code: protected function describeStringDifference($first, $second, $identical)
      {
          if (is_object($second) || is_array($second)) {
              return $this->describeGenericDifference($first, $second);
          }
          $position = $this->stringDiffersAt($first, $second);
  
          return sprintf(
              'at character %s with [%s] and [%s]',
              $position,
              $this->clipString($first, 200, $position),
              $this->clipString($second, 200, $position)
          );
      }
docs: Creates a human readable description of the difference between
  a string and another variable.
  
  @param string $first        First string.
  @param mixed $second        String to compare with.
  @param bool $identical   If true then type anomolies count.
  
  @return string              Human readable description.