1. override
void debugFillDescription(List<String> description)

Accumulates a list of strings describing the current node's fields, one field per string. Subclasses should override this to have their information included in toStringDeep.

Source 

@override
void debugFillDescription(List<String> description) {
  super.debugFillDescription(description);
  switch (behavior) {
    case HitTestBehavior.translucent:
      description.add('behavior: translucent');
      break;
    case HitTestBehavior.opaque:
      description.add('behavior: opaque');
      break;
    case HitTestBehavior.deferToChild:
      description.add('behavior: defer-to-child');
      break;
  }
}