Number of lines in region. https://www.w3.org/TR/webvtt1/#webvtt-region-lines
X coordinate within the region which is anchored to the video viewport. https://www.w3.org/TR/webvtt1/#webvtt-region-anchor
Y coordinate within the region which is anchored to the video viewport. https://www.w3.org/TR/webvtt1/#webvtt-region-anchor
Scroll value of the region. https://www.w3.org/TR/webvtt1/#webvtt-region-scroll
X coordinate within the video viewport to which the region anchor point is anchored. https://www.w3.org/TR/webvtt1/#webvtt-region-viewport-anchor
Y coordinate within the video viewport to which the region anchor point is anchored. https://www.w3.org/TR/webvtt1/#webvtt-region-viewport-anchor
Width of the region. https://www.w3.org/TR/webvtt1/#webvtt-region-width
ID of the region. https://www.w3.org/TR/webvtt1/#webvtt-region-identifier