code: def ns_prefix(self, prefix, ns_uri):
          
          self._element.set_ns_prefix(prefix, ns_uri)
          return self
docs: Set the namespace prefix of the :class:`xml4h.nodes.Element` node
          represented by this Builder.
  
          :return: the current Builder.
  
          Delegates to :meth:`xml4h.nodes.Element.set_ns_prefix`.