code: protected function withinMessage($compare)
      {
          $dumper = $this->getDumper();
  
          return 'Within expectation [' . $dumper->describeValue($this->lower) . '] and [' .
                  $dumper->describeValue($this->upper) . ']';
      }
docs: Creates a the message for being within the range.
  
  @param mixed $compare        Value being tested.