public function build()
    {
        $values = array( 'access'           => false,
                         'genres'           => false,
                         'publication_date' => false,
                         'title'            => true,
                         'keywords'         => true,
                         'stock_tickers'    => true
        );
        foreach ($values as $value => $isEscaped) {
            if ( ! is_null( $this->{$value} )) {
                $this->addChild( sprintf( 'news:%s', $value ), $this->{$value}, $isEscaped );
            }
        }
    }