anchor.diff:  /** Pads [source] to [length] by adding spaces at the end. */
   String padRight(String source, int length) {
     final result = new StringBuffer();
  -  result.add(source);
  +  result.write(source);
   
     while (result.length < length) {
  -    result.add(' ');
  +    result.write(' ');
     }
   
     return result.toString();
  -}+}
  
positive.code: 
    buildAllowedList(Option option) {
      var allowedBuffer = new StringBuffer();
      allowedBuffer.add('[');
      bool first = true;
      for (var allowed in option.allowed) {
        if (!first) allowedBuffer.add(', ');
        allowedBuffer.add(allowed);
        if (allowed == option.defaultValue) {
          allowedBuffer.add(' (default)');
        }
        first = false;
      }
      allowedBuffer.add(']');
      return allowedBuffer.toString();
    }
  }
  
negative.code:     // to the next line.
      while (currentColumn != column) {
        if (currentColumn < NUM_COLUMNS - 1) {
          buffer.write(padRight('', columnWidths[currentColumn]));
        } else {
          buffer.write('\n');
        }
        currentColumn = (currentColumn + 1) % NUM_COLUMNS;
      }
  
      if (column < columnWidths.length) {
        // Fixed-size column, so pad it.
        buffer.write(padRight(text, columnWidths[column]));
      } else {
        // The last column, so just write it.
        buffer.write(text);
      }
  
      // Advance to the next column.
  