The requested ticker mode for this subtree.
The effective ticker mode of this subtree may differ from this value if there is an ancestor TickerMode with this field set to false.
If true and all ancestor TickerModes are also enabled, then tickers in this subtree will tick.
If false, then tickers in this subtree will not tick regardless of any ancestor TickerModes. Animations driven by such tickers are not paused, they just don't call their callbacks. Time still elapses.
final bool enabled;