Description
   Overloads an XML Namespace and binds all its elements to a PHP 
   object, that must provide startElement($element, 
    $attributes)() and endElement($element, 
    $cdata)() methods.
  
   If the PHP object provides a initObserver($namespacePrefix,
    $transformer)() method it is automatically called with the
   registered namespace prefix and a reference to the XML_Transformer
   object.