MutationObserver provides developers a way to react to changes in a DOM. It is designed as a replacement for Mutation Events defined in the DOM3 Events specification.
WebVTT is a format for displaying timed text tracks (e.g. subtitles or captions) with the <track> element. The primary purpose of WebVTT files is to add text overlays to a <video>. WebVTT is a text based format, which must be encoded in UTF-8 format. Where you can use spaces you can also use tabs.
The Web Performance API allows web pages access to certain functions for measuring the performance of web pages and web applications, including the Navigation Timing API and high-resolution time data.