Clarify step 4.3 of adoption agency algorithm

[stasoid]

Fixes #9559

• At least two implementers are interested (and none opposed):
  • Already matches Chromium, WebKit
  • Gecko
• Tests are written and can be reviewed and commented upon at:
  • Add test for AAA step 4.3 html5lib/html5lib-tests#197
• Implementation bugs are filed:
  • Chromium: no need
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=2049083
  • WebKit: no need
  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): no need
  • Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): no need
• The top of this comment includes a clear commit message to use.

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

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/parsing.html ( diff )

[annevk]

The Participation Agreement requires the use of your full name. You can correct it at https://github.com/whatwg/participant-data/blob/main/individuals.json.

[stasoid]

Done: whatwg/participant-data#90