code: def xml(self):
          
          root = Element('UsernameToken', ns=wssens)
          u = Element('Username', ns=wssens)
          u.setText(self.username)
          root.append(u)
          p = Element('Password', ns=wssens)
          p.setText(self.password)
          root.append(p)
          if self.nonce is not None:
              n = Element('Nonce', ns=wssens)
              n.setText(self.nonce)
              root.append(n)
          if self.created is not None:
              n = Element('Created', ns=wsuns)
              n.setText(str(DateTime(self.created)))
              root.append(n)
          return root
docs: Get xml representation of the object.
          @return: The root node.
          @rtype: L{Element}