Add oncontentvisibilityautostatechange

[vmpstr]

The contentvisibilityautostatechange event was added in CSSWG:
https://www.w3.org/TR/css-contain-2/#content-visibility-auto-state-changed

An issue was raised that rightly points out that oncontentvisibilityautostatechange should also be added in line with design principles

This PR does this.

• At least two implementers are interested (and none opposed):
  • Blink supports this
  • Gecko ...
  • WebKit ...
• Tests are written and can be reviewed and commented upon at:
  • https://wpt.fyi/results/css/css-contain/content-visibility?label=master&label=experimental&aligned&q=content-visibility-auto-state
• Implementation bugs are filed:
  • Chromium: NA
  • Gecko: NA
  • WebKit: NA
  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): NA
  • Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): NA
• MDN issue is filed:
  • https://developer.mozilla.org/en-US/docs/Web/API/Element/contentvisibilityautostatechange_event
• The top of this comment includes a clear commit message to use.

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

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/dom.html ( diff )
/indices.html ( diff )
/webappapis.html ( diff )

[vmpstr]

/cc @Loirooriol

[Loirooriol]

This feature is implemented in all major browsers

Blink only seems to implement the IDL attribute, not the content attribute. Gecko doesn't seem to implement either.

Tests are written

These tests don't seem to cover oncontentvisibilityautostatechange as an IDL or content attribute.

[vmpstr]

Tests are written

These tests don't seem to cover oncontentvisibilityautostatechange as an IDL or content attribute.

I landed some changes to https://wpt.fyi/results/css/css-contain/content-visibility/content-visibility-auto-state-changed.html?label=master&label=experimental&aligned&q=content-visibility-auto-state to use the IDL and content attribute

This feature is implemented in all major browsers

Blink only seems to implement the IDL attribute, not the content attribute. Gecko doesn't seem to implement either.

I meant the ContentVisibilityAutoState change event, but I can see how the intent of the question is specific to the spec change, not to the feature that has these attributes.

/cc @emilio @nt1m to see if there is support

[emilio]

Seems fine if we want to keep doing on* attributes? I always found them a bit of an antipattern. Have we done this for other recent events?

[vmpstr]

It's part of the design principles right now: https://w3ctag.github.io/design-principles/#always-add-event-handlers so I figured it's still a pattern that we encourage. If that's not the case, then we should probably change the design principles and figure out if anything needs to be done with the existing on* attributes. I don't have a strong opinion either way

[domenic]

Yep, we don't want to remove this useful functionality for new events :)

[domenic]

So actually we should remove this:

• https://drafts.csswg.org/css-contain-2/#eventdef-element-contentvisibilityautostatechange already defines the event; we shouldn't have multiple such <dfn>s in the ecosystem.

• The table says "The following table lists events fired by this document, excluding those already defined in media element events and drag-and-drop events.". I'm not sure this is followed perfectly, but we should probably follow it.

This means we'll add an xref to the definitions section pointing to https://drafts.csswg.org/css-contain-2/#eventdef-element-contentvisibilityautostatechange .