internal HtmlTemplateElement(Document nodeDocument, string prefix = null)
     : base(Name, nodeDocument, prefix)
 {
     if (!GetIsTemplateDocument(nodeDocument))
     {
         var templateDocument = (Document)nodeDocument.CloneNode();
         SetIsTemplateDocument(templateDocument, true);
         SetTemplateDocument(nodeDocument, templateDocument);
         nodeDocument = templateDocument;
     }
     Content = new DocumentFragment(nodeDocument);
 }