This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
A visual representation would help to get the difference between region anchor point and region viewport anchor point. As per feedback from Andreas Tai: http://lists.w3.org/Archives/Public/public-texttracks/2015Feb/0005.html
https://github.com/w3c/webvtt/pull/179
Diagram was added