protected function getFontFamily(string $fontname = null): string
    {
        /**
         * Font sets to be used for PDF documents:
         *
         *   - Arial           - Times             - Tahoma
         *   - Georgia         - Trebuchet         - Courier
         *   - Lucida          - Lucida-Bright     - Palatino
         *   - Garamond        - Verdana           - Console
         *   - Monaco          - Helvetica         - Calibri
         *   - Avant-Garde     - Cambria
         */
        return array_key_exists(strtolower($fontname), $this->fontFamily)
            ? $this->fontFamily[strtolower($fontname)]
            : $this->fontFamily['default'];
    }