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);
  description.add('decoration:');
  description.addAll(_decoration.toString('  ', '    ').split('\n'));
  description.add('configuration: $configuration');
}