code: private function formatC(&$str) {
      if (strstr($str, '%C')) {
        if ($this->dayFrac == 0)
          $df = "{$this->day}.0";
        else
          $df = round($this->day + $this->dayFrac, 7);
  
        $str = str_replace('%C', str_pad($df, 10, 0, STR_PAD_LEFT), $str);
      }
    }
docs: Day with leading zero and fraction (added for AstroDate)
  @param type $str