The mode of the text track, represented by a value from the following list:
'disabled': The track is disabled.
'hidden': The track is hidden.
'showing': The track is showing.
- A disabled track is not displayed and exposes no active cues, nor fires cue events.
- A hidden track is not displayed but exposes active cues and fires cue events.
- A showing track is displayed, exposes active cues and fires cue events.