PHPePub\Core\EPub::addCustomMetadata PHP Method

    function addCustomMetadata($name, $content)
    {
        if ($this->isFinalized) {
            return;
        }
        $this->opf->addMeta($name, $content);
    }

 /**
  * @param EPub   $book
  * @param string $seriesName
  * @param string $seriesIndex
  * @param string $sortTitle
  */
 public static function setCalibreMetadata($book, $seriesName, $seriesIndex, $sortTitle = null)
 {
     $book->addCustomMetadata("calibre:series", $seriesName);
     $book->addCustomMetadata("calibre:series_index", "" . $seriesIndex);
     if (!empty($sortTitle)) {
         $book->addCustomMetadata("calibre:title_sort", $sortTitle);
     }
 }