The reason for this is that the setting is set [here](https://github.com/andreasgal/vtt.js/blob/master/vtt.js#L117). We get a cue-setting and switch through the names; If it's 'region' we parse it and then add it to the cue as this is the name of the attribute on the IDL. So either we keep it like this or we would need to pass in "regionId" as the setting we're setting in the parseOptions() call back.