1. CSS overflow property

    Originally a single property for controlling overflowing content in both horizontal & vertical directions, the `overflow` property is now a shorthand for `overflow-x` & `overflow-y`. The latest version of the specification also introduces the `clip` value that blocks programmatic scrolling.

  2. ECMAScript 5

    Full support for the ECMAScript 5 specification. Features include `Function.prototype.bind`, Array methods like `indexOf`, `forEach`, `map` & `filter`, Object methods like `defineProperty`, `create` & `keys`, the `trim` method on Strings and many more.

  3. High Resolution Time API

    Method to provide the current time in sub-millisecond resolution and such that it is not subject to system clock skew or adjustments. Called using `performance.now()`

  4. HTTP/2 protocol

    Networking protocol for low-latency transport of content over the web. Originally started out from the SPDY protocol, now standardized as HTTP version 2.

  5. HTTP/3 protocol

    Third version of the HTTP networking protocol which uses QUIC as transport protocol. Previously known as HTTP-over-QUIC, now standardized as HTTP/3.

  6. matches() DOM method

    Method of testing whether or not a DOM element matches a given selector. Formerly known (and largely supported with prefix) as matchesSelector.

  7. Context menu item (menuitem element)

    Method of defining a context menu item, now deprecated and [removed from the HTML specification](https://github.com/whatwg/html/issues/2730).

  8. Object.observe data binding

    Method for data binding, a now-withdrawn ECMAScript 7 proposal

  9. Offline web applications

    Now deprecated method of defining web page files to be cached using a cache manifest file, allowing them to work offline on subsequent visits to the page.

  10. Passkeys

    Passkeys, also known as Multi-device FIDO Credentials, provide users with an alternative to passwords that is much easier to use and far more secure.

  11. Scoped attribute

    Deprecated method of allowing scoped CSS styles using a "scoped" attribute. Now [removed from the specification](https://github.com/whatwg/html/issues/552) and replaced by the [@scope CSS rule](/css-cascade-scope).

  12. ES6 Template Literals (Template Strings)

    Template literals are string literals allowing embedded expressions using backtick characters (`). You can use multi-line strings and string interpolation features with them. Formerly known as template strings.

  13. XMLHttpRequest advanced features

    Updated functionality to the original XHR specification including things like file uploads, transfer progress information and the ability to send FormData. Previously known as [XMLHttpRequest Level 2](https://www.w3.org/TR/2012/WD-XMLHttpRequest-20120117/), these features now appear simply in the XMLHttpRequest spec.

  14. elementinternals api: ariavaluenow

  15. element api: ariavaluenow

  16. htmltablecellelement api: nowrap

  17. htmlunknownelement api

  18. performance api: now

  19. css property: flex-wrap: nowrap

  20. css property: text-wrap-mode: nowrap

  21. css property: text-wrap: `nowrap`

  22. css property: white-space: nowrap

  23. javascript built-in: date: now

  24. javascript built-in: temporal api: temporal.now interface

  25. javascript built-in: temporal api: temporal.now interface: temporal.now.instant()

  26. javascript built-in: temporal api: temporal.now interface: temporal.now.plaindate()

  27. javascript built-in: temporal api: temporal.now interface: temporal.now.plaindateiso()

  28. javascript built-in: temporal api: temporal.now interface: temporal.now.plaindatetime()

  29. javascript built-in: temporal api: temporal.now interface: temporal.now.plaindatetimeiso()

  30. javascript built-in: temporal api: temporal.now interface: temporal.now.timezone()

  31. javascript built-in: temporal api: temporal.now interface: temporal.now.zoneddatetime()

  32. javascript built-in: temporal api: temporal.now interface: temporal.now.zoneddatetimeiso()