For 4.3, we used the Mozilla browser-compat-data to remove types and features which are not used in any browser.

We base the lib.dom.d.ts on the specifications from W3C and WHATWG. These specifications are like all projects, and have some cruft on them over time. Now, we check the data powering caniuse.com to see if there are any implementations of a specification before including the types from that spec in the lib.dom.d.ts.

This is automated and running across a lot of specifications, so there's a possibility it has some overreach and we're open to bringing some back if we missed a common case. Some of the types removed: Account (this is now free to use in your own apps 🎉), AssertionOptions, RTCStatsEventInit, MSGestureEvent, DeviceLightEvent, MSPointerEvent, ServiceWorkerMessageEvent and WebAuthentication.