code: public function section($separator, $first = 0, $last = 0)
      {
          $sections = explode($separator, $this->string);
  
          $total = count($sections);
          $first = intval($first);
          $last = intval($last);
  
          if ($first > $total) {
              return null;
          }
          if ($first > $last) {
              $last = $first;
          }
  
          for ($i = 0; $i < $total; $i++) {
              if ($i < $first || $i > $last) {
                  unset($sections[$i]);
              }
          }
  
          $string = implode($separator, $sections);
  
          return new self($string);
      }
docs: Returns a section of the string.
  
  @param  string $separator
  @param  integer $first
  @param  integer $last
  @return StringHelper