anchor.diff:          'details': details,
         });
       }
  -    if (previousIndex < content.length) {
  +    if (previousOffset < content.length) {
         // Last region of unmodified content.
         regions.add({
           'modified': false,
  -        'content': content.substring(previousIndex),
  +        'content': content.substring(previousOffset),
         });
       }
       return regions;
  
positive.code:   List<Map> _computeRegions(UnitInfo unitInfo) {
      String content = unitInfo.content;
      List<Map> regions = [];
      int previousIndex = 0;
      for (var region in unitInfo.regions) {
        int offset = region.offset;
        int length = region.length;
        if (offset > previousIndex) {
          // Display a region of unmodified content.
          regions.add({
            'modified': false,
            'content': content.substring(previousIndex, offset),
          });
          previousIndex = offset + length;
        }
        List<Map> details = [];
        for (var detail in region.details) {
  
negative.code:           'isTarget': true,
            'target': 'o${target.offset}',
          });
          previousOffset = offset + length;
        }
      }
      if (previousOffset < content.length) {
        // Last non-target region.
        targetRegions.add({
          'content': content.substring(previousOffset),
          'isTarget': false,
        });
      }
  