code: protected void appendDocumentElementIndication(StringBuilder sb, Document doc) {
          sb.append("<");
          sb.append(doc.getDocumentElement().getNodeName());
          sb.append("...>");
      }
docs: Appends a short indication of the document's root element like "&lt;ElementName...&gt;" for {@link
  #getShortString}.
  
  @param sb the builder to append to
  @param doc the XML document node
  
  @since XMLUnit 2.4.0