The ValidityState interface represents the validity states that an element can be in, with respect to constraint validation. Together, they help explain why an element's value fails to validate, if it's not valid.
The VRDisplayCapabilities interface of the WebVR API describes the capabilities of a VRDisplay — its features can be used to perform VR device capability tests, for example can it return position information.
WindowTimers is a mixin used to provide utility methods which set and clear timers. No objects of this type exist; instead, its methods are available on Window for the standard browsing scope, or on WorkerGlobalScope for workers.
The Worker interface of the Web Workers API represents a background task that can be easily created and can send messages back to its creator. Creating a worker is as simple as calling the Worker() constructor and specifying a script to be run in the worker thread.
The WorkerNavigator interface represents a subset of the Navigator interface allowed to be accessed from a Worker. Such an object is initialized for each worker and is available via the WorkerGlobalScope.navigator property obtained by calling window.self.navigator.
The AudioChannelManager interface of the AudioChannels API includes features for managing your device's audio channels, including setting what channel's volume to affect when the volume buttons are pressed inside a particular app.