anchor.diff:    /// Clears the previously calculated total indent of this nesting level.
     void clearTotalUsedIndent() {
       _totalUsedIndent = null;
  -    _parent?.clearTotalUsedIndent();
  +    parent?.clearTotalUsedIndent();
     }
   
     /// Calculates the total amount of indentation from this nesting level and
  
positive.code: 
    @override
    String toString() {
      if (_parent == null) return indent.toString();
      return '$parent:$indent';
    }
  }
  
negative.code: class NestingLevel extends FastHash {
    /// The nesting level surrounding this one, or `null` if this is represents
    /// top level code in a block.
    final NestingLevel? parent;
  
    /// The number of characters that this nesting level is indented relative to
    /// the containing level.
  