protected static function _types($type = null) {
		$types = static::$_types + array(
			'html'         => array('text/html', 'application/xhtml+xml', '*/*'),
			'htm'          => array('alias' => 'html'),
			'form'         => array('application/x-www-form-urlencoded', 'multipart/form-data'),
			'json'         => array('application/json'),
			'rss'          => array('application/rss+xml'),
			'atom'         => array('application/atom+xml'),
			'css'          => array('text/css'),
			'js'           => array('application/javascript', 'text/javascript'),
			'text'         => array('text/plain'),
			'txt'          => array('alias' => 'text'),
			'xml'          => array('application/xml', 'application/soap+xml', 'text/xml')
		);

		if (!$type) {
			return $types;
		}
		if (strpos($type, '/') === false) {
			return isset($types[$type]) ? $types[$type] : null;
		}
		if (strpos($type, ';')) {
			list($type) = explode(';', $type, 2);
		}
		$result = array();

		foreach ($types as $name => $cTypes) {
			if ($type == $cTypes || (is_array($cTypes) && in_array($type, $cTypes))) {
				$result[] = $name;
			}
		}
		if (count($result) == 1) {
			return reset($result);
		}
		return $result ?: null;
	}