Define rules for these tags, then in
inc/config.php:
// goth font [[]]
$config['markup'][] = array("/\[\[(.+?)\]\]/", "<goth>\$1</goth>");
// garamond font (())
$config['markup'][] = array("/\(\((.+?)\)\)/", "<gara>\$1</gara>");
// glow :: ::
$config['markup'][] = array("/\:\:(.+?)\:\:/", "<glow>\$1</glow>");