https://lists.w3.org/Archives/Public/public-html/2014Feb/0082.html
Re: TextTrack questions from Silvia Pfeiffer on 2014-02-16 (public-html@w3.org from February 2014)
https://developer.mozilla.org/en-US/docs/Web/API/TextTrack/mode
TextTrack: mode property - Web APIs | MDN
The TextTrack interface's mode property is a string specifying and controlling the text track's mode: disabled, hidden, or showing. You can read this value to...
web apistexttrackmodepropertymdn
https://lists.w3.org/Archives/Public/public-html/2011Sep/0088.html
[Bug 14105] New: Drop MutableTextTrack and make TextTrack always mutable from...
new dropbug