code: public function reverse()
      {
          $length   = $this->length();
          $reversed = '';
          while ($length-- > 0) {
              $reversed .= mb_substr($this->string, $length, 1, $this->encoding);
          }
  
          $this->string = $reversed;
          return $this;
      }
docs: Reverse the sequence.
  
  @return StringBuilder