The region property of the VTTCue interface returns and sets the VTTRegion that this cue belongs to.
A VTTRegion object.
In the following example a new VTTCue is created, then the value of region is printed to the console.
let video = document.querySelector("video");
let track = video.addTextTrack("captions", "Captions", "en");
track.mode = "showing";
let cue = new VTTCue(0, 0.9, "Hildy!");
console.log(cue.region);
track.addCue(cue);