HTML5 is a markup language used for structuring and presenting content on the World Wide Web. It is the fifth and current version of the HTML standard - wikipedia 
__Web Messaging__ or __cross-document messaging__, is an API introduced in the WHATWG HTML5 draft specification, allowing documents to communicate with one another across different origins, or source domains while rendered in a web browser - wikipedia
This HTML5 technology is built into modern browsers and uses the Window.postMessage method.
This HTML5 technology is built into modern browsers and uses the Window.postMessage method.
__WebVTT__ (Web Video Text Tracks) is a World Wide Web Consortium (W3C) standard for displaying timed text in connection with the HTML5 <code><track></code> element- wikipedia