anchor.diff:        throw const NoMoreElementsException();
       }
   
  -    // _next is set by #hasNext
  +    // _next is set by [hasNext].
       var next = _next;
       _next = null;
       return next;
  
positive.code: }
  
  class _MatchImplementation implements Match {
    const _MatchImplementation(
        String this.pattern,
        String this.str,
  
negative.code:       int this._end,
        List<String> this._groups);
  
    int start() => _start;
    int end() => _end;
    String group(int index) => _groups[index];
  