private static void ClearUnsafeHtmlNode(HtmlNode htmlNode)
{
var attributes = htmlNode.Attributes.Where(attribute => !StringHelper.Contains(ValidAttributes, attribute.Name));
attributes.Each(attribute => htmlNode.Attributes.Remove(attribute));
if (htmlNode.HasChildNodes)
{
htmlNode.ChildNodes.Each(childNode => ClearUnsafeHtmlNode(childNode));
}
}