WHATWG updates for 2026

[JohnRiv]

For the WHATWG Review Drafts we reference, we should update to more recent versions if they exist and are supported by the major browsers.

• DOM Standard
• Fetch Standard
  • Currently includes 4 exceptions to review as well
• Fullscreen API Standard
• HTML Standard
  • Currently includes 5 exceptions to review as well
• Notifications API Standard
• WebSockets Standard
• XMLHttpRequest Standard

Worth noting that https://urlpattern.spec.whatwg.org/ is a new WHATWG standard, but https://wpt.fyi/results/urlpattern shows it’s not fully supported

As we have done in years past (2025, 2024, 2023, 2022, 2021, 2020, 2019), this issue will track that work.

[JohnRiv]

Based on the same dates we've done in the past, the potential set for WMAS2026 would be:

• DOM: June 2025 - Link to diff from June 2024 to June 2025
• Fetch: December 2025 - Link to diff from December 2024 to December 2025
• Fullscreen API: January 2026 - Link to diff from July 2024 to January 2026 (note the January 2026 Review Draft is the first January publication since January 2023; the previous two years had no January Review Drafts)
• HTML: January 2026 - Link to diff from January 2024 to January 2026
• Notifications API: January 2026 - Link to diff from January 2025 to January 2026
• WebSockets: no new Review Draft since the September 2023 publication - Link to diff from September 2023 to HEAD
• XMLHttpRequest: August 2025 - Link to diff from February 2024 to August 2025 (note the August 2025 Review Draft is the first draft published since the previous February 2024 Review Draft)

[JohnRiv]

Research for above, plus the existing exceptions for Fetch and HTML:

• ❌ DOM - Essentially 2 new features were added, and both have WPT tests that fail for at least 1 browser, so we should leave it at the June 2024 draft:
  • moveBefore() - a state-preserving atomic move API
    • https://dom.spec.whatwg.org/review-drafts/2025-06/#dom-parentnode-movebefore
    • https://wpt.fyi/results/dom/nodes/moveBefore/
    • Chrome and Firefox pass, Safari fails (0/50 tests pass in Safari stable)
  • Scoped Custom Element Registries
    • https://dom.spec.whatwg.org/review-drafts/2025-06/#element-custom-element-registry
    • https://wpt.fyi/results/custom-elements/registries/
    • Chrome and Safari pass, Firefox fails (0/5 tests pass in Firefox stable)
• ⚠️ Fetch - 1 new feature commit has WPT tests that fail for at least 1 browser:
  • ❌ fetchLater() - deferred fetching API
    • https://wpt.fyi/results/fetch/fetch-later/
    • Chrome passes most tests (38/47), Firefox and Safari fail (2/47 each)
  • also the 4 current exceptions need to remain:
    • ❌ Sec-Purpose: prefetch header - still fails in Safari (0/3), Chrome partial (2/3)
    • ❌ "json" destination for JSON modules - Safari 27/30, Chrome/Firefox 28/30; minor remaining failures
    • ❌ Setting the proper realm of result of Response arrayBuffer() - still fails in Safari (0/1)
    • ❌ Partition Blob URL fetches by Storage Key - mixed results across browsers
• ✅ Fullscreen API - only bug fixes, no new features
• ❌ HTML: the vast majority of the new features added across both years aren't fully supported, so we should leave HTML at the January 2024 version:
  • From January 2024 to January 2025 (previously identified in WMAS2025 research):
    • media element pseudo-classes - Chrome does not support (proposed for Chrome 152); Firefox and Safari pass
      • https://wpt.fyi/results/css/selectors/media/media-loading-state.html
      • https://wpt.fyi/results/css/selectors/media/media-playback-state.html
      • https://wpt.fyi/results/css/selectors/media/sound-state.html
    • Allow elements with display:contents to be focusable - all browsers fail (0/1)
      • https://wpt.fyi/results/css/css-display/display-contents-focusable-001.html
    • back/forward cache NotRestoredReasons API - Firefox and Safari fail (0/12 each)
      • https://wpt.fyi/results/performance-timeline/not-restored-reasons
    • pageswap event - Firefox fails (2/23)
      • https://wpt.fyi/results/html/browsers/browsing-the-web/history-traversal/pageswap
    • writingsuggestions="" attribute - Firefox and Safari fail (6/80 each)
      • https://wpt.fyi/results/html/editing/editing-0/writing-suggestions
    • autocorrect attribute - Chrome fails (1/9); Firefox and Safari pass
      • https://wpt.fyi/results/html/editing/editing-0/autocorrection
    • popover=hint - Firefox (1/7) and Safari (2/7) fail
      • https://wpt.fyi/results/html/semantics/popovers/popover-types-with-hints.html?label=master&label=experimental&aligned
    • dialog closedby="" and requestClose() - Safari fails
      • https://wpt.fyi/results/html/semantics/interactive-elements/the-dialog-element/dialog-closedby.html
      • https://wpt.fyi/results/html/semantics/interactive-elements/the-dialog-element/dialog-requestclose.html
  • From January 2025 to January 2026 (new for WMAS2026):
    • commandfor & command attributes (invoker commands) - Chrome shipped (135), Firefox and Safari have mixed support per WPT
    • customizable <select> - Chrome only; Firefox and Safari fail (6-7/175 pass vs Chrome 66/175)
      • https://wpt.fyi/results/html/semantics/forms/the-select-element/customizable-select/
    • Scoped Custom Element Registries - Firefox fails (follows DOM pattern)
    • moveBefore() integration - Safari fails (follows DOM pattern)
    • :heading and :heading() pseudo-classes - no browser support yet
    • headingoffset & headingreset attributes - no browser support yet (Chrome "In development")
    • speculation rules prefetch - Chrome mostly passes, Firefox and Safari mostly fail
      • https://wpt.fyi/results/speculation-rules/
    • Origin API - very new, minimal WPT coverage
    • ImageData Float16Array support - no WPT data found
    • CanvasColorType (float16) - Chrome "No active development" per chromestatus
    • focus-without-user-activation permission policy - all browsers fail most tests (3/11 pass each)
• ⚠️ HTML previous exceptions:
  • ❌ CSS module scripts - Firefox now passes (15/15), but still not supported by Safari (2/15 pass)
  • ✅ The hidden=until-found HTML attribute and the beforematch event - all 3 browsers now pass at WPT
  • ✅ Navigation API - Baseline 2026
  • ⚠️ CloseWatcher - Firefox now passes (65/65), but Safari still fails (6/65) per WPT & MDN
  • ❌ showPicker() support for <select> elements - Chrome and Firefox now support it, but Safari still behind a flag per MDN
• ✅ Notifications API
• ✅ WebSockets
• ✅ XMLHttpRequest