1. HTTP Live Streaming (HLS)

    HTTP-based media streaming communications protocol

  2. 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.

  3. 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.

  4. 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).

  5. SVG fonts

    Method of using fonts defined as SVG shapes. Removed from [SVG 2.0](https://www.w3.org/TR/SVG2/changes.html#fonts) and considered as a deprecated feature with support being removed from browsers.

  6. WebTransport

    Protocol framework to send and receive data from servers using [HTTP3](/http3). Similar to [WebSockets](/websockets) but with support for multiple streams, unidirectional streams, out-of-order delivery, and reliable as well as unreliable transport.

  7. XMLHttpRequest advanced features

    Adds more functionality to XHR (aka AJAX) requests like file uploads, transfer progress information and the ability to send form data. Previously known as [XMLHttpRequest Level 2](https://www.w3.org/TR/2012/WD-XMLHttpRequest-20120117/), these features now appear simply in the XMLHttpRequest spec.

  8. http status code: 103

  9. http status code: 301

  10. http status code: 302

  11. http status code: 303

  12. http status code: 304

  13. http status code: 307

  14. http status code: 308

  15. http status code: 403

  16. http status code: 503