highlight method
      
  
Future
highlight(
    
- int index, {
- bool cancelExistHighlights = true,
- Duration highlightDuration = _highlightDuration,
- bool animated = true,
override
    highlight the item
Implementation
@override
Future highlight(int index,
    {bool cancelExistHighlights: true,
    Duration highlightDuration: _highlightDuration,
    bool animated: true}) async {
  final tag = tagMap[index];
  return tag == null
      ? null
      : await tag.highlight(
          cancelExisting: cancelExistHighlights,
          highlightDuration: highlightDuration,
          animated: animated);
}