HTML 5.1 Implementation report

This report outlines known implementations for the features added between HTML 5.0 and HTML 5.1.

Implementation information is documented in the relevant Github issue, Pull Request (PR), or documentation for developers.

Documented changes

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
`HTMLInputElement.reportValidity()`	Chrome, Opera	Y	N	N	N
`HTMLMediaElement.fastseek()`	N	Y	N	N	Y
`HTMLElement.forceSpellcheck()`	All
`<Input type="week">`	Yandex, Chrome	N	Y	N	N
`<input type="month">`	Chrome, Yandex	N	Y	N	N
`<input type="datetime-local">`	Yandex, Chrome	N	Y	N	N
`ImageBitmap` interface	Chrome, Opera	Y	N	N	N
`<picture>`	Chrome, Opera, Yandex	Y	Y	N	Y
`<img srcset="">`	Y	Y	Y	N	Y
`<details>` and `<summary>`	Y	Y	N	N	Y
`<iframe allowfullscreen>`	All
`registerProtocolHandler()`	Y	Y	N	N	N
`<menu type="context">`	Chrome, Opera, Yandex	Y	N	N	N
`<menuitem>`	Y	Y	N	N	N
`XMLDocument` interface	Y	Y	Y	Y	Y
Restore `<a rev="">`	No browser behaviour required					Search engines, RDFa validators - Google, Yandex, …

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
Add `oncopy`	Y	Y	N	N	Y
Add `oncut`	Y	Y	N	N	Y
Add `onpaste`	Y	Y	N	N	Y
Modify header/footer content model to allow `<header>` and `<footer>` descendants	No browser implementation requirement					Not implemented in W3C Validator. test case
Allow blank `<option>`	Y	Y	Y	Y	?
Change `mousewheel` event to `wheel` event	Y	Y	Y	Y	Y	According to https://developer.mozilla.org/en-US/docs/Web/Events/wheel - which has a test that could be adapted. But I suspect there is one in WPT
Make stepup/down algorithm reflect reality	Yandex, Opera, Chrome	Not Testable	Y	Not Testable	N
Allow `<figcaption>` anywhere in `<figure>`	Y
Add `HTMLMediaElement.srcObject`	Y	Y	Y	N	Y
Make `<script>`'s `event` and `htmlFor` IDL attributes reflect the content attributes	Yandex	Y	Y	Y	4/5 tests	WPT test
Clear `autoplaying` flag when autoplaying	Y	?	Y	Y	?
Make `navigator.javaEnabled()` a method	Yandex, Opera	Y	Y	Y	?
Support `width="0"` except for `<td>`	Y					test for img
Make `toblob()` callback non-nullable	Yandex	Y	N	N	N	manually checked if `document.createElement('canvas').toBlob(null)` throws…
Make meta refresh parsing reflect reality	Yandex	Y	Y	Y	Y	With `url=` optional.
Make meta refresh parsing reflect reality	N	Y	Y	Y	N	With no semicolon.

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
Add `history.scrollRestoration`	Y	Y	N	N	N
Clarify manual scroll restoration mode	Y	Y	Y	Y	Y

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
Allow cross-origin `<track>` and `eventSource`	Yandex	*	?	?	Y	Firefox doesn't seem to show the captions, despite loading them. A very manual test…
Allow cross-origin `<track>` and `eventSource`	Yes?	Yes?	?	?	?	`eventSource` appears to work cross-origin with the correct headers in related testing of Blink (Yandex) and Gecko, but this feature may not have been tested thoroughly. The bugfix was in one piece of the spec that covers both cases.
Let `FrameElement` return null in cross-origin situations	?	Y	?	?	Y	Rough test
Change `ImageBitmap` to allow cross-origin content	Y	Y	Not Testable	Not Testable	Not Testable

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit
`<fieldset>` no longer utilises `HTMLFormControlsCollection`	N	Y	Not Testable	Not Testable	Y
Make `<fieldset>.elements` return an `HTMLCollection`	N	Y	Non Testable	Non Testable	Y
Reference `namedItem` method from `HTMLCollection` not `HTMLOptionsCollection`	N	Y	Y	N	N

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
Describe SVG versions implemented in browsers	Opera, Yandex	Y	N	N	Y	`non-scaling-stroke` for `vector-effect` - test
	Y					`class` attribute
	Yandex	N	Y	Y	Y	`tabindex` attribute
	Y					Allow ARIA attributes - demonstrated by multiple examples
Make SVG `<title>` first child not last	Yandex, Chrome	Y	N	N	Y	Yandex, Firefox, Chrome and Safari all expose the first `title` child in raw SVG. In SVG embedded in HTML, Firefox and Safari expose the first child `title` element as a tooltip

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
Make `<thead>` and `<tfoot>` ordering reflect reality	Y	Y	Y	Y	Y
Add specific `HTMLTableElement` types	Yandex	Y	Y	Y	N
Disallow `<tfoot>` before `<tbody>`	No browser behaviour required					Not implemented in validator.w3.org

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
Add `requestAnimationFrame`	Y
Add callout to detach from `<media>`	Y					For MSE
Integrate Resource Hints	Not Testable					prefetch feature
Make `HTMLAllCollection` to match WebIDL	Y
Integrate encoding specification	Y					Defer some encoding specifics to WHATWG Encoding spec
Take account of `srclang` when rendering `<track>`	Not Testable					For WebVTT
Define `enqueueJob()` and `nextJob()` monkeypatching ECMAScript	Y	Y	Y	N	Y	Explains Promise resolution in terms of Microtasks -- tests Promises use Microtask timing

	Blink	Firefox - Gecko	Edge	Internet Explorer	Safari - Webkit	Notes
Add CSP-list to the global object	Not Testable					Not testable implementation detail to support CSP.
Add hooks for inline elements	Y	Y	Y	N	Y	script/style-src 'unsafe-inline' applies to element
Add hooks for CSP and Realms from ECMASCript	Y	N	N	N	Y	Much of this change is Not Testable, except for nonce support IDL (on style/script)
Move "https state" from `Window` to `Document`	Not Testable					Implementation detail: conceptual storage of HTTPS State.

:dir CSS selector matching: Only in Firefox. This defines how a CSS selector works with HTML when implemented, so the lack of implementation doesn't cause interop problems for browsers. A warning for authors not to rely on this feature yet is in the specification.
.tFoot and .createTFoot to always insert at the end: Only in Firefox. There is poor interoperability of this in general, so it is unlikely to affect Web Compatibility, but this change matches a similar one in the WHATWG specification. A warning for authors not to rely on this feature yet is in the specification.
Promise rejection handling with rejectionhandled and unhandledrejection events: This features is currently only known to be implemented in blink, and a warning to authors that it is not yet reliable is in the specification.

probablySupportsContext: This convenience function for canvas has no known implementation. A warning for authors not to rely on this feature yet is in the specification.
Use close() blob from File API: This method does not appear to have implementation, and may in future be removed from File API. In the HTML specification, it is mentioned in an algorithm, to take account of any implementation, in a way that means partial implementation does not introduce an interoperability problem. A warning for authors not to rely on this feature is in the specification.
CSP hooks for inline events and styles: This part of CSP does not appear to have implementation, but seems likely to be implemented in the near future. In the HTML specification, it is mentioned in an algorithm, to take account of any implementation, in a way that means partial implementation does not introduce an interoperability problem. Warnings for authors not to rely on this feature yet are in the specification.