whatwg/html

* Introduce new link loading infrastructure, specifically algorithms to
  fetch and process linked resources that are overridable by the
  individual link types. This replaces the previous "obtain the
  resource" algorithms with something more structured and rigorous.
* Specify the order in which style sheets are removed, created/added,
  their corresponding load/error events are fired, and scripting is
  unblocked from a loading style sheet.
* Replace "style sheet done" flag with Document's "script-blocking style
  sheet counter", which works in tandem with the "contributes a
  script-blocking style sheet" conditions, which replaces the definition
  of "a style sheet that is blocking scripts".
* Change <link> load/fire events to be fired from tasks queued on the
  networking task source, instead of the DOM manipulation task source.
* Handle much of what #3544 set out to do, minus defining and explicitly
  fetching a style sheet's critical subresources.

Fixes #3610.

Tests: web-platform-tests/wpt#14899

The "unit of related similar-origin browsing contexts" concept is inaccurate.

Helps with #4198.

This also addresses a missing agent variable introduction.

Hiding interface objects is no longer a thing the web platform does.

Helps with heycam/webidl#430.

Closes #4025.

Also, as an editorial change, this unifies phrasing for when a parser
was created as part of the HTML fragment parsing algorithm; as noted in
#4290 (review), we
had a lot of different slight variations.

These would improve whatwg/dom#717 and #4204.

Tests: web-platform-tests/wpt#14814.

This line was accidentally deleted in c501dd8.

- Add formdata event and FormDataEvent interface
- Fire it in "constructing the entry list" algorithm
- Introduce "constructing entry list" flag of a form element to avoid recursive submission.

Tests: web-platform-tests/wpt#14637.

Change to XMLHttpRequest: whatwg/xhr#231.

This fixes a part of w3c/webcomponents#187.

This isn't strictly needed for @@toStringTag, @@hasInstance, and @@isConcatSpreadable, but "then" can be overridden and therefore cannot be handled earlier on. Handling them all at the same time leads to cleaner code.

Tests: already tested by wpt.

Fixes #4251.

getContextAttributes() here behaves the same as it does for
WebGLRenderingContext; see
https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.2. This
was previously discussed in
https://github.com/WICG/canvas-color-space/blob/master/CanvasColorSpaceProposal.md#feature-detection.

Closes #2563.

Supersedes and closes #4127. Closes w3c/webcomponents#760.

Callers do not anticipate it returning undefined in this case and browsers already throw.

Tests: will be added as part of https://bugzilla.mozilla.org/show_bug.cgi?id=1363208.

Fixes #4252.

In particular, an idle period should start in the case where there are
tasks, but they are all associated with non-fully-active documents.
Fixes #4212.

Fixes #4220, by making the algorithm consistent with the current
implementations in Blink and WebKit, as well as the existing web
platform tests. Now, innerHTML of void elements returns the empty string
even in cases where child nodes are present.

Tests (preexisting): https://wpt.fyi/results/html/syntax/serializing-html-fragments/serializing.html

We do not generally include domintro descriptions for
attribute-reflecting properties.

The "URL that was originally to be fetched" isn't clear about which URL
that actually was. This makes it clear that we use the request's current
URL when available, or the response's URL when not.

For javascript: URLs, this fixes them to match 2/3 browser behavior.
6440cca regressed the algorithm by
deleting the actual usage site of the address variable. This change
reintroduces the use of address, although in a simpler way, by appending
address to the request's URL list, instead of using the "override URL"
concept which was removed.

Fixes #3953.

Closes #1565 by preserving the special case; discussions there and in
https://bugzilla.mozilla.org/show_bug.cgi?id=1281375#c7 indicate that
the special case is more web-compatible.

Tests:

* https://github.com/web-platform-tests/wpt/blob/7ed525acfb4133c1177fdb1ff8477e2a6469e6b4/html/browsers/history/the-location-interface/location_hash.html#L24
* https://github.com/web-platform-tests/wpt/blob/7ed525acfb4133c1177fdb1ff8477e2a6469e6b4/html/semantics/embedded-content/the-iframe-element/iframe_javascript_url_01.htm
* web-platform-tests/wpt#14288
* web-platform-tests/wpt#14316

This is not a normative change, just a new, more layered, specification
mechanism (using CSS instead of prose).

Closes #4158.

This addresses a portion of the proposal in #3255.

Although this attribute was in fact common to both <audio> and <video>,
it was not listed as such alongside other such common attributes, which
could be confusing. Fixes #4159.

This adds a domintro for the developer-facing import() and import.meta
integrations, as well as cutting and including content more
appropriately for the module, event loop, runtime script errors,
unhandled promise rejections, and event handlers sections.

#4183 (comment)
discusses potential further improvements.

Fixes #4189.

Issue for tests: web-platform-tests/wpt#14256.

Missed in 840e22f.

See w3c/webappsec-csp#364 for more details.

Some previous copypasta in the definition of [Transferable] mentioned serialization instead of transfer in one place.

Last usage of duplication was removed in 16485bf and isn't supported by the API. The order is also not significant ("stylesheet alternate" is fine).

This codifies this in the semantics.

Fixes #3097.

Closes #3295. This also fixes a related inaccurate assert in EnqueueJob,
putting in guards for a null active script there as well and adding
examples explaining the various scenarios.

Fixes #4094.

As an editorial change, this also introduces references to the new
"newline normalization" primitive in Infra, and uses that where
appropriate in the parsing and textarea parts of the spec.

This change aligns the HTML calls to "Report long tasks" with the recent
change to Long Tasks in w3c/longtasks#50.

These steps do a variety of things that only make sense back on the main thread.
The intention here was that fetching not block the main thread. However, that is
already the case even without going in parallel, given the "async algorithm"
framework of the script-fetching algorithms. (That framework is admittedly a bit
unclear; see whatwg/infra#181.)

Closes #3895.

Closes #3628.