1. @DomName('TextTrack.addRegion')
  2. @DocsEditable()
  3. @Experimental()
void addRegion(VttRegion region)

Source 

@DomName('TextTrack.addRegion')
@DocsEditable()
@Experimental() // untriaged
void addRegion(VttRegion region) =>
    _blink.BlinkTextTrack.instance.addRegion_Callback_1_(this, region);