code: @Override
    public String getPrefix(String namespaceURI)
    {
      if (namespaceURI == null || !namespaceURI.equals("http://www.christofreichardt.de/java/tracer"))
        throw new IllegalArgumentException("Accept only default namespace.");
      
      return "dns";
    }
docs: Returns the prefix for the fixed namespace "http://www.christofreichardt.de/java/tracer". Other namespaces will cause
  an IllegalArgumentException.
  
  @param namespaceURI the namespace URI
  @return the prefix "dns"