public static function getByUrl($url, $limit = 0, $prefix = 'Pop\\Feed\\Format\\')
{
$options = self::getSource($url);
$class = class_exists($prefix . $options['format'] . '\\' . $options['service']) ? $prefix . $options['format'] . '\\' . $options['service'] : $prefix . $options['format'];
return new self(new $class($options, $limit));
}