anchor.diff:  part of domelement;
  +
  +typedef dynamic _Callback(DomElement target);
   
   abstract class ContentCapable {
     String get html => nativeElement.innerHtml;
  
positive.code:       List<Node> childNodes = nativeElement.childNodes;
        Node firstChild = childNodes.length > 0 ? childNodes.first : null;
        nativeElement.insertBefore(element.nativeElement, firstChild);
      } else {
        throw new ArgumentError('Valid values are: String|Element|DomElement');
      }
    }
  
negative.code:     nativeElement.text = new HtmlEscape().convert(value);
    }
  
    void append(
        dynamic /* String|Element|DomElement|(DomElement) => dynamic */ source) {
      if (source is String) {
        nativeElement.insertAdjacentHtml('beforeend', source,
            treeSanitizer: new NullTreeSanitizer());
  