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