code: public XmlStringBuilder element(String name, Date content) {
          assert content != null;
          return element(name, XmppDateTime.formatXEP0082Date(content));
      }
docs: Add a new element to this builder, with the {@link java.util.Date} instance as its content,
  which will get formatted with {@link XmppDateTime#formatXEP0082Date(Date)}.
  
  @param name element name
  @param content content of element
  @return this XmlStringBuilder