1. EventTarget.addEventListener()

    The modern standard API for adding DOM event handlers. Introduced in the DOM Level 2 Events spec. Also implies support for `removeEventListener`, the [capture phase](https://dom.spec.whatwg.org/#dom-event-capturing_phase) of DOM event dispatch, as well as the `stopPropagation()` and `preventDefault()` event methods.

  2. 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.

  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. SPDY protocol

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 Superseded by HTTP version 2.

  6. Scoped CSS

    Allows CSS rules to be scoped to part of the document, based on the position of the style element. The attribute has been [removed from the current specification](https://github.com/whatwg/html/issues/552).

  7. 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.

  8. Add to home screen (A2HS)

    The ability for a user to "install" a website and use it as if it was a natively installed app. To enable this behaviour, a website must serve a valid Web App Manifest and load it's assets through a [Service Worker](https://caniuse.com/#feat=serviceworkers).

  9. 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.

  10. headers HTTP header: Cookie2

  11. headers HTTP header: Set-Cookie2

  12. HTTP status code: 200

  13. HTTP status code: 201

  14. HTTP status code: 204

  15. HTTP status code: 206

  16. HTTP status code: 302

  17. HTTP status code: 412

  18. HTTP status code: 425

  19. HTTP status code: 502