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 toString.

Source 

@override
void debugFillDescription(List<String> description) {
  super.debugFillDescription(description);
  description.add('content: ${contentExtent.toStringAsFixed(1)}');
  description.add('container: ${containerExtent.toStringAsFixed(1)}');
  description.add('range: ${minScrollOffset?.toStringAsFixed(1)} .. ${maxScrollOffset?.toStringAsFixed(1)}');
}