this approach. This (#2) is also roughly what we did for mutation events.

[domenic]

For any following along, I've posted whatwg/sg#253 to attempt to encapsulate the above guidance into the working mode.

[domenic]

Per discussion in #7867 (comment), Firefox has shipped this to stable for 2 releases at 100%. That meets the bar we've discussed above, so I think this is ready to merge.

I'll plan on doing that by Monday Japan time unless more discussion happens in the meantime.

[emilio]

@domenic ping to get this merged? :)