1. HTTP Live Streaming (HLS)

    HTTP-based media streaming communications protocol

  2. HTTP/3 protocol

    Upcoming version of the HTTP networking protocol, which is currently a draft. Previously known as HTTP-over-QUIC. Uses QUIC as its transport layer protocol.

  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. 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.

  7. http status code: 301

  8. http status code: 302

  9. http status code: 303

  10. http status code: 304

  11. http status code: 307

  12. http status code: 308

  13. http status code: 403

  14. http status code: 503