anchor.diff:    /// the preceding \LMHash{} block should stop before the line of
     /// this \LMHash{} command.  Note that hash blocks may stop earlier,
     /// because they cannot contain sectioning commands.
  -  int getStartLineNumber() => null;
  +  int? getStartLineNumber() => null;
   }
   
   class HashMarkerEvent extends HashEvent {
  
positive.code: //
  // NB: This utility assumes UN*X style line endings, \n, in the LaTeX
  // source file received as input; it will not work with other styles.
  
  // @dart = 2.9
  
  // ignore_for_file: constant_identifier_names
  
  
negative.code:   // reached), so [endLineNumber] will be initialized in a separate
    // scan.  Also note that the block may end earlier, because a block
    // ends if it would otherwise include a sectioning command.
    int? endLineNumber;
  
    HashMarkerEvent(this.startLineNumber);
  
  