1. Audio element

    Method of playing sound on webpages (without requiring a plug-in). Includes support for the following media properties: `currentSrc`, `currentTime`, `paused`, `playbackRate`, `buffered`, `duration`, `played`, `seekable`, `ended`, `autoplay`, `loop`, `controls`, `volume` & `muted`

  2. Autofocus attribute

    Allows a form field to be immediately focused on page load.

  3. calc() as CSS unit value

    Method of allowing calculated values for length units, i.e. `width: calc(100% - 3em)`

  4. Text API for Canvas

    Method of displaying text on Canvas elements

  5. ChaCha20-Poly1305 cipher suites for TLS

    A set of cipher suites used in Transport Layer Security (TLS) protocol, using ChaCha20 for symmetric encryption and Poly1305 for authentication.

  6. COLR/CPAL(v0) Font Formats

    The COLR table adds support for multi-colored glyphs in a manner that integrates with the rasterizers of existing text engines. COLRv0 only supports pure colors, does not support gradients, transformations and various blending modes.

  7. COLR/CPAL(v1) Font Formats

    COLRv1 is an improved version of COLRv0, this is also part of the OpenType specification. COLRv1 supports additional graphic capabilities. In addition to solid colors, gradient fills can be used, as well as more complex fills using other graphic operations, including affine transformations and various blending modes.

  8. CSS background-position edge offsets

    Allows CSS background images to be positioned relative to the specified edge using the 3 to 4 value syntax. For example: `background-position: right 5px bottom 5px;` for positioning 5px from the bottom-right corner.

  9. CSS clip-path property (for HTML)

    Method of defining the visible region of an HTML element using SVG or a shape definition.

  10. CSS Generated content for pseudo-elements

    Method of displaying text or images before or after the given element's contents using the ::before and ::after pseudo-elements. All browsers with support also support the `attr()` notation in the `content` property.

  11. selector list argument of :nth-child and :nth-last-child CSS pseudo-classes

    The newest versions of `:nth-child()` and `:nth-last-child()` accept an optional `of S` clause which filters the children to only those which match the selector list `S`. For example, `:nth-child(1 of .foo)` selects the first child among the children that have the `foo` class (ignoring any non-`foo` children which precede that child). Similar to `:nth-of-type`, but for arbitrary selectors instead of only type selectors.

  12. CSS zoom

    Non-standard method of scaling content.

  13. disabled attribute of the fieldset element

    Allows disabling all of the form control descendants of a fieldset via a `disabled` attribute on the fieldset element itself.

  14. Form validation

    Method of setting required fields and field types without requiring JavaScript. This includes preventing forms from being submitted when appropriate, the `checkValidity()` method as well as support for the `:invalid`, `:valid`, and `:required` CSS pseudo-classes.

  15. HEIF/ISO Base Media File Format

    HEIF (High Efficiency Image File Format) is a standard developed by the Moving Picture Experts Group (MPEG) for storage and sharing of images and image sequences. Can use `.heif` or `.heic` file extensions.

  16. sandbox attribute for iframes

    Method of running external site pages with reduced privileges (e.g. no JavaScript) in iframes.

  17. seamless attribute for iframes

    The seamless attribute makes an iframe's contents actually part of a page, and adopts the styles from its hosting page. The attribute has been removed from both [the WHATWG](https://github.com/whatwg/html/issues/331) and [the W3C](https://github.com/w3c/html/pull/325) HTML5 specifications.

  18. autocomplete attribute: on & off values

    The `autocomplete` attribute for `input` elements indicates to the browser whether a value should or should not be autofilled when appropriate.

  19. accept attribute for file input

    Allows a filter to be defined for what type of files a user may pick with from an `<input type="file">` dialog

  20. Minimum length attribute for input fields

    Declares a lower bound on the number of characters a user can input.

  21. Pattern attribute for input fields

    Allows validation of an input field based on a given regular expression pattern.

  22. maxlength attribute for input and textarea elements

    Declares an upper bound on the number of characters the user can input. Normally the UI ignores attempts by the user to type in additional characters beyond this limit.

  23. readonly attribute of input and textarea elements

    Makes the form control non-editable. Unlike the `disabled` attribute, `readonly` form controls are still included in form submissions and the user can still select (but not edit) their value text.

  24. Selection API

    API for accessing selected content of a document, including the `window.getSelection()` method, as well as the `selectstart` & `selectionchange` events on `document`.

  25. SPDY protocol

    Networking protocol for low-latency transport of content over the web. Superseded by HTTP version 2.

  26. SVG effects for HTML

    Method of using SVG transforms, filters, etc on HTML elements using either CSS or the foreignObject element

  27. TLS 1.2

    Version 1.2 of the Transport Layer Security (TLS) protocol. Allows for data/message confidentiality, and message authentication codes for message integrity and as a by-product message authentication.

  28. CSS3 2D Transforms

    Method of transforming an element including rotating, scaling, etc. Includes support for `transform` as well as `transform-origin` properties.

  29. CSS3 3D Transforms

    Method of transforming an element in the third dimension using the `transform` property. Includes support for the `perspective` property to set the perspective in z-space and the `backface-visibility` property to toggle display of the reverse side of a 3D-transformed element.

  30. Trusted Types for DOM manipulation

    An API that forces developers to be very explicit about their use of powerful DOM-injection APIs. Can greatly improve security against XSS attacks.

  31. User Timing API

    Method to help web developers measure the performance of their applications by giving them access to high precision timestamps.

  32. WebGPU

    An API for complex rendering and compute, using hardware acceleration. Use cases include demanding 3D games and acceleration of scientific calculations. Meant to supersede WebGL.

  33. WOFF - Web Open Font Format

    Compressed TrueType/OpenType font that contains information about the font's source.

  34. WOFF 2.0 - Web Open Font Format

    TrueType/OpenType font that provides better compression than WOFF 1.0.

  35. offscreencanvasrenderingcontext2d api: gettransform

  36. offscreencanvasrenderingcontext2d api: resettransform

  37. offscreencanvasrenderingcontext2d api: settransform

  38. offscreencanvasrenderingcontext2d api: transform

  39. videoframe api: format

  40. css property: hyphens: hyphenation dictionary for german, reformed orthography of 1996 (de, de-1996, de-de, de-at, de-*)

  41. css property: text-underline-offset

  42. types: `<position>`: four-value syntax for offset from any edge

  43. javascript built-in: intl: datetimeformat: supportedlocalesof

  44. javascript built-in: intl: listformat: supportedlocalesof

  45. javascript built-in: intl: numberformat: supportedlocalesof

  46. javascript built-in: intl: relativetimeformat: supportedlocalesof

  47. javascript statement: `for await...of`

  48. javascript statement: `for...in`

  49. javascript statement: `for...of`

  50. javascript statement: `for...of`: closing iterators